UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Hodel, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
Library of Congress Cataloging-in-Publication Data 

Main entry under title: 

Underground coal mine lighting handbook. 

(Information circularlunited States Department of the 

Interior, Bureau of Mines; 9074) 

Bibliographies. 

Supt. of Docs. no.: I 28.27: 

Contents: v. 1. Background-v. 2. Application. 

1. Mine lighting. 2. Coal mines and mining. 

I. Lewis, W. H. (William H.) 11. Series: Information circular (United States. Bureau 

of Mines); 9074. 

TN309.U47 
Page Page 

Abstract ............................. 1 

Introduction .......................... 2 

Chapter 1.-Light measuring techniques and 

instrumentation ....................... 2 

Portable photoelectric photometers ......... 2 

Photocell characteristics ............... 2 

Color correction ..................... 2 

Cosine correction .................... 3 

Sensitivity ........................ 3 

Purkinje shift ...................... 3 

Calibration ........................ 3 

Photometer zeroing .................. 4 

Temperature and humidity effects ........ 4 

Contamination ..................... 4 

Stray light ........................ 4 

Go, no-go coal mine photometer ........... 4 

Making illuminance measurements ......... 4 

Making luminance measurements .......... 5 

Making reflectance measurements ......... 5 

Other measuring instruments ............ 6 

Chapter 2.-Illumination regulations for underground coal mine environments and equipment . . 7 

The primary illumination standard and 

its basis ........................... 7 

Applying the illumination standard in the 

mine environment .................... 7 

Additional standards for implementing face 

illumination systems .................. 8 

Electrical requirements ............... 8 

Antiflicker requirements .............. 10 

Requirements concerning luminaires in a 

blasting zone ...................... 11 

Antiglarerequirements ............... 11 

MSHA STE program ................... 11 

Value of STE program to mine operators and 

some important limitations ............. 12 

STE application process and information 

requirements ....................... 12 

Application form .................... 12 

Machine layout drawing ............... 13 

One-line diagram .................... 13 

Electrical schematic .................. 13 

Light measurement data ............... 14 

Short-circuit calculations 

(longwall-stationary systems) .......... 16 

Specifying optional equipment on STE 

applications ........................ 16 

MSHA review of STE applications ......... 16 

Modification of STE-approved designs ....... 17 

Requirements for installation of lighting 

systems ........................... 18 

Inspection of face lighting systems ......... 18 

Procedures for STE-approved systems ...... 19 

Procedures for non-STE-approved systems . . 19 

Instruments and techniques for taking 

light measurements ................. 19 

Additional requirements to improve 

visibility underground ............... 20 

Chapter 3.-Lamps and ballasts ............ 21 

Criteria for lamp performance 

characterization ..................... 21 

Incandescent lamps .................... 22 

Principle of operation ................. 22 

Life-efficacy relationship ............... 22 

Krypton-filled ...................... 24 

Tungsten-halogen ................... 24 

Fluorescent lamps and ballasts ............ 25 

Principle of operation ................. 25 

Types ............................ 25 

Performance characteristics ............ 25 

Fluorescent ballasts .................. 27 

Ballast heating and related design 

considerations ..................... 28 

High intensity discharge lamps. high-pressure 

sodium and mercury vapor ............ 28 

Mercury vapor lamps .................. 29 

Functional description ................ 29 

Efficacy-lumen output ................ 29 

Spectral energy distribution ............ 29 

Lamp life ......................... 29 

Effect of voltage variation .............. 30 

Flicker ........................... 30 

Ballasts .... .'. .................... 30 

High-pressure sodium lamps ............. 32 

Principle of operation ................. 32 

Efficacy-lumen output ................ 32 

Lumen depreciation ................. ‘. 32 

Spectral energy distribution ............ 32 

Lamp life ......................... 33 

Effect of voltage variation .............. 33 

Flicker ........................... 33 

Ballasts .......................... 33 

Chapter 4.-Available mine lighting hardware . . 36 

Overview ........................... 36 

Hardware evaluation ................... 37 

Ruggedness and durability ............. 38 

Electrical reliability .................. 40 

System servicing .................... 42 

Illumination performance .............. 43 

Miscellaneous ...................... 44 

Chapter 5.-Design and evaluation of coal mine 

illumination systems ................... 45 

Recommended design methodology ......... 45 

Information collection and assembly ....... 45 

Generate illumination system concept 

alternatives ....................... 46 

Illumination system concept evaluation 

considerations ..................... 48 

Install lighting system ................ 50 

Evaluate installed system .............. 50 

Design methods and considerations ......... 50 

Durability ......................... 50 

Component mounting methods and 

considerations ..................... 51 

Methods to evaluate and reduce discomfort 

glare ............................ 56 
CONTENTS- Continued 

Page 

Chapter 6.-Installing and maintaining mine 

lighting systems ....................... 58 

Guidelines for system installation .......... 58 

Preparation ........................ 58 

Mounting luminaires ................. 59 

Housing and connecting power conditioning 

equipment ........................ 59 

Cable installation ................... 60 

Gland protection .................... 61 

Guidelines for system maintenance ......... 61 

Maintenance approach ................ 61 

Exchange maintenance ................ 62 

Scheduled and preventive maintenance .... 62 

Record keeping ..................... 63 

Maintenance training ................. 63 

Recommendations for minimizing lamp 

mortality and lamp replacement costs ...... Assessing lamp costs ................. Assessing increased lamp mortality in 

mine applications ................... Factors causing increased mortality of 

lamps in mine application ............. Measures to improve lamp life and lamp 

servicing suggestions .................. Group relamping ..................... Appendix A.-Federal specifications for lighting 

face equipment and coal mine, longwalls ...... Appendix B.-Specifications of available area 

luminaires and power-conditioning systems 

approved for application in underground coal 

mine working places .................... 

ILLUSTRATIONS 

1 . Function of color correcting filter on response of photocells ................................ 2 . Diffusing cover for cosine correction on photometers ..................................... 3 . Photocell orientation for making illumination measurements ............................... 4 . Photocell fitted with adapter for luminance measurements ................................ 5, Reflected-incident light comparison method for measuring reflectivity ........................ 6 . Luminance standard comparison technique for measuring reflectivity ......................... 7 . Resistance-grounded neutral grounding circuit ......................................... 8 . Longwall power distribution circuit for breaker setting calculation ........................... 9 . Intrinsically safe pilot circuit with explosion-proof connector ............................... 10 . System layout drawing ......................................................... 11 . One-line diagram ............................................................. 12 . Electrical schematic diagram ..................................................... 13 . "Unfolded-box" diagram for presenting light measurement data ............................. 14 . Significance of interreflections when taking light measurements in mine simulators .............. 15 . STE system approval plate ....................................................... 16 . Procedure for using go, no-go photometer when clearance permits holding the meter 5 ft from entry walls . . 17 . Procedure for using go, no-go photometer when clearance does not permit holding meter 5 ft from entry walls . . 18 . Lamp mortality curve example .................................................... 19 . Common shapes of mine lamps and letter designations ................................... 20 . Construction of typical incandescent lamp ............................................ 21 . Spectral energy distribution of tungsten at 3, 000 K ..................................... 22 . Effect of voltage variation on the operating characteristics of incandescent filament lamps .......... 23 . Construction of typical fluorescent lamp ............................................. 24 . Specular energy distribution curves for common fluorescent phosphor mixtures .................. 25 . Change in light output of a fluorescent lamp as a function of ambient temperature ............... 26 . Change in light output and wattage of a fluorescent lamp as a function of line voltage ............. 27 . Dual-lamp, series-sequence-type. rapid-start fluorescent ballast circuit ........................ 28 . Typical mercury vapor lamp construction ............................................ 29 . Spectral energy distribution of a typical clear mercury vapor lamp ........................... 30 . Mercury vapor lamp ballasts ..................................................... 31 . Typical high-pressure sodium lamp construction ........................................ 32 . Spectral energy distribution of typical high-pressure sodium lamp ........................... 33 . Lamp characteristics that must be accommodated in high-pressure sodium lamp ballast design ....... 34 . Trapezoid specification for high-pressure sodium lamp ballast performance defined by lamp characteristics and upper-lower wattage limits ................................................ 35 . Important aspects of ballast characteri_stic curves ....................................... 36 . High-pressure sodium lamp ballasts ................................................ 37 . Important cage design distinctions ................................................. 38 . Tubing versus clamp-style packing glands ............................................ 

Page 
Page 

39 . Effect of gland orientation on cable routing ........................................... 39 

40 . Alternative wiring configurations for dc application of incandescent headlamp pairs ............... 41 

41 . Example photometric profile diagram ............................................... 48 

42 . Typical mine simulator used to establish STE data ...................................... 48 

43 . Methods of luminaire protection ................................................... 51 

44 . Example of damage to lighting hardware ............................................. 51 

45 . Example luminaire mountings that improve durability ................................... 52 

46 . Example power supply mountings .................................................. 53 

47 . Example of principal lines of sight for a roof bolting machine .............................. 53 

48 . Disability glare diagram ........................................................ 54 

49 . Apparent contrast versus visibility ................................................. 54 

50 . Glare shields used to reduce disability glare .......................................... 54 

51 . Disability glare versus luminaire position ............................................ 54 

52 . Luminaire orientation change to reduce disability glare .................................. 55 

53 . Luminaire selection and placement to reduce disability glare ............................... 56 

54 . Luminaire orientation change to reduce discomfort glare .................................. 57 

55 . Discomfort glare versus luminaire brightness and area ................................... 57 

56 . Example of retrofitted glare diffusers ............................................... 58 

57 . Quick-release luminaire bracket ................................................... 59 

58 . Recommended gland guard designs ................................................. 61 

59 . Effects of vibration and shock on lamp filaments ....................................... 65 

60 . Shadowgraph to test fluorescent lamp filament continuity ................................. 66 

61 . Laboratory measured mortality curves for lamp types used in coal mining applications ............. 69 

B-1 . Joy Manufacturing Co . model 500131-33 and 500131-35 luminaires .......................... 77 

B-2 . Mdunkin Corp . model 100164 luminaire ............................................. 79 

B-3 . Mdunkin Corp . model 100/30H, 100115, and 10016 luminaires .............................. 79 

B-4 . Mdunkin Corp . model 400-A and 4003 luminaires ..................................... 79 

B-5 . Mine Safety Appliances Co . model LX2401 luminaire .................................... 81 

B-6 . Mining Controls Inc . model 21322 luminaire .......................................... 81 

B-7 . Mining Controls Inc . tungsten-halogen luminaire ....................................... 81 

B-8 . National Mine Service Co . model 5401-0012, 5401-01 11, 5401-0004, and 5401-0103 luminaires ....... 83 

B-9 . National Mine Service Co . model 5401-0202 and 5401-0293 luminaires ........................ 83 

B-10 . National Mine Service Co . model 5402-0995 luminaire ................................... 83 

B-11 . Ocenco Inc . model 30M and 1513M luminaires ......................................... 85 

B-12 . Ocenco Inc . model 16M luminaire .................................................. 85 

B-13 . Ocenco Inc . model AR-150 luminaire ................................................ 85 

B-14 . Service Machine Co . model D513 luminaire ........................................... 86 

B-15 . West Virginia Armature Co . model 18400-24 and 18400-18 luminaires ........................ 87 

B-16 . West Virginia Armature Co . model 14812D luminaire ................................... 87 

B-17 . Installation and wiring schematics . for intrinsically safe fluorescent systems on a typical coal mine longwallface .................................................................. 88 

B.18 . Installation and wiring schematics for explosion-proof fluorescent systems on a typical coal mine longwallface .................................................................. 89 

TABLES 

1 . Trailing cable maximum allowable instantaneous circuit breaker settings ...................... 9 

2 . Cable resistance based on conductor size .............................................. 10 

3 . Comparison of field modifications of STE's and STE extensions ............................. 17 

4 . Headlight equivalence listing ..................................................... 18 

5 . Categories of available lighting hardware and identification of U.S. manufacturers ............... 36 

6 . Summary of illumination performance differences dependent on lamp types utilized in a luminaire .... 44 

7 . Common mechanisms that mechanically damage luminaires on mobile coal mine face machines ...... 47 

8 . Example illumination system concept evaluation ....................................... 49 

9 . Scheduled maintenance checklist for mine illumination systems ............................. 63 

B-1 . Joy Manufacturing Co . system alternatives ........................................... 77 

B.2 . Joy Manufacturing Co . luminaire specifications ........................................ 77 

B-3 . McJunkin Corp . system alternatives ................................................ 78 

B.4 . McJunkin Corp . luminaire specifications ............................................. 78 
Page 

B-5. Mine Safety Appliance system alternatives ........................................... 79 

B-6. Mine Safety Appliance luminaire specifications ........................................ 80 

B-7. Mining Controls Inc. system alternatives ............................................. 80 

B-8. Mining Controls Inc. luminaire specifications .......................................... 80 

B-9. National Mine Services Co. system alternatives ........................................ 82 

B-10. National Mine Services Co. luminaire specifications ..................................... 82 

B-11. Ocenco Inc. system alternatives ................................................... 84 

B-12. Ocenco Inc. luminaire specifications ................................................. 84 

B-13. Service Machine Co. system alternatives ............................................. 86 

B-14. Service Machine Co. luminaire specifications .......................................... 86 

B-15. West Virginia Armature Co. system alternatives ....................................... 86 

B-16. West Virginia Armature Co. luminaire specifications .................................... 87 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

A ampere kW kilowatt 

"C degree Celsius 1 b pound 

CIS cycle per second lm/W lumen per watt 

OF degree Fahrenheit mA milliampere 

fc footcandle min minute 

fL footlambert nm nanometer 

ft foot ~ct percent 

ft2 square foot s second 

ft/s foot per second sr steradian 

h hour V volt 

h/d hour per day W watt 

in inch W/ ft watt per foot 

in2 square inch Yr year 

K kelvin 

I + 

SELECTED CONVERSION FACTORS 

Abbre- Unit of measure viation To convert to- Multiply byc/in2 candle per square inch candle per square meter 0.000645 i footlambert ,00221 

c/m2 candle per square meter candle per square inch 1,550 i footlambert .2919 

fc footcandle lux 10.76 

fL footlambert candle per square inch 452.4 i candle per square meter 3.426 

lx lux footcandle .092903 
UNDERGROUND COAL MINE LIGHTING HANDBOOK 

(In Two Parts) 

2. Application 

Compiled by W.H. Lewis1 

ABSTRACT 

This Bureau of Mines report and its companion report (Information Circular 

9073) have been prepared as a complete reference on underground coal mine 

lighting. This report discusses system design criteria and procedures, data and 

specifications to aid in selection of suitable mine lighting hardware, and guidelines for system installation and maintenance. Topics include light measuring 

techniques and instruments, illumination regulations for underground coal mine 

environments and equipment, lamps and ballasts, available mine lighting 

hardware, design and evaluation of coal mine illumination systems, and installation and maintenance of a mine lighting system. 

'Electrical engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

This Bureau of Mines report and its companion report, 

Information Circular 9073, have been prepared as a complete reference on underground coal mine lighting. The 

reports are intended to assist those persons who design, 

install, andlor maintain mine lighting systems in making 

appropriate decisions. 

This report discusses system design criteria and procedures, data and specifications to aid in selection of suitable mine lighting hardware, and guidelines for system 

installation and maintenance. Topics include light measuring techniques and instruments, illumination regulations for underground coal mine environments and equipment, lamps and ballasts, available mine lighting hardware, design and evaluation of coal mine illumination 

systems, and installation and maintenance of a mine lighting system. The report provides information to insure an 

understanding of the numerous, complex, and interrelated 

factors that must be considered to design and implement a 

mine lighting system that will satisfy human needs for 

good vision and comfort. 

The design of good lighting systems for underground 

coal mines is no easy task because of the unique environment and work procedures encountered in coal mines. The 

primary objective of these reports is, therefore, to identify 

the major problems encountered in this lighting application and to provide guidance in the solution of these 

problems. If they are carefully designed and implemented, 

lighting systems provide mine workers improved visibility and contribute to improved safety, productivity, and 

morale. Properly designed lighting systems can prove to 

be a very cost-effective investment for the mine operator. 

This report was prepared by BCR National Laboratory 

(BCRNL), Monroeville, PA, under Bureau of Mines contract 50113063. The following contributed significantly to 

the production of the report: J. Yingling and K. Whitehead, BCRNL; A. Szpak, ADS Engineering and Design, 

Inc.; and personnel of the CIE Mine Lighting Committee, 

the Illuminating Research Institute, and Applied Science 

Associates, Inc. 

CHAPTER 1 .-LIGHT MEASURING TECHNIQUES AND INSTRUMENTATION 

Lighting, from the viewpoint of engineering data and 

computations, is discussed in Bureau of Mines Information Circular (IC) 9073. Instruments are, however, required 

to evaluate lighting systems and components. The field of 

light measurement is called photometry, and the instruments used to measure lighting are called photometers. 

Many types of photometers are available to measure 

light energy and related quantities, including illumination, 

luminance, luininous intensity, luminous flux, contrast, 

color, and visibility. The discussion in this report is limited to photometers used to measure illumination, E, and 

luminance, L, from which other quantities, such as reflectivity and luminous intensity, may be computed. 

The photometer is one of the most important tools for 

illumination system design and evaluation. Specific uses 

for underground mine illumination system measurements 

areVerification of compliance with illumination and luminance specifications in the regulations; 

Evaluation of illumination system design options; 

Calculation of reflectance of mine and mine simulator 

surfaces; 

Checking light distribution; 

Checking illumination depreciation over time; and 

Evaluation of discomfort and disability glare. 

Before taking measurements with a photometer, care 

must be taken to insure that a luminaire or illumination 

system is in the proper condition to satisfy the purpose of 

the measurements. An adequate warmup period should 

be allowed for fluorescent, sodium vapor, and mercury 

vapor luminaires. For instance, the light output of some 

types of fluorescent luminaires can be twice as great as 

initial levels after a 30-min warmup period. The light output of some luminaires (especially incandescent) can vary 

widely with deviations in line voltage from nominal. Dirty 

luminaires, obstructions, or deviations in luminaire mountings and orientations from specifications can significantly 

alter illumination levels. 

PORTABLE PHOTOELECTRIC PHOTOMETERS 

The portable photoelectric photometer consists of a 

photocell that receives light and converts it into an electrical signal that is conditioned through an electrical circuit 

and is displayed on a visual meter. The meter reading is 

proportional to the light energy level received by the 

photocell. 

Even the more simple and durable photometers are 

delicate instruments that can give highly erroneous results 

when improperly used or calibrated. Proper instruction in 

the use and calibration of photometers cannot be overstressed. Many factors can cause significant errors in the 

measurements in the very low light levels typical of underground coal mines. Photometers are available in a variety 

of models ranging from the low-cost, handheld units, which 

are very convenient but have limited accuracy and range, 

to more expensive, and more accurate but less portable 

units. 

The following major factors affecting the accuracy of 

photometers should be understood and considered before 

purchasing and using a unit. 

Photocell Characteristics 

Photocells used in portable photometers have been 

improved significantly in the past few years. New design 

photometers that utilize silicon photocell technology have 

distinct advantages when compared with selenium photocell photometers. Silicon photocells are more stable and 

exhibit a more uniform (linear) response in output with a 

change in light level. Selenium photocells are more prone 

to change in calibration with time and also can exhibit a 

memory (hysteresis) effect when measured light levels vary 

significantly. When exposed to illumination, the output of 

photocells decreases over a period of time because of fatigue. 

Therefore, the meter should be exposed to the light level 

being measured for as long an adaptation period as necessary; i.e., until the meter reading stabilizes. 
Color Correction Sensitivity 

The response of the human eye (spectral luminous 

efficiency) for photopic (daylight) vision is shown in figure 

1, along with the response curve for a typical uncorrected 

selenium photocell. Note that the response of the cell differs significantly from that of the eye. This difference would 

cause a significant error in the measurement of visible 

light if the cell were not color corrected. This problem is 

corrected by the placement of filters on the surface of the 

photocell, which adjusts the response of the assembly to 

closely match that of the human eye. The response of a 

color-corrected photocell is also shown in figure 1. 

Cosine Correction 

The response of a photocell changes as the angle of 

light impinging on its surface changes. At high angles of 

incidence, a greater portion of incoming light is reflected 

from the cell surface. This is because the reflectance of 

most surfaces increases as the angle of incidence increases. 

Also, the photocell support frame may prevent some light 

from reaching the photocell. Errors in light measurement 

caused by these factors alone may be as much as 25 pct. 

The problem is corrected by placement of a diffusing cover 

over the photocell as shown in figure 2. This cover adjusts 

the level of light received by the cell to the correct proportion for various angles of incidence. A screening ring is 

also provided on some designs to reduce the light passing 

through the raised edge of the diffuser at very high angles 

of incidence. 

UNCORRECTED - SELENIUM 

LIGHT CELL 

AVERAGE RESPON 

OF HUMAN EYE 

WAVE LENGTH (MILLIMICRONS) 

Figure 1.-Function of color correcting filter on response of 

photocells. 

COSINE CORRECTING INCIDENT LIGHT 

DIFFUSER \ I/ 

COLOR -[ 

Illumination and luminance levels in underground coal 

mines are very low. Regulations call for an average luminance of 0.06 fL and incident illumination levels in the 

range of 2.0 fc. Photometers used for the design and evaluation of underground coal mine illumination systems 

should have full-scale ranges to accurately display levels 

in these ranges. For instance, when using a meter with a 

full-scale range of 30 fc to measure a level of only 2 fc, 

just the zero adjustment and error in reading the meter 

can be very significant. Remember, the difference between 

a level of 1 to 2 fc means a 100 pct error in luminous 

energy. Overdesigning an underground mine illumination 

system to accommodate for poor instrumentation is an 

expensive alternative because of the relatively high cost of 

mine illumination system components. For the engineering design and evaluation of underground coal mine illumination systems, it is recommended that the photometer 

sensitivity be such that a full-scale range of no more than 

0 to 3 fc is available. The meter should, of course, have 

other selectable ranges for higher level measurements, 

perhaps to 50 fc or greater. A meter with high sensitivity 

and accuracy permits the very necessary fine tuning of 

lighting systems needed to meet the stringent lighting 

regulations. 

In designing mine lighting systems, luminance measurements are often required to determine the reflectance 

of the simulated mine surfaces. For luminance measurements, meters with an available full-scale setting of 

approximately 0 to 0.1 fL are recommended. 

Purkinje Shift 

When luminance levels occur that are below approximately 0.01 fL, the eye functions with only rod (scotopic) 

vision and the luminous sensitivity curve is shifted. This 

is called the Purkinje shift, which is discussed in IC 9073 

(chapter 3). Photometers used in underground mine illumination are calibrated for rod and cone vision (photopic) 

because the 0.06-fL regulation is in the photopic range. 

Photometers that automatically compensate for the 

Purkinje shift are not currently available. For measurements below 0.01 fL, a photometer should be color corrected to match the scotopic luminous sensitivity curve. 

Calibration 

Calibration is a method by which the response of a 

photometer is set to match a working standard. Probably 

the most significant source of error in illumination measurements is inaccurate instrument calibration. Photometers are sensitive instruments that are susceptible to loss 

of calibration. Meter calibration should always be checked 

both before and after any series of light measurements. 

Various types of standards are available or can be 

devised for calibration purposes. Most importantly, they 

must ultimately be traceable to a primary lighting standard in a national physical laboratory. 

The following are suggested methods of maintaining 

a standard for photometer calibration. 

SELENIUM CELL / I 

4" DIA. PRESSURE PAD 

Figure 2.-Diffusing cover for cosine correction on photometers. 

The meter can be calibrated with the use of a precision 

calibration incandescent lamp specifically manufactured 

for this purpose. This must be done with accurate control 

of lamp voltage and according to procedures recommended 
by the lamp manufacturer. These lamps have limited life 

and should be used only as recommended by the supplier. 

The working meter can be compared with a second reference meter that is periodically calibrated by the meter 

supplier. This reference meter would be used solely for 

calibration purposes. Use of the reference meter for other 

purposes would totally defeat its usefulness as a working 

standard. 

The meter can be calibrated with a reference standard 

specifically designed by the manufacturer for the specific 

meter. These devices frequently employ nuclear standards. 

Photometer Zeroing 

It is important to check photometer zeroing prior to 

taking measurements. If an analog meter is used, this 

requires setting the meter reading to zero with the photocell completely covered. It should be verified that the meter 

remains correctly zeroed, when the photometer scale selector is changed. A photometer that cannot be properly zeroed 

on all scale ranges should be repaired and recalibrated. 

Improper zeroing can be the source of significant error in 

the low-coal mine illumination levels. 

Temperature and Humidity Effects 

Wide temperature variations affect the performance 

of photocells. Prolonged exposure of selenium photocells at 

temperatures above 120" F will permanently damage them. 

Silicon photocells are less susceptible to temperature variation when compared with selenium photocells. Exposure 

of a photometer to corrosive high-humidity conditions 

should be kept to a minimum. Photometers should certainly never be stored underground. Hermetically sealed 

cells provide greater protection from the effects of both 

temperature and humidity. It is recommended that a desiccator be packed with meters taken underground. 

Contamination 

In underground coal mines, dust can rapidly accumulate on the photodetector surface and diminish measurement accuracy. Moisture and dust can enter photometer 

enclosures and cause component corrosion or wear. These 

factors can easily affect the accuracy and useful life of an 

instrument. Photometers should be kept in a well sealed 

case and, to avoid contamination, should be removed only 

when they are to be used. The photodetector surface should 

be kept very clean, and care taken to use a cleaning method 

that will not scratch the surface. 

Stray Light 

Miner cap lamps can be a significant source of error in 

underground coal mine illumination system measurements. Care must be taken to insure that cap lamps do not 

contribute to surface luminance or impinge on the photodetector surface. It is best to turn off all cap lamps in the 

area when taking lighting measurements. 

THE GO, NO-GO COAL MINE PHOTOMETER 

Most photometers are not permissible, and, therefore, 

cannot be used inby the last open crosscut in underground 

coal mines. These meters are used only for the design and 

evaluation of illumination systems by engineering personnel. 

The go, no-go photometer is a luminance level indicator developed and approved specifically for use by Mine 

Safety and Health Administration (MSHA) personnel to 

monitor the compliance of underground coal mine illumination systems. It is permissible and can therefore be used 

inby the last open crosscut. This meter provides a quick 

"go, no-go" indication to show whether the luminance of 

surfaces is below or above the 0.06-fL level required. 

The go, no-go photometer is designed for convenient 

carrying by inspectors and other persons responsible for 

checking and/or maintaining light levels in compliance 

with regulations. Its size is 4.25 by 2.70 by 0.85 in, it is 

color corrected, and it has a calibration accuracy of 20.1 

pct. The lens' light acceptance angle is 26", which allows 

the meter to average the surface brightness of a circular 

field 3 to 5 ft2 in size when the meter is held 4 to 5 ft from 

the surface being measured. 

The instrument contains a red emitting diode lamp 

that is activated if the measured luminance is below 0.06 

fL and a green diode lamp that is illuminated if the measured luminance is greater than 0.06 fL. 

The photometer can be calibrated by periodically 

returning it to the manufacturer or with the use of a tritium illumination standard (supplied by the manufacturer), 

which is traceable to the National Bureau of Standards. 

This standard has a natural life of 6 yr, after which time it 

must be returned to the manufacturer for replacement. 

Complete procedures for the use of this instrument to 

evaluate the compliance of an illumination system are 

published by MSHA.~ 

MAKING ILLUMINANCE MEASUREMENTS 

Considerable error in measurements can occur if the 

light meter photocell is not positioned correctly for the 

type of illuminance measurement being taken. In mine 

lighting, illuminance measurements are typically taken 

for the following purposes. 

To determine the incident luminous energy (footcandles) 

on a surface. 

To determine the light output characteristics of a luminaire. 

To determine if illuminance levels are sufficient to qualify the illumination system for MSHA approval. 

First of all, it is important to recognize that the photocell is designed to generate an output signal that is proportional to all the light impinging on it and passing through 

an imagined hemisphere below which the photocell is 

placed with the lens facing directly up. Therefore, if a 

measure of illuminance impinging on a surface is required, 

the photocell should be placed flat against the surface, as 

shown in figure 3A. This reading will yield the footcandles 

(lumens per square foot) of luminous energy that is intercepted by the surface. 

When determining the candlepower distribution of a 

luminaire, the photocell should be pointed directly at the 

luminaire, as show in figure 3B. The candlepower curve 

can then be computed using the inverse square law, E = 

2Mine Safety and Health Administration. Handbook of Underground 

Coal Mine Illumination Requirements. 1980, p. 22. 
PHOTOCELL 

(POINTED TOWARDS 

LUMINAIRE) 

LIGHT 

SOURCE / 

0 

B- CANDLEPOWER MEASUREMENT 

PHOTOCELL 

MEASURED 

SURFACE 

C- METHOD ALLOWED FOR STE APPROVAL 

Flgure 3.-Photocell orlentatlon for maklng lllumlnatlon measurements. 

MAKING REFLECTANCE MEASUREMENTS 

The total reflectance of a surface was defined in IC 

9073 as p = 4 reflected light/+ incident light, where 4 

reflected is the total reflected flux and 4 incident is the 

total incident luminous flux. 

Accurate measurements of the reflectance of surfaces 

such as a coal face can be a complex task because, when a 

surface is not a diffuser, the reflected flux can be scattered 

nonuniformly. Methods for the measurement of the reflectance of coal surfaces are briefly discussed in the following 

paragraphs. No standard method has been established for 

the measurement of coal reflectance. 

The reflected-incident light comparison method is a 

convenient and simple means to measure reflectance if a 

surface is a good diffuser. For a perfect diffuser, reflectance can be computed using the equation p = L1/E. 

Although coal has a specular component in its reflective 

Flgure 4.-Photocell fltted wlth adapter for luminance measurements. 
characteristics, the cleaved surfaces are often not well oriented and, therefore, it may be considered a diffusing surface and for some purposes perfectly diffusing. A standard 

portable photometer equipped to measure both illuminance 

and luminance can be used in this method of reflectance 

measurement. Illuminance is measured by placing the photocell flat on a uniformly illuminated surface as shown in 

figure 5. 

With the photometer in the luminance measurement 

mode, the surface luminance is measured and care is taken 

that the area being measured is within the conical acceptance angle of the luminance photodetector. Surface reflectance can then be computed with the preceding equation. 

This is the method utilized by MSHA to approve coal mine 

simulators, which must have a surface reflectance no 

greater than 5 pct. Note that measurement error is introduced when the surface is not a perfect diffuser. Also, care 

must be taken to insure that the presence of instrumentation or the operator does not interfere with the actual light 

levels. 

The reflectance standard comparison method is a 

method by which the reflectance of an unknown surface is 

determined by comparing the luminance of a standard of 

known reflectivity to the luminance of the surface being 

tested. The reflectance of the surface being tested can be 

computed with the equation p = ps (LtL,), where p is the 

reflectance of the surface being tested, ps is the reflectance 

of the known standard surface, L is the luminance of the 

surface being tested, and L, is the measured luminance of 

the standard surface. This method is depicted in figure 6. 

The acceptance angle of the photometer must be SUEciently small to insure that the measured luminance is 

within the area of the standard surface. 

This method is adaptable to controlled laboratory 

measurement conditions because sample sizes need not 

be large. Commission Internationale de 1'Eclairage (CIE) 

standard conditions for using this method state that 'the 

source of illumination shall be at an angle of 45" from the 

perpendicular to the surface to be tested and that viewing 

should be perpendicular to the surface. 

The gonioreflectance method of reflectance measurement is one in which angles of incidence of light and viewing angles are varied to determine the spectral reflectance 

characteristics of a surface. A variety of test methods can 

be constructed to perform gonioreflectance measuremenk3 

OTHER MEASURING INSTRUMENTS 

Many types of instruments are available for the purpose of evaluating lighting in the workplace. In addition 

to the physical photometers previously discussed, there 

3Trotter, D. Reflectance Measurements in Mining. 

Hitchcock, L. C. Development of Minimum Luminance Requirements for 

Underground Coal Mining Tasks. 

are narrow field luminance meters and photographic 

photometers. 

Luminance meters such as the Prichard photometer 

and spotmeters are available for the luminance measurement of small sources such as control panels, luminaire 

surfaces, and machine components for the determination 

of contrast levels and visibility. These meters are highly 

accurate devices used mainly for research and development purposes. 

Photographic techniques can be used to measure 

luminance, contrast, and visibility, as well as to maintain 

a permanent record of conditions. Considerable care must 

be used to insure that the photographic process has the 

same spectral response as the eye and that the recorded 

scene depicts the observed and measured conditions. 

AREA Of 

UNIFORM 

LUMINANCE 

ANGLE 

\ 

ILLUMINANCE 

PnoTocELL 

LUMINANCE 

PnOTOCELL 

Figure 5.-Refiected-incident light comparison method for 

measuring refiectivity. 

k SURFACE OF UNKNOWN REFLECTlVlT Y 

LUMINANCE PHOTOMETER 

4s0 

1 \ \2 LIGHT SOURCE 

SURFACE OF 

Figure 6.-Luminance standard comparison technique for 

measuring refiectivity. 
CHAPTER 2.lLLUMlNATlON REGULATIONS FOR UNDERGROUND COAL MINE 

ENVIRONMENTS AND EQUIPMENT 

This chapter consolidates and explains the regulations, 

interpretations, and official enforcement policies that govern the implementation of lighting in underground coal 

mines in the United States. Note that it does not discuss 

regulations governing illumination component design, 

which are discussed in chapter 4. 

These regulations are found in or referenced in part 

75.1719 of the Code of Federal Regulations (CFR). They 

have four major thrusts: 

1. Specification of required illumination levels and the 

particular areas of the mine that must meet these levels. 

(75.1719-1) 

2. Specification of standards (primarily electrical) to be 

observed when implementing lighting systems to prevent 

the systems from posing additional hazard to worker or 

machine. (75.1719-2) 

3. Specification of procedures for making light measure- 

.merits to verify compliance with the illumination standards. (75.1719-3) 

4. Specification of requirements, in addition to illumination, to increase visibility in the mine environment. 

(75.1719-4) 

THE PRIMARY ILLUMINATION STANDARD 

AND ITS BASIS 

It must be borne in mind that published lighting 

values are not the complete answer to the problem 

they are meant to help solve, for whenever a stage of 

knowledge is reached upon which a code is based, 

unsolved problems still remain.4 

This statement may be applied, of course, to the U.S. 

lighting regulations. Anyone implementing a lighting system on the basis of these regulations should not view the 

standards as a "cookbook prescription" for optimum lighting. Rather, these standards are only intended to specify 

minimum requirements for meeting the priority visual 

needs of the mine-face situation. The status of current 

knowledge and the necessary accommodations to account 

for variability of mining circumstances make specification 

of more extensive standards, at least for the present, 

inappropriate. To realize the optimum benefit from mine 

lighting, it may be desirable to exceed these minimum 

requirements in some instances and to consider additional 

factors. A thorough discussion of design considerations is 

presented in chapter 5, "Design and Evaluation of Coal 

Mine Illumination Systems." 

The "cornerstone" of the U.S. lighting code is expressed 

in provision 75.1719-1(d) of the CFR. "The luminous intensity (surface brightness) of surfaces that are in a miner's 

normal field of vision of areas in working places that are 

required to be lighted shall be not less than 0.06 footlamberts. . ." 

The following points should be noted about this specification. 

1. The requirement is expressed in terms of luminance 

rather than illuminance. This is the preferred method of 

First work cited in footnote 2. 

expressing standards since only the physical measure of 

luminance correlates the what the eye sees (see IC 9073, 

chapter 2). Moreover, by specifying luminance rather than 

illuminance, the standard is, theoretically, uniform regardless of variability in environmental reflectivity. The disadvantages of expression of standards in luminance terms is 

that (1) luminance measurements are more difficult to 

make, and (2) design requires accurate knowledge of 

reflectivity. 

2. The statement that 0.06 fL applies to "surfaces that 

are in a miner's normal field of vision" is an explicit recognition that mine lighting should accommodate peripheral 

vision. As noted in IC 9073, chapter 3, peripheral vision is 

important in mining for (1) early recognition of conditions 

that might give prewarning of potential safety hazards in 

the peripheral field and (2) performance of tasks that 

require knowledge of the relative spatial relationships 

among objects separated by significant distance in the 

surroundings. Light on all surfaces in a miner's normal 

field of vision eliminates the "tunnel vision" effect of the 

narrow cap lamp beam and overcomes beam cutoff by 

machine structure or posts. Provision that this light illuminates these surfaces to 0.06 fL insures response of all 

the eye's photoreceptors to light impulses in the observzr's 

field of view, particularly in th'e peripheral field (see IC 

9073, chapter 3). 

3. Research shows that the 0.06-fL level is adequate for 

performance of a major portion of mining tasks (fine perception of details is generally not required). Most of those 

tasks where greater levels are desirable are performed at 

close range and the cap lamp acts as a supplement to the 

general lighting for adequately meeting these lighting 

requirements. 

4. The 0.06-fL general level of luminance is low enough 

that adaptation problems in going from the illuminated 

area to darker areas of the mine are not severe. 

APPLYING THE ILLUMINATION STANDARD IN 

THE MINE ENVIRONMENT 

The Federal coal mine lighting standards apply to all 

self-propelled mining machines utilized inby the last open 

crosscut. The reason for requiring illumination around 

these machines and in this area of the mine, as opposed to 

other machines and other areas of the mine, is because 

here is where (1) machine-worker activity is most concentrated and (2) hazards are most serious and most likely to 

develop. 

The standards are expressed in terms of specific 

machine vicinities to be lighted to a surface brightness of 

at least 0.06 fL. These vicinities vary, depending upon 

machine type, mining method, and seam height. They have 

been selected primarily on the basis of the objectives stated 

previously; i.e., lighting needs for adequate peripheral 

vision and adequate visibility for task performance and 

hazard identification. 

The specific machine vicinities to be illuminated to 

the 0.06-fL standard are identified in CFR 75.1719-1(e) (1) 

through (e)(6). In enforcing these standards, certain accommodations have been made by the Mine Safety and Health 

Administration (MSHA), so that the effective standards 
are consistent with the current status of mine lighting 

technology. The accommodations are in recognition of problems with discomfort glare, hardware maintenance, eficient utilization of fixture candlepower, etc., which currently cannot be alleviated through system design and 

installation with available hardware and techniques. Policy in enforcing the illumination standards is based upon 

extensive and continuing postaudit of the impact of the 

standards and reflects a commitment by MSHA as a proponent of both good and practical lighting within the intent 

and scope of CFR 75.1719. 

Appendix A identifies the standards that apply to the 

various machines and environments, the latest enforcement policies for these standards, and explanatory comments. 

In complying with these standards, the mine operator 

has the option of mounting luminaires on the machine or 

separate from the machine, for example, temporarily 

mounting them along roof and ribs. The latter option is 

typically referred to as "area-lighting." Because of practical difficulties with area-lighting systems, nearly all systems now utilized employ machine-mounted fixtures. Area 

and machine-mounted systems are compared in detail in 

chapter 6. 

The seam height used for lighting application requirements at a mine is equal to the normal extracted height. In 

cases where entry dimensions vary across the entries of a 

working section, the lowest dimension may be used to determine the lighting requirements that apply to that situation. 

On sections where the seam is extracted in two or more 

lifts (e.g., the upper 10 ft and lower 10 ft of a 20-ft seam), 

the lighting system must meet the requirements for both 

seam heights. 

, In addition to the illumination of face machine vicinities, it is a Federal requirement that each person who goes 

underground wear an approved personal cap lamp. 

ADDITIONAL STANDARDS FOR IMPLEMENTING 

FACE ILLUMINATION SYSTEMS 

Implementation of lighting systems at the coal mine 

working face presents considerable potential for creation 

of additional hazard or risk to personnel and equipment. 

Because of this, it has been necessary to establish additional standards to guide such implementation. The scope 

of this section is limited to those standards presented or 

referenced in CFR 75.1719-2, which affect MSHA approval 

of a lighting system design as implemented by a mine 

operator. 

Electrical Requirements 

The purpose of the electrical standards is to insure 

that lighting systems are implemented in such a manner 

that prevents creation of electrical shock, fire, or methanedust ignition hazard. 

First and foremost, CFR 75.1719-2(a) requires that all 

lighting fixtures and components utilized on face illumination systems be permissible. This means that (1) system 

components must be "certified" in accordance with the provisions of part 26 of the CFR or other parts referenced 

therein and (2) systems synthesized from these certified 

components must receive a Certificate of Approval for permissibility in accordance with part 26. The latter involves 

assuring compatability of the certified components and a 

check that certified components are used when necessary. 

The provisions of part 26 are discussed in detail in chapter 

4. These design criteria are directed at hazards such as 

ignition of methane-air mixtures, excess surface temperature of components, electrical shock, etc., and their purpose is to assure that design of the individual components 

and the total system is adequate for safe implementation 

in a coal mine. 

Note that the application of diffusers on luminaire 

lens may alter the permissibility of these components 

(depending upon the resulting heat dissipation characteristics and the chemical compatibility of the diffuser with 

the lens material). Approved diffusion materials include 

~eflon~ fluorocaron polymer, Kapton polyimide film, Myler 

polyester film, nylon film of various thicknesses, sandblasted polycarbonate, and spray-on frostings. Diffusion 

materials should be approved in combination with a 

particular luminaire. MSHA maintains an updated list on 

such approved combinations. 

In addition to this general requirement for utilization 

of permissible components and systems, there are some 

supplemental electrical standards, primarily directed at 

preventing the system from posing an electrical shock 

hazard, which must be incorporated in proposed lighting 

systems. These standards differ for two different classes of 

lighting systems defined as follows: 

Machine mounted.-Lighting fixtures are permanently 

mounted upon mining machinery and power for the lighting system is derived from a power source on the machine. 

Stationary.-Lighting fixtures are mounted independent 

from the machine and power is supplied to the fixtures 

through trailing cables. Longwall, shortwall, and area 

lighting systems fit into this category. 

The reason for this differentiation is that (1) personnel are much more likely to come in bodily contact with 

stationary lighting fixtures while the fixtures are energized and (2) stationary fixtures are not in contact with an 

electrically grounded medium as are machine-mounted fixtures (i.e., the machine frame). Hence, stationary systems 

present a greater risk of causing electrical shock and more 

stringent precautions are warranted. 

Supplementary Standards Applicable to 

Stationary Lighting Systems 

Maximum Voltage Restriction (75.1719-2(c)(2)).-To 

reduce shock potential, the voltage on power systems supplying alternating current fixtures is limited to 70 V phaseto-neutral (i.e., 120 V phase-to-phase). This is the standard voltage used on all available longwall lighting systems. The limit on dc fixtures is 300 V. The latter restriction might apply in application of an area lighting system 

in a dc mine. 

Grounding Requirements (75.1719-2 and 75.701).- 

All stationary ac lighting systems that provide power to 

the lighting fixtures and/or system power conditioning 

units at voltages greater than 100 V phase-to-phase 

(applies to all currently available longwall light systems) 

must incorporate a "resistance-grounded-neutral" grounding circuit which limits fault current to less than 5 A. 

Also, the size of the ground conductor in all cables must 

Reference to specific products does not imply endorsement by the Bureau 

of Mines. 
equal the cross-sectional area of the power conductor for 8 

AWG or smaller power conductors or one-half the crosssectional area of the power conductors 6 AWG or larger. 

Most lighting systems in use employ 8 AWG or smaller 

cable and, hence, require the same size ground conductor 

as the power conductor. Finally, the current rating of the 

ground-fault resistor must meet Institute of Electrical and 

Electronics Engineers (IEEE) specification 32-1972 for 

"extended time rating." (Specification is available from 

any MSHA District or Subdistrict office.) This is to insure 

that the grounding circuit is capable of maintaining low 

fault current for extended time periods should the protective circuitry which monitors ground faults fail to deenergize the circuit. 

The circuit of figure 7 shows advantages over other 

grounding circuits (e.g., same circuit without a grounding 

resistor) in the event of a ground fault (short circuit 

between line and neutral) by (1) maintaining low current 

flow after the fault occurs and (2) maintaining metal parts 

in contact with the fault at low potential minimizing the 

shock hazard. The same circuit is required for all portable 

mining equipment, except that the current restriction is 

smaller for stationary lighting systems. The resistor is 

sized using Ohm's law-R equals V line to neutral divided 

by I maximum; 70 V/5 A or 14 ohms. Some designs employ 

slightly larger resistors, which would reduce the ground 

fault current below 5 A. 

Trailing Cable Requirements (75.600-75.607).- 

Cables to stationary lighting systems (includes longwalls) 

are considered trailing cables and therefore all statutes of 

CFR 75, Subpart G, "Trailing Cable," apply to use of these 

cables. These statutes, which will not be discussed in detail 

here, address jacket flame-resistance, circuit protection, 

splicing, and procedures for breaking connections. 

Circuit Breakers, Circuit Breaker Settings (75.1719- 

(2)(e) and 75.601-11.-A circuit breaker, or other approved 

device, must be utilized to protect the circuit from overloads and short circuits (e.g., damage of insulation). The 

instantaneous current setting at which the circuit breaker 

deenergizes the circuit is also specified. When stationary 

(longwall) systems are field inspected prior to issuance of 

a system acceptance (discussed later), a demonstration that 

the breaker is properly working is required. The following 

is a discussion of the method for determining the circuit 

breaker setting. 

Breaker settings must comply with two criteria in the 

CFR: 

1. 75.601- 1 .-Maximum allowable instantaneous circuit 

breaker settings are specified for trailing cables dependent on conductor size, as given in table 1. 

2. 75.17 19-2(e).-Maximum allowable instantaneous circuit breaker setting should not exceed one-half the available fault current. 

The criterion that yields the lowest ampere setting 

dictates the breaker setting of the particular lighting system in question. 

Determination of the setting that complies with the 

first criterion is straightforward and involves simply reading from table 1 the setting that corresponds to the 

minimum size cable in the circuit protected by that breaker. 

The following formula is accepted for determining the 

breaker setting in accordance with the second criteria: 

Maximum breaker setting = Imin,, = 0.5 [(KB E,+,+)/q]. 

Table 1 .-Trailing cable maximum allowable 

clrcult breaker Instantaneous settings, amperes 

Imin,++ is the minimum allowable fault current, phase-tophase, in amperes. 

KB is the breaker "tolerance factor" dependent on type 

of breaker utilized in the system, as follows: 

Conductor 

size, A WG Setting 

14 ...... 50 

12 ...... 75 

10 ...... 150 

Breaker type K~ 

1. Current transformer (CT), relay and contactor . . . . . . . . . . 0.90 

2. "Mine duty" breaker (manufacturer specifies tolerance of low and 

high instantaneous settings to be k10 pct of nominal setting) . . .85 

3. Standard breaker . . . . . . . . . . . . . . . . . . . . . . . . . . .70 

Conductor 

size, A WG Setting 

8 . . . . . . . 200 

6 . . . . . . . 300 

E is the voltage, phase to phase. 

G?s the cable resistance of the continuous current path 

to any termination that yields the highest total resistive 

value (this would correspond with the minimum fault 

current). 

GROUNDING RESISTOR 

MAX. 5 AMP 

- 14 OHMS GROUND WIRE FAULT CURRENT 

TRANSFORMER SECONDARY 

-- 1V ONLY FROM 

EXPOSED HOUSING 

TO GROUND 

- 

I RESISTANCE OF MAN 

I 

I 

I -- - - - - -- .-. -L - 

Figure 7.-Resistance-grounded neutral grounding clrclll* 
I+ may be calculated knowing the size and length of 

trailing cable utilizing the values shown in table 2. 

Table 2.-Conductor reslstance based on conductor slze, 

ohms per thousand feet 

The basis of this relationship is Ohm's law, I = E/Z, 

used in all standard fault current analyses. In the case of 

stationary lighting systems, other impedances such as cable 

inductance and transformer primary and secondary impedance are insignificant relative to the magnitude of conductor resistance, RT. The constant, 0.5, is the required safety 

factor specified in 75.1719-2(c). 

Conductor 

size, A WG Resistance 

14 ...... 3.4 

12 ...... 2.14 

10 ...... 1.35 

As an example, a typical longwall system might use 

785 ft of 8 AWG cable protected by a standard breaker to 

distribute power to power conditioning units along the 

face, as depicted in figure 8. 

The first criterion yields a maximum breaker setting 

of 200 A, which corresponds with utilization of minimum 

size 8 AWG conductors (see table 1). 

Applying the formula for the second criterion: 

Maximum breaker setting = I, = 0.5[(K, . E, )/I+]; 

0.5 [(O. 7)(120)/(785)(0.878/1000)1 or 61 A. The seconcf cr~terion yields the lowest breaker setting, hence, it controls 

the maximum setting permitted for this particular system 

design. 

Conductor 

size, A WG Resistance 

8 ...... 0.878 

6 ...... .552 

Supplementary Standards Applicable to 

Machine-Mounted Lighting Systems 

Grounding Requirements.-Lighting fixtures in contact with the machine frame are electrically grounded 

through the machine grounding system. However, there is 

considerable potential for such fixtures to be severed from 

the machine and in such a state would be ungrounded, 

presenting a shock hazard. For this reason a separate 

ground conductor from the fixture housing to the machine 

main frame is required. The preferred method of doing 

this is to utilize a cable with a separate ground conductor 

in the supply cable to the fixture and to tie the fixture to 

the grounded lighting power supply or power distribution 

box. At the time the illumination standards were first 

implemented certain machines, especially shuttle cars, utilized only two-conductor cable to supply power to the 

already existing luminaires. Since substitution of a threeconductor cable, with ground wire, would involve extensive modifications, an external grounding shunt from a 

luminaire to the machine frame is permitted as a temporary measure. The two-conductor cable is to be replaced 

upon the next machine rebuild. 

Intrinsically Safe Pilot Circuits on Explosion-Proof 

Connector Equipped Systems 

For ease of maintenance, many explosion-proof lighting systems, both stationary and machine-mounted, now 

employ explosion-proof connectors at strategic locations to 

permit quick disconnect of system components (luminaires 

and power supplies) without disturbing packing glands. If 

such connectors are uncoupled while energized, the leads 

will be exposed, which creates a hazardous condition. 

Intrinsically safe pilot circuits as discussed in the following paragraph, can be used to deenergize the circuit branch 

feeding power to the connector and eliminate such a possibility of exposed and energized leads. Use of such circuits 

on explosion-proof connector equipped systems is required 

in some States and is highly recommended regardless of 

where the application is made. 

An intrinsically safe pilot circuit is typically a modification of a ground check circuit that is used to monitor 

continuity of the ground conductor. A transformer places a 

low, intrinsically safe potential across a circuit formed by 

an additional conductor called a pilot wire shunted to the 

ground conductor (see figure 9). A relay monitors current 

in this loop and will deenergize the entire circuit if the 

current reaches zero (indicating continuity is broken). If 

the pin and socket arrangement shown in figure 9 is used 

for the internal connections within the connector, the pilot 

circuit will be broken first, tripping the relay and deenergizing the circuit before power leads A and B are exposed. 

(On systems without ground fault, monitoring will require 

a separate circuit which runs with the power cabling.) 

Antiflicker Requirements 

The potentially harmful effects of flickering light 

sources have been discussed in IC 9073 (chapter 3). 

t 785 FEET 

Flgure 8.-Longwall power dlstrlbution clrcult for breaker settlng calculation. 

n 

8/3 CABLE 

0.878 oHMs/THousAND FEET 

n 

120 v 

n 

STANDARD BREAKER 

+ 

K = 0.70 b POWER I 

POWER CONDITIONING 

CONDITIONING UNIT 

UNIT 
TRANS 

LOAD 

SHUNTED 

TERMINAT 

AT 

ION 

X/P CONNECTOR WITH PIN 

AND SOCKET CONNECTIONS 

Flgure 9.-lntrlnslcally safe pllot clrcult wlth exploslon-proof connector. 

75.1719-2(c) requires lighting fixtures to be operated at 2. Headlights and other directional luminaires should 

power greater than 50 CIS. This would create a flicker of not be located behind machine-operator stations where the 

100 pulses per second on arc discharge lamps which is operators would be looking back into them. In particular 

beyond the threshold for human perception. This is gener- they should not be applied on the front of the bolter. 

ally not a problem since most light sources operate at 60 3. Any fixture within the operator's line of sight, when 

CIS from utility power or at much higher frequencies when he or she is performing routine tasks at the operator's 

solid state ballasts (see chapter 3) are used. station or machine control area, should be shielded and/or 

acceptably diffused. 

Requirements Concerning Luminaires in 

a Blasting Zone 

To prevent the possibility of lighting circuitry initiating an explosion, all circuits to light fixtures in a zone 

where shooting is to occur (typically on longwalls) must be 

deenergized prior to removing shunts from the blasting 

caps. In addition, to prevent the blast from damaging the 

fixtures-perhaps voiding permissibility characteristics of 

the luminaires through lens damage or an electrical fault+ 

MSHA STE PROGRAM 

It is the responsibility of each mine operator to1. Meet the relevant standards for illuminating each 

workplace as specified in appendix A; and 

2. In doing this, utilize systems that comply with the 

supplementary system-design standards outlined in the 

previous subsection. 

one of the following two measures must be taken: The Statement of Test and Evaluation (STE) program 

Fixtures located within 50 ft of the area where the has been established by MSHA to facilitate compliance 

shot is being fired must be removed. with these two requirements. 

2. Fixtures within this area must be protected against The STE program is administered by MSHA's Apflying debris (e.g. by hanging belting). proval and Certification Center (A&CC), a group that 

approves products and systems for use in underground 

From a maintenance viewpoint, the second option is 

often not desirable. Guards, such as suspended belting, 

can protect the fixtures from flying debris and maintain 

the integrity of the fixture housing. However, they offer 

little protection against shot percussion, which can damage luminaires internally, particularly fluorescent lamps. 

It is recommended that connector equipped longwall lighting systems be equipped with' a quick-release mounting 

system (see chapter 6) to allow removal, rather than 

guarding, of at least those luminaires in the immediate 

shot vicinity. 

Antiglare Requirements 

It is a requirement that illumination systems be 

designed and installed to minimize discomfort glare. Concrete standards for realizing this do not exist at this time; 

however, it is recommended that a system be reviewed 

with respect to the following criteria, which represent some 

of the most significant glare problems: 

1. Fixtures should not be mounted under canopies without backshielding. 

mines. ~ightin~ system design and application data are 

submitted to the A&CC group by system designers, including manufacturers and mine operators. This information 

is reviewed to determine system compliance with relevant 

requirements of the CFR and, if these requirements are 

satisfactorily met, A&CC issues an approval, called a statement of test and evaluation (STE), to the party submitting 

the design for review. 

Mine operators may then implement the design in 

their mines and be guaranteed compliance with the illumination standards as long as the approved design and application specifications are initially and continually met in 

the actual installation. This includes proper maintenance 

of the system with respect to permissibility, cleanliness, 

and operativeness of system components. 

An important aspect of the STE program is that the 

light measurements used in issuance of an STE approval 

may be obtained from an approved simulated mine environment using simulated models, or mockups of mining 

machinery. The following are benefits of this process. 

1. The measurements obtained in the simulated environment are assumed applicable for any actual mine utilizing the given equipment and within the dimensional 
restraints established in the simulator. Hence, an approval 

is given on the basis of a particular machine model and 

entry size and is independent of a particular mine. 

2. The actual design process is simplified because it is 

conducted in a controlled environment where measurements are easily taken, and variations in layouts are easy 

to establish and test. 

3. Access to a mine is unnecessary. This makes it convenient for independent firms with expertise in lighting, such 

as lighting hardware manufacturers and mining machinery 

manufacturers, to establish system designs on behalf of 

the mine operators. 

VALUE OF THE STE PROGRAM TO MINE 

OPERATORS AND SOME IMPORTANT 

LIMITATIONS 

Before continuing, it should be realized that an installed lighting system need not have an STE approval to 

be in compliance; there is no requisite for an STE in the 

CFR. However, it is generally to the mine operator's advantage to purchase systems that already have an STE 

approval or to obtain an STE approval for a design that 

does not have one. 

The primary advantage of an STE-approved design 

over a non-STE-approved design is that the STE is a substitute for on-site light measurements in determining 

Whether the system is in compliance with the illumination requirements. An inspector will not take light measurements if1. The inspected installation meets the approved design 

and application specifications; i.e., machine-model number and its actual geometric configuration correspond with 

those given in the. STE, luminaires are located and oriented as shown on the STE within specified allowable 

tolerances, and the system is being operated in entries 

with dimensions within the limits specified on the STE; 

and 

2. The inspected system is properly maintained; i.e., all 

luminaires are operable, and the lens on all fixtures are 

clean permitting full transmission of light. 

On a non-STE-approved system, light measurements will 

be taken to determine if the system complies with the 

lighting standards. Moreover, inspectors may elect to 

repeat these measurements on any future inspection, particularly in instances where entry dimensions, or other 

variables that may affect realized luminance levels, change. 

For practical reasons, light levels on simulatordesigned systems are verified using illumination (footcandle) rather than luminance (footlambert) measurements. This involves assuming a uniform reflectance of 

coal which then applies to all simulator designed systems. 

The reflectivity of coal specified in the regulations is 4 pct, 

which results in an illumination requirement of 2 fc to 

achieve a luminance of 0.06 fL (this derivation is explained 

at the end of this section). Actual fresh coal reflectivities 

have been reported from as low as 1 pct to as high as 10 pct 

(4 pct was representative). 

A higher reflectivity in a particular mine would give 

the designer more flexibility in sizing, locating, and diffusing luminaires if an STE were not obtained, since, in this 

case, compliance would be assessed on the basis of on-site 

luminance measurements that account for the higher 

reflectivity. The operator wishing to design a system using 

actual reflectivity must consider the more rigorous inspection of non-STE-approved systems and that 'Ijust meeting 

but not exceeding" 0.06 fL is not necessarily a priority or, 

in some cases, even appropriate design objective. 

Mine operators should also consider that if improper 

maintenance, e.g., dirty lens, results in the necessity of 

on-site measurements of an STE-approved system during 

an inspection, these measurements will be luminance 

measurements. In a low reflectivity mine, the "safety 

margin," where actual design levels exceeded 0.06 fL, will 

be reduced or nonexistent, thereby increasing the possibility of receiving a citation. Hence, keeping an STE-approved 

system clean is highly important. 

It should be noted that the STE approval process is 

only concerned with the particular design requirements of 

the CFR. As noted previously these are only minimal standards and often it is desirable to exceed these light levels 

and consider additional factors when establishing a design. 

Specific examples include the desirability of providing 

greater light levels to raise the adaptation state of the 

eyes reducing contrast and glare problems from some luminaires, and the desirability of providing higher light levels 

on particular tasks .(e.g., the coal face on continuous 

miners). In short, an STE-approved system should not be 

construed as an "optimally designed" system. These designs 

should be reviewed carefully; their performance in meeting visual' needs carefully assessed. Guidelines for reviewing them are discussed in chapter,5. 

In IC 9073, the relationship between luminance, L' 

(footlamberts), illumination, E (footcandles), and reflectivity, p, was given as E = Lr/p. 

Direct application of this relationship in the case of 

simulator-designed systems would create an unrealistic 

illumination design value because light output from luminaires will decrease with time because of reduction in lamp 

output (lumen depreciation, see chapter 3) and deterioration of the transmittance characteristics of the fixture lens. 

A more realistic result is obtained by modifying the formula with a light loss factor, Z: E = L1P.Z. The accepted 

value for Z is 77 pct. 

The modified formula is used to determine the required 

illumination design value, which is equivalent to a luminance of 0.06 fL when coal is assumed to be a perfectly 

diffuse reflector with a reflectance of 4 pct: E = L1P.Z; 

0.06/(0.04)(0.77) or 1.95, =2 fc. 

STE APPLICATION PROCESS AND INFORMATION 

REQUIREMENTS 

Any party, including mining companies, lighting hardware manufacturers, face equipment manufacturers, and 

consulting groups, may submit an illumination system 

design for an STE approval. 

The following information must be submitted in such 

applications. 

Application Form 

One of two forms are available depending on whether 

the design is for longwalls or room-and-pillar face machines. The form identifies the basic application parameters of the design-machine type(s) and model(s), minimum- and maximum-entry dimensions. Other information is requested to facilitate processing of the application. 
Machine Layout Drawing 

The machine layout drawing (fig. 10) is used to present the spatial design of the lighting system. Dimensioned 

drawings of the machine to be lighted (typically plan and 

profile views) show location and orientation (and in some 

cases acceptable tolerances in location and orientation) of 

luminaires and shields. Notes on the application of diffusers must also be included. For longwalls the drawing must 

show the lighting system layout on the face supports, 

headgate, tailgate, and control station. 

One-Line Diagram 

The one-line diagram (fig. 11) is the basic document 

used for review of permissibility of the lighting system. 

The diagram represents the physical assembly of certified 

components used to construct the system, with one line 

used to show electrical interconnections between the 

components. Information requirements include (1) identification of all certified components used to construct the 

system, including explosion-proof numbers and numbers 

of certification reference drawings, if applicable; (2) specification of cable sizes and outside diameters; (3) specification of cable diameter range accepted by gland entrances 

to explosion-proof enclosures and switches; (4) notes relevant to special installation requirements necessary to 

maintain permissibility; and (5) delineation of permitted 

electrical configuration options and identification of optional equipment. 

It is acceptable to standardize one-line diagrams for 

any particular luminaire-power supply combination. Once 

approved initially, the same one-line diagram may be submitted with future STE applications and need not be 

reapproved, saving significantly on approval time and costs. 

It is advisable that such diagrams be sufficiently generalized, yet comprehensive enough to include all possible alternative arrangements and optional equipment that might 

be utilized in an actual field installation. 

Electrical Schematic 

The electrical schematic, figure 12, is simply a wiring 

diagram utilized to detail interconnections between electrical components. The diagram need not detail the whole 

system but should include all representative parts and be 

adequate to show a purchaser of the system how to wire it. 
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Flgure 11 .-One-llne dlagram. 

On longwalls (and other stationary lighting systems) 

this drawing (or supplementary one, as required) should 

also show the systems incorporated to meet the special 

electrical requirements of stationary systems as discussed 

in the previous section (resistance-grounded-neutral, 

grounding circuit, required circuit-protective devices, pilot 

circuits, etc.). 

Light Measurement Data 

These data are used to verify that the system meets 

the light level requirements specified in the regulations, 

appendix A, for the particular machine type and seam 

height application. Incident light measurements must be 

taken for each 2- by 2-ft area on the surfaces surrounding 

the machine at the maximum entry dimensions for which 

the STE applies. Typically, they are reported on an "unfolded box" diagram, figure 13, where surfaces representing the roof, ribs, face, and floor are divided into 2- by 2-ft 

squares and indication is given simply whether incident 

light measured at these areas exceeds or is less than 2 fc. 

These measurements must come from one of three 

sources: 

1. Applicant's approved simulator (discussed at the end 

of this section). 

2. Beckley (WV) Electrical Testing Center (BETL) 

simulator.-This simulator is available for use at a fee to 

interested parties. It is also used by BETL personnel to 

solve special lighting problems for mine operators. A subsequent section discusses this service in more detail. 

3. Field data.-Field measurements at the mine site by 

BETL personnel can be utilized in establishing an STE. 

These are obtained upon mine operator request. A fee is 

charged for obtaining them and this practice would be 

dependent on availability of BETL personnel. 

All longwall STE approvals require an on-site inspection by BETL representatives to verify light level compliance and installation details as specified in the STE 

application. These are conducted at the applicant's expense. 

Luminaires must be installed in accordance with the 

machine layout drawing at the headgate, control station, 

and a representative area of the face and travelway. The 

tailgate is usually not required to be lighted for this inspection (getting power to the tail would be difficult for a partial installation) but accurate tailgate drawings and simulator light measurements must be submitted with the STE 

application. If those drawings are found inaccurate upon 

field inspection, an additional field inspection might be 

required, at the applicant's expense, to inspect installed 
Figure 12.-Electrical schematlc dlagram. 

P = 0.04. ONLY 4 PERCENI 

OF LIGHT REFLECTED 

MOST OF FLUX ARRIVING 

A1 P COMES DIRECTLY FROM 

THE SOURCE. REFLECTED 

Figure 14.-Signlflcance of Interreflectlone when taklng llgM 

measurements In mlne slmulatore. 

RIGHT RIB 

Flgure 13.-"Unfolded-box" dlagram for presentlng llgM measurement data. 

tailgate-area lighting. These light measurements are necessary in addition to simulator values because of the many 

sources of shadows on actual faces, which cannot be accurately simulated. 

It has often been the case that mine operators have 

filed for an STE for a longwall lighting system after the 

system was installed and operating. In such event it would 

be to the operator's advantage to file for the STE promptly. 

This would insure that the on-site light measurements are 

least affected by the various time-related factors that tend 

to reduce system light output. 

Construction of an environment to accurately simulate a mine for lighting design purposes is relatively simple because of the low reflectivity of the mine environment. 

Figure 14 illustrates a light source in a mine entry. 
If the reflectivity of the perimeter walls was high, significant amounts of the light arriving at P would have 

been reflected from the other surfaces. However since coal 

mine reflectivities are low, averaging only 4 pct, light corning directly from the source comprises nearly all of the 

light reaching P; interreflections are negligible. This means 

accurate incident measurements can be made without 

locating actual walls of similar reflectivity to coal to simulate the entry perimeters; rather, it is only necessary to 

take incident reading at the points that define the wall. 

The only requisites for a simulator that would be capable 

of simulating any size entry are (1). its dimensions exceed 

the maximum size of entry to be simulated and (2) all 

walls must be painted with low reflectivity paint. 

Specific MSHA requirements for construction and use 

of simulators follow: 

1. The building should exclude exterior light such that 

measurements, with an artificial light source in the simulator turned off, are less than 0.1 fc at any point. 

2. The walls, floor, and ceiling must have a reflectivity 

less than 5 pct. This is achievable with most commercial 

flat-black paints. To assist the operator of the simulator in 

confirming this, MSHA will measure the reflectance of a 

sample of the selected paint on the materials used to construct the walls of the simulator. 

3. Cosine and color corrected incident photometers (see 

chapter I), calibrated to standards traceable to the National 

Bureau of Standards, must be used to take light measurements. BETL offers such calibration at a fee for any party 

operating an approved simulator. 

4. A gridwork should be established on the floor and at 

the perimeter planes that define the entrv roof, ribs, and 

facesuch that these planes are divided into>- by 2-ft sguare 

fields. Incident light measurements are made at all intersecting lines on this gridwork. In many simulators, such a 

gridwork is established by suspending wires 2 ft apart in a 

given plane and locating a marker every 2 ft along the 

wire. The photometer head may be angled to the light 

source for maximum reading. Light measurements on the 

floor begin 1 ft from the machine perimeter. 

5. Room temperature should be monitored and recorded 

when measurements are made because temperature can 

affect photometer calibration and light output of fluorescent lamps. 

6. MSHA will initially inspect the facility and observe 

techniques used to take light measurements. This inspection may be repeated at any future date. 

Short Circuit Calculatibns (Longwall-Stationary 

Systems) 

Using the procedure detailed previously "short-circuit" 

calculations must be submitted to determine maximum 

allowable breaker settings. To do this, it is necessary to (1) 

determine the current path of the system to the termination that yields highest resistive value, (2) specify cable 

diameters and lengths accordingly, and (3) specify type 

and tolerance factor of the system circuit breaker. The 

BETL field inspector of the lighting system will also require 

a demonstration of the operativeness of the circuit breaker 

upon field inspection of the lighting system. 

SPECIFYING OPTIONAL EQUIPMENT ON 

STE APPLICATIONS 

As noted previously, systems may be specified in applications for STE approval so that they include various equipment or configuration options. To simplify paperwork 

requirements for end users of the design, it is desirable 

that useful options be specified in the one-line drawing. In 

the STE approval process, review of the optional components would be limited to determining (1) the permissibility of the components or system, and (2) that additional 

luminaires do not create objectionable glare for the machine 

operators. 

The following illustrate desirable options to specify on 

STE applications: 

1. Additional headlights might be specified as an option 

on continuous miners and other face machines since many 

operators prefer having higher light levels on the face. 

2. Adjustable headlights are desirable on face drills to 

supplement face lighting on drill hole positions (MSHA 

will not consider adjustable headlights in meeting the Federal standard, hence all such lights are "supplementary"). 

3. Permissible connectors are desirable in many applications. 

MSHA REVIEW OF STE APPLICATIONS 

STE applications are submitted to BETL, a division of 

A&CC located at the MSHA Academy in Beckley, WV. 

The following procedure is used in reviewing the application. 

1. The one-line diagram is forwarded to the Division of 

Electrical Safety, another subdivision of A&CC in 

Triadelphia, WV, for review of the permissibility of the 

proposed system in accordance with the system requirements contained or referenced in part 26 of the CFR. If the 

one-line diagram has been previously approved, this is 

verified by BETL and the diagram is not resubmitted to 

the Division of Electrical Safety. Total system approval 

times are reduced from an average of 3 weeks to 1 week for 

applications with previously approved one-line diagrams. 

2. BETL reviews the light measurement data to see if 

the system as depicted in the machine layout drawings is 

in compliance with the illumination standards that apply 

to the particular application. This review may or may not 

require mocking up the machine in the BETL simulator 

and taking measurements. The "reasonableness" of the 

measurements based on BETL experience with similar 

design has bearing on whether the machine is simulated 

at BETL. If the measurements are found in error, BETL 

may request a visit to the applicant's simulator to inspect 

the facility and review measurement procedures. All 

longwall applications require an on-site inspection with 

the system installed as specified in the drawing on representative areas of the face to verify compliance of the light 

measurements. 

3. BETL reviews the machine-layout drawing and specifications of shields and diffusers to determine whether the 

design causes excessive discomfort glare. This evaluation 

may require resimulation of the design in the BETL 
laboratory. This evaluation, although subjective, is based 

upon extensive experience of BETL personnel relative to 

the acceptability of lighting systems in the field. Operator's 

stations are evaluated with the greatest scrutiny. If the 

system is deemed to cause excessive glare, BETL will suggest changes to correct the problem. 

4. BETL reviews electrical schematic and short-circuit 

calculations (longwall only) for (1) verification that the 

electrical design complies with the requirements of CFR 

75.1719-2 and (2) adequate depiction of how the system is 

wired. 

Upon a favorable MSHA review of these four aspects, 

the applicant is awarded an STE approval identified by an 

approval number. 

MODIFICATION OF STE-APPROVED DESIGNS 

It has proven necessary to establish procedures for the 

modification of STE-approved lighting designs to accommodate the varying conditions of application that exist in 

the field. For example, actual machine geometry may vary 

from the STE geometry because of optional equipment, 

modifications, and variances in how the machine was built; 

fixtures may be located in the STE design where they are 

exposed to excessive mechanical hazard, lack anchor points 

for mounting, prevent machine servicing, or cause glare; 

or, in the case of longwalls, equipment configuration 

changes might occur between successive panels. 

Two procedures can be used for modifying STE design* 

field modification and STE extension. Table 3 explains 

and compares these two alternatives. As noted in the table, 

under both procedures any change is permitted that does 

not afTect machine permissibility or light level compliance. 

This includes addition of shields and diffusers, changes in 

luminaire locations, and changes in size or number of 

luminaires. 

Table 3.-Comparison of field modlfic 

As implied in the table, there are significant limitations in the application of a field-modified STE whereas 

designs that incorporate STE extensions may be applied 

the same as an STE design. Because of this important 

advantage and the availability of BETL and most lighting 

hardware manufacturers to assist operators in obtaining 

an STE extension, this is the recommended route for modifying an STE design in nearly all cases. A discussion of 

BETL as a resource in helping mine operators to solve 

lighting problems and the outline of a procedure operators 

may take to obtain an STE extension are presented at the 

end of this section. 

A common design modification sought by operators is 

to substitute one manufacturer's headlight for another. 

Photometrically (i.e., in terms of light output and distribution), there is approximate equivalence among most 70-W 

high pressure sodium, 100-W mercury vapor, and 150-W 

incandescent fixtures. BETL permits substitutions within 

the listing in table 4 and it is unnecessary to provide light 

measurements for such substitution in any application for 

an STE extension. It is necessary, however, to provide a 

new one-line diagram showing the substituted headlight. 

Because of frequent equipment changes on longwalls, 

especially between panels, there may be some question of 

the effect on the status of the STE approval. The STE, in 

general, is tied with the face supports and travels with 

them from section to section and mine to mine, so long as 

the application of the supports is within the seam height 

range specified in the STE. Most equipment changes can 

be covered by an STE extension. Examples where an extension would be required to maintain the status of the 

approval include 

Change in panline; 

Change in shearer or plow; 

Change in control unit; and 

Any change that modifies the configuration of the head 

or tail areas such as new crusher, new conveyor drives, 

:ations of STE's and STE extensions 

Field modification STE extension 

Modifications permitted. . . . . . . . . . Any change(s) that do not affect permissibility 

of the machine and maintain illumination levels 

required for machine application. 

Process for obtaining approval. . . . . . Application made by user (mine operator) to local 

MSHA district manager. Electrical inspector 

visits mine and (1) verifies light level compliance by taking luminance measurements 

with special go, no-go photometer,' and (2) 

checks permissibility of the machine. 

Important aspects of 

resultant approval. 

Maximum entry dimensions for which the STE 

approval applies are-height, height where 

measurements taken plus 12 in; width, width 

where measurements taken plus 24 in. 

Applies to all similar machines in same mine 

when (a) they have the same STE number and 

(b) identical modifications are made to each 

machine. However, does not apply to other 

mines. 

Same as field modification. 

Application by STE approval holder (with exception of 

longwalls, typically a lighting hardware manufacturer) 

to BETL, submitting modified machine layout 

drawing, 1-line diagram, etc., as appropriate. Light 

measurements may be taken in a simulator or at the 

mine site (by BETL representative). 

Cooperation of BETL and most lighting manufacturers 

enables the mine operator to initiate an effort to 

obtain an STE extension even if he or she is not 

the approval holder. 

Maximum entry dimensions for which the approval 

applies are independent of any particular mine site 

and represent the maximum capability of the system. 

Approval applies to application of the modified design 

in any mine. This is helpful to multimine companies 

and other companies having the same problem. 

' The reflected light (luminance) measuring instrument used by MSHA inspectors when it is necessary to field-inspect lighting systems. In this case, the 

instrument is calibrated to give a favorable signal (i.e., system complies) at an illumination level of 0.05 fL. 
Table 4.-Headlight equivalence listing' 

(Explosion-proof approved for 100-W mercury vapor, 70-W sodium, and 150-W incandescent fixtures) 

Manufacturer Model or 

Dart 

Certificate 

number 

Control Products ....... 2002, 2003, 2004 WP 1468-28 

Crouse-Hinds ......... MHLl B WP 2301-1 

Guyan ............ 5234 WP 984-4 

Huntington Brass ....... 380, 381, 382 WP 1774-2 

700 WP 2659-0 

Manufacturer Model or 

part 

Certificate 

number 

JOY ............. 57 1 390-1 0000 WP 1275-1 

McJunkin .......... 2000 WP 2145-5 

Mining Controls ....... 20043 WP 2372 

Mosebach ......... FL38150SPX10 WP 1851-4, 5 

Ocenco ........... HE-1 00X WP 2320 

' An extension can be obtained to substitute between any 2 headlights on this list without light measurements, including substituting mercury vapor for sodium, 

etc. 

different supports in this vicinity, new transfer point REQUIREMENTS FOR INSTALLATION OF 

arrangement. LIGHTING SYSTEMS 

Changes in seam height and number of supports such 

that the limits specified in the STE are exceeded would 

also require an extension. Foresight should be used to originally specify ranges to cover future application of the 

longwall equipment. 

In addition to conducting technical review of lighting 

system designs, BETL is available to help mine operators 

resolve problems they have encountered in implementing 

mine-lighting systems. The following are some of the services BETL can provide at no cost to the operator. 

1. Assisting the mine operator in establishing appropriate design modifications and obtaining STE extensions to 

resolve various problems. 

2. Reviewing hardware alternatives with the operator 

for a particular application. 

3. Identifying, for the operator's review, currently available STE's for a particular machine model and seam height. 

4. Verifying calibration of mine operators go, no-go photometers (recalibration, if necessary, would be the operator's responsibility). 

5. Establishing new lighting designs for difficult applications. 

6. Assisting mine operators and independent machine 

shops in making design modifications, including integration into the machine, when installing lighting systems 

during equipment rebuild. 

For example, say, at a given mine, all the bolter operators on a particular model machine are experiencing a 

glare problem with a particular luminaire (it is preferable 

that reported glare problems are consistent among the 

various machine operators). The mine could contact BETL 

and explain the problem. BETL would send representatives to the mine and, in conjunction with mine personnel, 

modifications would be established to resolve the problem. 

After the modification has proven successful, BETL would 

then contact the lighting manufacturer to develop revised 

machine-layout and one-line drawings (one-line drawings 

only required if the electrical components are changed) or 

have the mine operator develop them. The revised layouts 

and drawings would then be submitted to BETL in an 

extension application. 

It should be emphasized that visiting BETL representatives have neither the intent nor authority to issue citations for lighting violations. Mine operators are urged to 

take advantage of this valuable resource. Contacting BETL 

is a good first step when any significant lighting problem 

is being experienced. 

All mobile-face machines and longwalls have a "total" 

machine or system approval for use in coal mines. The 

addition and electrical integration of a lighting system is 

viewed as a modification of the total machine design, which 

could potentially void the machine approval. Hence, a field 

modification must be applied for by the mine operator on a 

machine-by-machine basis before installing a lighting 

system, regardless of whether the lighting system does or 

does not have an STE approval. With STE-approved 

systems, required documentation for a field modification 

is simply the one-line diagram of the STE with any additional information denoted to show exactly how the lighting system will be electrically integrated into the particular machine in question (e.g., switches, fusing, entrance 

glands). For non-STE-approved systems, the operators 

would be required to make their own equivalent drawings. 

Before installing the STE-approved system, mine 

operators should confirm that external machine geometry 

and dimensions agree with the machine depicted in the 

STE layout drawing. If any deviations exist that alter the 

light distribution of the system (e.g., machine is equipped 

with certain options or it has been modified), the STE 

would not apply and an STE extension would have to be 

obtained. 

Luminaires, diffusers, and shields must be installed 

as specified on the machine layout drawing. The following 

tolerances are permitted by MSHA in locating or orienting luminaires: Fluorescent luminaires, * 12 in; highpressure sodium luminaires, * 12 in; incandescent luminaires, It6 in; and headlights, 55". 

Problems in meeting these requirements, for example, 

inadequate anchor points for mounting the luminaire, the 

fixture is specified to be installed in undesirable locations 

such as on an explosion-proof enclosure or frequently 

removed coverpan, etc., may be encountered. In such event 

the operator should consider modifying the lighting system design through the STE-extension process. 

For STE-approved systems, a metal plate containing 

pertinent information about the STE (see figure 15) is 

required to be attached to the machine near the machine 

permissibility plate. This plate is generally furnished by 

the lighting hardware suppliers. 

INSPECTION OF FACE LIGHTING SYSTEMS 

Field inspection of lighting systems involves checking 

that (1) the permissibility of the lighting system is being 

maintained and (2) the system is meeting the applicable 
Flgure 15.-STE system approval plate. 

Federal lighting standards. Permissibility checks are made 

in accordance with criteria discussed in chapter 6, "Installing and Maintaining Mine Lighting Systems." Procedures for verifying compliance with the lighting standards 

vary for STE- and non-STE-approved lighting systems. 

Procedures for STE-Approved Systems 

As noted previously, an STE guarantees the mine operator compliance with the lighting standards as long as the 

approved design and application specifications are being 

met in the actual installation. Under these circumstances 

inspectors can not take light measurements. The review 

will simply consist of the following: 

1. Verification that the lighting fixtures are properly 

located and oriented as specified in the STE machine layout 

drawing. 

2. Verification that all lighting fixtures are oper:ating 

properly. 

3. A check to see that excessive coal dust, dirt, or other 

material is not present on the luminaires and light transmission is not being blocked by any nonspecified means. 

4. A check to see that entry dimensions are within the 

limits specified in the STE. 

5. verification that the system is being operated in compliance with other requirements specified in the STE. For 

example, if use of a ventilation curtain at the headgate or 

tailgate area of a longwall has affected the design of the 

lighting system in that area, such a curtain must actually 

be in place when inspected, or light measurements may be 

taken. 

Mine operators should keep the STE cover page and 

machine-layout drawing(s) on file at the mine for this 

inspection. 

If the actual installation fails to meet one or more of 

these specifications, this alone does not permit issuance of 

a citation. Rather, light measurements must be made to 

establish that the system is not meeting required light 

levels. (This is necessary because compliance with an STE 

itself is not a requirement but just a means for meeting 

the Federal lighting standards.) Instruments and techniques used in taking these measurements are discussed 

later in this section. 

Procedures for non-STE-Approved Systems 

Light measurements are necessary for verification that 

non-STE-approved systems are in compliance with the 

lighting standards. These will be taken upon the initial 

inspection and may be repeated upon any future inspection at the inspector's discretion. In general they will not 

be repeated unless improper maintenance, changes in 

layout, or changes in entry dimensions imply that the light 

levels provided by the system might be reduced. 

Instruments and Techniques for 

Taking Light Measurements 

The go, no-go photometer, discussed in chapter 1, is 

the only instrument permitted to be used in taking light 

measurements for inspection purposes. The instrument has 

no numerical scale; it emits a green light when the measured luminance exceeds or is equal to 0.06 fL and a red 

light when measured luminance is less than 0.06 fL. 

The machine to be measured should be positioned in a 

nonrockdusted entry. Positioning requirements vary for 

each machine depending on the lighting standards that 

apply to that machine. Appendix A describes these requirements for each particular category. In general, positioning 

requires (1) centering the machine if the requirement is 

that the entire entry must be lighted, or (2) locating ribs 

or face at the edge of the lighting perimeter if the requirement is that the standard must be met only within a certain distance of the machine. 

Compliance with the 0.06-fL standard is determined 

by measuring the average luminance of each square or 

circular field, 3 to 5 ft2 in area, on the surfaces required to 

be lighted. The go, no-go photometer yields the average 

luminance of any surface subtending the 27" solid viewing 

angle through which the instrument's lens accepts light. 

Thus, the procedure used to take measurements for compliance verification is to hold the meter perpendicular to the 

surface to be measured at a distance between 4 and 5 ft 

from that surface (fig. 16). 

When clearance does not permit the meter to be held 

at this range, the procedure is revised as follows: 

1. Divide the surface in question into 2- by 2-ft square 

fields. 

2. At each corner of each square field, hold the go, no-go 

photometer perpendicular to the surface at a 2-ft distance 

from the surface. The instrument will be measuring the 

average luminance over an area of 100 in2 (see figure 17). 

3. If one or more of the four readings in the 2- by 2-ft 

field yields a green light, the field is assumed to be in 

compliance. Only if all four readings yield a red light is 

the field deemed not in compliance (see figure 17). 

Measurements should not be taken on areas where 

shadows are cast by manually set jacks or timbers or by 

ventilation curtains. 

For STE-approved systems, light measurements should 

be taken utilizing the techniques discussed only at the 

surfaces illuminated by luminaire(s) that are improperly 

maintained or fail to comply with the specifications of the 

STE. In doing so, the inspector will visually examine the 

affected area and take measurements at the "darkest spot" 

apparent from such examination. 
4 so. w FT 

Flgure 16.-Procedure for uslng go, no-go photometer when 

clearance permlts holdlng the meter 5 ft from entry walls. 

For non-STE-approved systems, measurements may 

be taken at any surface required to be illuminated. Typically the inspector will visually examine surfaces and take 

measurements, utilizing the previously described techniques, at the "dim" spots. 

Additional Requirements To Improve 

Visibility Underground 

As noted in IC 9073 (chapter 3), the provision of artificial illumination is not the only means to improve the 

visibility of objects and details underground; reflectivity 

and contrast characteristics of the environment itself may 

be altered to achieve improved visibility. In recognition of 

this, the following provisions are required in underground 

mining: 

1. The paint utilized on all exterior surfaces of face 

machines must have a reflectance of at least 30 pct except 

100 SO. IN. 

/ 

NONCOMPLIANCE COMPLIANCE 

Figure 17.-Procedure for uslng go, no-go photometer when 

clearance does not permlt holdlng meter 5 ft from entry walls. 

on surfaces where highly reflective paint would adversely 

affect visibility. The major exception is the interior of cab 

surfaces where high reflected light levels from cap lamp 

and/or interior-mounted luminaires would cause excessive contrast that could be detrimental to visibility between 

the cab interior and the darker surroundings the machine 

operator is observing. 

2. If area lighting systems are used in the vicinity of 

self-propelled face machine instead of machine-mounted 

systems, reflectors must be used to make the machines 

more visible (the luminaires would serve this purpose on 

machine-mounted systems. The reflectors must be at least 

10 in2 in surface area. One is required at the outby end of 

continuous miners and loaders and both the inby and outby 

ends of all other face machines. 

3. Six square inches of reflective tape or equivalent 

reflective material are required on the front, both sides, 

and back of miners' hardhats. 
CHAPTER 3.LAMPS AND BALLASTS 

Lamps and ballasts are the basic building blocks of 

lighting hardware and systems. This chapter addresses 

the lamps and ballastry utilized in U.S. underground coal 

mine application, explaining their functional and performance characteristics, particularly as they are relevant to 

mining application. This information is an important basis 

for success in hardware selection and system design, 

implementation, and maintenance. 

CRITERIA FOR LAMP PERFORMANCE 

CHARACTERIZATION 

The following is a list of performance criteria commonly used to characterize performance of lamps and their 

associated circuitry. 

Spectral Energy Distribution.-As discussed in IC 9073 

(chapter 2), light sources broadcast their energy at different wavelengths, and this affects the perception of both 

color and brightness. A spectral energy distribution curve 

shows the relative amounts of the total electromagnetic 

radiation emitted by a source at each wavelength within 

the visible range of the spectrum. In mining application, 

this information is useful as a basis for judging (1) the 

color rendering ability of a lamp, which may be important 

in the performance of certain tasks such as blast and electrical wiring, perception of color-coded signs, etc.; and (2) 

the efficiency of the source under circumstances of low 

background illumination (scotopic vision) where "green" 

wavelength light is more readily perceived. Spectral energy 

distribution curves, which show energy emission beyond 

the visible portion of the spectrum, are useful in evaluating heat (infrared) and ultraviolet radiation production of 

the lamp. 

Efficacy.-Efficacy is a measure of the efficiency of a 

lamp in converting electrical energy into visible light 

energy. In strict terms, efficacy cannot be equated to 

efficiency. The efficiency of an energy converting device is 

a ratio of input power to useful output power, expressed as 

a percentage. For example, an electric motor consuming 

100 kW of electrical power might deliver 75 kW of mechanical power to the drive shaft it turns and is said to exhibit 

75 pct efficiency. However, as noted in IC 9073 (chapter 21, 

all light energy is not perceived equally by the eye. A 

human weighting function must be considered to account 

for the varying perception of brightness dependent on the 

wavelength of light. This is taken into account in the measure of light energy and its expression in terms of the 

lumen. Hence, a related measure, efficacy, is used to measure the efficiency of light sources and is presented in 

terms of lumens output per watt input or lumen per watt. 

As noted in IC 9073, the most efficient light sources in 

producing a perception of brightness would emit all light 

energy at the wavelength of greatest sensitivity-555 nm. 

If a lamp could convert 100 pct of its power to 555-nm 

wavelength light, it would have an efficacy of 680 lm/W. 

In most cases, however, a more balanced distribution is 

desirable. If a source has a spectral distribution curve that 

parallels the spectral luminous efficiency curve (IC 9073, 

chapter 2), the maximum efficacy of that lamp would be 

about 200 lm/W. Some available lamps approach this 

efficacy but have some problems in wavelength balance. 

In mine lighting, efficacy is important with respect to the 

following: 

1. Assessing power requirements and costs of alternative systems. Systems using high efficacy lamps will have 

lower power requirements and costs than ones using low 

efficacy lamps. Note that published efficacy value usually 

does not consider wattage consumption of associated circuitry (transformers, resistors, line losses, ballasts). These 

must be added for a complete power assessment. 

2. Evaluating suitability ofthe lamp in meeting light 

output requirements for a particular application. Many 

mine applications require high light levels, while at the 

same time, it is desirable to minimize the number of 

fixtures. Lamps with higher efficacy are generally better 

able to meet this need without producing an excessive 

level of heat (an important consideration in coal mining 

luminaire design). 

Lumen Depreciation-Mean Lumens.-The amount of 

light energy emitted by a lamp diminishes significantly 

(up to 33 pct) over the course of its service life. Depending 

on the type of lamp, output reduction is caused by different mechanisms, which have an effect even in the mildest 

operating environments. Lumen depreciation is usually 

given as the ratio of lumen output at the end of lamp life to 

the initial lumen output. Lamp wattage consumption also 

decreases over time, but not as fast as lumen depreciation; 

hence, there is also some efficacy depreciation over lamp 

life. In general, the percentage of efficacy decline is less 

than the percentage of lumen depreciation. Note that lumen 

depreciation accounts only for light loss from the lamp. 

This will usually be less than light loss from the luminaire due to deterioration and dust and dirt accumulation 

over time, which also contribute to diminished light output. 

Lumen depreciation is an important consideration in system design for mining application, especially when developing designs in simulators. In many applications, premature lamp failure and difficult housekeeping circumstances 

complicate quantitative consideration of lumen depreciation. Mean lumens, the average lumen output of the lamp 

throughout its rated life, is the most meaningful quantity 

to consider for design purposes. 

Lamp Mortality-Rated Lamp Service Life,-Degradation of lamp operational parts during the course of lamp 

service life eventually results in failure. In lamp design, 

the question of economics is always considered jointly with 

lamp service life. Some lamp designs could be modified to 

increase service life, but this would result in efficacy reductions that could increase operating costs to the point that 

the lamps would be uneconomical for most applications. 

All lamps, of course, do not realize equal life. Rated lamp 

service life is a statistical quantity defined as the life 

achieved by the median lamp of a large group of lamps 

burned under controlled conditions. Fifty percent of lamps 

will have failed by the time rated service life is reached, 

and 50 pct will remain operational. A plot of lamp failures 

versus time is called a lamp mortality curve (fig. 18). Control parameters in development of these statistics are the 

burn cycle (length of time the lamp is burned before shutting off and restarting) and the input voltage (maintained 

at design specification). Mercury vapor lamps are an 

exception. These lamps have extremely long life, and efficacy drops to a point where it is considered uneconomical 
PERCENT RATED LIFE 

Figure 18.-Lamp mortality curve example. 

to continue burning after only one-third of the lamps have 

failed. Hence, published mercury vapor lamp values life 

values are at the 33-pct-failed point. 

In mining application, laboratory-based measurements 

of lamp life will frequently be irrelevant because of the 

harsh operating circumstances of this application. Lamp 

suppliers may present generalizations on lamp economics 

which are relevant to most applications, but do not apply 

to the underground coal mine. Therefore, the problem 

should not be ignored. Evidence shows that total lampassociated costs can be very high in mining applications. 

Site performance data should be collected as a basis for 

guiding appropriate decisionmaking to reduce these costs. 

In this regard, procedures for evaluating, and subsequently 

reducing lamp-associated costs, are presented in chapter 

6. 

Lamp Shapes.-Lamps are available in different 

shapes which, in conjunction with lamp dimensions, are 

important with respect to luminaire configuration and light 

control. Figure 19 shows the more common lamp shapes 

and corresponding abbreviations. Light center length is 

an important dimension for some lamp types when they 

are used in conjunction with reflectors. 

INCANDESCENT LAMPS 

Principle of Operation 

As described in IC 9073 (chapter 2), any material 

heated to a high temperature will emit electromagnetic 

radiation. For example, a horseshoe glows in the blacksmith's hearth. This process of light production is called 

incandescence and is the principle involved in operation of 

an incandescent lamp. Basically, an incandescent lamp 

(fig. 20) consists of a small-diameter tungsten wire called 

a filament, supported in an inert environment to prevent 

oxidation. An electrical potential (voltage) is placed across 

the filament, and current is passed through it, generating 

heat because of the filament's electrical resistance. Filament temperature rises to a high steady-state value and 

the filament emits electromagnetic radiation in the ultraviolet, visible, and infrared portion of the spectrum. Tungsten is the material of choice in construction of the filament because of its ductility, desirable emission characteristics (because of its high melting temperature), and its 

reasonable strength and relatively slow evaporation at high 

temperature. Evaporation, however, eventually does take 

its toll and causes a break in tungsten filament continuity, 

ending useful incandescent lamp life. 

TUBULAR 

STANDARD 

PAR PARABOLIC 

ALUMINIZED 

REFLECTOR 

BT BULGE TUBE 

U U-SHAPED 

Figure 19.-Common shapes of mine lamps and letter designations. 

/FILL GAS 

FILAMENT 

LEAD-IN 

* ,SUPPORT WIRES 

, BUTTON 

/ 

BUTTON ROD 

EXHAUST TUBE '&BASE 

Figure 20.-Construction of typical incandescent lamp. 

Life-Efficacy Relationship 

As noted, an incandescent body produces electromagnetic radiation across a broad portion of the electromagnetic spectrum (see figure 21). Light source efficiency 

requires that as high a portion of this radiation as possible 

be in the visible portion of the spectrum. This is achieved 

by increasing the temperature of the body. Increased 

temperature, however, increases the rate of material 
0 500 1000 1500 2000 2500 3000 

WAVELENGTH IN NANOMETERS 

Figure 21 .-Spectral energy distribution of tungsten at 3,000 

K. 

evaporation, reducing the life of the lamp. Hence, the key 

of incandescent lamp design is achieving an optimum balance between life and efficacy. In this regard, the following important design aspects are noted: 

1. Filament Electrical Character.-A filament can essentially be viewed as a resistor. Physically, its resistance is 

increased by increasing its length or decreasing its diameter. Power consumption follows Ohm's law (P = IE = 

E2/R). For equal voltage lamps, filament resistance will 

decrease (shorter and/or larger diameter filaments), as 

lamp wattage increases. For equal wattage lamps, filament resistance will increase (smaller diameter and/or 

longer filaments), as voltage increases. 

2. 'Filament Heat Dissipation Character.-Heat dissipation from a lamp is undesirable because it indicates input 

power is being converted to heat rather than useful light. 

Dissipation is proportional to the surface area of the 

filament. For equal wattage lamps, filaments will have 

smaller surface areas for low-voltage lamps than for highvoltage lamps. For equal voltage lamps, high-wattage 

lamps will have smaller surface area filaments than lowwattage lamps. This implies that greater efficacy is achievable on low-voltage and on high-wattage lamps. For 

example, a 150-W, 120-V lamp produces about 34 pct more 

light than three 50-W, 120-V lamps. Note also that lowvoltage, high-wattage lamps have greater diameter filaments, which improves their mechanical strength. These 

lamps are frequently applied in mining application. 

3. Filament Evaporation-Fill Gas.-Filaments must be 

operated in an inert atmosphere to prevent oxidation. Originally they were operated in a vacuum. However, it was 

found that introduction of inert gases (nitrogen, argon, 

krypton) reduced filament evaporation. This enables operating at higher temperatures, improves efficacy, and 

improves service life. Heat losses from convection, however, 

must also be contended with. Heavy molecular weight gases 

(e.g., krypton) are better than light molecular weight gases 

(e.g., argon) because convective losses are less. Expense 

prevents wholesale application of heavy gases. Miners' cap 

lamps are an exception and are krypton-filled to minimize 

battery drain. Note that for low-wattage lamps (in the 

case of 120-V lamps, those 40 W or less) with relatively 

high surface area filaments, convective heat losses are 

very high. Introduction of inert gases shows no advantage 

for these lamps and they are operated in vacuum. 

4. Filament Shape and Supports.-Filaments can be 

made in various forms. The wire may be straight or wound 

in coiled and coiled-coil fashion. The coiled and, to an even 

greater degree, the coiled-coil configurations improve efficacy by reducing convective heat losses. They also contribute to the mechanical strength of the filament. Filaments 

are supported in various configurations depending on 

length and diameter and the required mechanical strength 

which, in turn, is dependent on intended service application. Support wires, however, conduct heat away from the 

filamant, also reducing efficacy. To summarize, the best 

service-life, efficacy compromises are reached with lowvoltage, high-wattage, krypton-filled lamps with coiledcoil filaments and a minimum of support wires consistent 

with necessary mechanical strength of the filament for the 

intended application. 

Spectral Energy Distribution 

Figure 21 shows the spectral energy distribution of 

tungsten at 3,000 K. Three points are significant with 

respect to this distribution: 

1. The distribution is continuous across the entire range 

of the visible spectrum. Hence, color resolution is not a 

problem with incandescent lamps. In fact, most individuals feel that incandescent lighting is most "natural" in 

color because of their past experience with it. 

2. The distribution is weaker in the shorter ultraviolet 

wavelengths where the eye is most sensitive under scoptic 

conditions (not a consideration in machine lighting). 

3. A high proportion of energy is emitted in the infrared 

region. This energy is easily converted to thermal energy 

and may cause discomfort problems for personnel in certain circumstances. 

Lamp Efficacy Relative to Other Lamps 

The efficacy of a typical rough service incandescent 

lamp applied in mine application is about 14 lm/W. This 

compares to efficacies of about 26 1mlW for a very high 

output fluorescent lamp, 53 1mIW for a high output fluorescent lamp, 44 lm/W for mercury vapor lamps, and 75 to 

100 1mlW for high-pressure sodium lamps. Hence, incandescent lamps have the lowest efficacy of all mine lamps 

and the highest power costs for a given light output. 

However, other advantages, as follows, contribute to their 

wide use. 

Lumen Maintenance 

Two mechanisms cause lumen depreciation over the 

life of an incandescent lamp: 

1. Sublimated or evaporated tungsten from the filament 

condenses on the inner surface of the lamp bulb and absorbs 

a portion of the light output. 

2. Filament sublimation and evaporation result in a 

thinner, higher resistance filament. This decreases lamp 

wattage (since power is inversely proportional to resistance) 

and reduces light output. 

Lumen depreciation is generally less for incandescent 

than other mine lamps; typically a 15 pct reduction occurs 

over lamp life. 
Lamp Life 

Typical rated service life for incandescent lamps is 

about 1,000 to 2000 h. Although this is a fraction of the 

rated service life for gas discharge (fluorescent, mercury 

vapor, and high-pressure sodium) lamps, the actual realized life differential may be much less under the difficult 

circumstances of mine application. The reader is referred 

to chapter 6 for discussion of lamp life and economics in 

mine application. 

Power Requirements 

Appropriately selected incandescent lamps can be 

installed directly across the line on both ac and dc power 

systems. Auxiliary power conditioning equipment for mine 

application is minimal, limited to transformers or voltagedrop resistors. Circuit simplicity is a major reason why 

incandescent lamps are so popular in mine lighting. 

Additionally, incandescent lamps remain operational when 

supply voltage fluctuates, although, as outlined in the 

following, this does affect lamp performance. 

Lamp Performance Versus Operating Voltage.-The 

operating characteristics of incandescent filament lamps 

vary considerably as the operating voltage is varied from 

nominal. Lamp life, lumen output, lumens per watt, and 

watts for an incandescent filament are plotted versus the 

percent of normal operating voltage in figure 22. 

Lamp life is very sensitive to changes in the operating 

voltage. For example, if a typical 150-W parabolic aluminized reflector (PAR) 38 headlamp is rated by the manufacturer to have an output of 1,730 lm and rated life of 

2,000 h at 120 V, the operating life of 2,000 h can be 

expected if the voltage is held to 120 V. If the voltage is 

increased to 130 V then, from figure 22, the reduction in 

life can be computed as follows: 

Percent normal voltage = 130 X 1001120 or 108 pct. 

From the lamp life curve in figure 22 the percent life is 40 

pct. Therefore, the reduced lamp life at 130 V would be: 

Lamp life = 2,000 h X 0.4, or 800 h. If the voltage is 

decreased to 110 V then the increased lamp life can be 

computed as follows: Percent normal voltage = 110 X 

1001120 or 92 pct. The percent life from figure 22 is 300 pct 

and the increased lamp life would be: Lamp life = 2,000 X 

3.0 or 6,000 h. 

Note that this seemingly small voltage variation of 8 

pct results in a lamp life variation from 800 to 6,000 h. 

This example illustrates the significant desirability of 

limiting overvoltage operation of incandescent lamps, and, 

if practical, operating these luminaires at reduced voltage. 

The lumen output of incandescent lamps also varies 

greatly with change in operating voltage. Referring to figure 22 and for the preceding example at 130 V, the 

increased lumen output can be computed as follows: Percent normal volts = 130 X 1001120 or 108 pct. From the 

lumen curve in figure 22 the percent lumens is 130 pct and 

the increased lamp lumen output is: Lumen output = 1,730 

X 1.3 or 2,249 lm. At 110 V the lumen output is: Percent 

normal volts = 110 X 1001120 or 92 pct. The percent 

lumens is 68 pct and the reduced output is: Lumen output 

= 1,730 X 0.68 or 1,180 lm. 

Rough and Vibration Service Lamps.-Where shock 

andlor vibration occur-typical in-mine lighting application-rough or vibration service lamps should be used. 

4 0 60 8 0 100 12 0 14 0 

PERCENT NORMAL VOLTAGE 

Figure 22.-Effect of voltage variation on the operating characterlstics of incandescent fllament lamps. 

Standard incandescent lamps designed for stationary lighting are simply not applicable for this type of service. The 

filaments on incandescent lamps become soft and pliable 

when heated and are readily broken. Rough service lamps 

employ a multiple filament support construction that provides resistance to filament breakage. These lamps are 

designed for applications where intermittent shock occurs. 

Vibration service lamp construction employs tungsten with 

a special crystalline structure that permits sagging but 

resists breaking of the filament coils when subject to 

vibration. Designed for applications where high-frequency, 

low-amplitude vibration occurs, vibration service lamps 

offer little shock resistance, and cannot be burned in a 

horizontal position. The extra filament supports of vibration service filaments are utilized to prevent shorting of 

the coils when they sag. In general, incandescent lamps 

utilized on face machines should be rough-service rated. 

Vibration-service lamps may have application in other 

areas of the mine where high-frequency, low-amplitude 

vibration might be found, e.g., pump houses. 

Krypton-Filled 

In a standard incandescent lamp the bulb is filled 

with an argon-nitrogen mixture. Some special purpose 

lamps are filled with krypton gas. As noted previously, the 

krypton gas conducts heat more slowly from the filament 

and retards filament evaporation better than the standard 

argon-nitrogen gas mixture. The result is improved lamp 

efficacy and increased lamp life. Miners cap lamps use 

krypton gas-filled lamps to reduce battery drain. Krypton 

gas may increase efficacy by 7 to 20 pct. Krypton gas-filled 

PAR 38 lamps are available and some have been tested in 

mine applications. While significant increased lamp life 

was reported, the high cost of these lamps (five to six times 

that of a regular lamp) has limited their use. The life 

ratings of two available 150-W PAR 38 krypton lamps are 

4,000 h compared with 2,000-h life rating for a typical 

150-W standard PAR 38 lamp. Lumen output of these particular krypton PAR 38 lamps is slightly less than the 

standard PAR lamp. 

Tungsten-Halogen 

A tungsten-halogen incandescent lamp differs from 

the standard incandescent lamp in that the light source is 

housed in a small quartz bulb (quartz bulbs offer greater 

heat resistance than milk-glass used in standard incandescent lamps) that contains a tungsten filament and is filled 

with a halogen gas such as iodine. 
Normally, tungsten, as it evaporates from a filament, 

is deposited on the inner surface of a bulb and causes 

blackening. In the halogen lamp, the evaporating tungsten combines with the halogen gas and forms a tungstenhalogen compound that continues to circulate within the 

bulb. As the compound circulates near the filament, it is 

broken down and tungsten is redeposited on the filament. 

This process, called the tungsten-halogen regenerative 

cycle, increases lamp life and significantly reduces lumen 

depreciation over the life of the lamp. For example, the 

rated life for a particular 150-W PAR 38 tungsten-halogen 

lamp is 4,000 h compared with 2,000 h for a standard 

150-W PAR 38 lamp. Note that the temperature of the 

quartz jacket is very high (about 500" F) because of its 

proximity to the heated filament. This high temperature 

must be maintained to prevent deposition of the tungstenhalogen compound on the bulbs. 

FLUORESCENT LAMPS AND BALLASTS 

Principle of Operation 

The fluorescent lamp (fig. 23) is classified as an arc 

discharge light source. The lamp is filled with mercury 

vapor and a small amount of inert gas. The cathodes are 

covered with an electron-emissive material (i.e., a material that produces abundant free electrons when heated), 

and a fluorescent material (phosphor). When the lamp is 

energized, passage of electric current through the cathodes causes them to heat and release electrons. Voltage 

across the lamp causes these electrons to travel at high 

speed from one cathode to the other in the form of an 

electric arc. During the arcing process, these electrons collide with the gaseous mercury atoms, energy is absorbed 

and valence electrons in the mercury atom are shifted to a 

higher orbit. After time, these displaced electrons fall back 

to their original orbits, and they release electromagnetic 

energy, primarily at discrete wavelength bands in the 

ultraviolet portion of the spectrum. The ultraviolet energy 

is, in turn, absorbed by the phosphor coating which reemits 

the ultraviolet energy as electromagnetic energy in the 

visible portion of the spectrum. The color (wavelength 

mixture) of visible light produced depends upon the chemical composition of the phosphor coating. Fluorescent lamps, 

like the other gas discharge lamps, require use of supplementary devices called ballasts for proper lamp operation. 

Several categories of fluorescent lamps exist today, 

differing primarily in the technique utilized for lamp 

starting. The earliest fluorescent lamps were of the "preheat" type, which required the use of a starter. With this 

lamp type, the cathodes are preheated to emit electrons to 

aid in the striking of the arc at lower voltage. The starter 

is an automatic device that applies current to the cathodes 

for a period long enough to adequately heat them and then 

opens to stop the current flow and allows full voltage with 

an inductive spike to be applied across the two cathodes. 

"Instant start" lamps were developed next, primarily 

as an attempt to overcome the slow starting of preheat 

lamps. They rely on a very high starting voltage (400- 

1,000 V) to start the arc without cathode preheating. This 

simplifies auxiliary circuit requirements, but the required 

ballasts are large and expensive. The high-voltage starting requirement prevents application of instant start lamps 

PHOSPHOR COATING 

\ LEAD-IN WIRES BASE AND 

\ CONTACTS 

GLASS BULB MERCURY AND ARGON CATHODE. COILED COIL 

SUPPORT ARC TUNGSTEN COATED WITH 

ELECTRON EMISSIVE MATERIAL 

Flgure 23.-Constructlon of typlcal fluorescent lamp. 

in mining because it might present a potential shock or 

ignition hazard. 

Rapid-start lamps start quickly without the use of a 

starter. They are constructed utilizing continuously heated 

cathodes with low electrical resistance. The continuous 

heating is provided by special windings in the lamp ballast. 

Starting time for rapid-start lamps is almost as fast as 

instant-start lamps. The lamp circuit is more complicated 

than an instant-start lamp circuit but the ballast is smaller 

and cheaper because voltage requirements are reduced. 

All U.S. fluorescent mine lighting systems use rapid-start 

lamps, and they will be the emphasis of the remaining 

discussion of fluorescent lamps. 

Performance Characteristics 

Lamp Efficacy 

Fluorescent lamps are much more efficient than incandescent lamps in the conversion of electric energy to visible energy. Only high-pressure sodium lamps offer greater 

efficacy among the lamps applied in underground coal mining application. High efficacy offers advantage not only in 

power costs but also permits cooler operating temperature, 

an important consideration in the design of mine lighting 

fixtures. Note that in some cases, fluorescent mine lamps 

are driven at high frequency via solid-state ballasts. This 

further improves efficacy relative to standard 60-cycle lamp 

drive. 

Surface Intensity 

The entire bulb acts as the apparent light source on 

fluorescent lamps rather than the small filament or arc 

tube on other types of mine lamps. Since average lamp 

surface intensity is equal to the total emitted lumens 

divided by the apparent surface area of the source (IC 

9073, chapter 2), surfqce intensity is generally lower for 

fluorescent lamps. This may offer advantage with respect 

to glare in some design instances, but other factors must 

be considered for a complete assessment (see chapter 4 of 

IC 9073 and chapter 5 of this report). 

Lumen Output: Standard, High, and Very or Super 

High 

Because large fixtures are not desirable in mine application but high lumen quantities are often necessary, there 

is incentive for application of fluorescent lamps with high 

lumen output per unit size. Standard 1-in-diam lamps are 

driven at 10 Wlft at a current of 430 mA. If special design 

features are incorporated to regulate mercury vapor pressure at higher temperature, rapid-start lamps can be driven 

at higher current levels, producing more light from a given 

size lamp. High output (HO) 1-in-diam lamps are driven 

at 14 Wlft at 800 mA and very or super high output (VHO 
or SHO) lamps are driven at 25 Wlft at 1,500 mA. This 

increases light output significantly, but there is loss in 

efficacy, especially in the case of VHO-SHO lamps. Because 

of higher cost and surface intensity (which may require 

more diffusion), lower efficacy and lamp life, and greater 

lumen depreciation, VHO-SHO lamps should be applied 

only in instances where high-lumen output is necessary 

and achievement of design objectives through use of additional luminaires is undesirable. 

Lumen Maintenance 

Both deterioration of the phosphor coating and lamp 

blackening (caused by sputtering of the electron emissive 

coating from the cathodes through collision of arc particles), 

cause lumen depreciation during the life cycle of a fluorescent lamp. Lumen depreciation is very high (up to 10 pct) 

during the first 100 h of lamp operation. Because of this, 

manufacturer lumen ratings are based on performance 

after 100 h of lamp burn. This fact should be taken into 

account when designing systems in simulators or measuring light output with new lamps. Lumen depreciation is 

about 18 pct of the 100-h lumen output value for standard 

fluorescent lamps over a life span of 20,000 h. Lumen depreciation of HO and VHO-SHO lamps is about 23 pct and 27 

pct over 9,000- and 7,500-h service lives, respectively. Note, 

however, that the rate of lumen depreciation is much 

higher in the early portion of the life cycle of these lamps. 

However, since their life is shorter, this factor diminishes 

end-of-life differences relative to standard lamps. 

Spectral Energy Distribution 

As implied, different lamp spectral distributions can 

be obtained with different phosphor coating mixtures. Figure 24 shows distributions obtained for some of the standard mixtures. As can be seen, emission occurs in a continuous band with exception of peaks at certain discrete 

wavelengths. These peaks represent direct radiation in 

the visible spectrum from the mercury discharge and comprise only about 10 pct of total lumen output. Because of 

the well-balanced, continuous nature of the curve across 

the entire visible spectrum, color resolution is not a problem with fluorescent lamps. Note that lamps with higher 

emission in the red portion of the spectrum (e.g., Deluxe 

Warm White) tend to appear more "natural" (i.e., closer to 

sunlight and incandescent light with which we are most 

familiar). This is realized, however, at some loss of efficacy 

and because of the importance of high efficacy in many 

mine applications, the lamps utilized are generally standard Cool White. 

Lamp Life 

Fluorescent lamps typically have a much longer rated 

life than incandescent lamps. The rated life of typical rough 

or vibration service incandescent lamps is approximately 

1,000 h. The rated life of typical fluorescent lamps applied 

in mines range from 7,500 to 20,000 h. Note that the shorter 

life values apply to the VHO-SHO and the HO lamps, and 

the longer values apply to standard fluorescent lamps. 

"Normal" fluorescent lamp failure is due to the depletion 

of the electron-emissive material on the cathodes. This 

material degrades more rapidly during the starting cycle. 

Usually, fluorescent lamp life ratings are based on one 

start every 3 h. Accordingly, more frequent starts will 

WARM WHITE DELUXE WARM WHITE 

DAYLIGHT 

300 400 500 600 700 300 400 500 600 700 

WAVELENGTH IN NANOMETERS 

Figure 24.-Specuiar energy dlstrlbution curves for common 

fluorescent phosphor mixtures. 

tend to decrease lamp life, while less frequent starts will 

increase it. The cathode filaments in fluorescent lamps are 

of rigid construction and less prone to failure under shock 

and vibration conditions than their incandescent counterparts. Performance requisites posed by mine application, 

both electrical and mechanical, can be severe; hence rated 

life figures are not reliable for comparing mine lamps. 

Chapter 6 discusses factors causing premature lamp failure, 

compares the performance of different lamp types under 

these conditions, and suggests remedies if problems are 

encountered. 

Lumen Output as a Function of Lamp Temperature 

The light output of a fluorescent lamp varies with the 

temperature of the bulb wall. This temperature affects the 

vapor pressure of the mercury, which changes the light 

output. The change in light output of a typical HO fluorescent lamp as a function of ambient temperature in still air 

is shown in figure 25. Note that both high and low temperatures can reduce light output. This curve illustrates the 

importance of allowing sufficient warmup time when measuring illumination levels in fluorescent lighting systems 

and the importance in considering operating temperature 

in the design of efficient lamp enclosures. 

Effect of Voltage 

Overvoltage operation of fluorescent lamps produces 

an arc at higher than rated current. Thia deteriorates the 

electron-emissive cathode coating, causing lamp blackening, reducing life, and increasing the rate of lumen depreciation. Conversely, low voltage may be insufficient to heat 

the cathode, greatly prolonging the starting procedure 

(especially in humid conditions). This condition is especially destructive of the emissive coating, significantly 

reducing lamp life. Figure 26 shows lumen output and 
AMBIENT TEMPERATURE, OF 

FOR A TYPICAL HIGH OUTPUT FLUORESCENT 

LUMlNAlRE IN STILL AIR 

Figure 25.-Change in light output of a fluorescent lamp as a 

function of amblent temperature. 

PERCENT RATED VOLTAGE 

FOR A 2-LAMP RAPID START BALLAST 

Figure 26.-Change in light output and wattage of a fluorescent lamp as a functlon of llne voltage. 

wattage versus percent nominal line voltage for a typical 

fluorescent lamp. It can be seen that both undervoltage 

and overvoltage reduce efficacy (although the effect is not 

as significant as for incandescent lamps). Also, sudden 

voltage drops can extinguish the lamp arc. Because of these 

effects, and the fact that ballast life is also affected by 

voltage variation, it is important that fluorescent lamp 

circuits be specified that are compatible with the character of the existing voltage supply. 

Flicker 

In the past, stroboscopic effect caused by lamp flicker 

(IC 9073, chapter 3) could create a serious hazard in industrial application of fluorescent lamps. Although the lamp 

arc is generated at 60 CIS, the phosphors exhibit a phenomenon called "phosphorescent action" which causes light 

transmission to continue or "carry over" during the periods of the cycle where mercury discharge activity is low or 

zero. In modern lamps the level of carry-over is very high, 

minimizing output variations; hence, stroboscopic effect is 

generally not a problem. Stroboscopic effect can be serious, 

however, near the end of lamp life or when the circuit is 

not functioning properly. Proper maintenance of fluorescent systems is important to prevent this problem from 

occurring. Connection of ballasts across alternate leads of 

a three-phase supply is an additional precaution to further 

smooth output variations since one lamp of the circuit 

operates at its "peak" while the other is at its "valley" 

(most fluorescent mine lighting circuits are not set up this 

way, however). 

Fluorescent Ballasts 

Fluorescent, as well as the other arc discharge lamps, 

cannot be operated directly across a voltage supply because 

all arc discharge lamps exhibit what is known as a negative resistance characteristic. If connected directly across 

a voltage source and the arc is initiated, electrical resistance across the lamp decreases and lamp current flow 

increases with time. This continues, and in just a short 

period of time such a high current level is reached that the 

lamp is physically destroyed. For successful lamp operation, 

ari auxiliary electrical impedance, the ballast, must be 

introduced in the line to limit current flow. This is the 

principle function of all ballasts and the one from which 

the name of the device was derived. That is, their major 

role is to stabilize or "ballast" lamp operation at a reasonable energy level. 

Ballasts have auxiliary functions in addition to current limiting. In the case of rapid-start fluorescent lamps, 

the type most frequently used in mine face operations, the 

important ballast auxiliary functions are (1) provision of a 

controlled amount of electrical energy to the lamp cathodes to provide an adequate supply of free electrons, and 

(2) provision of a sufficiently high electrical potential 

(voltage) across the lamp electrode to assure the initial arc 

will strike. Note that cathode heating must be provided 

both before starting and during lamp operation, 

Most ballasts use core-and-coil construction. Insulated 

windings (coils) around an iron core form an inductor that 

is capable of limiting current flow with relatively small 

internal power consumption. Two or more windings may 

be coupled to form a transformer capable of (1) raising line 

voltage to the level required for striking the arc, andlor 

(2) regulating the power to the lamp with variations in 

line voltage. Capacitors are used in conjunction with these 

basic circuit elements for various purposes including powerfactor correction, current regulation, and assistance in lamp 

starting. These components may be encased and impregnated with a fill compound (e.g., asphalt) which protects 

the components from the weather, improves heat transfer, 

and reduces the noise produced by the ballast. 

Figure 27 shows the basic circuit employed in the construction of dual-lamp, series-sequence-type, rapid-start 

ballasts-the most widely applied core-and-coil ballast in 

underground coal mine lighting. When the ballast-lamp 

circuit is closed, special windings in the ballast provide a 

small heating current to the lamp electrodes, liberating 

electrons and reducing the voltage level required to start 

the lamp. As can be seen, lamp 2 is shunted by a capacitor. 

This momentarily places nearly full ballast secondary voltage across lamp 1, causing it to start. Once lamp 1 starts, 
Figure 27.-Dual-lamp, series-sequence-type, rapid-start fluorescent baiiast circuit. 

i-----------, 1 

the voltage across the lamp drops (i.e., lamp resistance 

decreases) and nearly full secondary voltage now appears 

across the shunted capacitor and lamp 2, causing it to 

start. Once lamp 2 starts, the two lamps operate in series. 

During a brief warmup period, lamp current will increase 

in both lamps until stable, hot cathode operation is reached. 

Now, the system formed by the lamps and ballasts operates in a steady-state condition. Assuming supply voltage 

is nominal, the electrical operating parameters of the system'should be conducive to long component life and good 

performance at close to nominal lamp operating voltage 

and current specifications. Note that this dual-lamp ballast is smaller and less expensive than two single-lamp 

ballasts. However, ballasts that operate more than two 

fluorescent lamps are generally not economical. 

Ballast Heating and Related 

Design Considerations 

I 

I 

I 

I 

I 

I 

Excessive heat is almost always the cause of reduced 

ballast life in any application. Under normal conditions, 

an average ballast life of about 12 yr can be expected. A 

12-h/d duty cycle is assumed in this rating and should 

ballasts operate for longer cycles, life is reduced proportionately. For example, if a mine application calls for a 

24-h/d duty cycle, expected ballast life is about 6 (12 divided 

by 2) yr. Chapter 6 discusses the mechanisms of heatrelated failure, diagnosis, and remedies involving changing of the application character. The following is a discussion of some design features that affect ballast heating. 

For realization of rated ballast life, ballast case temperature should not exceed 90" C and internal ballast coil 

temperture should not exceed 110" C. Class P ballasts incorporate a thermal protector within the ballast case, which 

disconnects the ballast from the power line when the internal temperature limit is exceeded. Most ballasts employ 

an automatic resetting thermal protector that recloses the 

circuit when ballast temperature falls. This device can 

reduce the incidence of ballast failure, but it is_ important 

that when the device is triggered, the cause of the problem 

I >lkLAsT I I -7 

I 

-- C., 

8 

I 

should be isolated and action should be taken to eliminate 

it. (See chapter 6.) 

Ballast case fill compound varies in its ability to conduct heat from the coils. A superior fill material will reduce 

coil temperature and extend ballast life. Traditionally, ballasts have been filled with asphalt, but many manufacturers offer a material with higher silicon content, which 

improves heat conductivity and subsequent dissipation. 

Additionally, asphalt tends to soften when hot, and, depending on ballast mounting position, may separate (sag) from 

the ballast case and reduce heat transfer. A material that 

does not soften at high temperature is preferable. 

Manufacturers make "premium" ballasts that reduce 

power consumption and, correspondingly, heat generated 

by the ballast. This is achieved primarily through the use 

of larger diameter conductors in the construction of the 

coils. These ballasts cost more than standard ballasts and 

are intended for application where adequate heat dissipation is difficult to achieve and/or reduction of energy consumption is desirable. Because of the high incidence of 

heat induced core-and-coil ballast failure in mining application, ballasts that apply this principle should be sought. 

Lack of availability, however, is a problem in acquiring 

some fluorescent mine lamps. 

All of these heat-related features are very important 

in a mining application. Since many of the core-and-coil 

ballasts available from mine lighting hardware suppliers 

are off-the-shelf items from the major ballast manufacturers (e.g., Jefferson, Advance Transformer, General Electric, 

and Universal), it is recommended that the supplier be 

questioned concerning these features. If the features are 

not incorporated in the standard equipment, desirable substitutions may be possible. 

4 

High-Intensity-Discharge Lamps - High-Pressure 

Sodium and Mercury Vapor 

SERIES 

=C START 

CAPAClT OR 

I 

High-intensity-discharge (HID) lamp types, which are 

used in mining, include high-pressure sodium (HPS) and 

mercury vapor (MV) lamps as well as other types such as 

the various metal halide lamps. The basic light-producing 

technique is similar to that used in fluorescent lampselectrons in an electric arc between two lamp electrodes 

collide with gaseous metallic atoms producing electromagnetic radiation through shift of the metals7 valence electron from a high-energy to a low-energy orbit. The major 

differences in the light-producing process of HID and fluorescent lamps are as follows: 

1. The partial pressure of the metal vapor in the HID 

lamp is higher than the mercury vapor pressure in fluorescent lamps. (HID lamps are often referred to as "high" 

pressure lamps. The adjective high is relative to the pressure level in fluorescent and low-pressure sodium lamps. 

Actually, pressure within the lamps is seldom more than 

twice atmospheric.) This is obtained by confining the arc 

to a small, insulated tube. The result is that the wavelengths of the light energy produced tend to be longer 

(note that fluorescent lamps produce initially in the ultraviolet region), and although still at discrete regions, the 

wavelength band at these regions is broader. 

2. Since the electromagnetic energy produced is in the 

visible range, phosphors are not required to convert the 

energy to wavelengths in the visible portion of the spectrum. 
3. The arc is operated at higher energy density than the 

fluorescent lamp arc, enabling greater lumen output from 

a physically smaller lamp. 

HID lamps include the most efficient, compact, and 

long-lived light sources available. The operating characteristics of the two HID lamps applied in underground 

mining application-mercury vapor and high-pressure 

sodium-are discussed in the following sections. 

MERCURY VAPOR LAMPS 

Functional Description 

Figure 28 shows the component parts of a mercury 

vapor (MV) lamp. The arc tube is where the light is 

produced. It consists of two operating electrodes with an 

electron-emissive coating, a starting electrode, some liquid mercury, and argon gas. A ballast is required to provide proper voltage and current to the lamp at the various 

phases of the lamp operating cycle. 

When the lamp is started, a voltage is placed across 

(1) the lower operating electrode and the adjacent starting 

electrode, and (2) across the two operating electrodes. 

Argon gas is readily ionized between the lower operating 

and the starting electrodes at this potential and an arc is 

formed between these two electrodes. A resistor in series 

with the starting electrode limits current flow through the 

arc. 

Heat is the important byproduct of the argon arc and, 

as time passes, it vaporizes more and more of the liquid 

mercury. This lowers the resistance across the two operating electrodes to a point where the arc across the operating and starting electrodes is supplanted with an arc across 

the two operating electrodes. This arc produces visible electromagnetic energy via the arc discharge process discussed 

in the preceding section. 

SHOCK ABSORBER OROSlLlCATE 

SPRING SPACER TABS GLASS BULB 

ERCURY AND ARGON 

INERT FILL GAS GAS SUPPORT ARC 

OR VACUUM 

OUARTZ ARC TUBE 

OPERATING 

ELECTRODES STARTING ELECTRODE 

ARC TUBE 

MOUNT FRAME 

SHOCK ABSORBER 

SPRING SPACER TABS 

STARTING RESISTOR 

MECHANICAL BASE WITH 

DATE RECORDING FEATURE 

Figure 28.-Typical mercury 

w 

vapor lamp construction. 

After this main arc is initially struck, more and more 

of the mercury vaporizes and more light is produced until 

a steady-state condition is reached when all the mercury 

has been vaporized. The time until the lamp reaches steadystate operation is called the warrnup period and takes from 

5 to 7 min. 

A large dip in voltage level or dropout of the supply 

voltage lasting one-half cycle or longer causes the conducting electrons in the arc to neutralize and extinguishes the 

arc. In this circumstance, the arc will not restrike immediately because of the high vapor pressure in the lamp, which 

prohibits reignition of the argon arc. A cooling down period 

(3-10 min) is necessary until the starting cycle can be 

initiated again. 

The arc tube is constructed of quartz fused silica to 

withstand the high temperatures. The outer bulb serves 

the purposes of (1) containing an inert (nitrogen) atmosphere around the arc tube to prevent oxidation of the 

leads and supports, which would occur at high temperature in an oxygen environment, (2) maintaining proper 

temperature of the arc tube and regulating mercury vapor 

pressure, and (3) absorbing ultraviolet radiation produced 

by the lamp so that is not transmitted to the environment. 

Eff icacy-Lumen Output 

Lumen depreciation over the service life of MV lamps 

is high relative to the other lamps used in mine application, 

ranging from 30 to 45 pct. Note, however, that this depreciation occurs over a very long life. The rate of depreciation is 

not excessive and high depreciation may not be an important consideration in applications where realized service 

life is greatly diminished from rated life. Like the other 

arc discharge lamps, lumen depreciation is highest during 

the first 100 h and rated initial lumen output is at the 

100-h point. The primary mechanism that causes lumen 

reduction is the "sputtering off' of electron emissive material when arc particles collide with the electrode. This 

material is deposited on the arc tube where it absorbs a 

portion of the generated light. A low number of burn hours 

per start accelerates lumen depreciation. 

Spectral Energy Distribution 

MV lamps emit most of their light at four discrete 

wavelengths (fig. 29). Although these wavelengths are 

spread across the spectrum providing reasonable color resolution for most applications, the spectral emission curve 

is not continuous. As a result, orange- and red-colored 

objects appear brownish and this may deter color code resolution on materials such as blast and electrical wiring if 

MV lamps are the primary source of illumination. Note 

that MV lamps are available with a phosphor coating on 

the inside of the outer bulb. This coating converts ultraviolet radiation produced by the lamp into visible radiation 

similar to the process in effect on fluorescent lamps. This 

improves efficacy and smooths wavelength distribution 

somewhat. 

Lamp Life 

MV lamps have the longest rated life of all the mining 

lamps (16,000-24,000 h). Note that because of lumen 
0 - - .- 

u 300 400 500 600 700 a WAVELENGTH (NANOMETERS) 

Flgure 29.-Spectral energy dlstrlbutlon of a typlcal clear mercury vapor lamp. 

depreciation, rated life values are normally given for the 

point where only one-third of the lamps have failed. The 

sputtering of electron emissive material (previously discussed) raises steady-state lamp operating voltage above 

the voltage available from the ballast, ending lamp life. 

Short burn periods and frequent lamp starting will accelerate this mechanism and decrease lamp life. Other factors 

affecting lamp life are discussed in the following sections. 

Effect of Voltage Variation 

Increases in line voltage applied to an MV lamp and 

ballast-and-lamp system increase the wattage consumed 

by the lamp. This, in turn, increases the temperature of 

the arc tube, which can have the following effects: 

1. If wattage is especially high for a long duration, the 

arc tube may bulge or shatter, ending lamp life. 

2. Sputtering of the electron emissive coating is increased, accelerating lumen depreciation and reducing 

lamp life. 

Continuous operation at low voltage makes restarting 

of the lamp arc at every half cycle more difficult. This also 

increases the rate of sputtering of the electron emissive 

coating, which reduces lamp life and increases lumen 

depreciation. Short-duration voltage fluctuations have little effect on lamp life and lumen depreciation. However, 

as noted previously, excessive voltage dips or dropouts, 

even for as short a duration as one-half cycle, can cause 

the lamp arc to extinguish and a long delay is incurred 

until the lamp again becomes operable. On machinemounted installations, these dips are frequently encountered and this serious operational problem has limited the 

use of MV lamps on face machines. The choice of a ballast 

has significant effect on the impact of voltage variation on 

mercury lamp performance, and this matter is discussed 

in a subsequent section. 

Flicker 

Lumen output drops to zero every half cycle on an MV, 

lamp. Potentially, the stroboscopic effect (IC 9073, chapter 

3) could be a significant problem. To minimize this effect, 

the vicinity where such an effect might occur should be 

illuminated with two lamps on a lead-lag ballast with lowcurrent crest factor or by two lamps or more on separate 

phases of a three-phase circuit. Phosphor-coated lamps 

present less of a flicker problem than clear lamps because 

of the presence of the phosphorescent action discussed 

previously. 

Ballasts 

MV lamps, like the fluorescent lamps discussed previously, exhibit a negative resistance characteristic and 

must be ballasted to limit current flow through the lamp. 

An additional function performed by the ballast is to supply a high voltage across the main and starting electrode 

to initiate the starting arc and, subsequently, to initiate 

and sustain the main arc. Numerous ballast designs are 

available for MV lamps and they are summarized in figure 30. They differ in the following characteristics: 

cost.- he more windings and material required, the 

more expensive the ballast. Utilization of a capacitor also 

increases ballast cost. 

Starting Versus Operating Current.-With some ballast 

designs, starting current is higher than operating current. 

With others, the reverse is true. This impacts sizing of 

conductors and fusing-circuit breaker requirements. 

Power Factor (PF).-High-PF electrical equipment is 

generally more desirable than low-PF equipment because 

current requirements to deliver a given level of power are 

reduced. This reduces the required size of conductors and, 

accordingly, reduces wiring costs. Available ballast and 

lamp designs differ in the inherent PF under which the 

system is operated. On those designs with inherent low PF, 

improvement can be achieved through the addition of a 

PF-correcting capacitor. However, the cost of the capacitor 

may make it more advantageous to go with a design with 

an inherently good PF. 

Crest Factor.-Crest factor on an ac system is the ratio 

of peak voltage or current to the root-mean-square (RMS) 

value, which represents the "average" value. For a standard sinusoidal waveform, crest factor is 1.41. Highintensity discharge lamp ballasts are generally designed 

to distort the waveform so the voltage crest factor is higher 

than 1.41. This enables one to provide a sufficient peak 

voltage to start the arc with a lower cost ballast. Moreover, 

if properly designed, RMS voltage for a high voltage crest 

factor waveform will not greatly exceed that for a lower 

voltage crest factor waveform and this is important in 

sustaining the arc. Although high-voltage crest factor is 

generally desirable, high-current crest factor is not. It can 

increase flicker problems, accelerate lumen depreciation 

(by increasing sputtering), and reduce lamp life. 

Line Voltage Regulation.-The effects of variation of 

supply voltage levels on the lamp-ballast system differ 

greatly depending on ballast design. Some designs can 

tolerate wide variation with minimal effect whereas others must be operated close to nominal. The impact on lumen 

depreciation, lamp life, lumen output, and ballast life is 

very significant. Because of the tendency for mine power 

systems to be poorly regulated, this factor should be given 

great attention. 

Extinction Voltage.-Probably the most important consideration regarding the application of MV lamps to mining application is the ability of the lamp-ballast system to 
tolerate voltage dips without extinguishing the lamps and lighting suppliers provide autoregulator ballasts because 

necessitating recycling. Ballasts vary greatly in their abil- of the combination of reasonable cost and performance. 

ity to "ride through" voltage dips. However, the performance edge of regulator ballasts, espeAs can be seen in figure 30, regulator and auto- cially with respect to lamp extinction, may justify the extra 

regulator ballasts offer the best performance, especially cost of these ballasts in some case. Note that they are 

with respect to voltage regulation and extinction voltage, off-the-shelf items for the MV lamps used in mining appliwhich are so important in mining application. Most mine cation and may be substituted for autoregulator ballasts. 

INPUT 0 

REACTOR 

Simplest mercury ballast deslgn. Consists of a wlre coll around 

an Iron core that serves as a reactor or "choke." Function Is 

slmply to llmlt current to the lamp. Voltage requirements for 

startlng are provlded by the llne. A capacltor may be used to 

Improve power factor. 

Advantages: 

Inexpenslve. 

Low Internal power consumption. 

Low current crest factor. 

Qulck lamp warmup. 

Dlsadvantages: 

Poor regulator of llne voltage varlatlon, +5 V Ilmlt. 

Will tolerate only 15 pct voltage dip for a maximum of a few 

cycles. 

Hlgher lamp startlng than operatlng current. 

Low power factor (50 pct) unless corrected. 

Llne voltage must be adequate for lamp startlng; particular 

problem for hlgher wattage lamps. 

VOLTS 

REGULATOR (CONSTANT WATTAGE) 

Constructed wlth two electrlcally Isolated wlndlngs slmllar to 

a transformer. Conflguratlon can raise voltage level for lamp, If 

necessary. Current Ilmltlng accomplished by secondary wlndIng (magnetlcally saturated) and a capacltor In serles with lamp. 

Power factor Is leadlng not lagging, unllke reactor and lag 

ballasts. 

Advantages: 

Excellent voltage regulatlon, +13 pct change In llne voltage 

changes lamp wattage 22 pct. 

Wlll tolerate 50 pct voltage dips for 4 s without lamp extinction. 

lnherently hlgh power factor (90 pct). 

Lower startlng than operatlng current. 

lsolatlon from malns reduces shock hazard. 

Dlsadvantages: 

Expensive. 

Somewhat hlgher current crest factor. 

INPUT pR1m 

CAP 

0 SEC , L 

VOLTS 

1, 

VOLTS 

CAP 

COM COM 

LAG (AUTOREACTOR, AUTOTRANSFORMER) 

Prlnclple of operation Is same as reactor ballast, the only 

difference Is that it Is configured as an autotransformer to boost 

voltage to levels required totlnltlate and malntaln arc. This ballast may be power-factor corrected wlth a capacltor but cost ls 

comparable to the autoregulator ballast, which offers better 

performance. 

Advantages: 

Same as reactor ballast. 

Dlsadvantages: 

Same as reactor ballast except lag ballasts can operate hlghwattage lamps on low-voltage supply clrcults. 

AUTOREGULATOR (CONSTANT WATTAGE 

AUTOTRANSFORMER) 

Combines lag and regulator ballast prlnclples. Constructed 

as autotransformer wlth a capacltor In serles wlth lamp. Colls 

and capacltor provide current Ilmltlng, whereas autotransformer 

deslgn provldes voltage boost. Considerable coupling of prlmary to secondary provldes reasonable regulatlon. Power factor Is leadlng. 

Advantages: 

Moderate cost. 

Reasonable voltage regulatlon, 210 pct change In llne voltage changes lamp wattage +5 pct. 

lnherently hlgh power factor (90 pct). 

Starting current usually lower than operatlng current. 

Dlsadvantages: 

Somewhat high current crest factor. 

No lsolatlon between primary and secondary. 

Figure 30.-Mercury vapor lamp ballasts. 
HIGH-PRESSURE SODIUM LAMPS 

Principle of Operation 

Figure 31 shows the construction of a high-pressure 

sodium (HPS) lamp. The arc tube is smaller in diameter 

than the arc tube of an MV lamp and is made of a translucent high-transmissivity, polycrystalline-alumina ceramic. 

Contents of the arc tube include two operating electrodes, 

mercury-sodium amalgam, and xenon gas. The tube is 

small in diameter, confining the arc so that the high temperatures necessary to vaporize sodium are more readily 

obtained. The special ceramic is necessary to withstand 

the heat and resist sodium attack. (Materials engineering 

of the arc tube and its interconnection to the power leads 

was a major feat in the development of HPS lamps because 

of the high temperature and presence of free sodium.) The 

small tube diameter prevents use of a starting electrode to 

obtain warmup as is used on MV lamps. In the case of HPS 

lamps, a special ballast circuit is utilized to provide a shortduration, high-voltage spike across the main electrodes, 

which readily ionizes the xenon gas. (Note that because of 

its short duration, this spike is low energy.) Similar to the 

arc process of an MV lamp, the xenon arc vaporizes the 

amalgam that enters the arc stream. Lumen output increases until a steady-state operating condition is reached 

in about 3 min. 

Like MV lamp arcs, the arc HPS lamp will extinguish 

if the voltage dips. However, the necessary degree of cooling and time requirements to restrike the arc are considerably less than those required on MV lamps (approximately 1 

min versus 3-10 min). With special starting aids, this time 

can be reduced to almost zero. Also, there is another important difference between MV and HPS lamps. Since at 

steady-state operation in an MV lamp all the mercury is 

vaporized, arc tube pressure and lamp operating voltage 

remain relatively constant over lamp life. In an HPS lamp 

there is excess amalgam and throughout lamp life changes 

occur that increase arc tube temperature and pressure. 

This increases the amount of amalgam that is vaporized 

and increases lamp voltage. Ballasts must be designed to 

accommodate this voltage change, and, as will be discussed, 

it has impact on lamp failure. 

Efficacy-Lumen Output 

HPS lamps have the highest efficacy of the mine lamps 

applied at the coal face. In fact, HPS lamps have the best 

efficacy of all the polychromatic-wavelength lamps available; only monochromatic, low-pressure sodium lamps have 

higher efficacy. Like MV lamps, HPS lamps offer high 

lumen output in a compact source. In very high seams, 

they may be the only practical source for meeting light 

level requirements. The low wattage HPS lamps (e.g., 50- 

70 W) have significantly lower efficacy than the higher 

wattage (100-150 W) mine lamps. 

Lumen Depreciation 

The mechanism of lumen depreciation in HPS lamps 

is similar to that of MV lamps. However, lumen depreciation of HPS lamps is very low considering their long life. 

Mean lumens average only a small fraction below initial 

lumen rating and net lumen depreciation is about 20 pct. 

The changing lamp wattage characteristic over the life of 

an HPS lamp has the effect of maintaining near constant 

lumen output for about the first 40 pct of lamp life (depending on the ballast design), and the rate of depreciation increases from this time onward. Note that published 

lumen depreciation curves for HPS lamps measure lumen 

output at constant lamp wattage. They are not representative of field performance because of the changing lamp 

wattage characteristic. 

Spectral Energy Distribution 

At the high pressure and temperature levels in the 

HPS arc tube, an effect called self-reversal improves the 

spectral character of the light emitted by HPS lamps. The 

natural emission of sodium in the visible spectrum is at 

two closely spaced wavelengths, 589.0 and 589.6 nm. In 

the self-reversal process, the sodium absorbs the 589.0- 

and 589.6-nm light and rebroadcasts it at higher and lower 

wavelengths. The net effect is a continuous emission somewhat weak in the shorter (blue and green) wavelengths. 

HPS lamps have a golden white tone (see figure 32). Color 

rendition can be a problem with HPS lamps, but they do 

permit better rendition than MV lamps. 

BASE WlTH DATE 

RECORDING FEATURE 1 

ARC TUBE 

SUPPORT STRUCTURE, 

OPERATING ELECTRODES 

WlTH ELECTRON 

EMISSIVE MATERIAL 

INERT FILL GAS 

OR VACUUM 

MERCURY /SODIUM 

MALGAN AND XENON 

GAS SUPPORT ARC 

POLYCRY STALLINEALUMINA ARC TUBE 

auKOSILICATE 

GLASS BULB 

w 

Flgure 31 .-Typical high-pressure sodium lamp construction. 

WAVELENGTH (NANOMETERS) 

Flgure 32.-Spectral energy distribution of typical highpressure sodium lamp. 
Lamp Life 

HPS lamps have very long rated lamp life, 24,000 h. 

As previously noted, the mechanism of normal lamp failure involves the changing voltage character of the lamp 

throughout its life. The steady-state lamp operating voltage rises above that which is available from the ballast. 

Note that a failed lamp will continue to start and warmup. 

However, once the voltage to sustain the arc rises above 

that available from the ballast, the arc will extinguish. If 

the power is not turned off, an HPS lamp that has failed in 

this manner will continue to cycle on and off. 

Effect of Voltage Variation 

Like all other mine lamps, the effect of high line voltage is detrimental to lamp life. High line voltage (1) raises 

the steady-state lamp operating voltage and wattage and 

shortens the period that the available ballast voltage is 

sufficient to start the lamp arc, decreasing lamp life; and 

(2) accelerates the mechanisms that cause lamp voltage 

rise and this also reduces lamp life. High-energy voltage 

transients tend to damage the leads in the outer bulb. 

Sustained high-voltage operation has little effect on efficacy, but does accelerate lumen depreciation. Like MV 

lamps, severe voltage dips or voltage dropouts can extinguish the HPS lamp arc. Restrike, however, can be achieved 

instantly with special starting aids. 

Flicker 

Like MV lamps, lumen output drops to zero every half 

cycle on HPS lamps and the stroboscopic effect can be a 

pqoblem in some applications. Connecting these lamps to 

alternate leads of a three-phase power supply is one way 

to prevent this problem. 

Ballasts 

The function of HPS ballasts differs significantly from 

that of MV ballasts. One difference involves provision of a 

high-voltage, short-duration pulse to initiate the xenon 

arc when starting the lamp. This is provided by an auxiliary device called a starter or striker. The second difference involves varying lamp operating characteristics 

(voltage and wattage), which are dependent on several 

factors. HPS lamp ballasts should be capable under these 

changing characteristics of maintaining lamp electrical 

operating parameters within certain limits consistent with 

reasonable lamp performance and life. As a result, HPS 

ballasts are generally larger and more expensive than their 

MV counterparts. 

Three factors contribute to varying lamp electrical 

operating parameters: 

1. HPS lamps exhibit large lamp operating voltage 

increases (or decreases) as lamp wattage increases (or 

decreases). This occurs because HPS lamps have excess 

amalgam, and, as lamp wattage increases, more amalgam 

is vaporized. MV lamps, on the other hand, have no excess 

arc metal, and lamp voltage remains relatively stable with 

increases in wattage. The implication of such a lamp 

wattage-voltage relationship is that it is important that 

HPS lamp ballasts be capable of limiting lamp wattage 

changes with changes in line voltage. 

2. As noted, HPS lamp operating voltage increases as 

the lamp ages. This effect is caused by several factors. 

First, increased arc tube blackening throughout lamp life 

raises arc tube temperature and pressure. This, in turn, 

increases the level of amalgam that is vaporized and, hence, 

raises lamp steady-state operating voltage. Additionally, 

some of the sodium material will react with arc tube 

components, changing the ratio of sodium to mercury in 

the amalgam, which also raises operating voltage. Even if 

lamps can be operated at constant wattage throughout 

their life, lamp operating voltage will gradually increase 

and eventually will exceed that available from the ballast, 

ending useful lamp life. 

3. At nominal operating wattage, the range of lamp operating voltages is wide for new lamps. HPS lamp manufacturing techniques are not so refined that narrow electrical 

performance specifications can be obtained at a reasonable unit manufacturing cost. Impurities, slight changes 

in arc tube cold spot temperature, material variances, etc., 

make precise manufacturing control impossible. Typically 

a 515-pct range in voltage is accepted as nominal lamp 

wattage. 

Figure 33 summarizes the effect of these factors. Figure 33A shows the wattage-voltage character of the lamp. 

The increasing steady-state operating voltage throughout 

lamp life has the effect of causing the line to "march" to 

the right over time as depicted in figure 33B. The manufacturing variances impact the starting point of the march 

as depicted in figure 33C. 

AS LlNE VOLTAGE INCREASES, LAMP 

WATTAGE AND LAMP VOLTAGE 

INCREASE AS DEFINED BY THIS LINE. 

I NOMINAL LAMP 

VOLTAGE 

1 I 

I 

LAMP VOLTS 

A. EFFECT OF WATTAGE VARIATION (WHICH MAY RESULT FROM 

CHANGING LlNE VOLTAGE) ON LAMP OPERATING VOLTAGE 

7 TO THE RIGHT AS THE LAMP AGES. 

LAMP VOLTS 

B. EFFECT OF LAMP VOLTAGE RISE RESULTING FROM LAMP AGING 

MANUFACTURING TOLERANCES AFFECT WATTAGE STARTING POINT FOR THE RIGHTWARD 

"MARCH" OF WATTAGE/VOLTAGE LINE 

AS LAMP AGES. 

LAMP VOLTS 

C. EFFECT ON MANUFACTURING TOLERANCES 

Figure 33.-Lamp characterlstlcs that must be accommodated 

In hlgh-pressure sodium lamp ballast design. 
Because of these effects, lamp manufacturers have set 

up specifications for HPS ballast performance in the form 

of a trapezoid diagram (fig. 34). These diagrams define the 

maximum allowable variations in lamp voltage and wattage that the ballast may permit. The minimum lamp wattage is the minimum wattage at which the lamp will provide reasonable lumen output. The maximum wattage line 

is the maximum figure 34 wattage at which the lamp can 

be operated and still have reasonable life and lumen 

depreciation rates. The minimum voltage line is defined 

by the lower end of tolerated manufacturing range; e.g., 

for a 100-V nominal lamp, this line intersects 85 V (0.85 X 

100) at nominal lamp wattage. The maximum voltage line 

is placed at the maximum voltage level at which the ballast can reasonably be expected to provide adequate voltage to keep the lamp operating. Once lamp steady-state 

voltage requirements exceed this level, the lamp has failed. 

Superimposed on the trapezoid diagram is a ballast 

characteristic curve (fig. 35A). This haystack shaped curve 

depicts how a particular ballast design will operate a lamp 

(i.e., at what lamp wattage levels) as lamp voltage changes 

during its life. Note that the curve stays within the confines of the trapezoid. When line voltage increases or 

decreases, the ballast characteristic curve will shift up or 

down accordingly but will not change significantly in shape. 

The shape of the curve varies depending on ballast 

design and is useful in evaluating performance of the 

resulting ballast-lamp system (fig. 35A). The ideal ballast 

characteristic curve would be a horizontal line at nominal 

lamp wattage and would not shift up or down for changes 

in line voltage. Such a ballast would be too expensive to 

manufacture. However, some moderately priced ballasts 

maintain lamp performance close to this line with a relatively small hump. The amount of vertical shift of the 

ballast characteristic curve with changes in line voltage 

also varies depending upon ballast design (fig. 35B). Ballasts that yield curves with less of a hump and less vertical shift are preferred to those with a high hump and large 

vertical shift because they have better regulation ability. 

Some ballasts yield a characteristic curve that rises significantly above the nominal lamp wattage line as lamp voltage rises (fig. 35C). These ballasts will accelerate lamp 

failure because continued lamp operation at high wattage 

will accelerate the rate of lamp voltage rise and shorten 

the period until available ballast voltage is insufficient to 

maintain lamp operation. 

There are three main categories of HPS ballast designs. These are depicted in figure 36 along with a discussion of the shape of their ballast characteristic curve and 

their relative performance advantages and disadvantages. 

Frequently, lag ballasts are provided for mine application 

of HPS lamps. Although less expensive, they perform poorly 

on applications where line voltage tends to fluctuate. Lead 

ballasts are preferable; they offer reasonable performance, 

especially with respect to line voltage variation, at moderate cost. Regulator ballasts may better maintain good lamp 

life for operation at high line voltage but care must be 

taken in heat sinking these ballasts, and they may not be 

available for certain mine lamps. Mine hardware suppliers should be contacted concerning ballasts substitution if 

deemed desirable. 

Instant-restart starting aids are available for HPS 

mine lamps and they reduce the time duration of lamp 

outages caused by voltage dips to a fraction of a second. It 

is recommended that users request these devices when 

purchasing HPS hardware. 

I UPPER WATTAGE LIMIT I i 

MANUFACTURING 

TOLERANCE 

MAX. VOLTAGE AT 

NOMINAL WATTAGE 

LOWER WATTAGE LIMIT 

I 

(NOMINAL VOLTAGE 

1 I 

LAMP VOLTS 

Flgure 34.-Trapezoid speclflcatlon for hlgh-pressure sodlum 

lamp ballast performance deflned by lamp characterlstlcs and 

upper-lower wattage Ilmlts. 

THE "IDEAL" HPS BALLAST CHARACTERISTIC. 

OPERATES LAMP AT NOMINAL WATTS 

REGARDLESS OF LAMP VOLTAGE. 

GOOD BALLAST CHARACTERISTIC WHICH 

REGULATES LAMP WATTAGE CHANGES 

FOR CHANGES IN LAMP VOLTAGE. 

POOR BALLAST CHARACTERISTIC WHICH 

PERMITS WIDE LAMP WATTAGE VARIATION 

I 

AS LAMP VOLTAGE CHANGES. 

LAMP VOLTS 

A. LAMP WATTAGE REGULATION FOR CHANGES IN LAMP VOLTS AS LAMP AGES 

POOR REGULATING BALLAST GOOD REGULATING BALLAST 

I 

LAMP VOLTS LAMP VOLTS 

0. LAMP WATTAGE REGULATION FOR CHANGES IN LINE VOLTAGE 

GOOD BALLAST CHARACTERISTIC WHlCH 

OPERATES BALLAST CLOSE TO WATTAGE 

MOST OF LAMP LIFE. 

POOR BALLAST CHARACTERISTIC WHICH 

OPERATES BALLAST ABOVE NOMINAL WATTAGE MOST OF LAMP LlFE AND 

ACCELERATES FAILURE. 

LAMP VOLTS 

C. AVERAGE LAMP WATTAGE THROUGHOUT LAMP LlFE 

Flgure 35.-Important aspects of ballast characterlstlc cunres. 
INPUT STARTER 

LAG (REACTOR) 

Consists of a simple choke; autotransformer may be Incorporated If llne voltage Is Insufficient for arc maintenance. Capacltor used for power factor correction. Ballast characterlstlc curve 

Is flat relatlve to other types; vertlcal displacement Is large wlth 

changes in llne voltage. 

Advantages: 

Inexpensive. 

Good lamp wattage regulatlon as lamp voltage lncreases 

throughout lamp Ilfe. 

Low Internal power consumptlon. 

Dlsadvantages: 

Poor lamp regulatlon wlth changes In llne volts, only &5 pct 

voltage tolerable. 

Comblned regulatlon for change In llne volts and lamp volts Is 

worse than other types. 

INPUT pRJ 

CAP 

INPUT 

LEAD 

Compromlse unlt that comblnes performance characterlstlcs 

of regulator and lag ballasts. Characterlstlc curve has low vertlcal shlft In the event of llne voltage changes but has a hlgher 

hump than any other type. 

Advantages: 

Moderate cost. 

Good lamp wattage regulatlon wlth changes In llne volts, ?I0 

pct. 

Comblned regulatlon for change In llne volts and lamp volts Is 

better than lag ballasts but not as good as regulator ballasts. 

Dlsadvantages: 

Moderate Internal power consumptlon. 

Lamp wattage regulatlon as lamp voltage lncreases thr~ughout lamp llfe Is worse than other categorles. 

STARTER 

REGULATOR (CONSTANT WATTAGE) 

Essentlally voltage regulator clrcult that controls llne voltage 

varlatlons in power provlded to lag-type ballast. Characterlstlc 

curve Is relatlvely flat. Llttle vertlcal dlsplacement of curve wlth 

changes In llne voltage. 

Advantages: 

Good lamp wattage regulatlon as lamp voltage lncreases 

throughout lamp Ilfe. 

Good lamp wattage regulatlon wlth changes In llne volts, 510 

pct voltage tolerable. 

Comblned regulatlon for changes In llne volts Is best of all 3 

typesDlsadvantages: 

Expenslve. 

Hlgh Internal power consumptlon. 

Flgure 36.-Hlgh-pressure sodlum lamp ballasts. 
CHAPTER 4.AVAlLABLE MINE LIGHTING HARDWARE 

The objectives of this chapter and appendix B are as 

follows: 

1. Identification of currently available hardware and 

presentation of major specifications as an information base 

to assist users in making comparisons. 

2. Discussion of the salient design features that impact 

performance (to be used as a decisionmaking guide in hardware selection). 

OVERVIEW 

Table 5 identifies and categorizes the mine lighting 

hardware (area luminaires approved for use at the coal 

face) currently available in the United States. This categorization is based on the following appropriate major 

design and application demarcations. 

1. Lamp Type.-Systems are available that utilize 

fluorescent, high-pressure sodium (HPS), incandescent, and 

tungsten-halogen sources. Systems using mercury vapor 

(MV) lamps are available, but currently are not being 

actively marketed because of drop out problems that result 

from voltage dips in the supply power (see chapter 3). 

2. Circuit Designation.-Luminaires, power supplies, 

and interconnecting wiring utilized at the working face 

must be designed so that they cannot cause dust ignition 

or an ignition of a methane-air mixture at concentrations 

Table 5.-Categories of available lighting hardware and ldentiflcatlon of U.S. manufacturers 

Ballast Lamp Machine Manufacturer 

location and type Shape Power power 

FLUORESCENT SYSTEMS-EXPLOSION PROOF 

Integral: ........ t ac 

....... ........ ..... National Mine Service.' 

Solid state Tubular HO-VHO Mine Safety Appliances.' 

dc ........ Mine Safety Appliances. 

U-shaped ....... Standard ..... ac ........ National Mine Service. 

Core and coil ..... Tubular ........ Standard ..... ac ........ McJunkin.' 

Remote: 

Solid state ....... Tubular ........ HO-VHO ..... ac ........ 

........ McJunkin. 

dc ( Do. 

National Mine Service. 

Diesel. ...... McJunkin. 

West Virginia Armature. 

Joy Manufacturing. 

National Mine Service. 

Core and coil ..... Tubular ........ HO-VHO ..... ac ........ McJunkin. 

Bacharach Instruments. 

Crouse Hinds. - -- - 

FLUORESCENT SYSTEMS-INTRINSICALLY SAFE (POWER LEADS AND LUMINAIRE) -- -- - 

Remote: Solid state ... Tubular ........ Standard ..... ac ........ Service Machine. 

FLUORESCENT SYSTEMS-INTRINSICALLY SAFE (POWER LEADS ONLY) 

ac ........ ... ........ ..... ....... Ocenco.' 

Integral: Solid state Tubular Standard dc .) OCenco, 

Diesel. 

HIGH-PRESSURE SODIUM SYSTEMS-EXPLOSION PROOF 

Remote: 

........ t ....... . ......... ........ dc 

Solid state NAp NAp 1 McJunkin. 

Diesel. ...... 

..... ......... ........ ........ McJunkin. 

Core and coil NAp NAp ac Mining Controls, Inc. 

West Virginia Armature. 

Crouse Hinds.' 

STANDARD INCANDESCENT SYSTEMS-EXPLOSION PROOF 

........ t ...... . ......... ........ ........ ac 

...... 

McJunkin. 

NAp NAp NAp NAp dc Mining Controls, Inc. 

Diesel. West Virginia Armature. 

Ocenco. 

TUNGSTEN-HALOGEK-EXPLOSION PROOF 

........ NAp ...... NAp . NAp ......... NAP ........ ........ Mining Controls, Inc. 

Diesel. ...... 

HO-VHO High output, very high output. NAp Not applicable. ' Systems have been applied on longwalls. All systems may be applied on mobile face machines. 
in the explosive range. One of two design approaches may 

be utilized to meet this objective: 

Explosion-Proof Design.-Power components are housed 

in an enclosure capable of withstanding internal explosions without damage to the enclosure or discharge of flame 

(30 CFR 26.2(h)). 

Intrinsically Safe (IS) Design.-A fixture, a combination of parts, or an electrical circuit are designed such that 

they will not cause ignition of flammable methane-air mixtures in any normal operation, during an intended 

manipulation, or when accidentally broken, if properly 

installed and powered by a voltage that does not vary 

excessively from the nominal rating (30 CFR 26.2(0). 

Certain fluorescent lighting systems are rated IS. The 

two manufacturers of IS system-Ocenco, Inc., and Service Machine Co.-have very different designs to meet the 

IS criteria. The Ocenco system power supply produces low 

voltage (12 V) dc power with voltage and current monitoring and limiting circuits to produce failsafe intrinsically 

safe power to drive the luminaires. A solid-state inverter 

ballast integral to the luminaire converts the 12-V dc power 

to a high-frequency lamp drive power. The Service Machine 

power supply produces a very high-frequency, mediumvoltage power that is intrinsically safe and drives the lamps 

directly. Hence, only the cabling is intrinsically safe on 

the Ocenco system, whereas, both the cabling and luminaires are intrinsically safe on the Service Machine system. 

3. Ballast Location.-Lamp ballasts may be located 

integral to the luminaire or remotely in a separate explosion-proof enclosure. Intregally ballasted luminaires were 

initially developed for application on longwalls, primarily 

to facilitate wiring. Relative merits of the two designs are 

discussed in detail in a subsequent section. 

4. Ballast Type.-Ballasts to condition power for lamp 

starting and drive may utilize either conventional coreand-coil or solid-state ballast technology. The major reasons for application of solid-state ballasts in mine lighting 

are (1) the reduced size of these ballasts and (2) the ability 

of solid-state ballasts to convert any source power (ac or 

dc) to a suitable lamp drive power. Because of one or both 

of these characteristics, solid-state ballasts have been 

widely applied where standard ac power is not available 

(i.e., the IS systems and for dc and diesel machines) and on 

integrally ballasted systems. Solid-state ballasts drive 

lamps at high frequency, hence, yielding improved efficacy for the arc-discharge lamps. It should be noted that 

application of solid-state ballasts on dc machines generally requires additional voltage regulation and transient 

suppression circuitry. 

5. Lamp Shape.-Lamp shape is an important distinction for fluorescent luminaires, affecting luminaire profile 

and photometrics. Most fixtures use standard T-shaped 

lamps of various lengths, and wattages, which are housed 

in cylindrical luminaries. A National Mine Service fixture 

utilizes small, U-shaped lamps that enable a relatively 

flat profile and incorporation of a unique lamp shielding 

technique in the fixture lens (see appendix B). 

6. Lamp Power.-Lamp drive power is another important distinction for fluorescent luminaires. "Standard" 

1-in-diam T-shaped lamps are driven at 400 mA, consuming about 1 W per inch of length. For the purposes of 

increasing lumen output from a given luminaire size; lamps 

that operate at higher current have been developed. Lamps 

that are designed to operate at 800 mA are designated 

high output (HO), produce approximately 40 pct more 

lumens than 400 mA lamps, and consume about 50 pct 

more power. Lamps that operate at 1,500 mA are designated very high output or super high output (VHO or SHO), 

produce about 100 pct more lumens than 400-mA lamps, 

and consume about 200 pct more power. It is evident that 

this increased light output is achieved at the expense of a 

loss in efficacy and an increase in luminaire surface 

intensity. Because of these disadvantages it is important 

that a need for the additional light output exist before 

applying these lamps. 

7. Machine Power.-All mine lamps are driven on alternating current, with the exception of incandescent and 

tungsten-halogen light sources, which can use either ac or 

dc power. (There has been some experimentation with dc 

drive of fluorescent and MV lamps, but these systems are 

not commercially available.) For arc-discharge systems 

applied on dc and diesel machines, lighting power supplies 

are constructed with provision for producing alternating 

current for powering the lamps. On dc machines, most 

systems rely on solid-state inverter ballasts to obtain the 

alternating current although additional voltage dropping, 

voltage regulating, and transient suppression hardware is 

typically provided. One IS system inverts the power to 

high frequency ac and then conditions it with circuitry 

similar to that utilized in its ac power supply. Systems 

available for diesel machines use generators or alternators to generate electrical power and, respectively, are coupled with dc or ac power supplies. Appendix B provides a 

functional description of the various power condition systems available. 

Readers are referred to appendix B for detailed information and photographs of area illumination hardware 

approved for application at the coal mine face. 

HARDWARE EVALUATION 

Selection of appropriate hardware is a very important 

aspect of successful illumination system design and implementation. As an aid to selection, this section delineates 

major hardware design features that have significant 

impact on field performance. Note that no particular luminaire or power conditioning system is optimum regarding 

all aspects of performance. A decision to select particular 

components requires careful consideration of the performance tradeoffs between the alternative candidates. The 

characteristics of the application must be considered to 

establish the relative importance of these tradeoffs. For 

example, luminaire durability may be much more important on one application than on another. Moreover, concurrent consideration should also be made of the feasibility 

and cost of altering specifications for the application or 

modifying the hardware to compensate for particular 

weaknesses, while exploiting other strengths (e.g., adding 

supplementary guards to protect a relatively fragile luminaire with other positive performance aspects such as high 

lumen output, easy servicing, etc.). 

The following is an identification and discussion of 

salient features that have been demonstrated to have significant impact with respect to four major performance 

criteria-ruggedness and durability, electrical reliability, 

system servicing, and illumination performance. In addition, a miscellaneous category addresses other important 

performance aspects. When appropriate, the discussion 

identifies application characteristics that make consideration of the feature especially important. 
Ruggedness and Durability 

With existing machine designs and illumination hardware, a degree of exposure of illumination system components to the hostile mine environment is necessary. Because of this, the implementation of lighting systems on 

face machines has, at some mines, resulted in a significant 

increase in maintenance load and costs. The importance of 

system ruggedness varies greatly from one application to 

another with mine conditions being a major determinant. 

Conditions such as a high ratio of machine-to-entry dimensions, undulating bottom, and poor roof can be very destructive to lighting systems. The following are major features 

that determine the ruggedness of the hardware itself. These 

features are important, but they should not be the sole 

basis for hardware selection. Other performance aspects 

are also very important. Moreover, in some applications, 

the layout of system components to avoid excessive exposure and the provision of supplementary protective structure has much more impact on system durability than the 

inherent strength of the hardware. 

1. Luminaire Cross-Section.-Minimized luminaire 

exposure to contact-impact forces frequently encountered 

on machine-mounted installations is generally easier to 

achieve with the low-profile fixtures (e.g., fluorescent 

luminaires). This is true because (1) low-profile fixtures 

offer greater clearance when they are exterior mounted, 

(2) locating the fixtures within the confines and protection 

of existing machine structure is possible in some instances, 

and (3) machine modifications to recess the fixtures are 

generally more feasible. Exposure of high-profile, exterior 

mounted, incandescent or high-intensity discharge (HID) 

luminaires can be a particular problem on machines where 

roof height exceeds machine frame height by slightly more 

than 12 in. On such applications, roof lighting is required 

and this would typically be accomplished by fixtures 

mounted on the machine top-deck. Clearance above a typical 8-in HID or incandescent luminaire would be minimal 

and potential for roofing would be high, especially on undulating roadways. 

2. Luminaire Length.-The relatively long length of 

certain fluorescent fixtures is a disadvantage in many 

applications because (1) when mounted in the horizontal 

plane, exposure to impact is relatively high; (2) a long 

span makes construction of a strong protective cage difficult, more and heavier cage members must be utilized 

which, in turn, reduce lumen output; (3) long length makes 

recessing and/or positioning the fixture within the confines of existing machine structure more difficult. Short 

fluorescent fixtures, less than 14 in are available, and 

they offset many of these disadvantages. Moreover, it is 

possible (and for photometric purposes, often desirable) to 

mount these luminaires in a vertical position on the sides 

of the machine where exposure to many impact hazards 

would be reduced relative to horizontal mounting on the 

machine top-deck or sides. High-pressure sodium (HPS) 

and incandescent luminaires are also short enough for 

vertical mounting on machine sides, however, construction of supplemental protective guards is frequently desirable in this case because of the high profile of these fixtures. 

3. Luminaire Housing Construction.-Housings of 

incandescent and HID luminaires are generally stronger 

than the fluorescent luminaire housings. For this reason, 

luminaires in this category are generally regarfled as more 

rugged. However, it should be noted that fixture exposure 

is greater in many applications. Even though the housings 

are durable, they are exposed and glass lens breakage 

may occur frequently, necessitating replacement of the 

luminaire. Also, note that dependent on size, materials, 

and design of housing members, differences in housing 

strength exist between alternative luminaires within the 

same category. Finally, the extremely high housing strength 

of certain luminaires in this category can be a problem 

when the fixtures are subject to impact in such a manner 

that they might be driven into the machine body. If 

machine covers are flimsy, forces may be transmitted to 

underlying components causing damage more sigificant 

than the loss of a luminaire. 

4. Protective Cage Designs.-Available luminaire 

guards and protective cages vary widely in their ability to 

protect luminaires from damage from the common contact 

and impact forces experienced by machine-mounted lighting systems. Indeed, some guards serve little more than a 

cosmetic purpose. The following points should be considered when evaluating cage designs: 

a. Mechanical isolation (weak mechanical interconnection) between the protective cage and the lamp housing is 

a desirable feature because it minimizes stress transfer 

between the cage and lamp housing. This can significantly 

reduce the degree of luminaire damage when impacted. 

b. Considering generalized guard designs (fig. 37), those 

with several, heavy "horseshoes" and light struts are preferable to those with few, light horseshoes and heavy struts. 

This is true because the horseshoes are more effective in 

breaking impacts than the struts are and when horseshoes 

are used in greater numbers the span of the struts is 

reduced, which increases their protective capability. It is 

also important to note that the struts have greater photometric impact than the horseshoes, especially if they are 

large in diameter. 

c. On some available cages, the longitudinal struts are 

tacked to the underside of the horseshoes rather than on 

the outside. These welds are easily broken and the bars 

can readily be pushed into the luminaire. 

d. Some manufacturers offer heavy-duty cages as options 

with their luminaires. Photometric impact must be assessed when utilizing these cages, but their addition has 

proven feasible and beneficial in many cases without 

requiring the use of additional luminaires to meet lighting requirements. 

5. Packing Glands.-Maintenance of the structural 

integrity of packing glands is of great importance to mine 

operators because damage can create a hazardous situation and void the permissibility of the lighting system. 

Various design features impact gland durability and the 

, "HORSESHOES" 

A. SEVERAL. HEAVY HORSESHOES B. FEW. LIGHT HORSESHOES 

AND LIGHT STRUTS AND HEAVY SIRUIS 

Figure 37.-Important cage deslgn dlstlnctlons. 
durability of the cables and associated conduit feeding the 

luminaires and power supply enclosures. They include the 

following: 

a. Tubing Versus Clamp-Style Glands (see figure 381.- 

The following points are relevant when comparing these 

gland styles: 

(1) Clamp-style glands offer better strain relief than 

most tubing designs. This should reduce the frequency of 

incidents of pulling cable out of the gland opening, which 

voids the permissibility of the gland. This type of failure is 

a particular problem on certain longwall installations, especially chock faces. 

(2) Clamp-style glands offer greater impact resistance 

and are more easily dented than most tubing-style glands. 

(3) One disadvantage of clamp-style glands is that 

they currently are only available in 90" orientation. If 

cables must be routed tightly away from the gland exit, 

the clamp has a tendency to damage conduit. 

b. Gland Angle.-Some lighting suppliers offer options 

PPER OR STEEL SLEEVE 

A. TUBING STYLE 

INTEGRAL CLAMP 

c 

/ 

CAST ENTRY HOUSING 

in gland orientation angles (e.g., 45", 90°, straight), whereas U 

others do not. Appropriate gland angle for the luminaire 

location is desirable for the following reasons. B. CLAMP STYLE 

Flgure 38.-Tublng versus clamp-style packlng glands. 

(1) Proper gland angle permits good routing of cables 

away from the luminaire. This can greatly reduce cable 

exposure and stress damage to cable or conduit if the cable 

is routed away from the gland at a sharp angle (fig. 39.) 

(2) On certain explosion-proof enclosures, spacing of 

the gland entrances is such that if 90" threaded glands are 

used, it is necessary to remove one or more glands to gain 

access to the one desired because of lack of clearance 

between the adjacent glands. 

c. Number of Glands in System.-Obviously, the greater 

the number of glands used in a system, the greater the 

potential for gland failure and/or damage and for increased 

maintenance. Therefore, in selecting or designing a lighting system the number of glands utilized should be an 

important consideration. For example, IS systems have a 

reduced number of packing glands relative to explosionproof systems for a particular application. 

6. Lens (Polycarbonate-Lexan).-Polycarbonate and 

lexan lens material used on fluorescent luminaires has 

excellent impact resistance. However, there is some concern that this strength is reduced through aging. Laboratory tests have shown no significant heat-induced aging of 

polycarbonate after several thousand burn hours on luminaires with heat shields above the lamp cathodes (a feature of all currently approved luminaires). However, the 

lens in this test were kept clean, and the effect of dirt and 

grease is not known. A good lens cleaning program is thus 

recommended for this reason, as well as for minimizing 

the luminaire's lumen depreciation. Those polycarbonate 

lens with threaded ends might be prone to breaking more 

readily, failing at the weak area near the junction of the 

threads and the solid tube. 

It is important that polycarbonate and lexan lens be 

protected from the heat of welding torches and from weld 

splatter. Also, solvents containing hydrocarbons can react 

with and damage the lens. Flgure 39.-Effect of gland orlentatlon on cable routlng. 
7. Lens (Glass).-Glass lens breakage on HID and 

incandescent area luminaires is a common failure when 

these fixtures are mounted in exposed locations. It should 

be noted that when these lens fail, fixtures must be 

returned to the factory for replacement. Flame path criteria must be met in reinstallation of the lens; accordingly, 

the Mine Safety and Health Administration (MSHA) 

requires that the task be performed by an approved vendor. 

8. Cabling.-Systems with dual-glanded luminaires 

permit chaining of luminaires (i.e., feed-through wiring) 

off a single power lead. This may show an advantage on 

some longwall applications over single-glanded luminaires 

that require a separate lead from the power supply box to 

each luminaire. Dual-glanded systems require less cable, 

which reduces cable exposure and in turn reduces cable 

failures on longwalls that experience problems with roof 

rock falling between supports or with cables getting 

snagged on rock and pulled behind the supports. 

9. Materials.-The following materials-related problems have been reported in the field: 

a. Aluminum fixtures show the following disadvantages 

relative to steel, ductile iron, and brass: 

(1) They are more subject to breakage when impacted. 

A particular problem has been experienced on headlights 

with aluminum mounting "feet" or "tabs." For this reason 

one available fixture features bolted on tabs that can be 

replaced and mounted in alternative positions. 

(2) Threaded aluminum components are prone to gall 

from rockdust. 

(3) Salts found in some mines will attack aluminum 

components. 

b. Threads on brass components are easily stripped. 

Brass housings are more easily bent than steel. 

c. Steel lock screws on fixtures are prone to corrode 

in place after a period of time. 

Electrical Reliability 

Achievement of high electrical reliability levels for 

illumination systems has been difficult at many mines, 

with excessive rate of lamp failure the most widespread 

problem. The attainment of high reliability levels should 

be given much attention. Even in cases where parts and 

labor costs for making repairs are low, lighting system 

failures can be a significant drain on machine availability, 

with resultant associated high lost-production costs. The 

most important factor to consider is the compatibility of 

the system with the available power source on the particular machine application. Mine power systems are subject 

to wide deviation in supply voltage from nominal (both 

high and low), because of changes in the power system 

load and excessive voltage transients. 

Great care should be taken to establish the supply 

voltage characteristics for a given application and to select 

hardware capable of accommodating them. Selecting hardware based on nominal voltage specifications can result in 

serious error and, should, therefore, be based on site-specific 

measurements that are easily accomplished for establishing supply voltage and its variations. However, transient 

measurement is difficult to make. In some instances, particularly certain dc applications, a trial installation, with 

close monitoring of rate and cause of electrical failure, 

may be a desirable approach for determining the electrical 

reliability of the hardware. Results of these trials should 

make it possible to install power conditioning equipment 

in conjunction with the hardware supplier to achieve an 

acceptable level of reliability. 

Systems for dc Application.-Reports on the electrical 

reliability of illumination systems applied on dc face 

machines have been very mixed, with both reliable and 

unreliable performance reports for the various system 

designs available for this application. The limited field 

information available on the performance of dc systems 

prohibits a thorough discussion of the anticipated performance of the various design features of the candidate 

hardware. The following points, however, should be of some 

aid in making selection decisions. 

1. Consideration of Power Parameters.-Power parameters vary greatly from one dc application to another and 

have great impact on the reliability exhibited by a particular system design. "Normal" voltage available to the lighting power supply may differ significantly from the machine 

nominal voltage. Even though voltages on dc machines 

are typically specified in ranges, e.g., 250 to 300 V dc or 

500 to 600 V dc, it is not unusual for the effect of line load 

variations to produce sustained voltages up to 33 pct less 

than the lower range value or 25 pct above the upper 

range value. Moreover, ac ripple may produce peak voltages 25 pct in excess of the upper range value. Obviously, 

knowledge of the typical operating range for the particular machine in question would be of value in evaluating 

and specifying hardware, because available dc hardware 

designs vary significantly in their ability to regulate voltage and in the effect of voltage variation on system 

function. Moreover, minor design modifications can be 

made by the hardware supplier to improve system performance on some lighting systems on the basis of an accurately specified normal operating voltage level and the 

upper and lower values of the voltage variations. 

The second major power consideration is line transients, which can be caused by any of the following: 

a. Switching of large transformers and motors on the ac 

distribution line that feeds the dc rectifier on a section 

load center. These transients may produce, on the secondary side of the rectifier, very high voltage peaks that are 

generally short in duration. The problem is likely to be 

worse on systems employing vacuum switches on the ac 

line. 

b. Switching and arcing on the dc line itself can produce 

significant transients. These tend to be of lower peak voltage than those orginating on the ac line but are of much 

longer duration and are also bipolar (important when protecting solid-state circuits). 

c. Because line inductance tends to dissipate transients 

from other sources, the most serious transients can be those 

that originate from switching and arcing on the particular 

machine application itself. 

Field survey data show a significant difference in performance between systems applied on dc machines where 

the power originates at load-center-based rectifiers fed from 

ac primary distribution, and those where mine distribution is dc (trolley line or dc cable). In the former case, good 

electrical reliability was frequently achieved on both arc 

discharge and incandescant systems. In the latter case, 
problems were much more severe, no doubt attributable to 

the poorer voltage regulation and extreme transient 

conditions. It is recommended that knowledge of the character of the application (field measurements and circuit 

analysis) be obtained as a basis for dc hardware selection 

decisions. 

2. Incandescent Versus Arc Discharge Systems.- 

When comparing incandescent to arc discharge (fluorescent 

and HID) systems for operation on dc power the following 

points are relevant: 

Incandescents can operate directly on dc power requiring minimal supplementary power conditioning hardware. 

Generally, simple, rugged voltage drop resistors comprise 

the circuit in addition to the lamps. Alternate circuits for 

dc application of headlamps are shown in figure 40. 

Arc discharge systems (fluorescent and HID) convert 

the dc to some form of ac to drive the lamps. This requires 

use of inverters and supplementary circuit protective 

devices to prevent damage from transients and poor voltage regulation. Extreme voltage fluctuations, however, can 

damage the protective components as well as the other 

circuit constituents. 

Operationally, incandescent lamps are less affected 

by voltage fluctuations than other lamps. Temporary overvoltages and undervoltages, including transients, will not 

extinguish the lamps and have little effect on the lamp 

characteristics including minimal life reduction. Voltage 

dips will extinguish gas discharge lamps, with considerable restart time required for HID'S (HPS lamps restart 

quicker than MV lamps and time can be further reduced 

with ah instant restrike starting aid). Moreover, transient 

voltage spikes can damage the arc tube of HID lamps, 

greatly reducing lamp life. 

Because of the inherent advantages, incandescent systems have seen wide application on dc equipment. On applications where voltage fluctuation problems are extreme, 

incandescent systems will probably yield the best reliability. When implementing these systems, it is important 

that drop resistors be sized for the actual operating voltage rather than nominal voltage. Undersized resistors will 

overdrive the lamp, greatly reducing its life. Lumen outDropping resistor /4 4 

Headlight 

0 

PARALLEL 

Advantages: 

Easy to wire, only 3 leads required. 

lsolatlon of falled lamp slmple If 1 lamp 

falls. 

Second lamp remalns in operatlon If 1 

lamp falls. 

Dlsadvantages: 

Llfe of remalnlng lamp shortened when 

1 lamp falls unless It Is replaced Immediately. 

put from an incandescent lurninaire is, of course, less than 

a gas discharge luminaire. This limits application in higher 

seam heights. 

3. Comparison of Gas Discharge Lamp Alternatives.- 

Available dc power conditioning systems for use with gas 

discharge lamps vary significantly in provision to regulate supply voltage and to protect components from voltage transients (see appendix B for a description of these 

systems). It is important to consider these features in conjunction with the application parameters when assessing 

hardware suitability. 

Lamp Life.-Costs incurred because of reduced lamp 

life can be very significant in mining applications, and 

realization of long average lamp service life should be given 

great consideration when making hardware selection 

decisions. Although life differential between alternative 

lamp types is a performance characteristic that might be 

highly touted by a hardware supplier, it is important to 

recognize that these rated values are frequently based on 

laboratory tests rather than field measured values. Mine 

application conditions are harsh and statistics have shown 

that (1) rated service life is seldom achieved on mine 

application, frequently not even approached, and (2) rated 

service life is also an invalid basis for making relative 

comparisons between alternative lamps. Determination of 

the best lamp with respect to life performance requires 

careful analysis of the characteristics of the application 

including the approach that will be taken in maintaining 

the system. The reader is referred to chapter 6 for a detailed 

comparison of lamp types and a suggested approach for 

lamp selection, installation, and maintenance. 

Comparison of Core-and-Coil Ballasts.-Standard coreand-coil ballasts have a long expected life-approximately 

6 yr with a 24-h/d duty cycle. Frequently, this life is not 

realized in mine application. Poor heat dissipation environments, shorting of the power leads, overvoltage 

operation, and protracted operation with failed or nearfailed lamps are major factors contributing to ballast overheating and reduced ballast life. Ballast designs differ in 

their tolerance of these conditions. Moreover, concerning 

overvoltage and undervoltage operation, ballasts differ in 

their ability to regulate lamp voltage and current, and 

Dropping resistor 

Headlight '4 

SERIES 

Advantages: 

Easy to wire, only 3 leads requlred. 

Llfe of remalnlng lamp Is not shortened 

when 1 lamp fails. 

Dlsadvantages: 

Isolation of failed lamp dlfflcult If 1 lamp 

fails (neon indicator can reduce problem.) 

Second lamp does not remain In operation If 1 lamp falls. 

Headlight /@d 4 

SERIES-PARALLEL 

Advantages: 

lsolatlon of falled lamp slmple If 1 lamp 

falls. 

Second lamp remalns In operatlon If 1 

lamp falls. 

Llfe of remalnlng lamp not shortened If 

1 lamp fails. 

Dlsadvantages: 

More dlfflcult to Install; 5 or 6 leads 

requlred. 

Figure 40.-Alternative wiring conflguratlons for dc appllcatlon of Incandescent headlamp palrs. 
this affects the service life realized by the lamps. Specific 

features of note include: 

Dual-lamp parallel fluorescent ballasts are available and 

have been applied because they can simplify troubleshooting procedures relative to series dual-lamp ballasts. Field 

experience has not been favorable, however, because they 

tend to frequently fail from overheating. Leads shorting 

was cited as the cause of most overheating incidents. 

As previously noted, widely variable line voltage is a 

circumstance found in many mine lighting applications. 

Compromising performance for cost, many mine lighting 

hardware suppliers do not provide the best available ballast for regulating line voltage variation. Chapter 3 identified major ballast designs available for mine lamps and 

discussed their performance tradeoffs. If the application 

warrants concern, it is recommended that users consult 

hardware suppliers for information on the design of the 

ballast they supply. Since many ballasts are off-the-shelf 

items, substitution of better performance ballasts may be 

possible, dependent on their availability. 

As noted in chapter 3, by using more material (i.e., larger 

diameter conductors for coils) ballast power consumption 

and heat production can be reduced. In many mine applications this feature is desirable because the heat dissipation 

character of the environment where the ballasts are 

mounted is poor or overvoltage conditions might exist. Ballast manufacturers have given many names to ballasts 

designed using this principle including "premium," "lowheat," and "energy-saver" ballasts. 

Multitap ballasts available from some mine lighting 

hardware suppliers may offer improved performance in 

applications where line voltage deviates from nominal but 

tends to be consistently high or low. 

An integrql instead of a remote ballast approach may 

yield improved ballast performance in some installations. 

This is particularly true for systems requiring a large number of luminaires (and many ballasts), and where supply 

power is poorly regulated. 

Heat Dissipation Character.-As noted, overheating of 

electrical components, especially ballasts, can be a major 

problem in mine lighting. The heat dissipation character 

of a candidate power supply should be checked. Factors to 

review include the contact area of heat-producing components with the enclosure of heat-sinking materials mounted 

in the enclosure and the component packaging arrangement. Problems have been experienced with systems using 

several ballasts tightly stacked. An increase in temperature of just a few degrees can greatly reduce ballast life. 

Chapter 6 discusses this problem in greater detail. 

Transformers.-The following are two important criteria for evaluation of the auxiliary lighting system power 

transformers: 

1. High-Low Voltage Taps.-Operating voltage at the 

machine frequently deviates from nominal but lighting 

system components have little tolerance for deviation from 

specification. Transformers with high-low taps allow compensation on the basis of measured actual values and can 

improve system performance. 

2. Kilovolt-Ampere Capacity.-On systems where additional headlights are added beyond MSHA statement of 

test and evaluation requirements, it is necessary to check 

that transformer capacity is adequate. Instances where 

this was overlooked and capacity was exceeded have been 

reported quite frequently. 

Line Losses.-Voltage drop attributable to line losses 

can be a problem on longwall installations. The resulting 

low voltage can cause -lamps to frequently extinguish and 

significantly shorten the service life of fluorescent lamps. 

Design features that minimize line losses include the 

following: 

Use of conductors of sufficient size to keep voltage drops 

low. 

Reduced number of lamps in a single line or even use of 

an individual line to each lamp (this will increase required 

number of power supply andlor junction boxes). 

Use of more than one power distribution line along the 

face. 

Use of autotransformers as voltage boosts. 

Line loss problems can usually be avoided through 

careful specification of the system configuration. 

System Servicing 

Regulations require that lighting systems be maintained in fully operable condition at all times during production operations. Occasionally, this might force shutdown of a machine to make repairs on the lighting system, 

and, the associated lost-production costs can be very high. 

Because of these costs and the high cost of maintenance 

labor, it is very important that lighting systems be implemented so that they are quickly and easily serviced. This 

requires that fault diagnostic procedures be few and uncomplicated and that repairs can be made quickly. Available 

hardware varies greatly concerning these performance, 

aspects, and the major determinants of these performance 

criteria are outlined in the following sections. 

Explosion-Proof Versus Intrinsically Safe Systems. 

-Regulations require that persons performing maintenance work on explosion-proof systems be certified electricians. This is not a requirement for working on intrinsically safe systems or any part of a lighting circuit that is 

intrinsically safe. Because certified electricians are scarce 

at many mines and are usually involved with projects of 

higher priority, the implementation of intrinsically safe 

systems might facilitate conduct of lighting system maintenance on certain installations, particularly longwalls. 

Housing of Power Conditioning Components.-The 

number and type of power conditioning components required for a lighting system varies depending on the size 

of the system and the available machine power. Explosionproof enclosures offered by the lighting hardware suppliers to house these components should be reviewed with 

respect to (1) size compatibility with the components to be 

housed, and (2) the packaging arrangement of components 

within the enclosures. Many hardware suppliers offer a 

limited number of different-sized explosion-proof enclosures 

to house their power conditioning equipment. Size should 

be adequate to house the required components in an acceptable packaging arrangement but not so large that locating 

the box on the machine is a problem, forcing a compromise 

between protection and accessibility. Some manufacturers 

have required the use of two boxes to house the components for certain systems. This can increase accessibility 

problems for certain diagnostic tests in the event of electrical failures. Component packaging arrangements greatly 

affect the ease of making diagnostic tests and component 

exchanges. Criteria for review include component spacing 

(also affects temperature buildup), ballast stacking arrangement, and connection of the components to the 
enclosure; a systematic, efficient, and easy to trace wiring 

arrangement with a complementary terminal strip layout; 

and the use of plug connections between components. 

Lamp Change Difficulty.-Luminaires vary greatly in 

the degree of difficulty required to make lamp changes. 

The importance of this factor depends on whether failed 

lamps are changed at the face or whether the entire luminaire is replaced in an exchange maintenance program. In 

the former case, lamp change procedures should be reviewed very carefully. Points to check for include the 

following: 

What is necessary for lamp access? Fixtures with 

threaded or slip-fit endcaps are preferable over those where 

a bolt-attached end plate must be removed. Headlight 

designs vary significantly in requirements for accessing 

the lamp. Lamp changing is facilitated by designs where 

removal of the lens retainer exposes the entire lamp. 

How is the lamp retained? This is significant when comparing fluorescent luminaires. Cartridge-type lamp holders with plug-type connection to the lamp power are generally easy to change, although pin alignment can be difficult 

on some designs. Those that use the ground wire to hold 

the fluorescent lamp-socket assembly together can be very 

difficult to work with underground. 

Incandescent Versus Arc-Discharge Systems.-The circuit simplicity of incandescent systems makes them very 

easy to troubleshoot. Ballast failure is not a possibility 

and, if wired in parallel, all common system failures can 

be isolated or narrowed between a few alternatives on the 

basis of which lamps are burning. Neon bad-lamp indicators can be used to facilitate fault isolation of series wired 

lamps. 

''As a general rule, because of ballast and circuit 

configurations, failures on gas discharge systems tend to 

be more ambiguous and are more difficult to isolate. Also, 

off-standard voltage levels can confuse electricians who 

have had little experience with this type of equipment. 

Advantages of Modular Construction.-Modular construction, the isolation of electrical components into functional groupings generally with convenient plug-in connection to the circuit, greatly facilitates fault isolation. This 

is true because of the following: 

1. Circuit redundancy is an easily used advantage. Leads 

can be switched to an existing duplicate modular unit to 

test for a suspect lead. 

2. New units can readily be substituted for suspected 

faulty ones to test the status of the suspect unit. 

3. Detailed fault isolation within a modular unit is 

unnecessary, or at least unnecessary to perform at the 

face. Replacing the unit reduces the number of causes that 

must be investigated before identifying the cause of a failure and implementing a remedy. This simplifies and minimizes troubleshooting. It is possible that obvious manifestations of a failure, e.g., which light(s) will not operate, 

can make deduction of the cause of the failure self-evident 

without the conduct of tests. 

Specific instances where modular construction resulted 

in significant benefits in fault isolation include the following: 

Integrally Ballasted Luminaires.-These fixtures are 

generally equipped with connectors that in effect combine 

the lamp and ballast into a single functional unit that is 

readily exchanged. Faults are more easily identified and 

repaired since the ballast is dedicated to a single lamp and 

isolation within the group is unnecessary at the face. 

Modular Construction of Certain Electronic Intrinsically 

Safe Systems.-On certain systems, circuits are built on 

functionally distinct plug-in circuit cards. Failure manifestations usually make fault isolation simple and testing is 

easily achieved by substituting duplicate cards. 

Use of Explosion-Proof Connectors To Isolate Units. 

--Specification of explosion-proof connectors to isolate units 

(usually power supply boxes) is generally optional and left 

to user discretion. These connectors can reduce downtime 

for making system repairs in some instances. Generally, 

testing would proceed to check components most likely at 

fault. If these are not found to be damaged, more detailed 

isolation is not performed. Rather, the entire unit is 

exchanged with a new one. This specification is more practical and useful on some systems than others. 

Series-Wired, Dual-Lamp, Core-and-Coil Ballasts. 

-Cable faults, lamp failure, and ballast overheating are 

common failures on some system installations. With duallamp ballasts that drive the lamps in series, any one of 

these failures can cause the same manifestation-the lamps 

on the circuit do not light. Troubleshooting to isolate the 

particular fault among the possibilities may require a relatively extensive series of tests that might require access to 

the power supply enclosure. Time requirements for fault 

isolation are excessive relative to fault isolation of singlelamp ballasts. Dual-lamp ballasts that drive the lamps in 

parallel are available and would simplify fault isolation. 

However, field experience has shown them to be unreliable in mining application because they overheat quickly 

when leads are shorted. 

Connectors and Slip-Fit Glands.-Systems employing 

connectors facilitate diagnosis of cable faults because of 

easy access to the leads. This is particularly important on 

longwalls where cable faults may be common and procedures for localization may be tedious. Both connectors and 

slip-fit glands greatly facilitate component exchange. 

Accommodations for Connecting Power Leads.-Available luminaire designs vary greatly in requirements for 

connecting power leads. The following points are relevant 

for evaluation from an installation-servicing aspect. 

1. Adequate Space.-Spatial requirements for connection of six-lead luminaires in particular are large and some 

designs require special routing of the leads to make the 

connections. 

2. Terminal Strips and Spring-Loaded Connections. 

-Luminaires with these devices for making connections 

are easier to install and exchange than those with wirenut connections. Terminal strips also facilitate testing for 

diagnosis of cable faults. 

Illumination Performance 

Chapter 3 was devoted to a discussion of the intrinsic 

performance differences of the various lamps used in coal 

mine face lighting systems. Although these differences are 

significant, the major determinant of the success of a system from an illumination viewpoint lies more in the careful and creative deployment of the hardware than in the 

inherent performance differences among the available 

luminaires. 
Summary of Lamp Performance Differences.-Many 

important differences in lamp performance have been 

pointed out previously with respect to electrical reliability 

criteria. Table 6 summarizes lamp performance differences 

that are related to illumination system performance. 

Luminaire Photometrics.-The suitability of a luminaire's photometric profile (as might be expressed by an 

isofootcandle curve) is very dependent on the designer's 

objective in a particular application. Two general points, 

however, are of significance: 

1. In low and medium seam heights, lumen distribution 

requirements are such that it usually is not possible to 

decrease the number of luminaires in the system by using 

luminaires with higher lumen output. Indeed, high-output, 

small-size luminaires may decrease the uniformity of illumination levels, which might be undesirable. 

2. Most mine luminaires emit the greater portion of their 

lumen output perpendicular to the lamp axis as opposed to 

the parallel direction. Since in illumination system design 

there is usually a need for greater light output in the 

horizontal plane than the vertical plane (room length and 

width are usually greater than room height) it is advantageous to mount luminaires vertically. Short fixtures facilitate such utilization. Manufacturers can usually provide 

photometric data on their fixtures and this information 

can be of great value in the initial stages of the design or 

design modification process. MSHA's Beckley (WV) Electrical Testing Center may also be a source of such data. 

Miscellaneous 

Luminaire Repair and Salvage.-Damaged luminaires 

are generally salvagable items. In addition to consideration of the initial cost of the fixture and its inherent 

durability, one should also consider typical salvage-repair 

costs. These vary widely from one luminaire to another 

depending on typical extent of damage, design, materials, 

and manufacturer's markup for replacement parts. It is 

recommended that purchasing agents survey the hardware 

suppliers who offer rebuild services and the service companies that repair mine lighting hardware to obtain typical 

cost figures for reconditioning luminaires. 

Important Operational Aspects.-It is important that 

illumination systems remain operational at all times. Systems with luminaires that frequently stop functioning 

(drop out) can create a very annoying and possibly hazardous circumstance. The following points are significant in 

this regard: 

HID lamps are most subject to dropping out when voltage dips. MV lamps will not restart for some period of time 

(4-5 min). HPS lamps will restart quicker (90 s) and instant 

restart can be achieved if a special lamp starter is utilized 

or solid-state ballasts are utilized. It is recommended that 

these starting aids be specified by the user on conventionally ballasted systems. 

Most systems transform machine power to 120 V ac to 

operate the ballasts. Higher voltage ballasts are available 

for direct connection to machine power. However, this 

reduces isolation on the lighting circuit and creates potential for lighting system faults to trip machine power-an 

undesirable event. Use of high voltage ballasts should, 

therefore, be avoided. Excessive line losses can create 

operational problems with fluorescent systems on longwalls. As mentioned previously, careful system specification can avoid this problem. 

Hardware Supplier Services.-The services provided 

by mine lighting hardware suppliers can be as important 

in many applications as the quality of the hardware they 

provide. A supplier under consideration should be questioned concerning the following services: 

Availability of field representatives to supervise initial 

or special installations. 

Availability of installation, maintenance, and troubleshooting training courses or seminars with adequate documentation of installation and maintenance procedures. 

Table 6.-Summary of iiiumination performance differences dependent on lamp types utiiized in a iuminare 

Performance Incan- Tungsten- Fluorescent High-intensity discharge 

aspect descent halogen Standard High output VHO-SHO HPS MV 

Efficacy .... 

Lumen output 

versus size. 

Surface intensity of 

bare lamp. 

Color rendition. 

Flicker; potential for 

stroboscopic 

effect. 

Lamp extinction when 

voltage dips. 

Lumen depreciation over 

rated service life. 

Low ...... Low,betterthan High.. ... High.. .... Moderate ..... Veryhigh .... High. 

incandescent 

Moderate ... High ..... Low ..... Moderate ... Morethanhigh . .do ....... Very high. 

high output. 

High ...... Veryhigh ... Low ..... ..do. Moderate, high ... .do ....... Do. 

Excellent ... Excellent ... Good .... Good ..... Good ....... Usually Poor. 

acceptable. 

Notaproblem Notaproblem. .. .. .(I) ...... .(I) ....... .(I) ......... .(2) ....... (2) 

. .do ....... .do ...... Possible, not Possible, not Possible, not .. (7 ....... likely likely. likely. 

(7 

Low ...... Low, less Moderate .. M~derate.~ .. M~derate.~ .... Verylow .... High,over 

than in- very long 

candes- life. 

cent. 

HPS High-pressure sodium. MV Mercury vapor. VHO-SHO Very high output, super high output. ' Unlikely to be a problem except near end of lamp life. Proper maintenance important. 

May be a problem. Can be avoided through careful design. 

A significant problem, especially with MV lamps, which take a long time to restrike. 

Much depreciation occurs in early part of lamp life. 
Assistance in causal diagnosis of frequent electrical Assistance in filing STE applications for longwall lightfailures. Willingness to modify standard power condition- ing systems. 

ing system to accommodate specific mine requirements. Proximity of distributors and service representatives. 

Assistance in illumination system design modification, Availability of hardware rebuild-exchange programs. 

including filing papers for STE extensions. Location of other authorized repair service vendors. 

CHAPTER 5.DESlGN AND EVALUATION OF COAL MINE ILLUMINATION SYSTEMS 

The design of underground coal mine illumination systems that provide improved visibility and safety, meet the 

minimum specifications of Federal regulations, and are 

well accepted by the mine worker and mine operator is a 

difficult task requiring great care and effort. As outlined 

in chapter 1 of IC 9073, consideration of numerous interrelated factors such as severe environment, extremely low 

reflectance of coal, occurrence of objectionable glare problems, is required. 

A well-designed illumination system can provide 

important benefits to the machine supplier and user 

including 

Improved safety. Hazards, especially in the mine workers' 

peripheral field of vision, can be more readily detected. 

Improved overall areal perspective and task visibility, 

which could assist in improving task performance and, 

ultimately, productivity by improving both the quality and 

speed of vision. 

Conversely, a poorly designed system can cause significant problems such as 

Excessive glare which may result in operator visual discomfort or visibility diminished significantly from what 

could be achieved. 

Excessively increased machine maintenance and resulting increased production costs. 

The purpose of this chapter is to present guidelines for 

the design and evaluation of illumination systems, to present methods to address the various types of problems 

encountered, and to provide design examples. Only the 

design of equipment-mounted illumination systems is 

discussed. Workplaces can also be illuminated by luminaires not mounted on the machinery. These systems, 

called area illumination systems, have to date proved to 

be an impractical approach for illuminating underground 

coal mines. Their major problems are that they must be 

moved separately as the workplace advances and added 

electrical cables further encumber the already crowded 

workplaces. 

This chapter consists of two major parts. First, a recommended methodology is presented for proper conduct of 

the design process. Although strict adherence to this methodology may not be possible in all cases, it does provide a 

useful problem solving framework for this difficult design 

activity. Secondly, the major problems of system designi.e., minimizing discomfort and disability glare, achieving 

ruggedness-are addressed directly with suggested techniques and methods of analysis. 

Recommended Design Methodology 

The following sections define the major tasks required 

to complete and refine the design of an effective illumination system. 

Information Collection and Assembly 

Establishing comprehensive definitions of (1) the characteristics of the application and (2) the specific performance objectives to be met with the illumination system is 

an important prerequisite for conduct of design activity. 

One should note that these characteristics and objectives 

vary significantly, at least at the machine model level 

and, frequently, on an application-specific level. It is recommended that the designer commence his or her task 

with a comprehensive effort to collect and assemble data 

that establish the following information as a basis for subsequent effort. 

Machine Data.-Obtain machine design data including mechanical assembly, electrical, and machine dimensional drawings. Verify that the machine construction is 

as the documentation depicts. Machines are frequently 

modified in the field, and manufacturers often provide 

standard assembly drawings that do not include significant user-specified modifications. Small differences in 

machine construction can radically affect illumination system design. 

If practical, establish site-specific electrical operating 

parameters as a basis for selection of hardware that will 

perform reliably. These information needs are discussed 

in detail in chapter 4 of this report. 

Assess the potential for illumination hardware integration into machine design. The machine for which the 

system is being designed should be inspected, preferrably 

in the presence of someone intimately familiar with both 

machine operation and construction (manufacturer's representative or appropriate mine maintenance personnel). 

Existing dead space should be documented as well as practical machine modifications for creating accommodations 

to recess lighting hardware. Additionally, the feasibility 

of installing add-on protective structures should be assessed. 

Care should be taken to insure adequate provision for 

anchoring these structures and to insure that they will not 

interfere with machine operation. Comprehensive photographic documentation should accompany this assessment 

because it will greatly facilitate the subsequent design 

effort. The photographs should include size reference; e.g., 

a candidate luminaire. 

One should define the machine servicing requirements 

and procedures. It is important that the lighting system 

does not significantly impede accessibility for conduct of 

these tasks. 

On machines where the machine deck serves as a base 

for work activity, especially roof bolters, spatial allocation 

for tool and supply storage and for work surfaces should be 

defined. This accommodation should be considered as part 

of the lighting system design. 

Regulations.-Determine the maximum and minimum 

dimensions of the workplace to be illuminated, keeping in 

mind future working places where the machine will be 

applied. Establish whether the illumination system must 

meet high- or low-seam regulations or both. 
Compile pertinent illumination system regulations and 

Mine Safety and Health Administration (MSHA) policies 

that apply to the specific machine in question. These data 

should include the areas required to be illuminated, types 

of luminaires permitted at various machine locations, and 

any other special conditions that apply to the machine and 

seam height. The current lighting regulations and the latest enforcement policies are included in appendix A. 

Questions regarding the design and application of lighting 

systems should be directed to the following agencies: 

Regulations and Enforcement: MSHA, Box 1166, Building F, MSHA Academy, Beckley, WV 25801. 

Hardware and System Approval: MSHA Approval and 

Certification Center, Box 201B, Industrial Park Boulevard, 

Triadelphia, WV 26059. 

Application Assistance: MSHA Technical Support Center, Box 1166, Building F, MSHA Academy, Beckley, WV 

25801. 

Assess Visual Needs Through Task Analysis.-Task 

analysis is an important basis for illumination system 

design. The general procedure for conducting this analysis 

involves 

a. Defining major tasks (e.g., tramming, positioning the 

face drill, pulling trailing cable, etc.) performed with or in 

the vicinity of the machine. 

b. Defining the information required for safe and eficient performance of various mining tasks. 

c. Defining the specific visual features that provide the 

required information. 

The result of such analysis is a definition of principal 

work stations, workers' iines of sight, visual attention 

locations, and relative acuity needs. Use of this basic information will improve decisions regarding appropriate illumination and will identify areas where consideration of 

glare is most critical. The best resource for this information is direct contact with the machine operators, ideally 

those same individuals who will be utilizing the illuminated machine, since this will identify task procedures 

that have been adopted at the particular mine. Some discretion will be necessary in prioritizing these visual needs, 

since a comprehensive analysis covering all task procedures and visual requirements is impractical. Also, it is 

important not to neglect changes in work procedures with 

respect to different parts of the mining cycle (e.g., advance 

versus retreat mining). 

Establish User Prefirences for Hardware.-The 

designer should attempt to comply with general user preferences for particular hardware design features (contact 

maintenance and electrical supervisors and safety directors). Rationale for these preferences should be requested, 

and hardware performance criteria considered most important should be identified. 

Document Relevant Mine Conditions and Likely Hardware Damage Mechanisms.-Mine conditions have great 

bearing on the requirements for system ruggedness. In 

this regard, important criteria include 

Ratios of machine dimensions to entry dimensions. 

Bottom undulations. 

Bottom conditions that may require machines be frequently pushed. 

Roof conditions where draw slate falls on a miner-loader 

could be a problem. 

Salt use in mine, which could cause problems with corrosion of exposed aluminum. 

Potential rock falls between adjacent supports on longwalls. 

Table 7 lists mechanisms that have frequently been 

responsible for damage of luminaires on the various face 

machines and it identifies mine conditions that make these 

mechanisms a particular problem. The information in this 

table, with an appropriate complement of site-specific data, 

can provide a useful basis for establishing a hardware 

deployment scheme that will exhibit adequate ruggedness. 

A Suggested Technique for Information Assembly.-A 

good working document for the subsequent design effort 

can be constructed by developing a series of transparent 

overlays. A separate overlay can be constructed to document each information category that has been defined on 

a spatial basis; e.g., work stations-lines of sight, feasible 

recessing locations, areas required to be illuminated to the 

0.06-fL standard, machine servicing requirements, relevant luminaire damage mechanisms, etc. These provide 

convenient documentation and one or more can be overlaid on a line drawing of the machine to assist the designer 

in consideration of the multiple interrelated factors bearing on a successful design solution. 

Generate Illumination System Concept Alternatives 

As previously explained, because of the numerous and 

interrelated technical considerations involved, mine lighting system design is very complex. It is currently best 

accomplished through a trial-and-error approach making 

extensive use of simulators. The objective of this task is to 

present a procedure to eficiently establish the "top" alternative concepts for the application in question. These alternatives will undoubtedly present performance tradeoffs. 

Accordingly, final selection of the best alternative is the 

subject of the "Illumination System Concept Evaluation 

Considerations" section. A recommended procedure for 

establishing these alternatives is as follows. 

Selection of Hardware Candidates.-For practical 

reasons, preliminary selection of candidate hardware for 

the design application is necessary before detailed system 

design commences. Major hardware performance differences on the basis of their salient design features have 

been discussed in chapter 4 and will not be further detailed 

here. A recommended procedure for identifying good candidates for system design is as follows: 

1. Using application characteristics as defined in the 

"Information Collection and Assembly" section, establish 

strict specifications on hardware performance (e.g., power 

parameters, lumen output requirement). Application of 

these specifications to the candidate hardware will eliminate certain categories from consideration. 

2. Compare viable hardware alternatives and evaluate 

the relative merits of each type. This procedure should 

identify the particularly weak contenders and permit their 

elimination from consideration. 

3. Explicitly identify the weak points of the remaining 

hardware alternatives. For each weak point, assess the 

feasibility of compensating for this weakness in system 

design for this application (e.g., placing fragile luminaires 

where they will not be damaged). 

4. Summarize (e.g., tabularize) performance characteristics and the relative feasibility of compensating for weakness for each of the remaining alternatives. Select the top 
Table 7.-Common mechanisms that mechanically damage lumlnalres on moblle coal mlne face machines 

Mechanism 

Rockfall directly on fixture ..... 

Rock sliding onto fixture when cutting 

boom raised. 

Conveyed rock impacting fixture. 

Roof contact with fixture.' ...... 

Rib contact with fixture. ...... 

Bottom contact with fixture. .... 

Contact with other machines (e.g., 

when pushed). 

Materials and supplies thrown on 

deck. 

Pinching between 

machine parts. 

Conditions that influcence frequency and extent of damage 

Roof-rib conditionefall frequency, fall 

massiveness, kinetic energy at im-- 

pact (i.e., less massive falls cause 

damage in high entries.) 

t Tendency for rock accumulation on 

cutting boom (draw slate). 

Massiveness of rock ........ 

Conveyed material size ....... 

I Machine frame-height-to-entry-height 

ratio-higher ratio, greater likelihood 

of such damage. 

1 Bottom condition-amage frequently 

occurs when traversing undulations, 

particularly for caterpillar-mounted 

machines. 

Protrusions from roof (e.g., header 

blocks). 

I Seam height-fixtures are usually side 

mounted in low seam heights because roofing is a more immediate 

hazard. However, ribbing incidents 

then increase. 

Visibility of fixtur-fixtures that operators cannot see are damaged more 

frequently. 

Bottom conditions--poor bottom 

condutions may force operator to 

resort to extreme maneuvering on 

occasion. 

Bottom condition-amage usually 

occurs when traversing undulations. 

Not applicable. 

Machines most vulnerable 

TY pe 

Locations where damage 

most likely to occur 

Continuous 

miners. 

Top-deck (or atop canopy) mounted 

luminaires, particularly on inby end of 

machine. 

. .do ....... Fixtures mounted on cutter boom or 

just outby boom hinge (primarily 

headlight lens damage, but also 

fluorescent fixtures if rock is massive). 

Loader ..... Top-deck mounted fixtures 

near conveyor. 

Continuous Top-deck mounted fixtures. 

miners. 

Bolters ..... Top-deck mounted fixtures or vertically 

mounted fixtures that protrude above 

machine frame. 

Cutters ..... Top-deck mounted fixtures. 

Loaders ..... Do. 

. 

Bolters ..... All side-mounted luminaries, but 

especially those remote from the drill 

station on single-head bolters. 

Side-mounted or overhanging fixtures 

Loaders ..... on side opposite operator cab. 

. , 

Continuous Fixtures mounted beside overhead 

miner. canopy plate (occurs during rib cleanup or *hen turning crosscuts.) 

Cutters ..... 

.... Side-mounted fixtures on outby end of 

Face drills the machine. 

Shuttle cars. Fixtures protruding from side of 

machine. 

Bolters ..... Low or vertically mounted fixtures on 

inby and outby end of machine. 

. .do ....... Side-mounted fixtures on outby end of t the machine. 

Cutters ..... Do. 

Bolters ...... Top-deck mounted fixtures. 

Cutters ..... Headlights on cutter boom. 

Bolters ..... Luminaires mounted on drill booms 

near articulation point. 

' It is common practice to side mount fixtures in low seam heights because 

significant overall than rockfill and ribbing incidents. 

few alternatives on the basis of superior anticipated performance or easy compensation for weak performance, giving 

greatest weight to those performance attributes that are 

most important in the application in question. Isolation of 

one hardware candidate is inappropriate at this time since 

information will improve as one continues with the design 

process. 

Conduct Preliminary Photometric Analysis.-Before 

actual design work is conducted in the mine simulator, 

preliminary photometric work should be done "on paper" 

so that approximate number of luminaires and layouts 

can be established beforehand and simulator work can be 

the "fine tuning" effort it should be. This preliminary 

analysis involves the following: 

1. Calculate the minimum total lumens to illuminate 

the workplace. An initial estimate of the lumens required 

can be made by multiplying the total area of all surfaces to 

be illuminated to the 2-fc (lumens per square foot) level. 

The actual lumens required will be substantially greater, 

roofing is a more immediate hazard. Because of this, roofing incidents are less 

typically three times this value. This calculation can be 

used to assess the practicality of using low-output luminaires. 

2. Evaluate the advantages of various luminaire illumination distribution (isofootcandle) patterns to assess their 

relative merits. Photometric curves, generally available 

from the manufacturers, show the lighting patterns in specific planes through the center of the luminaire. These 

curves can be overlaid on sketched profile drawings of the 

machine as shown in figure 41. This task should identify 

luminaires that have advantageous photometric profiles 

and provide a rough estimate of the total number and 

general layout of luminaires required. While helpful, the 

use of these diagrams is limited since it is difficult to depict 

the complex three-dimensional shapes of photometric profiles and the additive values of overlapping profiles. Also 

this technique does not show shadowing and diffusing 

effects and the lighting profile alterations due to recessing 

of luminaires, addition of glare diffusers, and protective 

structure around the luminaires. 
simulator at the location specified in MSHA statement of 

test and evaluation (STE) procedures. A machine mockup 

should closely simulate the machine profile. Materials that 

are suitable include wood, cardboard, and styrofoam foam 

core laminate. The foam core laminate is very easy to 

work with since it can be readily fabricated into shapes 

using a simple hand cutter. Complex forms can be constructed by nailing or by gluing shapes together with a hot 

melt glue gun. The surface of materials should have a 

maximum reflectance of 30 pct to simulate the minimum 

reflectance required for machinery surfaces. Remember 

the MSHA regulations specify that simulator surfaces, 

including the floor must have a reflectance of less than 5 

pct. This can be accomplished with the use of flat black 

paints or black cloth. The floor must be kept free of loose 

dirt and dust that can readily increase its reflectance. A 

typical mine simulator is shown in figure 42. 

Select promising design approaches on the basis of the 

preliminary comparison of specifications and the photometric study. Obtain luminaires for evaluation in the simulator and mount them on the mockup. Measure illumination levels and adjust the system until the required 

illumination levels are achieved on all surfaces. (Light 

measurement procedures are discussed in chapter 1.) 

Evaluate specific task visibility requirements and 

adjust the system, as necessary, to provide the task illumination required. For example, this may be the provision of 

additional illumination of the trailing cable on a loading 

machine or added control panel illumination on a longwall 

operator's station. 

concepts. Consider recessing components with existing 

machine structures as much as possible. Add protective 

guards or bumpers where needed. Consider methods of 

integrating luminaire mounting within existing structures. 

Consider methods of mounting - illumination components 

that improve machine access such as hinged luminaires 

and power supply support structures. Simulate these structures if they may possibly change light profiles. 

Resolve more than one viable illumination system concept using other luminaire types and/or arrangements. 

Compute the relative amount of discomfort glare of each 

concept from principal worker locations using procedures 

discussed in IC 9073, chapter 4. 

Illumination System Concept 

Evaluation Considerations 

Many factors play an important role in the selection 

of an illumination system and its components. When more 

than one system is being considered, the use of a formal 

tradeoff analysis, such as the comparison in table 8, is 

recommended to insure an objective approach is used in 

the selection of illumination system components and the 

overall design. This approach requires generating alternative illumination system concepts that satisfy the illumination requirements and comparing each of them against 

the evaluation criteria included in table 8 and discussed 

briefly in the following sections. 
Table 8.-Example lllumlnatlon system concept evaluatlon 

Lighting system concept 

Rating Design objective factor 1 2 3 4 

Numeric rating: 

Task lighting 2 3 6 4 8 1 2 1 2 

effectiveness. 

Glare ........... 1.5 3 4.5 4 6 2 3 1 1.5 

Area lighting 1 3 3 3 3 3 3 3 3 

effectiveness. 

Durability ......... .75 3 2.25 2 1.5 3 2.25 3 2.25 

Maintenance access .... .75 2 1.5 2 1.5 2 1.5 3 2.25 

Reliability ......... .75 2 1.5 2 1.5 3 2.25 3 2.25 

Lamp life ......... .5 2 1 2 1 3 1.5 4 2 

Evaluation factor ...... NAP NAP 19.75 NAP 22.5 NAP 15.5 NAP 15.25 

Subjective rating: 

Number of luminaires ... NAP 

Component cost ...... NAP 

Installation cost ...... NAp -- - 

NAp Not applicable.'Excellent4, good-3, fair-2, poor-1. 2Rating scale times rating factor. 

Task Lighting Effectiveness Maintenance Access 

Enhanced illumination of task areas is often desired. 

Examples of enhanced illumination of task areas are 

Increased face illumination for continuous miners, face 

drills, and cutters. 

Enhanced illumination of the room bolting zone and drill 

chuck on bolters. 

Enhanced illumination of machine controls such as 

operator panels on longwalls, chock actuator valves, methane monitor dials, and machine operating controls. 

Glare 

The alternative concepts should be compared from the 

standpoint of discomfort and disability glare especially in 

the direction of principal lines of sight. Remember that 

glare is not a function of luminaire brightness alone but 

also luminaire size, position, background brightness, etc. 

Concepts with reduced glare should be strong candidates 

since glare can be a significant cause of annoyance and 

complaint by workers. 

Area Lighting Effectiveness 

Area lighting effectiveness is judged by, first of all, 

determining how well the concept meets the illumination 

levels required. Secondly, concepts that provide even levels of illumination are preferred since they require less 

undesirable adaptation as a worker looks in different 

directions. 

Durability 

Lighting system components should be evaluated from 

the standpoint of maintenance accessibility. For example, 

tasks such as ease of changing lamps or replacing and 

servicing luminaires in the various mounting locations 

should be compared for the various concepts. Lamp replacement is a continuing task that should be easy to accomplish to promote system acceptance. 

Poorly placed or mounted lighting system components 

can impede maintenance access to the machine itself. Concepts that minimize machine maintenance access are 

preferred. Simplicity in troubleshooting the alternative 

circuit concepts should be evaluated. 

Reliability 

Illumination system component reliability is a significant factor in coal mine lighting systems. Reliability is 

difficult to evaluate because of the lack of comprehensive 

operating and maintenance data on mine lighting components and because component reliability often depends on 

factors such as the type of machine, mine power system 

characteristics, and lighting system circuit design 

characteristics. Because of the complexity of this subject, 

it is suggested that the reliability of candidate components be qualified through interviews with other users 

with similar mines, machines, electrical power (ac, dc, and 

voltage level) and, if possible, voltage variation characteristics. Lighting system component suppliers should be 

a good source for locating reference mines. Some of the 

factors that should be considered when assessing the comparative reliability of alternative concepts and circuits have 

been discussed in chapters 3 and 4. 

Illumination system durability is a function of both Lamp Life 

component design and the protection provided by the 

mounting methods. Therefore, if a highly durable lumi- Lamp life ratings alone can be very misleading when 

naire must be mounted in a manner that exposes it to evaluating the reliability of alternative illumination sysdamage, the concept rating would be low as compared with tems since circuit reliability and operating conditions 

the rating resulting from mounting a less durable lumi- (including shock and vibration, and voltage variation) can 

naire in a well-protected manner, which could result in a be more important than rated lamp life. 

high durability rating. 
Number of Luminaires Required 

A low number of luminaires is a desirable system feature that implies simplicity and generally less maintenance because of fewer lamps. However, the quality of the 

illumination should not be sacrificed simply to minimize 

quantity, i.e., the number of luminaires. 

Component and Installation Cost 

Initial lighting equipment costs, required machine 

modification costs, and replacement part costs should be 

compared to identify low-cost viable approaches. Installation costs can vary widely depending on the degree of 

machine modification required. 

A tabular method, such as the one outlined previously, 

forces the evaluation of each concept with respect to various design objectives and assists in eliminating bias by 

presenting all of the major assessment factors. For instance, 

although concept 3 in table 8 is the lowest cost design, its 

poor task lighting effectiveness may result in the selection 

of a more expensive approach with improved task illumination. This charting method identifies which concepts 

have serious deficiencies such as the poor glare rating for 

concept 4. 

Once ratings with respect to the individual attributes 

of system performance have been defined, the general procedure for applying this method is as follows: 

1. Using the information previously developed during 

the designing of each system, assign a rating to each design 

objective using the scale indicated, i.e., 1 through 4. 

2. Multiply this rating value by the rating factor listed 

for each objective and record the result on the table. 

3. Add the individual scale values to give a numerical 

evaluation factor for each system. The system with the 

highest evaluation factor should be the best choice. 

In the example shown in table 8, several points related 

to the use of the table are illustrated. 

1. The rating factor value for each objective would be 

assigned in the order of importance as judged by the user, 

with the numerical value indicating his or her evaluation 

of its importance relative to the other objectives. For 

example, task lighting was considered the most important 

objective and was 1.33 times more important than glare, 

be manufactured, and of machine modifications. Emphasis should be on design of highly durable structural 

components. Install the system in accordance with the STE. 

Evaluate Installed System 

Illumination system problems and improvements are 

often revealed when a lighting system is put into service. 

Followup refinements should be a planned task to insure 

maximum performance and acceptance of the lighting 

system. 

Conduct a performance evaluation of the illumination 

system in the mine simulator, if possible, to insure required 

light levels and uniformity are attained and overheating 

of electrical components (ballasts, transformers, etc.) does 

not occur. Assess the performance of the illumination system when the machine is in service underground through 

interviews with the mine workers including machine 

operator, helpers, and section supervisors. In particular, 

monitor normal mining operations to determine whether 

the lighting component and worker glare protection provided are adequate. Correct problems that exist and submit an STE modification request if necessary. Remember 

problems such as discomfort and disability glare, poor work 

area visibility, and poor illumination system performance 

can substantially affect the mine workers' attitudes, their 

acceptance of a machine, and indeed worker safety. 

DESIGN METHODS AND CONSIDERATIONS 

Specific methods to address the major problems of 

developing an illumination system design are discussed in 

this section. Emphasis is placed on durability, methods of 

mounting components, discomfort and disability glare, 

and luminaire selection. 

Durability 

All mine luminaires are provided with metal housings or support frames to enhance their durability. Although the luminaires are quite substantial and durable, 

when improperly mounted or protected they can be very 

subject to damage. Physical damage of luminaires in the 

mine environment is a significant problem and a major 

cause of complaint by mine operators. Reasons for damaged luminaires are 

twice as important as area lighting, etc. Durability, main- Impact of protruding luminaires against mine surfaces. 

tenance access, and reliability were considered of equal Other equipment impact of luminaires that are not importance. highly protected. 2. No rating factor was assigned to the number of Falling portions of roof. This problem is of course most luminaires, component cost, and installation cost objec- prevalent on machines operating at or near the face and tives because they were considered to have minor rele- under unsupported roof. vance to system performance compared with the other 

objectives. o ow ever, if two evaluation factor values are 

equal or very close, one, or a combination of these three 

objectives, could be used to make the final system selection. 

For example, evaluation factors for systems 1 and 2 were 

close, but system 1 had lower component and installation 

costs and used one less luminaire. Therefore, since system 

1 performance is comparable to system 2, system 1 would 

appear to be the logical purchase choice. 

Install Lighting System 

Purchase all components. Prepare detailed drawings 

of all components, i.e., brackets, guards, etc., that need to 

A summary of the common mechanisms that are 

responsible for mechanical damage to luminaires has been 

presented in table 7. 

Simply relying on the luminaire structure to withstand these impact forces is not a feasible approach when 

designing an illumination system. If a placement location 

is subject to these very high forces, other structures are 

required to protect it. Because of their design configuration, 

fluorescent luminaire frames are particularly subject to 

impact damage. The exposed lens surfaces on machine 

lights are subject to damage if the luminaire is in a vulnerable location. Even sturdy headlamps are easily damaged 

unless protected. 
(C) IMPROVED PROTECTION (D) IMPROVED PROTECTION 

Figure 43.-Methods of lumlnaire protection. 

in this section. 

Power Supplies.-If a separate enclosure is used to 

house the illumination system power supply components, 

it should be a readily accessible location to facilitate service access. A well-mounted power supply with an integral 

light switch is shown in figure 46A. It is sometimes difficult to place power supplies in readily accessible locations. 

This is especially the case on compact, low-seam machinery. 

In figure 46B service access to the power supply on this 

low-seam machine was improved by ~roviding a hinged 

support for the adjacent luminaire and its support frame. 

Power supplies can often be mounted on simple hinged 

structures to improve machine maintenance access. It is 

much easier to simply rotate the enclosure out of the way 

compared to removing it from the machine when it impedes 

access. When hinged structures are provided, cabling can 

usually be flexed sufficiently and therefore need not be 

disconnected as in the case where the enclosure must be 

removed from the machine. 

Power supply components can also be placed inside 

existing machine power and control explosion-proof enclosures if sufficient space is available or was planned in the 

design of the equipment. The lighting system cost could be 

reduced using this method since a separate power supply 

enclosure for lighting would not be required. When using 

existing enclosures, care must be taken that the added 

power components do not result in overheating of the equipment in the enclosure. 

The Problem of Glare.-The designers of coal mine illumination svstems must be verv familiar with and sensi- " - 

Figure 44.-Example of damage to lighting hardware. tive to the problems caused by discomfort and disability 
RECESSED LUMlNAlRE IN A MODIFIED MACHINE STRUCTURE ADDED RUB RAIL TO PROVIDE LUMlNAlRE PROTECTION 

ADDED STRUCTURE IMPROVES LUMINAIRE PROTECTION ADDED BUMPER PROVIDES LUMINAIRE IMPACT PROTECTION 

Flgure 45.-Example lumlnalre mountings that improve dureblllty. 
(0) HINGED LUMlNAlRE SUPPORT STRUCTURES FACILITATE MACHINE 

AND LIGHTING POWER SUPPLY ACCESS 

Flgure 46.-Example power supply mountings. 

glare if they are to develop underground lighting systems 

that will be well received by the mine workers and which 

will not impede worker vision or reduce worker visual 

comfort. 

During 1979, two surveys were conducted by a joint 

UMWA-BCOA committee to identify problems associated 

with installed underground coal mine illumination systems. The most frequently identified problem that caused 

dissatisfaction, especially evident in low-seam mines, was 

glare. The severity of the problem was indicated by the 

finding that 63 pct of the low-seam miners wanted the 

lights removed while in high-seam mines 93 pct of the 

miners did not want the lights removed. However, many 

glare complaints were received in both high- and low-seam 

mines. Although in general the high-seam illumination 

systems were well received by the miners, approximately 

85 pct of the illumination systems observed contained problem areas that generated complaints from the equipment 

operators or helpers. The majority of these complaints were 

caused by discomfort glare, disability glare, veiling luminance and afterimages from light sources. 

The studies identified the following causes of glare: 

Light fixtures placed in direct view of the operator or 

helper. 

Light fixture lenses that were not covered with diffusing materials. 

maximize visibility and minimize glare it is important to 

determine the principal locations and lines of sight for the 

machine operator and helpers. By knowing these lines of 

sight the lighting system designer canStress placement of luminaires in locations where they 

will not be viewed directly on a frequent basis; 

Determine where glare shields are needed; 

Identify locations where low-glare luminaires are needed; 

Estimate the degree of discomfort and disability glare; 

and 

Consider task illumination needs. 

Principal lines of sight are determined by understanding the machine operation and tasks to be performed by 

the operator and helpers. A typical roof bolting machine 

is shown in figure 47. As indicated, the bolting station 

operator has several principal directions of sight including 

the drill chuck-roof area being drilled, the bolt storage 

tray, and visual communication with a tramming operator. 

The tramming operator's principal lines of sight are in the 

direction of vehicle movement. It is these lines of sight 

that need particular attention since objectionable glare in 

these directions will almost certainly result in either visibility impedance or visual discomfort. Higher levels of glare 

can often be tolerated when the glare source is not located 

on a principal line of sight and when the source significantly improves task visibility. 

Methods To Evaluate and Reduce Disability Glare. 

-The two most significant forms of glare encountered in 

underground coal mines are disability glare and discomfort glare. In this section, methods to evaluate and reduce 
disability glare will be discussed. The reader is referred to 

IC 9073 (chapter 4) for a more in-depth discussion of the 

disability glare equations. 

Disability glare, which by definition reduces visibility, 

will also reduce visual performance. For example, when a 

miner directs his or her cap lamp in your direction the 

ability to see the miner and his or her surroundings are 

diminished, just as oncoming car headlamps significantly 

diminish your ability to see the roadway at night. Any 

light directed by a source in the field of view towards your 

eye will detract from your ability to see in the direction of 

the source. No simple method is available to determine 

the acceptability of a mine lighting system from the standpoint of disability glare. Methods are, however, available 

to reduce and to evaluate the disability glare of alternate 

lighting system designs on a comparative basis. Methods 

to reduce or eliminate disability glare include the following: 

The use of shielding to eliminate a glare source. 

Repositioning a luminaire. 

Increasing task and background luminance levels. 

Changing the orientation of a luminaire. 

Selection of luminaires that reduce illumination levels 

impinging on principal worker stations. 

Use of retrofitted glare diffusers. 

Let's examine some of these methods as they relate to 

the disability glare equations presented in IC 9073 (chapter 

4). A light source in the field of view of an observer creates 

a veiling luminance which can be represented by the equation L, = 10nE10~. L, is the veiling luminance, in footlamberts; E is the illumination, in footcandles, at a plane 

passing perpendicular to the line of sight of the observer; 

and 0 is the angle between the observer's line of sight and 

the glare source as depicted in figure 48. 

The apparent contrast of the task is represented by 

the equation C' = Ld - Lb/Lb + L,, where Lb is the 

background luminance, Ld is the luminance at the object, 

and C' is the apparent contrast between the visual task 

and its background as perceived by the eyes of the miner. 

First of all notice that C' is maximum when L, is 

zero. Therefore, presence of any light source visible to the 

' miner reduces the apparent contrast of the visual task. As 

the value of L, is increased, a point will be reached where 

C' is reduced to the threshold for perception, as indicated 

in figure 49. 

At this point the task object cannot be discerned from 

its background. It can, therefore, be concluded that visual 

perception is maximized when no glare sources are present in the visual field, and when glare sources are present, 

visual performance is enhanced as the level of L, eminating 

from a glare source is reduced. 

The use of shielding to eliminate a glare source is 

often a very effective method to reduce or eliminate a disability glare problem. The use of glare shields to maximize 

the visibility of a continuous miner operator is illustrated 

in figure 50. 

Note that without the glare shields, the miner's ability to perceive the face, ribs, roof, and floor would be substantially diminished. 

Repositioning a luminaire can significantly reduce disability glare. Notice in the equation for L, that its value 

can be reduced by increasing the angle, 0, or reducing the 

amount of light, E, from the glare source that impinges on 

the observer. For example, in figure 51A a luminaire is 

placed close to a roof bolt storage tray near the principal 

TASK BACKGROUND 

GLARE SOURCE 

PENDICUL 

OF SIGHT 

TASK 

I MINER'S LINE 

OF SIGHT 

-l 

Figure 48.-Disability giare dlagram. 

7 C' REDUCES AS L, VALUES INCREASE 

C' AT THRESHOLD OF VISIBILITY 

VISIBILITY THRESHOLD 

CONSTANT BACKGROUND 

LUMINANCE LINE 

BACKGROUND LUMINANCE 

Figure 49.-Apparent contrast versus visibility. 

/ 

OPERATOR 

a - r 

SHIELDS / 

I I I I I I IIIIII I/-- 

\ 

Figure 50.-Giare shields used to reduce disability giare. 

SHIELD m 

.T STORAGE BOL 

I 

1 

T STORAGE 

r,\ 

(A) HIGH DISABILITY GLARE (6) REDUCED DISABILITY GLARE 

Figure 51 .-Disabiiity giare versus iuminaire position. 
line of sight of the mine worker. In figure 51B the luminaire is shown repositioned to reduce disability glare. 

Assume that the improved positioning shown in figure 

51B results in the following changes in 8 and E values: Let 

8, = 58,; E - 0.25 E,. b: The resulting reduction in veiling luminance, L,, can 

be computed as follows: 

The luminaire movement resulted in a reduction of 

veiling luminance by a factor of 100. This example illustrates the large benefits that can be achieved when the 

placement of luminaires is carefully considered along with 

principal lines of sight of the mine workers. Note that 

with the luminaire in the lower position, the mine worker 

can also avoid looking directly at it while he or she is 

performing tasks. 

Increasing task and overall luminance levels can 

reduce disability glare if it is accomplished without increasing the luminance of the glare source. For example, assume 

the face is illuminated to 0.06 fL and the luminance of 

detail that is being viewed in the face is 0.2 fL. With no 

glare source in a continuous miner operator's field of view 

the resultant contrast is C' = Ld - Lb/b + L,; 0.2 - 

0.061D.06 + 0 or 2.33. 

If there is a luminaire in the miner's field of view that 

generates a veiling luminance, L,, of 0.05 fL, the apparent 

contrast of the detail being viewed will be reduced to C' = 

Ld - Lb/b + L,; 0.2 - 0.0610.06 + 0.05 or 1.27. 

As a result of increasing the face illumination three 

times by adding additional headlamps, the apparent contrast would be C' = 0.06 - 0.1810.18 + 0.05 or 1.82. 

Note that increasing the level of face illumination 

diminished the impact of the glare source. As a general 

rule, if the illumination, i.e., light falling on the mine and 

machine surfaces, can be increased without increasing 

glare sources in a worker's field of view, it will be beneficial in reducing disability glare. 

Changing the orientation of a luminaire can at times 

be an effective method to reduce disability glare. For 

instance, in figure 52A assume the vertically mounted 

luminaire is a point source that results in a 2.0-fc glare 

illuminance that impinges on a worker's principal work 

station. When the luminaire is rotated as shown in figure 

52B the illuminance is reduced to 0.2 fc as indicated. The 

resulting reduction in veiling luminance, L,, can be computed as follows: 

This reduction by a factor of 10 can significantly 

improve visibility and decrease disability glare. OfZen, just 

small changes in luminaire orientation can reduce glare. 

LUMINAIRE 

/ 

I 

/ 

\ \ ,- \ 

(A) INCREASED DISABILITY GLARE 

- - \ 

2.0 FOOTCANDLES 

n \ LuMINAIRE 

(0) REDUCED DISABILITY GLARE 

Figure 52.-Luminaire orlentation change to reduce dlsabiiity 

glare. 

This is especially true in low-seam applications where principal worker stations are confined to small areas and where 

luminaires are very close to the mine worker. This example illustrates the importance of simulating worker stations and evaluating the principal lines of sight when 

designing an illumination system. 

Selection of luminaires that reduce illuminance levels 

impinging on principal worker stations can reduce disability glare. Lumen outputs and light distribution patterns 

vary widely with sizes and types of luminaires. To minimize veiling luminance levels, the designer should select 

luminaires that minimize light levels impinging on principal worker stations. For example, the workers in figure 

53A are exposed to higher disability glare levels than in 

figure 53B. High-output luminaires must be very carefully placed if glare complaints are to be avoided. 

Use of retrofitted glare diffusers that reduce the light 

output of a luminaire in a specific direction can reduce 

disability glare. These diffusers can be any device that, 

when placed between the worker and luminaire, reduces 

the illuminance level impinging on the worker. They can 

be perforated metal screens, bars, or translucent plastic. 
MINING 

MACHINE 

(A) INCREASED DISABILITY GLARE 

G-$A'"::E 

I LUMINAIRES HEADLAMP 

(0) REDUCED DISABILITY GLARE 

Figure 53.-Luminaire selection and placement to reduce dlsabiiity giare. 

Methods To Evaluate and Reduce Discomfort Glare 

Discomfort and disability glare are distinctly different phenomenon. When a light source in a miner's field of 

view causes a sensation of annoyance or, in severe cases a 

sensation of pain, the light is considered a source of discomfort glare. Discomfort glare is often accompanied with disability glare, which is defined as a measure of visibility or 

visual performance reduction caused by a glare source. In 

this section, methods to evaluate and reduce discomfort 

glare will be discussed. The reader is referred to IC 9073 

(chapter 4) for a more in-depth discussion of the discomfort 

glare equations used. 

Discomfort glare often results when a luminaire is 

located near the principal line of sight of a mine worker. 

Physiologically, it is believed that the bright source causes 

the mine workers' eyes to attempt to adjust both to the 

rather low task luminance and the glare source. This causes 

a fatigue or annoyance and results in discomfort. The effect 

of looking directly into the headlamps of an oncoming mining machine is an example of severe discomfort glare. 

Both discomfort and disability glare become very significant design considerations when background illumination levels are low, as in underground coal mines. This 

fact is illustrated by the results of coal mine illumination 

surveys that indicate that glare is probably the most frequent cause of dissatisfaction with illumination systems, 

especially in low-seam mines where workers must often be 

stationed very close to luminaires and often cannot avoid 

looking towards glare sources. Both the discomfort and 

disability glare equations as well as common sense support this statement. For example, the glare caused by car 

headlamps ranges from severe at night to negligible during daylight. 

Methods to reduce or eliminate discomfort glare are 

similar to those to reduce or eliminate disability glare but 

in some respects differ significantly. They include the 

following: 

The use of shielding to eliminate a glare source. 

Repositioning a luminaire. 

Increasing task and background illuminance levels. 

Changing the orientation of a luminaire. 

Selection of luminaires having low surface luminance 

(brightness). 

Use of retrofitted glare diffusers. 

Each of these methods will be illustrated in the following 

discussion. 

The state-of-the-art of discomfort glare theory does 

not allow the coal mine lighting designer to determine 

whether a coal mine illumination system is acceptable or 

unacceptable from the standpoint of discomfort glare. It 

does, however, provide the designer with a means to compare alternative lighting systems and determine in an 

approximate manner which has less discomfort glare. 

The equations for discomfort glare result in the calculation of the following values which are a measure of visual 

comfort-discomfort glare rating (DGR) and visual comfort probability (VCP). 

The DGR value for a single glare source in the field of 

view of an observer can be computed using the following 

basic discomfort glare equation: DGR = LQIPFO.~~, where 

L is the brightness, in footlamberts, of the glare source 

in the direction of the observer; Q is a term that is a 

function of the size of the glare source and its distance 

from the observer; P is the position factor, a function of the 

location of the glare source in the field of view of the 

observer; and F is a measure of the average field luminance (brightness) including the averaged brightness of 

the glare source within the field. A complete definition of 

these terms is presented in IC 9073 (chapter 4). Higher 

computed DGR values mean increased discomfort glare. 

Discomfort glare sensitivity varies widely among 

individuals. As a result, a specific lighting system may not 

create discomfort glare for one individual but for another it 

may be quite discomforting. To accommodate for this 

variation in population sensitivity, a method for converting 

DGR values to VCP values was developed. Computation of 

VCP values (IC 9073, fig. 58) is an effective method to 

compare alternative lighting systems. General methods to 

reduce discomfort glare are discussed in the following 

paragraphs. 

The use of shielding can be an extremely effective 

method to eliminate a discomfort glare problem (see figure 

50). Note in the preceding equation that by eliminating a 

glare source, the value of L is reduced to zero and the DGR 

value is zero. 

Repositioning a luminaire in a manner that increases 

the position factor, P, can substantially decrease discomfort glare. Note from figure 56 of IC 9073 that position 

factors vary from 1 to 16 within the field of vision. The 

position factor is minimum when the glare source is on the 

observer's line of sight, therefore, glare sources should be 

offset from a worker's principal line of sight as much as 

possible. Note from figure 58 of IC 9073 that reducing the 

DGR value from 800 to 50 (a factor of 16) increases the 

VCP value from 5 to 95 pct. 
Increasing task and background luminance reduces 

discomfort glare. As discussed in chapter 4 of IC 9073, the 

field luminance term in the discomfort glare is represented 

by the equation. F = & o + L8w,0$5. This means that 

the field luminance is equa! to the average of all the light 

impinging on the observer within his or her total field of 

view of 5 sr. Increasing the luminance of the task and 

background (& value) will increase the F term value in 

the DGR value equation, thereby lowering the DGR value 

and reducing discomfort glare. Note, however, that increasing the F term by increasing the glare source brightness, 

L , will also increase the L value in the DGR equation, 

which would increase the DGR value and, therefore, discomfort glare. Because increasing the L, term will increase 

the glare source brightness term, L, in the DGR equation 

more rapidly than the F0.32 term, the overall effect is an 

increase in the DGR value. 

Changing the orientation of a luminaire can reduce 

discomfort glare. Assume the following conditions for the 

glare source depicted in figure 54A. 

Distance, R, from the worker to the glare source--5.0 R. 

Projected area of the glare source in the direction of the 

worker-0.3 R.2 

The source is a good diffuser with a brightness of 500 fL. 

Assume the following conditions for the same glare source 

which has been oriented as shown in figure 54B. 

Distance, R, from the worker to the glare source--5.0 R. 

Projected area of the glare source in the direction of the 

worker-0.05 R2. 

The source is a good diffuser with a brightness of 500 fL. 

Assume also that the average background luminance (not 

including the glare source luminance) is 0.25 fL and the 

glare source angle, 0, below the line of sight of the worker 

for cases a and b is 10". 

To evaluate the anticipated discomfort glare improvement in case b, the DGR and VCP values can be computed 

and compared for each case. The source brightness, L, and 

position factor, P, are the same in each case, therefore L 

= &, Pa = Pb, and DGR(,jDGR@, = (Q,IF;-~~) x (F~O.~ZP/ QL). -u 

Using the discomfort glare e uations from chapter 4 B of IC 9073, Q = 20.40 + 1.52w0. - 0.075, where w, the 

solid angle subtended by the glare source, is equal to w = 

A~/R~. R is the distance from the glare source to the 

observer and Ap is the projected area seen by the observer. 

For cases a and b, w, = 0.315~ = 0.012 sr; ob = 0.0515~ 

= 0.002 sr; Q(,, = 20.4(0.012) + 1.52(0.012~.~) - 0.075 = 

0.8. 

- i3g) = 

20.4(0.002) + 1.52(0.002~.~) - 0.075 = 0.4; F 

- ackground + (L"C08 glare source15; o background 

= w visual field - w glare source; F(,) = 0.25(5 - 0.012) + 

500(0.012) cos 10°15 = 1.4 fL; F@) = 0.25(5 - 0.002) + 

500(0.002) cos 10°15 = 0.45 fL; and (DGR)(,)I (DGR)(b, = 

(0.811 .4°-32) x (0.45~-~~10.4) or 1.4. 

The discomfort glare rating for case a is 1.4 times 

higher than for case b. By referring to figure 58 of IC 9073, 

it can be seen that the higher DGR values correspond to 

lower VCP values. Therefore, the lower DGR value of case 

b improves the VCP. This example also illustrates the 

rather complex relationship of lighting system variables 

as they affect discomfort glare. 

Selection of luminaires with low surface luminance 

(brightness) can reduce discomfort glare. For example, 

assume the luminaires shown in figure 55 have good diffusing surfaces, differ in luminance by a factor of 2.0, and 

LUMlNAlRE 

(A) INCREASED DISCOMFORT GLARE 

4 

311 r 

c== 

LUMlNAlRE 

\ \ \ 

(B) REDUCED DISCOMFORT GLARE 

Flgure 54.-Lumlnalre orlentatlon change to reduce dlscomfort glare. 

(A) INCREASED DISCOMFORT GLARE 

FOOTCANDLE 

PROFILE 

FOOTCANDLE 

PROFILE 

(B) REDUCED DISCOMFORT GLARE 

Flgure 55.-Dlscomfort glare versus lumlnalre brightness and 

area. 
produce equal illumination levels of 2.0 fc at the observer 

location. In this example Fa = Fb and Pa = Pb. 

The glare source brightnesses are calculated using 

the following relationship: La = TER~IA ; a(2) (52)/0.15 or 

1,047 fL; and Lb = n. (2) (52)/0.30 or 524 A. The solid angle 

subtended by each source is oa = Apl~2; 0.1515~ or 0.006 

sr; and ob = 0.3015~ or 0.12 sr. 

The source size-distance factor for each luminaire is 

Q = 20.40 + 1.52~O.~ - 0.075, Q, = 0.59 and Q, = 0.80. 

a -a 

~h: &scomfort glare rating for the bright source in 

case a is 1.5 times greater than case b even though the 

illuminance provided is equal. Therefore, using luminaires 

with reduced surface brightnesses can reduce discomfort 

glare when the luminaire must be within the field of view 

of a worker and discomfort glare is a problem. Note, 

however, that in many lighting installations the use of 

brighter small sources may be preferred because of luminaire placement, and orientation or shielding advantages. 

Also the directional characteristics of small, very bright 

sources such as headlamps can at times allow the designer 

to reduce glare by directing the beam away from worker's 

principal lines of sight. 

The use of retrofitted diffusers can reduce discomfort 

glare. The mining machine depicted in figure 56 has two 

rear-mounted fluorescent luminaires, which are required 

to provide illumination of the floor, ribs, and roof areas 

near the rear of the machine. It was also desirable to illuminate the floor area behind the machine to provide good 

visibility of the trailing and control cables. The use of 

standard fluorescent luminaires in these locations resulted 

in a significant degree of discomfort glare for the machine 

operator, whose principal work station is behind the 

machine. 

To reduce this glare, translucent plastic diffusers were 

placed between the operator and luminaires as shown in 

figure 56. The diffusers reduced the discomfort glare rating at the operator's principal station by a factor of 2.5 

while permitting maximum illumination of the ribs, roof, 

and floor adjacent to the machine and providing rearward 

illumination. The use of opaque glare shields would have 

further reduced the discomfort glare. In this case opaque 

CABLE 

Figure 56.-Example of retrofltted glare dlffusers. 

shields reduced the task visibility of the cables and floor 

behind the machine to undesirably low levels and use of 

the translucent diffusers was the best overall system. 

The brightness of current mine lighting luminaires 

cannot be reduced. As a result, at times, retrofitting diffusers is the best alternative available to the designer. 

The preceding example as well as the more in-depth 

discussion in chapter 4 of IC 9073, illustrate methods to 

analyze and reduce discomfort glare. These analytical 

methods provide means to understand discomfort glare 

and to analyze alternative solutions in an objective manner. 

It is hoped that further research in this area will result in 

the recommendation of specific DGR and VCP levels for 

coal mine lighting. 

CHAPTER 6.-INSTALLING AND MAINTAINING MINE LIGHTING SYSTEMS 

The salient features, of lighting hardware (chapter 4) 

and system design (chapter 5) are not the only factors 

having impact on lighting system performance. Installation and maintenance techniques also have a very significant bearing. This chapter presents installation and maintenance guidelines aimed at minimizing installation costs, 

improving component service life, minimizing machine 

downtime, ensuring acceptable system performance, and 

assisting in diagnosis of the cause of certain lighting 

problems. As such, it is directed at shop and maintenance 

supervisory personnel employed by the face equipment 

manufacturers, rebuild shops, and mines. 

of the lighting system. They should be aware of the numerous measures they can take (most are relatively minor in 

nature) to improve the protection of components, facilitate 

future servicing of lighting components and the machine 

itself, and improve performance of the system from a lighting viewpoint. Mine operators should insist on high installation standards from in-house and independent rebuild 

shops and original equipment manufacturers. In the case 

of the latter two, detailed specification of installation practice should be provided. What follows is an outline of major 

considerations important to a successful lighting system 

installation. 

Preparation 

GUIDELINES FOR SYSTEM INSTALLATION 

Typically installers are given an MSHA statement of 

It is essential that installers realize the effect the qual- test and evaluation (STE) package that includes the layout 

ity of their work will have on the subsequent performance drawings and wiring schematics to be used as the primary 
documents guiding the installation. These documents alone 

comprise an incomplete guide to installation, and installers should realize that they should take care in regard to 

unspecified aspects that have been left to their discretion. 

A review of STE specifications, in light of the actual 

machine upon which the system will be installed, should 

be performed before work is initiated. Important check 

points include the following: 

1. Do STE and actual machine model numbers correspond precisely (not just "root" model numbers)? If not, the 

STE may not be valid for the given machine. 

2. Do machine dimensions given on the layout drawing 

in the STE and on the actual machine correspond? Again, 

discrepancies will void the STE approval. Often, machine 

profile will differ because of optional equipment additions 

and changes made during previous rebuilds. In such event 

installers should contact lighting suppliers about obtaining an approval extension to cover their machine. 

3. Do suitable anchor points exist for mounting luminaires at the locations specified on the STE layout drawing? 

Unless greater tolerances are specified on the layout 

drawing, luminaires must be installed within 6 in of the 

location specified and at an orientation within 5" of that 

specified. In some early designs, oversights in the use of 

machine mockups resulted in such anchor point problems. 

4. Although the STE design should have been thoroughly reviewed prior to lighting system installation, a 

final review should be conducted at this time. Are luminaires located where they are particularly vulnerable to 

damage, where they will interfere with machine function 

(e.g., cable winding or boom swing), where they will hinder machine servicing, or where they are likely to cause 

glare problems? In the event of serious problems, it is 

suggested that a design modification be pursued. 

Mounting Luminaires 

Always bolt-connect luminaires to their mounting 

brackets so they can be readily removed; never weld luminaires to mounting brackets. 

Before mounting luminaires, compare their layout 

with the layout of machine covers. Luminaires that span 

more than one cover will hinder machine servicing. If 

possible, refabricate covers, altering their layout to eliminate this situation. 

Welding luminaire mounting brackets to explosionproof enclosures and permissible panels is not recommended because the heat from welding can cause warpage 

of the enclosures and panels. Bolt connection is, of course, 

impossible, because it would violate the permissibility of 

the enclosure. If the STE requires a fixture to be mounted 

atop an explosion-proof enclosure, attach the luminaire 

and bracket to a piece of plate that can span the enclosure. 

Support this plate on pieces of bar and bolt it to the machine 

at each end, at points adjacent to the enclosure. 

Mounting tabs are prone to breakage on many aluminum fixtures such as headlights. Take great care in preparing a mounting surface, making sure that it is flat so 

that stress is not introduced when bolting down the fixtures. 

Do not overtorque mounting bolts. Also, if possible, do not 

mount aluminum fixtures on surfaces prone to excessive 

vibration. 

On certain continuous miners installations, it may be 

desirable to install vertical strips of plating inby headlights to deflect rock sliding back off the boom. Be sure 

that the plates are not so high that they cut off the headlight beam. 

Use of hinged luminaire mounting brackets is generally not recommended because they are expensive to fabricate and, if the luminaire is exposed, bending quickly renders the brackets useless. In cases where a quick-release 

mount is desirable, the bracket shown in figure 57 is 

recommended. It is easier to fabricate than a hinged 

bracket and much more durable. 

The quick-release bracket shows the same advantage 

as hinge brackets when transporting machines; luminaires 

are simply released from the top deck and are wired to the 

side of the machine. Hinge brackets are, however, often 

beneficial on recessed luminaires (where the brackets are 

not so subject to damage) because they facilitate access to 

the luminaire for maintenance and lamp changing. 

It is frequent practice to fabricate 45" angle-brackets 

for fluorescent luminaires from a single length of angle 

iron and plate. Such brackets block transmission of light 

to the machine deck, reducing visibility of objects on the 

deck. It is recommended that angle brackets be sectionalized (e.g., using three supports, one at each end and one at 

the center) instead of a single length. Alternatively, windows might be cut into the solid bracket to allow light 

transmission. 

.When heavy-duty luminaires (e.g., most incandescent 

and high-pressure sodium (HPS) area luminaires and 

headlights) are installed, assess the strength of the luminaire mounting surface and determine underlying components. Rockfalls and other harsh impacts can drive these 

fixtures into the machine body and cause serious damage 

to underlying components. Reinforcement of the mounting, 

surface may be warranted. 

If possible, when bolting down luminaires, utilize rubber washers to act as shock and vibration dampeners for 

the purpose of increasing lamp life. 

Mounting brackets on longwalls should be of quickrelease design to facilitate takedown in event of damage, 

blasting, or panel move. 

Housing and Connecting Power 

Conditioning Equipment 

The most efficient arrangement for mounting the lighting system power conditioning equipment is to house it in 

the machine contactor box. Therefore, prior to ordering 

auxiliary explosion-proof boxes, an assessment should be 

made to determine if some, or all, of these components can 

be mounted in the contactor box, possibly eliminating the 

need for an auxiliary box, or reducing the necessary size of 

DECK 

Flgure 57.-Qulck-release lumlnalre bracket. 
such a box. Sizes of the auxiliary power conditioning boxes 

available from the hardware supplier should be reviewed 

carefully. Generally, smaller boxes are preferred because 

it is easier to find installation sites for them. However, 

packaging of lighting components within these boxes 

should be reviewed regarding (1) accessibility of components for electrical tests and component replacements, and 

(2) heat sinking (stacked ballasts may cause temperature 

problems). 

Important criteria for locating auxiliary power supply 

boxes include the following: 

1. Locations within machine profile are preferable to 

minimize potential for internal damage from impacts. 

2. On remotely ballasted or intrinsically safe systems, 

attachment to the machine frame should provide good heat 

dissipation (i.e., ideally attach so that the box has a high 

contact area with a machine surface of substantial thickness). This is desirable since most of these systems depend 

on the machine for adequate heat sinking. Also, boxes 

should not be mounted near heat sources on the machine. 

3. Mounting locations subject to excessive vibration 

should be avoided. Both solid-state and core-and-coil ballasted systems are subject to failure from vibration. 

4. Cab-mounting should, in general, be avoided because 

the boxes will crowd machine operators and the generated 

heat may be a source of discomfort. 

5. Accessibility of the boxes for future servicing is of 

primary importance. This aspect should not be compromised if the boxes are integrated into machine profile. 

6. On longwalls, locations out of the main walkway are 

preferable as long as the boxes are accessible. 

If extra headlights are installed in addition to those 

req;ired on the STE (a common practice on continuous 

miners and loaders), check to see that the transformer 

supplied with the system has adequate kilovolt-ampere 

capacity to accommodate the additional lamps. When the 

extra headlamps are low voltage, line losses should be 

taken into account in this assessment. 

Attach accurate wiring diagrams within explosionproof boxes as an aid to future servicing of the system. 

Do not use nominal machine voltage as a basis for 

connecting power leads to the lighting system transformers if alternative taps are available to accommodate deviations in actual machine voltage. Rather, it is best to base 

this connection on voltage measurements taken with the 

machine idle on the particular section the machine will be 

used. 

Cable Installation 

Care in routing and protecting cables is extremely 

important in all applications. Even when cable failure frequencies are not very high, incurred costs can be high 

because1. Shorted cables can be the cause of other electrical 

failures (e.g., some ballasts overheat and quickly fail when 

lamp leads are shorted); 

2. Troubleshooting delays can be significant depending 

on circuit design; and 

3. Cable changeout times can be significant (up to several hours) because of the dificulty in pulling and reinstalling cables through dificult routing paths and because 

of the necessity of repacking the explosion-proof glands. 

Route luminaire power cables under machine covers 

wherever possible but (1) avoid "pinch points" where cable 

can be squeezed between the cover and an underlying component if the cover is impacted, and (2) be sure that covers 

through which a cable is routed cannot easily shift and 

pinch or shear the cable. 

Inverted angle iron or pipes provide good protection 

for short top-deck or boom cable runs. Extended top-deck 

runs protected in this manner may create problems in 

servicing the machine if adjacent cover pans are spanned 

or if cables must be reinstalled. 

Care should be taken when installing cables that must 

pass through machine articulation points (e.g., booms, 

adjustable canopies, temporary roof supports. Cables should 

be tied back in a manner such that slack is adequate to 

prevent excessive tension (and eventual fatigue damage) 

when the joint is articulated and not so loose that the 

cable is easily snagged. 

Leave extra slack under machine covers upon which 

luminaires are mounted so that covers can be removed 

and set aside for access to the machine without removing 

the luminaire from the cover. 

If luminaire or explosion-proof housing packing glands 

are available in different angular orientations (e.g., 

straight, 45", and 90°), gland angles should be selected and 

installed to permit direct routing of cables under machine 

covers without sharp bends. This will minimize cable exposure and stress damage to conduit, insulation, or conductors. 

Although use of luminaires with attached pigtails and 

connectors is recommended for maintenance reasons, there 

is a tendency for operators to install these luminaires with 

the entire pigtail-connector assembly exposed. Care should 

be taken to route the pigtail directly under a machine 

cover, if possible. Optimum pigtail length will vary depending upon application of the luminaire, and standardization on a particular length for preassembly purposes may 

be undesirable. It is recommended that operators examine 

their particular applications to determine optimum pigtail length or lengths and have their replacement luminaires prewired accordingly. 

Junction boxes should be installed to break long cable 

runs where cable removal and reinstallation is difficult. 

Numerous mines have reported machine downtimes on 

the order of several hours for making such replacements. 

An application of a junction box on the luminaire side of 

conveyor cross-over channels is particularly useful because 

of the dificulty of removing and reinstalling cables through 

these typically crowded and dirt-plugged channels. A field 

modification may be required to enable installation of these 

boxes. 

On machines where the top-deck is used as a working 

surface and for carrying tools and supplies (roof bolters in 

particular), construct compartments and racks on these 

machines to accommodate these materials. Randomly 

throwing materials on the top-deck can frequently result 

in damage to cables and glands, and can also have an 

undesirable effect on light distribution. 

Conductor length between high-pressure sodium (HPS) 

lamps and ballasts should be limited to a maximum of 20 

ft to prevent dissipation of the high voltage starting pulse 

created by HPS ballastry. 

On systems where a number of luminaires are connected across the line to a power distribution lead (especially the low voltage dc systems), it is preferable that 

junctions be located as close to the source as possible to 

minimize line losses. 
Gland Protection 

Although explosion-proof packing gland replacement 

costs (in terms of parts cost and labor requirements) are 

generally low compared with costs of other lighting maintenance items, gland maintenance is given high priority 

at most mines because damaged glands void the permissibility of the lighting system and create a potentially hazardous condition. 

How Glands Are Damaged.-Fall of draw slate and 

roof rock is the most significant cause of gland damage. 

Minor slate falls will frequently damage glands without 

significantly damaging luminaires or other explosion-proof 

enclosures. Other damage mechanisms include (1) impacts 

incurred when workers throw tools and supplies on the 

machine deck (a particular problem on roof bolters), (2) 

contact with roof and ribs (more of a problem on certain 

fixtures where orientation of gland entrances results in 

gland exposure to roofing or ribbing), and (3) pulling of the 

cable from the gland entrance by various means. Design of 

the gland structure has significant bearing on the incidence of damage from impact and contact forces, and the 

reader is referred to chapter 4, "Available Mine Lighting 

Hardware," for a discussion of important design factors to 

consider in this respect. 

Design of Gland Guards.-Regardless of gland design, 

auxiliary guards and protective structures can be employed 

to reduce the incidence of gland damage from impactcontact forces. Care should be taken in the design of these 

structures; numerous guards employed in the field have 

proven ineffective because they were underdesigned. It is 

recommended that the following criteria be observed when 

designing gland guards: 

1. Thick plate or bar should be used to construct the 

guards. Thin and unreinforced plate, angle iron, or halfpipe sections are inadequate to withstand impacts. 

2. Leave substantial space between the guard structure 

and gland. This permits easy access for gland inspection or 

removal. Moreover, guards too close to the gland are easily pushed into the gland structure if deformed when 

impacted. A 2- to 3-in spacing between the guard and gland 

will permit the guard to bend into the yieldable cable rather 

than into the gland structure while breaking the impact. 

Figure 58 shows some recommended guard designs that 

meet these criteria. 

3. The cable feeding luminaires mounted alongside canopy structures on the cabs of various machines are often 

used as a handhold for exiting the cab, and eventually the 

cable is pulled from the gland. Installation of a handle on 

the canopy will prevent this tendency. 

GUIDELINES FOR SYSTEM MAINTENANCE 

Lighting system failures can have important consequences to mine operators for the following reasons: 

1. Repair costs, in terms of replacement parts and labor, 

are often significant, frequently several thousand dollars 

per machine on an annual basis. 

2. To legally operate a production machine, lighting systems must be operable. Hence, lost production costs may be 

incurred because of lighting failures. 

3. Electrical failures which void the permissibility of 

the machine create a serious safety hazard which may 

result in an accident or citation. 

A. "BAR"-STYLE GUARD (APPROPRIATE FOR ANY STYLE LUMINAIRE OR X/P HOUSING) 

8. GLANCE GUARD (APPROPRIATE FOR FLUORESCENT LUMINAIRES ONLY) 

C. C A G E O V E R H A N G (APPROPRIATE FOR FLUORESCENT LUMINAIRES ONLY) 

Flgure 58.-Recommended gland guard deslgns. 

4. Failures may result in noncompliance with the Federal illumination standards and a possible citation. 

First, this section addresses approaches to the maintenance of lighting systems. Here, suggestions are given for 

general procedures to improve (1) the degree to which the 

system operates "up to spec," and (2) the efficiency of maintenance operations, i.e., minimizing costs. Second, common hardware failures are discussed giving information 

to assist in establishing the cause and minimizing the 

frequency of such failures. 

Maintenence Approach 

Mine operators have long recognized the great potential for improving mine productivity by increasing the 

availability of the production machines. This has served 

as an impetus, in recent years, for more sophisticated maintenance programs, which include implementation of improved maintenance scheduling, preventive maintenance, 

record keeping, parts inventorying, and mechanic training. 

To minimize the burden posed by lighting maintenance, it 

must become an integral part of all these programs. 

Specifically, the key elements of an efficient approach to 

lighting maintenance include the following: 

1. Quick repair of failures at the face through component exchange, with subsequent detailed fault identification and component repair and salvaging performed at 

more suitable locations. 

2. Routine scheduled and preventive maintenance of the 

lighting system. 
3. Maintenance record keeping for use in decisionmaking. 

4. Mechanic training to familiarize these individuals 

with unique aspects of the lighting system and instruct 

them in procedures to follow in maintaining it. 

Exchange Maintenance 

Exchange maintenance is the process of system repair 

through the exchange of failed system modules (i.e., component groupings) with good modules, without detailed 

fault analysis of the particular failure(s) within the module. 

Advantages of this approach to maintaining lighting 

systems, over the alternative of detailed isolation of the 

failure and replacement-repair of failed components only, 

are the following: 

1. Troubleshooting time is reduced because fault isolation among the components comprising the module need 

not be performed at the face. Only the failed module need 

be identified. 

2. Assuming use of hardware compatible with exchange 

maintenance, overall repair time is reduced because component exchange can be performed quickly. 

3. Lighting troubleshooting knowledge requirements for 

the face mechanics are minimized, enabling them to perform lighting maintenance efficiently. 

4. When repairs are made during production shifts, lost 

production costs are minimized because the machine will 

be idle for a shorter period of time. 

5. Detailed repair work is done at a more favorable environment than the mine working face. 

As implied in the preceding, the selection and deployment of hardware compatible with changeout maintenance 

is necessary for the approach to be successful. Basically, 

system hardware must exhibit the following two characteristics: 

1. Common electrical failures should manifest themselves in such a manner that it is obvious, or ascertainable 

by minimal electrical testing, which system module has 

failed. 

2. Mechanical assembly of the system is such that the 

physical exchange of modules can easily be accomplished. 

The following are specific hardware design aspects to 

consider in regard to these characteristics. 

Series wiring of lamps (both incandescent and gas 

discharge) is undesirable because common failures (burntout lamps, bad ballasts, short circuit, etc.) may result in 

the same obvious manifestation-tho:! lamps on the circuit 

do not light. Resolution of the ambiguity when troubleshooting requires performance of a series of tests, which 

may take considerable time. Neon bad-lamp indicators can 

aid troubleshooting of series-wired incandescent, but some 

failures can still cause ambiguity. 

Incandescent systems connected directly across the line 

show advantage in fault isolation over ballasted systems 

because ballast failure is not a possibility. 

Integrally ballasted luminaires show advantage over 

remotely ballasted luminaires because it is unnecessary to 

distinguish between failed lamps and ballasts at the face; 

the whole assembly can be changed out. Moreover, power 

supply boxes need not be opened for ballast access. 

The use of line-installed connectors on the leads to 

power supply boxes and luminaires is very advantageous. 

They enable quick module (i.e., luminaire or power supply) 

exchange without disturbing internal connections. Replacement modules can be prewired so this work need not be 

done at the face. Finally, connectors facilitate access to 

conductors for making short-circuit and continuity tests to 

isolate cable faults. Slip-fit glands also show advantage 

when making component exchanges but are not as advantageous as connectors. 

Junction boxes should be strategically installed to 

break cable runs and facilitate replacement. 

Luminaires constructed so that the lamp housing can 

be removed and replaced without removing the wiring (see 

appendix B) show advantage in cases where line-installed 

connectors are not employed. 

Quick-release luminaire mounting brackets, which do 

not require bolt removal to remove the luminaire, can 

reduce time for making exchanges. Design of these brackets has been discussed previously. 

In addition to appropriate selection and deployment of 

hardware, an exchange maintenance program should be 

complemented with a good program for component reconditioning. Independent vendors and original hardware suppliers do this work, and their services should be considered. 

Typically, they will completely recondition the failed unit 

to make it operational, by performing the necessary repairs, 

including replacement of short-life, high-wear parts such 

as lenses, diffusers, lamps, etc. Some charge a flat rate, 

exchanging failed units for previously reconditioned ones. 

Certain repairs, such as glass lens replacement on some 

area luminaires, cannot be made at the mine and must be 

made by the original supplier or an authorized vendor. 

These services are not inexpensive, however, and for this 

reason it is recommended that mine operators screen failed 

components before sending them to the vendor. Components needing minor replacement (e.g., bad lamp) should 

be repaired in-house, whereas components should be 

shipped to the vendor if fault identification is difficult and 

repair will require skills, tools, or facilities not readily 

available at the mine. This can proceed most efficiently if 

failed units are shipped to a central location and a trained 

individual periodically screens the units. An adequately 

equipped bench should be available to the repair person 

for making electrical tests or identifying faults through 

good-part substitutions. 

The final requirement for implementing an exchange 

maintenance program is appropriate stocking of replacement units. Inventory levels should be consistent with 

usage, and an adequate number of units (in particular 

luminaires and cable assemblies) should be stored at the 

face with any possible preassembly, e.g., connecting pigtails and connectors, already performed. It should be noted 

that inventory requirements are somewhat higher for 

exchange maintenance. For small, low-overhead mines, 

this may appear to be a significant disadvantage of this 

maintenance approach, but should be offset by the benefits of improved availability. 

Scheduled and Preventive Maintenance 

Scheduled maintenance of lighting systems involves 

making lighting system checks and performing part of 

routine machine servicing during scheduled machine downtimes and maintenance shifts. Preventive maintenance is 

the replacement of components with predictable service 
lives prior to failure. The benefits of these practices include 

the following: 

Lighting failures will become less of a drain on the availability of the machine by reducing the incidence of fail 

ures during operating shifts. 

Condition of the system is constantly checked and 

maintained, preventing deterioration that diminishes the 

utility of the system and may create hazards and/or lead to 

permissibility citations. 

Table 9 provides a checklist for scheduled lighting 

system maintenance and inspection. It is recommended 

that these items be incorporated into the general machine 

inspection programs in place at the mine. 

Table 9.-Scheduled maintenance checkilst for mlne 

illumination systems 

Task Action 

Inspect explosion- Check for proper gap. 

proof glands. Check condition of sleeve (twisted or dented). 

Check set screw placement. 

Check conduit attachment; placement and tightness 

of hose clamps. 

Check for damaged or missing guards. 

Clean and inspect Clean lens in accordance with manufacturer's 

luminaire lens. recommendation. 

Check bonding of adhesive on glass lens. 

Look for crazing cracks, splitting or yellowing on 

polycarbonate; replace if discovered. 

Check for excessive polycarbonate scratches. 

Check cable Route away from pinch points (especially on longrouting. walls). 

Check for direct routing to machine covers with 

minimum exposure and kinking. 

Check for exposure of connectors. 

Check for dim or Replace immediately because they can damage balflickering lamps. lasts. 

Preventive maintenance efforts in lighting are limited because many hardware failures are caused by unpredictable incidents (e.g. impacts) rather than gradual 

wearout. Exceptions to this on some lighting applications 

include lamp failures and polycarbonate deterioration 

(scratching, clouding) through time. Group relamping; i.e., 

preventive maintenance of lamps; is discussed in detail in 

the "Group Relamping" section of this chapter. 

Record Keeping 

Good record keeping is necessary for obtaining reliable statistics on which to base maintenance program 

decisions. Uses of these statistics in lighting maintenance 

include the following: 

1. Establishment of optimum component inventory 

levels. 

2. Determining failure trends for use in the scheduling 

of preventive maintenance. 

3. Identification of maintenance troublespots and assessment of factors causing failures. 

4. Measurement of the performance of maintenance 

programs. 

Optimum inventorying of lighting components is 

analogous to inventorying any other maintenance item, 

and procedures will not be detailed here. Also, as noted 

previously, the primary use of preventive maintenance is 

in scheduled lamp replacement. 

The simplest way to objectively identify maintenance 

troublespots is to determine mean service life of the system components; i.e., mean time between failure (MTBF). 

This can readily be calculated from inventory depletion 

and machine operating records as follows: 

NF X N, MS, + Nb MS, + ... + N, MS, 

MTBF = - 

NS N, + Nb + ... + N, 

where MTBF equals mean time between failure for the 

component under consideration in machine shifts, NF is 

the number of failures (per inventory depletion records) 

during the period under consideration, N, is the number 

of components installed on machine type a, and MS, is the 

average number of machine shifts operated by each type a 

machine during the period under consideration. The other 

subscripts represent the different machines on which the 

component has been installed (e.g., a-miners, &bolter, 

c-longwall). The composite second term represents the 

average number of machine shifts that the component 

under consideration was operated during the period considered. For electrical components, MTBF values can be 

compared to rated component life values as an indication 

of performance; however, realized mine service life is generally less than rated value. 

For more detailed problem identification, individual 

components can be date-tagged when installed on the 

machine. In fact, some long-life high-intensity discharge 

lamps have a built-in tagging system. In addition to installation date, it is recommended that the machine on 

which the component is installed and perhaps the location 

of the fixture also be noted. When exchanged, service life 

can be recorded and the component can be examined for 

signs of the cause of failure. Knowledge of service life, the 

environment where the component operated, and component appearance upon failure can give insight to the cause 

of failures and what to do to resolve the problem. The following examples illustrate the application of this information: 

1. High incidence of lamp failure of those lamps at the 

tail end of a longwall panel relative to the middle or head 

end might indicate that line losses are causing undervoltage-related failures. 

2. High heat-related ballast failure rates on a particular machine relative to other machines on a line or load 

center may be indicative of a heat sinking problem on the 

machine rather than an overvoltage problem. 

3. High incidence of failed headlamps on a particular 

fixture may be indicative that the fixture is mounted on a 

high-vibration surface. 

Maintenance Training 

Lighting circuitry, particularly ballasted and solidstate systems, differs greatly from other mine circuitry 

and, potentially, may cause confusion for even experienced 

mechanics and electricians during electrical fault isolation. 

Maintenance training programs should address mine 

lighting, familiarizing these individuals with the function 

of the system and the procedures to be followed in its 

maintenance. Training program content will vary depending on the hardware types(s) utilized at the mine, and the 
variety that exists precludes a specific discussion of content here. The following general comments are made, 

however, regarding the formulation and content of a 

maintenance training program: 

1. Reference sources for troubleshooting information 

include (a) manufacturer representatives (some offer 

courses for mechanics), (b) troubleshooting charts and manuals available from lighting hardware manufacturers, and 

(c) generalized troubleshooting guides available from various lamp manufacturers. Some of the latter are in a very 

handy format. 

2. Content of troubleshooting procedures presented to 

the mechanics should be given careful consideration. It is 

doubtful that they will retain detailed procedures comprehensive of the entire fault tree. Rather, selectivity is 

recommended, defining in simplest fashion possible those 

procedures that enable quick and efficient isolation of the 

most likely faults. (An exchange maintenance program 

makes this approach more practical.) Diagnosis through 

component exchange is recommended, using duplicate components already in place if possible (e.g., connecting a luminaire known to be good in place of one not operating to 

establish whether the fault is within the luminaire or the 

circuit feeding it). 

3. Instruction should be given in the use of available 

troubleshooting and diagnostic aids (e.g., shorting plugs, 

cathode-heat tester, etc.) and these should be available on 

the section. 

4. Wiring connection diagrams should be attached to 

the hardware to permit efficient component exchange and 

minimize the likelihood of miswiring. 

RECOMMENDATIONS FOR MINIMIZING LAMP 

MORTALITY AND LAMP REPLACEMENT COSTS 

In underground mines, applications where "rated" 

lamp service life is realized are more the exception than 

the rule. Numerous factors are detrimental to realized service life, and correct diagnosis of those particular factors 

that reduce lamp life in a given application can be difficult. 

This section presents recommendations for minimizing 

costs incurred from high rates of lamp mortality and information for assessing the cause of excessive failures. 

Assessing Lamp Costs 

The following relationship can be used to establish 

lamp costs on an hourly basis and to determine the most 

economical lamp among alternatives: 

Lamp cost - Operating (power) cost + 

Hour Hour 

Initial lamp cost + Lamp replacement cost 

Mean service life Mean service life 

(hours) (hours) 

For most industrial and commercial lighting applications, use of this relationship is straightforward. Operating costs can be readily determined from published lamp 

and ballast wattage figures and local utility rates. Lamp 

replacement costs can be established by estimating labor 

charges, given the design configuration and lampchanging 

characteristics of the fixtures. Rated lamp life figures published by the manufacturer provide reasonable estimates 

of life expected in service. 

It should be noted that comparative calculations are 

performed on a lamp equivalent basis. If it takes 15 lamps 

of type a to do the same job as 10 lamps of type b, then the 

lamp cost per hour for lamp type a should be multiplied by 

a factor of 1.5 (15 divided by 10) for the comparison with 

type b to be valid. 

Use of this relationship to establish the cost of lamps 

used at the coal face is considerably more complicated and 

may yield results vastly different from those found in other 

industrial applications. This occurs because (1) rated lamp 

service life is an inaccurate estimate of actual service life 

realized in many coal-face applications of lamps, and (2) 

lamp replacement costs in some coal-face applications can 

be particularly high if machine-downtime and lostproduction costs must be considered. The major implications these factors have on an economic evaluation of mine 

lamps are as follows: 

1. Life values established through site-specific experience are greatly preferred over rated values for making 

lamp comparisons. If these data are to be established 

through trial or experimental lamp installations, great 

care should be taken to assure that mechanical and electrical application parameters are representative. 

2. In most nonmining applications of lamps, operating 

(i.e., power utilization) cost is the most significant determinant of total lamp costs. Here, use of the more expensive 

types of available lamps is easily justified by their operating costs being lower (i.e., their efficacy, see chapter 3, is 

higher) and their rated service life being longer than their 

cheaper counterparts. In mining applications, reduced service life increases the importance of initial lamp cost and 

lamp replacement costs relative to total lamp operating 

costs. Hence, use of expensive, high-efficacy lamps on the 

basis that they are cheaper overall to operate may not be 

the case in certain mining applications. 

3. Lamp replacement costs are usually the least significant determinant of total lamp costs on most nonmining 

applications. However, in some coal-face applications, it 

may be necessary to consider machine downtime and resulting lost-production costs in assessing the cost of making a 

typical lamp replacement. In cases where lost-production 

costs tend to be very high, e.g., on an extraction machine, 

the lamp replacement cost variable may be much more 

significant than power consumption or initial lamp cost. 

In such applications, using long-life lamps and taking measures to extend lamp life would be critical to minimizing 

costs. Conceivably, situations could arise where it would 

be cost effective to pay 500 pct more for a lamp that receives 

only a 100-pct increase in life. Accurate assessment of lost 

production costs, often very difficult to accomplish, is essential for making such a determination. 

In summary, determining the most economical lamp 

for a mine application is complex, but, because incurred 

lamp costs can be significant, efforts at making such an 

assessment are worthwhile. Site-specific data on expected 

lamp life and lamp replacement costs are necessary for an 

accurate assessment. 
Assessing lncreased Lamp Mortality 

in Mine Applications 

Numerous factors, many unique to mining applications, can reduce realized lamp service life. The following 

section discusses the mechanisms causing normal lamp 

failure, delineates factors likely to shorten service life in 

mine application, and suggests ways to diagnose these 

causes of shortened life. It must be realized that rated life 

is not reached by every lamp in an installation, even under 

ideal circumstances. Rated life normally means the life 

expected by the average lamp; 50 pct of the lamps will 

have failed by the time rated life is reached. In the case of 

mercury vapor lamps, lumen depreciation is greater than 

other types, and rated life is specified as the point where 

only one-third of the lamps have failed. Because of low 

lumen output relative to power consumption, use beyond 

this time period is not considered cost effective. For some 

lamps manufactured exclusively for coal-mine application, 

manufacturers have devalued rated life figures in anticipation of harsh operating circumstances. Hence, if actual life 

is approaching rated life of these lamps, one should not 

infer that significant improvements are not achievable. 

Operators are urged to determine the mean service life of 

the lamps they utilize (inventory depletion records make 

such calculations easy) and, if this life falls significantly 

short of rated values, operators should take measures to 

diagnose the cause(s) of high mortality. 

Factors Causing Increased Mortality 

of Lamps in Mine Application 

Incandescent Lamps 

Rated Life.-750 to 1,000 h, 2,500 to 3,500 h for extended service rated lamps. 

Cause of Normal Mortality.-Throughout the life of 

the lamp there is a gradual evaporation of the tungsten 

filament. This continues to a point where continuity of the 

filament is broken, ending the normal life of the lamp. 

The following are the likely causes of shortened incandescent lamp life in mine application: 

1. Machine Vibrations and Mechanical Shock.-When 

lamps are operating, their filaments are very hot and become somewhat soR and pliable. In this state, they are very 

susceptible to breaking when subjected to mechanical shock 

and machine vibrations. Mechanically induced failures can 

often be diagnosed by visual inspection. Figure 59 illustrates the general appearance of shock and vibration damaged filaments. Rough service lamps, constructed with special filament mounts to resist shock, have been shown to 

yield significantly improved lamp life in mine application. 

Vibration service lamps are designed with extra filament 

supports and utilize a special tungsten with a crystalline 

structure that makes it more flexible and vibration resistant. The intended application of this lamp is in environments exhibiting high-frequency, low-amplitude vibrations. 

Their shock resistance is marginal, hence in most face 

machine applications, rough service lamps are the preferred lamps to utilize. Vibration service lamps might, 

however, prove beneficial in some mine applications, e.g., 

pump rooms. It should also be noted that low-voltage lamps 

C-9 FILAMENT 

NORMAL VIBRATION SHOCK 

CC-6 FILAMENT 

NORMAL VIBRATION SHOCK 

Figure 59.-Effects of vlbratlon and shock on lamp4llaments. 

are inherently more resistant to mechanical damage 

because they employ large-diameter filaments. Use of lowvoltage lamps (12 and 32 V) has proven very beneficial on 

many installations and they are particularly recommended 

on shuttle car applications. 

2. High Line Voltage.-Incandescent filaments are 

heated as close to the tungsten melting point as is consistent with reasonable lamp life so that reasonable efficiency 

in converting electrical energy to visible light energy is 

obtained. Overvoltage greatly accelerates the tungsten 

evaporation rate and significantly reduces lamp life. The 

expected life of an incandescent lamp continuously driven 

at a particular overvoltage can be computed with the following formula: 

Nominal voltage 13.1 Expected life = Rated life 

Actual voltage 1 

For example, a 1,000-h, 150-W, 120-V incandescent lamp 

driven continuously at 130 V would have an expected life 

of only 350 h, indicating that minor overvoltages (in mining terms) have very serious effects on incandescent lamp 

life. In general, failures induced by high line voltage cannot be visually diagnosed. Line voltage can be checked 

with a standard voltmeter; a recording instrument is recommended for an accurate assessment. Note that overvoltages of short duration (e.g., transients) have little effect 

on incandescent lamp life. 

3. Other Instances of 0vervoltage.-On dc shuttle cars, 

installations have been made where the two headlights, 

wired in parallel, are in series with a single resistor, which 

drops voltage to the appropriate level for the headlights. 

When one headlight fails, circuit resistance increases, voltage drop across the resistor decreases, and the remaining 

operable lamp is overdriven. On a 300-V dc shuttle car 
utilizing a pair of 120-V headlights, the remaining operable lamp would see a 43 pct overvoltage, reducing its life 

to a matter of hours in many cases unless the failed lamp 

is immediately replaced. Other circuits can be utilized that 

eliminate this problem and are discussed in chapter 4. 

Rapid Start Fluorescent: Standard, High Output, 

and Very- or Super-High Output 

Rated Life.-7,500 to 10,000 h. 

Cause of Normal Mortality.-Lamp cathodes are coated 

with electron emissive material that supplies electrons to 

initiate and maintain lamp arc. This material is gradually 

depleted during lamp starting and burn cycles. Normal 

end of life occurs when emissive material is depleted on 

one or both cathodes. 

The following are the likely causes of shortened rapid 

start fluorescent lamp life in mine applications: 

1. Machine Vibrations and Mechanical Shock.-Vibration and mechanical shock can result in a continuity break 

in the heater circuit formed by the lamp cathode. Relative 

to incandescent lamps, resistance to vibration and shock 

induced failure is high because filament temperatures are 

lower. If a lamp fails without blackening of the sidewalls, 

it is likely that failure resulted from mechanical causes 

(blackening occurs with most electrical failures). On rapid 

start (RS) lamps, continuity can be checked using a continuity tester across the adjacent lamp contacts on the lamp 

end. A shadowgraph (fig. 60), permits visual inspection of 

cathode continuity. The percussive wave of face shooting 

practiced on longwalls frequently results in mechanical 

failure of fluorescent lamps. It is advised that longwall 

systems be equipped with quick-release mounts and lineinstalled connectors to enable removal of luminaires in 

the blast vicinity. 

2. Low Line Voltage.-Degradation of electron emissive 

material is greatest during lamp startup. Low voltage prolongs the lamp starting cycle, increasing the rate of depletion of the emissive material and reducing lamp life. Also, 

on high-output (HO) and very-high-output (VHO) lamps, 

it is essential that cathode heater voltage be maintained 

during lamp operation to avoid excessive degradation of 

the emissive material. Low line voltage will reduce cathode heater voltage during operation and reduce lamp life. 

Line voltage can be checked with a standard voltmeter 

(recording instrument preferred) and should be no more 

CARDBOARD WITH PINHOLE 

TABLE LAMP 

AND OBSERVE FILAMENI 

Flgure 60.-Shadowgraph to test fluorescent lamp fllament 

contlnulty. 

than 10 pct less than nominal voltage unless lower levels 

are specified by the ballast manufacturer. Slow starting is 

another sign of low line voltages. Low voltage problems 

may be encountered in cases where line losses are high, 

for instance at the end of longwall circuits and in mines 

where voltage regulation is poor. 

3. High Line Voltage.-High line voltage tends to cause 

the lamp to "instant start" without any thermal release of 

electrons from the cathode. This causes rapid deterioration of the cathode emissive material and reduces lamp 

life. Line voltage can be checked with a standard voltmeter (recording instrument preferred) and should be no more 

than 10 pct greater than nominal voltage unless higher 

levels are specified by the ballast manufacturer. A dense 

black spot about 112-in wide and extending halfway around 

the tube in the cathode vicinity can be a sign of an 

overvoltage problem, although similar spots can accumulate for other reasons. 

4. Improper Cathode Heating.-As implied, proper cathode heating must be maintained during starting for all RS 

lamps and for all but standard during operation or the 

electrode emissive coating will be prematurely exhausted 

and lamp life shortened. Causes of improper cathode heating include low line voltage, poor contacts at the lamp 

holder or terminal strips-lugs, ballast problems, or reduced 

heater circuit voltage at lamp filaments caused by line 

losses if ballast is very remote from fixture. Improper cathode heating is manifested by dense blackening from the 

base 2 to 3 in along the lamp similar to normal end-of-life 

blackening. Blackening caused by improper cathode heating may occur on one or both ends of the lamp. Manufacturers supply heater-circuit testers that are essentially resistors, which serve as a dummy load to draw proper cathode 

current, and a voltmeter attached in parallel. Go, no-go 

heater circuit indicators that essentially consist of incandescent lamps to serve as dummy loads, are not recommended for use in troubleshooting mine lighting circuits 

since low, not zero, heater voltage may be the problem in 

the case where remote ballasts are used. 

5. Wrong Lamp-Ballast Combination.-HO lamps 

should not be operated on ballasts designed for VHO and 

super-high-output (SHO) lamps and vice versa. In either 

case, both ballast and lamp life will be shortened. The 

effect would be more significant in the case where HO 

lamps are applied on VHO-SHO ballasts. 

6. Improper Ballast Operation.-Improper ballast operation may cause improper cathode heating, low or high 

starting voltage, and improper operating currents, all of 

which can reduce lamp life. Check proper operation by 

making current and voltage measurements specified by 

the ballast supplier. 

High Intensity Discharge: Mercury Vapor 

and High-Pressure Sodium 

Rated Life.-12,000 to 24,000 h (mercury vapor, MV) 

and 7,500 to 24,000 h (high-pressure sodium, HPS). 

Cause of Normal Morfulity.- In MV lamps, electron 

emissive material embedded in lamp electrodes is gradually depleted throughout the life of the lamp because of a 

sputtering off process caused by the impact of arc particles. 

This occurs to a point where it becomes difficult to produce 

ionization and strike the arc or to warm up the lamp to full 

light output. When ballast open circuit voltage is insufficient to strike the arc or warm up the lamp, end of life has 

occurred. 
In HPS lamps, operating voltages exhibit an increase 

with age (operating voltages in MV and other high intensity discharge (HID) lamps tend to remain constant). This 

occurs because (1) evaporated electrode materials blacken 

the arc tube and raise its temperature, which raises the 

partial pressure of the sodium-mercury amalgam arc material and increases operating voltage (HPS lamps have 

excess arc material whereas other HID lamps do not); and 

(2) sodium reacts with the arc tube, increasing the ratio of 

mercury in the arc material, which also tends to raise 

lamp voltage. The net effect is an approximate 2-V increase 

in lamp voltage per 1,000 burning hours. Whenever required lamp operating voltage exceeds voltage available 

from the ballast, effective lamp life is ended. Unlike MV 

lamps, HPS lamps will ignite and warmup at the normal 

end of lamp life; they extinguish as stable operating voltage is approached. Failed lamps will continue the startwarmup-extinguish-cool cycle until power is turned off. 

The following are likely causes for shortened HID lamp 

life in mine application: 

1. Machine Vibrations, Mechanical Shock, and Mishandling.-In both MV and HPS lamps, mechanically induced 

failures are most likely to occur upon (1) break in continuity of the internal leads to electrodes, (2) breaking or cracking of the arc tube, or (3) loss of vacuum between arc tube 

and lamp outer jacket. Such failures can generally be diagnosed by visual inspection; loss of vacuum will be manifested by oxidation of the metal support structure within 

the lamp. Lamp electrodes themselves are inherently resistant to mechanical failure. Care should be taken on transport of these expensive lamps into the mine. A loss of 

vacuum failure can occur if the lamp is too firmly tightened into a socket. Mechanically severe operating environments found on certain machines can cause other mechanical failures other than the three identified. 

2. High Line Voltage.-As explained, mortality of HPS 

lamps is dependent on the operating voltage rise of the 

lamps. High line voltage raises lamp operating voltage 

and thus shortens the period that voltage available from 

the ballast is sufficient to drive the lamp. Excessive line 

voltage may accelerate the rate of voltage rise of the lamp. 

The effects of high line voltage are very dependent on 

ballast design. Regulated or constant-wattage type ballasts or lead-circuit ballasts regulate the effects of line 

voltage variation and nominally will tolerate a 10 pct 

overvoltage. Lag-circuit ballasts are poor regulators and 

will only tolerate 5 pct overvoltage. (See chapter 3 for a 

discussion of these ballast categories.) Line voltage can be 

checked with a standard voltmeter. High ballast failure 

rate in conjunction with high lamp failure rate is a sign 

that there is a high-voltage problem. 

In MV lamps high line voltage will result in excessive 

temperatures on lamp electrodes and arc tube (MV arc 

tube material is not as heat resistant as HPS arc tube 

material) which is detrimental to realized service life. Bulging or shattering of the arc tube is a sign of overvoltage 

operation. As with HPS lamps, the effects of high line 

voltage on MV lamps are very dependent on ballast design. 

Autoregulator and, in particular, regulator ballasts regulate the effects of line voltage variation and will tolerate 

10 pct or more overvoltage. Reactor and lag ballasts are 

poor regulators and will tolerate at most a 5 pct overvoltage. (See chapter 3 for a discussion of these ballast 

categories.) Line voltage can be checked with a standard 

voltmeter. 

3. Low Line Voltage.-Low line voltage will result in 

reduced temperature of MV lamp electrodes which, in turn, 

makes it more difficult for the arc to start during each 

half-cycle and accelerates the deterioration of electron 

emissive material. As previously noted, this will eventually raise lamp starting voltage above that which can be 

supplied by the ballast and hence reduce lamp life. Undervoltage operation should be indicated by an early blackening of the arc tube. The effects of low line voltage are also 

very dependent on ballast design. Autoregulator and 

regulator ballasts regulate the effects of line voltage variation and will tolerate 10 pct undervoltage. Reactor and lag 

ballasts are poor regulators and will tolerate a 5-pct 

undervoltage. Low line voltage can be checked with a standard voltmeter, with measurement preferably made at normal operating load. 

4. Current-Voltage Surges.-Energy from surges can 

damage the arc tube, arc-tube seals, or leads to arc tube in 

the outer bulb of MV and HPS lamps. Damage is usually 

visually evident (damaged seals are evidenced by blackening). This is a likely cause if lamp life is very short. 

5. Improper Ballast Operation.--Shorted ballasts (capacitors) cause excessive current and will damage arc tube 

seals (evidenced by blackening in the seal area) of MV and 

HPS lamps. Ballast operation can be checked by making 

current, voltage, and continuity tests according to ballast 

manufacturer's specifications. Often ballast damage is visually evidentccapacitors will be swollen or the unit may be 

charred. 

MEASURES TO IMPROVE LAMP LIFE-LAMP 

SERVICING SUGGESTIONS 

Numerous measures can be taken by the mine operator to improve lamp life once the cause of lamp failure is 

diagnosed, as is shown in the following examples. 

In the case of mechanically induced failures (machine 

vibrations, mechanical shock, mishandling1. Boxes used by lamp manufacturers to package lamps 

are generally insufficient to withstand mine supply handling methods. Build a cushioned lamp box (e.g., lined 

with high-density foam rubber) for each mining section 

and use it to transport replacement lamps; 

2. On incandescent systems, utilize low-voltage, roughservice rated lamps. They have thicker, better supported 

filaments enabling them to better withstand shock; 

3. Insure that luminaire mounting surfaces are secure 

and do not amplify luminaire shock and vibration exposure; 

4. Incorporate shock dampening into luminaire mounts; 

e.g., rubber pads; 

5. Review luminaire design to see that it incorporates 

adequate measures for lamp-isolation and shock-dampening; 

6. Use of vibration service lamps may be warranted in 

some incandescent lamp applications such as pump rooms; 

7. On longwalls where frequent face-shooting is practiced, utilize luminaires with line-installed connectors and 

employ quick-release luminaire mounting techniques so 

that luminaires in the immediate shot vicinity can be readily removed. Percussion will damage lamps; and 

8. On machines where workers pound on machine decks 

(e.g., changing bits on bolters), take measures such as providing a work surface away from luminaire, move luminaire, etc. 
In the case of overvoltage-related failures1. On dc machines, size drop resistors in accordance with 

actual machine voltage, not nominal. Underdriving might 

be feasible on shuttle cars with twin incandescent headlights on each end because there usually is excess lumen 

output available; 

2. Transformers are available for lighting power supplies with taps for low and high line voltage; 

3. Use proper ballasts. Some standard ballasts provided 

by mine lighting suppliers only tolerate 25 pct voltage 

variation. Other alternatives are available (although more 

expensive and less energy efficient) to tolerate 5 10 pct or 

more; and 

4. On dc shuttle cars, there are alternative ways of dropping voltage and driving lamps as depicted in figure 40. 

The series or series-parallel arrangement is recommended 

for maximized lamp life, since the remaining lamp is not 

overdriven if one lamp fails. 

In the case of undervoltage-related failures1. Transformers are available for lighting power supplies with taps for high and low line voltage; 

2. Use proper ballasts. Some standard ballasts provided 

by mine lighting suppliers only tolerate 25 pct variation 

in line voltage. Other alternatives are available (although 

more expensive and less energy efficient) to tolerate + 10 

pct or more; 

3. Measures that may be taken on longwalls to reduce 

undervoltage problems include use of autotransformer voltage boosters, larger diameter and/or shorter length conductors, and fewer luminaires per power supply or distribution box; and 

4. Correct cable size and length problems if causing inadequate cathode heating voltage on remotely ballasted fluorescent lamps. 

It is important to replace failed or dimly burning fluorescent and HID lamps as soon as possible. Failure to do so 

can result in ballast overheating, damage to other lamps 

in the circuit, and, in the case of HPS sources, continued 

recycling of the lamp starter, which will cause its eventual 

failure. 

It is recommended that series-wired incandescent systems be equipped with neon bad-lamp indicators. These 

devices are simply miniature neon lamps that are shunted 

across the circuit at each incandescent lamp. When the 

lamp fails, and causes all lamps to remain dark, the neon 

indicator at the failed lamp lights, making it simple to 

identify the bad lamp in the circuit. 

GROUP RELAMPING 

Group relamping is the scheduled replacement of all 

the lamps in an installation at the same time, prior to 

anticipated burnout. This practice, widely utilized in 

industrial, commercial, office, and sports lighting, has 

advantages over the alternative--spot relamping (i.e., oneby-one replacement as lamp burnout occurs)-in certain 

mine lighting applications. Longwall and nonface installations most readily lend themselves to this practice, but it 

may offer important advantages for some face-machine 

installations as well. The major benefits of group relamping 

in a mining application follow: 

1. Depending upon the circumstances of the installation, 

there is potential for considerable savings in maintenance 

labor requirements for making lamp replacements. Lamp 

replacement costs in a group relamping program would 

typically be a fraction of the per-lamp costs for spot 

relamping because replacements can be made in an organized, assembly-line fashion and piece-by-piece transport of replacement stock is eliminated. 

2. By replacing lamps prior to the end of their life, the 

effects of depreciating light output, which occurs in all 

lamps as they age, are reduced. The installation is operated at high efficiency, maximizing lumen output per unit 

of energy consumption. Moreover, lens cleaning (and perhaps lens replacement) would be an integral part of a group 

relamping program, further improving lighting efficiency. 

Both these aspects improve the utility of the lighting system and reduce potential for citations. 

3. As noted previously, during the lingering-on period 

near the end of lamp life and, in some cases, after lamp 

failure occurs, energized ballasts will realize a temperature rise that shortens their useful life. Group relamping 

prior to failure would significantly reduce such damage. 

4. Federal law requires that lamp replacement on all 

systems that utilize explosion-proof luminaires be made 

by certified electricians. Group relamping performed on 

scheduled maintenance shifts would reduce the incidence 

of spot replacements on production shifts and not detract 

the work of these key personnel from the production effort. 

5. Group relamping is complementary to the exchange 

maintenance approach advocated in this report; in fact, it 

makes the changeout approach more viable. On-site group 

relamping will reduce the incidents where luminaires are 

removed from the mine just for lamp replacement. This 

would reduce luminaire inventory requirements for an 

exchange maintenance program. 

6. In cases where lamp failure results in high incurred 

cost because of machine downtime and lost production, 

group relamping during scheduled maintenance periods 

may reduce the incidence of failures during production 

periods, hence, reducing such costs. 

The concept of group relamping hinges on the predictability of lamp life. Figure 61 shows lamp mortality curves 

(percentage of lamps failed versus percentage of lamp life 

operated) for the type of lamps utilized in coal mines. The 

idea is to schedule group replacement prior to the steep 

part of the curve when failure rates begin to accelerate. 

The shape of the lamp mortality curve, labor costs for 

making spot versus group replacement, and lamp costs 

have bearing on the viability of group relamping and in 

scheduling the optimum replacement time. A step-by-step 

procedure for making such an analysis is presented at the 

end of this section. 

In many mining applications, the curves presented in 

figure 61 may not be applicable since realized life is often 

less than rated life and also, in such event, the trend of 

failures need not follow that indicated in the figure. Even 

though rated life is not realized, this does not mean group 

relamping is not viable. In these cases, it is necessary to 

establish installation specific lamp mortality curves by 

keeping records on lamp replacements (e.g., date tagging 
0 0 10 20 30 40 50 60 70 80 90 100 

PERCENT RATED LIFE 

- 

- INCANDESCENT 

- ,.,. -.- HPS 

0-0- MERCURY 

FLUORESCENT 

- 

- REPLACEMENT 

- 

- 

- 

, I I I I I I 

Figure 61.-Laboratory measured mortality curves for lamp 

types used in coal mlning applications. 

lamps). If the factors reducing lamp life are random in 

nature, as might be the case if most failures are the result 

of mechanical incidents, the shape of the curve might be 

such as to preclude group relamping; i.e., the rate of failures (the slope of the mortality curve) does not increase as 

mean service life is approached. In many applications, in 

particular most longwall and nonface installations, this is 

not likely to be the case. 

On room-and-pillar face machines, random failures 

are more likely; however, the high machine-downtime and 

lost-production costs incurred when lamp failure occurs on 

those machines warrants establishing lamp mortality 

curves and determining if group replacement is feasible. 

For example, it may prove very cost effective to replace 

the headlights on the continuous mining machines every 

weekend to avoid some of the incidents of downtime for 

making lamp replacements. 

The steps for arriving at the optimum time for scheduling group lamp replacement given a lamp mortality curve 

(i.e., percent lamp failures versus operating time) is as 

follows: 

1. Determine costs for making one-at-a-time replacements of all lamps in the installation as they fail. 

Labor time (h) Hourly rate Labor cost = 

Lamp change (including overhead) 

Lamps 

in installation. 

Cost Lamps Lamp cost = - X 

Lamp in installation. 

Total cost = Labor cost + Lamp cost. 

2. Determine cost incurred as group replacement is 

made. 

Labor time (h) Hourly rate Labor cost = 

Lamp change (including overhead) 

Lamps 

in installation. 

(Labor time would be less than that for one-at-a-time 

replacement.) 

Cost Lamps Lamp cost = - X 

Lamp in installation. 

Total cost incurred as group replacement is made = 

Labor cost + Lamp cost. 

3. Select a candidate time for scheduling group relamping. Optimally, this time should just precede the steep 

part of the lamp mortality curve. The candidate time usually should fall in the range of 65 to 85 pct of rated life. 

4. Using candidate time of step 3, determine the percentage of lamps that will have failed prior to the scheduled, group relamping date. For example, using figure 61, 

10 pct of the fluorescent lamps will have already failed if 

the scheduled group relamping time is 70 pct of rated lamp 

life. 

5. Multiply the percentage of lamps failed, obtained in 

step 4, by the total one-at-a-time replacement cost, step 1, 

to determine the cost of making those one-at-a-time replacements necessary prior to the scheduled group replacement. 

Add this figure to the total cost determined in step 2 to 

obtain the total cost to the point where group replacement 

is made. 

6. Adjust the cost obtained in step 5 to account for 100 

pct expected lamp life as follows: 

Equivalent cost at 100 pct life = Step 5 cost X 

100 pct expected life 

Percent expected life 

when group replacement 

made (per step 3) 

7. Repeat steps 3 through 6 for other candidate group 

replacement times. Select lowest cost alternative. 

From this procedure it is evident that group relamping 

is most viable when (1) lamps are inexpensive, increasing 

the significance of the labor savings yielded by group 

replacement in determining total cost, and (2) the rate of 

failures accelerates significantly as end of life approaches. 

It is quite possible that spot replacement as lamps fail 

may be more economic for expensive lamps that tend to 

fail uniformly over expected life. 

It is essential to note that this procedure does not 

account for machine-downtime and lost-production costs. 

If applicable, these costs should be added in step 1 of the 

procedure. They will have significant bearing on the conclusions of such an analysis, greatly increasing the viability of group relamping and, depending on the shape of the 

mortality curve, make replacements early in lamp life more 

attractive. 
against the mining machine or loader when positioned to 

receive material. 

Note I.-To allow for most efficient deployment of 

machine headlights, no light measurements are taken in 

the floor area between the cutter-boom or gathering-head 

hinge pin and the face. 

Note 2.-To permit location of fixtures in maintainable locations, no light measurements are taken within a 

1-ft perimeter of the machine. 

MACHINE POSITION FOR LIGHT MEASUREMENTS 

Centered in entry with inby end of cutterhead or gathering head no greater than 3 ft from the face. 

ADDITIONAL COMMENTS 

Pickup loader, i.e., loaders operated behind a continuous mining machine in surge material handling capacity, 

fall in this cateory. To prevent objectionable discomfort 

glare problems, the inby end of these machines are usually not lighting with directional luminaires (e.g., headlights). 

Roof lighting not required if seam height is less than 

12 in greater than machine frame height. 

need not be illuminated to the 0.06-fL standard. This 

accommodation is to prevent the necessity of employing 

undiffused or unshielded high-intensity fixtures to illuminate wide entries often found in low-coal mines. Otherwise, 

objectionable discomfort glare problems might result. 

MACHINE POSITION FOR LIGHT MEASUREMENTS 

Centered in entry with inby end of cutterhead or gathering head no greater than 3 ft from face. In cases where 

ribs do do not fall within 5 ft of machine, the machine is 

repositioned so that it is 5 ft from and parallel to the ribs 

to take these measurements. 

ADDITIONAL COMMENTS 

Pickup loaders, i.e., loaders operated behind a continuous mining machine in surge material handling capacity, 

fall in this category. To prevent objectionable discomfort 

glare problems, the inby end of these machines are usually not lighting with directional luminaires (e.g., headlights). 

Roof lighting not required if seam height is less than 

12 in greater than machine frame height. 
COSOOGSU

Centered in entry with inby end of cutterhead or gathering head no greater than 3 ft from face. In cases where 

ribs do not fall within 5 ft of machine, the machine is 

repositioned so that it is 5 ft from and parallel to the ribs 

to take these measurements. 

Roof lighting not required if seam height is less than 

12 in greater than machine frame height. 
tioned so that it is 5 ft from and parallel to the ribs to take 

these measurements. 

ADDITIONAL COMMENTS 

Roof lighting not required if seam height is less than 

12 in greater than machine frame height. 

A-6.-Rope-propelled cutters and rope-propelled 

auger miners in any seam height. 

AREAS TO BE ILLUMINATED TO 0.06 fL 

the boom spread and eliminate the necessity of locating a 

fixture here. 

MACHINE POSITION FOR LIGHT MEASUREMENTS 

Centered in entry with drill head distance X from the 

face. In this position, light measurements are taken on 

roof, floor, ribs, face, and exposed machine surfaces. In 

cases where ribs do not fall within distance X of machine, 

machine is repositioned to the distance X from the rib and 

light measurements are made (two repositioning5 required). 

As under note 2, measurements may be made on the supply tray vicinity with the drill heads together or spread a 

distance of 8 ft and in position for drilling or bolting on 

dual-head machines. 

ADDITIONAL COMMENTS 

Roof lighting not required if seam height is less than 

12 in greater than machine frame height. 

Pending development of low-glare illumination systems, no illumination is required on rope-propelled cutters. 

Design and operating procedures for these machines 

require that jacksetters work inby the machine where they 

would be exposed to objectionable discomfort glare and cap 

lamp signaling between these and other workers would be 

impaired. 
oo, oo, bs, ace, ad eposed ace suaces. cases 

where ribs do not fall within distance X of machine, 

machine is repositioned to the distance X from the rib and 

light measurements are made (two repositionings required). 

As under note 2, measurements may be made on the supply tray vicinity with the drill heads together or spread a 

distance of 8 ft and in position for drilling or bolting on 

dual-head machines. 

ADDITIONAL COMMENTS 

Lights only need be operated in the direction of travel 

at any given time. Lights may be turned off when they 

become a glare problem for personnel working on continuous mining machine or loader. 

On roof bolters integral to continuous mining machines, 

lighting to the 0.06-fL standard is still required in the 

vicinity of the operator's station. Roof lighting not required 

if seam height is less than 12 in greater than machine 

frame height. 
Perpendicular to and between 9 and 10 R from a relatively smooth coal surface. 

ADDITIONAL COMMENTS 

On scoops in particular, luminaires at one end of the 

vehicle must be top-deck mounted to meet specifications. 

This applies to cases where seam height exceeds frame 

height by only 6 to 8 in or less. In such event, top-deck 

mounted fixtures would be unmaintainable. 

Lights only need be operated in direction of travel at 

any given time. Lights may be turned off when they become 

a glare problem for personnel working on continuous mining machine or loader. 

used at all times. 

Roof areas upon which shadows are cast by a sideplate 

(i.e., gobplate) located on the edge of the roof canopy of 

the last support need not be illuminated to 0.06 fL. This 

eliminates the necessity of locating a fixture on the side of 

the roof canopy where, in many mines, it would be subject 

to mechanical hazard. 

jacks or timbers in the control center area need not be 

illuminated to 0.06 fL. 
Model 

Lamp: 

Type ............................................ Number .......................................... Designation ................................. Circuit design: 

Internal lo luminaire ........................ Leads to luminaire ......................... Guard standard ................................. 

Dimensional (w~th guard), in: 

Height ............................................ Wldth ............................................. 

11 ....................... fl. 

1 ....................... 1 

F24T12iCWISHO .. F18T12/CW/SHO. 

XP ........................ XP 

XP ....................... XP. 

Yes ....................... Yes. 

4-114 ................ 4-114. 

5-112 ..................... 5-112. 

Length ........................................... 30-118 ................... 24-118. 

Welght (with guard) ...................... Ib.. 32 ........................ 28. 

Materials: 

Lens ............................................. Polycarbonate ....... Polycarbonate 

Housing ............................... .. .... Steel .................. Steel. 

Guard .................... .................... ..do ................... Do. 

Integral ballast .................................... No ..................... No. 

Packing glands: 

Single or dual ............................... Single .................... Single 

Threaded or slip-fit ........................ Threaded ............. Threaded. 

Clamp or tubing .............................. Clamp .................. Clamp. 

Connection integral to luminaire ........ No ........................ No. 

Pigtail integral to luminaire. ................ No ...................... No. 

Separate XP connector supplied ....... No ................... No. 

Lamp cartridge: 

Utilized ...................................... Yes ....................... Yes. 

Connection type ................... ........... Wirenut ................ Wirenut. 

Primary application ........................... MFE ................... MFE. 

Ac or dc machine power ................... ac ......................... ac. 

Figure ................................................ 8-1 .................. 8-1. 

CW Cool Whlte. SHO Super-high output. 

fl Fluorescent. XP Explosion-proof 

MFE M~ne lace equipment. 

Figure El. Joy Manufacturing Co. model 500131-33 and 

500131-35 luminaires. 
Table B-3.-McJunkln Corp. system alternatives 

XP Ballasts 

Application or Lamp type Model Description 

IS Standard Solid state Integral Remote 

MFE, ac ....... XP X X VHO fl ....... 100164 None. 

100130 

MFE, ac ....... XP X X Standard fl ..... 10011 5 Do. 

10016 

MFE, ac ....... XP inc ......... 400-NS Do. 

Tubular inc .... 10016 inc Do. 

MFE, dc ....... XP X VHO f l ....... 100164 

MFE, dc ....... XP X HPS 4004s ('1 ........ MFE, dc ....... XP inc 4004s 

('1 ......... None. 

Tubular inc .... 10016 inc Do. 

MFE, diesel ..... XP X VHOf1 ....... 100164 

MFE, diesel ..... XP X HPS ........ 400-NS 

100130H 

Longwall ....... XP X X Standard fl ..... 10011 5H None. 

10016H 

- - 

fl Fluorescent. IS Intrinsically safe. XP Explosion-proof. 

HPS High-pressure sodium. MFE Mine face equipment. 

inc Incandescent. VHO Very-high output. ' Solid-state inverter ballasts are used to invert dc machine power to a high-frequency lamp drive power. Drop resistors are used tu reduce machine voltage 

to a level appropriate for the ballasts and an extensive transient suppression package (chokes, capacitors, and voltage trap resistors) is utilized to protect 

the system. 

Similar to dc power systems, uses solid-state inverter ballasts on diesel equipment lighting systems. Dc power is provided by a hydraulically driven generator 

with provision for flow control to maintain a constant voltage level with varying engine speed. 

NOTE.-No entry in a ballast column indicates the category is not applicable. 

Table B-4.-McJunklrs Corp. lumlnaire speclflcatlons 

Model 

Lamp: 

Type ............. inc.. ..... inc, HPS ....... f1 ......... fI ........ fl ........ 11. 

Number ............ 1.. ...... 1 ........... 1 ......... 1 ........ 1 ........ 1. 

Designation .......... 25 W TI0 150 W MV 70 or F24T12CWl F30T8lCW ... F 1 5T8lCW ... F6T5CW. 

clear. 150 W HPS. SHOII. 

Circuit design: 

Internal toluminaire ...... XP. ...... XP .......... XP ........ XP ....... XP ....... XP. 

Leadsto luminaire ....... XP. ...... XP .......... XP ........ XP ....... XP ....... XP. 

Guard standard ......... Yes ...... No .......... Yes ....... Yes. ...... Yes. ...... Yes. 

Optional guard available ..... NAp ...... No .......... NAp ....... NAp ...... NAp ...... NAP. 

Dimensions (with guard), in: 

Height ............. 3. ....... 6-112 ......... 3-112 ....... 3 ........ 3-112 ...... 3. 

Width ............. 5.. ...... 9.. ......... 4-112.. ..... 5 ........ 4-112 ...... 5. 

Length ............ 15-314 ..... 13-1 12 ........ 28-1 I2 ...... 49-1 I2 ..... 28-1 I2 ..... 15-314. 

Weight(withguard1 lb ..... 5. ....... '22, '53 ....... 10 ........ 20 ....... 10 ....... 5. 

Materials: 

Lens ............. Lexan ..... Tempered glass ... Lexan ...... Lexan ..... Lexan ..... Lexan. 

Housing ............ Steel. ..... Steel ......... Steel ....... Steel ...... Steel ...... Steel. 

Guard .............. .do. ..... NAp .......... .do ........ .do ....... .do ...... Do. 

Integral ballast .......... No. ...... No .......... No ........ Yes. ...... Yes. ...... Yes. 

Ballast: 

Solidstate ........... NAp ...... NAp ......... NAp ....... No ....... No ....... No. 

Core and coil ......... NAp ...... NAp ......... NAp ....... Yes. ...... Yes. ...... Yes. 

Input voltage ... V ac ... NAp ...... NAp ......... NAp ....... 120 ....... 120 ....... 120. 

Potted ............. NAp ...... NAp ......... NAp ....... No ....... No ....... No. 

Packing glands: 

Singleor dual ......... Dual ...... Single ........ Dual ....... Dual ...... Dual ...... Dual. 

Threaded or slip-fit ...... Threaded ... Threaded ....... Threaded ..... Threaded .... Threaded Threaded. .... Clamp or tubing ........ Tubing ..... Tubing ........ Tubing ...... Tubing ..... Tubing Tubing. ..... Connection integral to No., ..... No .......... No ........ No ....... No ....... No. 

luminaire. 

Pigtail integral to luminaire. ... No ....... No .......... No ........ No ....... No ....... No. 

Separate XP connector No ....... No .......... No ........ Yes ....... Yes, l5H. ... Yes, 6H. 

supplied. 

Lamp cartridge: 

Utilized ............ NAp ...... No .......... Yes ....... Yes. ...... Yes. ...... Yes. 

Connection type ........ NAp ...... NAp ......... Spade terminal .. Spadeterminal . Spadeterminal . Spade terminal. 

Primary application ..,...... MFE ...... MFE ......... MFE ....... Longwall .... MFE, 15; MFE, 6; 

longwall, 15H longwall, 6H. 

Acor dcmachine power. .... Both ...... Both ......... Both ....... ac ....... ac ....... ac. 

Figure .............. 8-3 ...... 8-4.. ........ 8-2.. ...... 8-3.. ..... 8-3.. ..... 8-3. 

CW Cool white. MFE Mine face equipment. :P Explosion-proof. 

inc Incandescent. MV Mercury vapor. Aluminum. 

fl Fluorescent. NAp Not applicable. Steel. 

HPS High-pressurization. SHO Super-high output. 
Figure B4.-McJunkln Corp. model 400-A and 400-5 lumlnaires. 

Table B-5.-Mlne Safety Appliances Co. system aiternatlves 

Ballasts 

XP ... 

Application or Stand- Solid Inte- Re- kmp hlpe Model Description 

IS ard state ~ral mote 

MFE, ac ..... XP 

MFE, dc ..... XP 

Longwall ..... XP 

HO fl ....... LX2401 None. 

HO R ....... LX2401 (I) 

HO fl ....... U2401 None. 

fl Fluorescent. IS Intrinsically safe. XP Explosion-proof. 

HO High output. MFE Mine face equipment. 

Resistors are used to dmp machine voltage to a level suitable for the solid-state inverter ballasts integral to the luminaire. The ballasts are protected from 

voltage spikes by a Zener diode. 

NOTE.-No entry in a ballast column indicates the category is not applicable 
Model U(2401 

Table 6-6.-Mlne Safety Appliances Co. lumlnalre speclflcatlons 

Model U(2401 

120 ac, 130 dc, 

300 dc. 

Yes. 

Lamp: 

Type ................. fl. 

Number ............... 1. 

Designation ............. F24T12ICWlHO. 

Circuit design: 

Internal to luminaire ......... XP. 

Leads to luminaire ......... XP. 

Guard standard ............ Yes. 

Dimensions (with guard), in: 

Height ............... 4-1 12. 

Width ................ 4-112. 

Length ................ 33. 

Weight (with guard) ...... Ib ... '24, 213. 

Materials: 

Lens ................. Polycarbonate. Housing ............... Steel, aluminum, 

malleable iron. 

Guard ................ Steel. 

Integral ballast ............. Yes. 

Ballast: 

Solid state .............. Yes. 

Core and coil ............ No. 

Dual. 

Threaded. 

Tubing. 

No. 

Ballast--Continued 

Input voltage ............. 

Potted ................ Packing glands: Single or dual ............ Threaded or slip-fit ......... Clamp or tubing ........... Connection integral to 

luminaire. 

Pigtail integral to 

luminaire. 

Separate XP connector 

supplied. 

Lamp cartridge: 

Utilized ................ Connection type ........... Primary application ........... 

Ac or dc machine power ........ Figure ................. 

No. 

CW Cool white. HO High output. XP Explosion-proof . Aluminum. 

fl Fluorescent. MFE Mine face equipment. ' Steel. 

Yes. 

Yes. 

Plug. 

MFE and longwall. 

Both. 

B-5. 

Table 6-7.-Mining Controls Inc. system alternatlves 

Ballasts 

XP 

A~~lication or Stand- Solid Inte- Re- Lamp type Model Description . . IS ard state gral mote 

MFE,ac ........ ..... XP inc. 21 322 None. 

MFE. ac ..... XP Tungsten-. NAP Do. 

MFE, .. ...... dc ..... XP do NAP Do. 

MFE, dc .. ...... ..... XP do NAP Do. 

IS Intrinsically safe. MFE Mine face equipment. XP Explosion-proof .' See figure 8-7. 

NOTE.-No entry in a ballast column indicates the category is not applicable. 

Table 6-8.-Mlnlng Controls Inc. lumlnalre speclflcatlons 

Lamp: 

Ty pe................. 

Number ............... Designation ............. Circuit design: 

Internal to luminaire ......... Leads to luminaire ......... Guard standard ............ Optional guard available ........ Dimensions, in: 

With guard: 

Height ............... Width ............... Length .............. Without guard: 

Height ............... Width ............... Length .............. Weight, Ib: 

With guard ............. Without guard ............ 

Model 2 1322 

inc. 

1. 

150 W. 

XP. 

XP. 

No. 

Yes. 

Materials: 

Lens ................. 

Housing ............... 

Guard ................ Integral ballast ............. Packing glands: 

Single or dual ............ Threaded or slip-fit ......... Clamp or tubing ........... Connection integral to luminaire. ... Pigtail integral to luminaire. ...... Separate XP connector supplied. ... Lamp cartridge: 

Utilized ............... Connection type .......... Primary application .......... Ac or dc machine power ....... Figure ................. 

Model 2 1322 

Tempered glass. 

Aluminum, brass, 

ductile iron. 

Steel. 

No. 

Dual. 

Threaded. 

Tubing. 

No. 

No. 

No. 

No. 

NAP. 

MFE and longwall. 

Both. 

B-6. 

inc Incandescent. XP Explosion-proof . Aluminum. 

MFE Mine face equipment. ' Standard. Brass. 

NAp Not applicable. Heavy duty. Ductile iron. 
Figure B-7.-Mining Controls Inc. tungsten-halogen luminaire. 
Table B-9.-National Mlne Sewlce Co. system alternatives 

Ballasts 

X P 

Application or Stand- Solid Inte- Re- Lamp type Model Description 

IS ard state gral mote 

MFE, ac ..... XP X X HOfl ...... 5401-001Z0111 None. 

5401 -000410103 

MFE,ac ..... XP X X Standard fl ... 5401 -020Z0293 Do. 

5402-0995 

MFE, dc ..... X P X X HOfl ...... 5401-0012/0111 (') 

540 1 -000410 1 30 

Longwall ..... XP X X Standard fl ... 5401 -020Z0293 None. 

5402-0995 

fl Fluorescent. IS Intrinsically safe. XP Explosion-proof. 

HO High output. MFE Mine face equipment. ' Dc power supplies use remotely mounted inverter ballasts to drive the lamp. A switching regulator unit called a "preregulator 120 dc" accepts machine 

power over a 200- to 600-V dc range and reduces or regulates it to 120 V dc for the inverter ballasts. The preregulator also has provision for transient protection. 

NOTE.-No entry in a ballast column indicates the category is not applicable. 

Table B-10.-National Mlne Sewlce Co. lumlnalre speclflcatlons 

Model 

'5401 -001 2, '540 1 -0004, '5401-0202, 

'5401 -01 1 1 25401-0103 '540 1 -0293 5402-0995 

Lamp: 

Type .................. fl ............ Number ................. 1 ........... Designation ............... F24T1 ZCWIHO .... Circuit design: 

Internal to luminaire .......... XP ........... Leads to luminaire ........... XP ........... Guard standard .............. No ........... Optional guard available ......... Yes .......... Dimensions, in: 

With guard: 

Height ................ 4-112 ......... Width ................. 5-318 ......... Length ................ 29-314 ......... Without guard: 

Height ................ 3-112 ......... Width.. ............... 5 ........... Length ................ 29-314 ......... Weight, Ib: 

With guard ............... ' 16-112, '18-112. .... Without guard ............. 10 ........... Materials: 

Lens .................. Polycarbonate ..... Housing ................ Aluminum ....... Guard .................. Steel weldment .... Integral ballast .............. No ........... Ballast: 

Solid state ............... NAp .......... Core and coil .............. NAp .......... Input voltage ......... V ac .. NAp .......... Potted ................. NAp .......... Packing glands: 

Single or dual ............. Single ......... Threaded or slip-fit ........... Threaded ....... Clamp or tubing ............ Clamp ......... Connection integral to luminaire ..... No ........... Pigtail integral to luminaire ........ No ........... Separate XP connector supplied ..... No ........... Lamp cartridge: 

Utilized ................. Yes .......... Connection type ............ Wirenut ........ Primary application ...-......... MFE .......... Ac or dc machine power ......... Both .......... Figure.. ................. 8-8 .......... 

CW Cool white. HO High output. 

fl Fluorescent. NAp Not applicable. 

fl. 

2. 

None. 

XP ........... XP ........... No ........... Yes .......... 

XP ........... XP ........... No ........... Yes .......... XP. 

XP. 

No. 

Yes. 

Polycarbonate ..... Aluminum ....... Steel weldment .... No ........... Polycarbonate ..... Aluminum ........ Steel weldment .... Yes .......... Tempered glass. 

Ductile cast iron. 

Steel-polycarbonate. 

Yes. 

NAp .......... NAp .......... NAp .......... NAp .......... Yes .......... No ........... 117 .......... Yes .......... No. 

Yes. 

117. 

Yes. 

Single ......... Threaded ....... Clamp ......... No ........... No ........... No ........... 

Single ......... Threaded ....... Clamp ......... No ........... No ........... Yes .......... Dual. 

Threaded . 

Tubing. 

No. 

No. 

No. 

Yes .......... Wirenut ........ MFE .......... Both .......... 8-8 .......... 

XP Explosion-proof. 

'Aluminum. 

Yes .......... Wirenut ........ MFE and longwall ... ac ........... B-9 .......... 

'Brass. 

'Bronze. 

No. 

NAP. 

MFE and longwall. 

ac. 

B-10. 
Figure 6-10.-National Mine Service Co. model 5402-0995 lurninaire. 
Table B-1 1 .-Ocenco Inc. system alternatives 

XP Ballasts 

Application or Stand- Solid Inte- Re- Lamp We Model Description, 

IS ard state gral mote 

MFE, ac ........... IS' 

MFE, ac ........... XP 

MFE, dc ........... IS' 

MFE. dc ........... XP 

MFE, diesel ......... XP 

Longwall ........... IS' 

Standard fl .......... 1513M 

Inc .............. AR-150 

Standard fl .......... 

inc .............. 

Standard fl ........... 

Standard fl .......... 

None. 

None. 

(') 

(4) 

None. 

-- - -- - -- - - 

fl Fluorescent. IS Intrinsically safe. XP Explosion-proof. 

inc Incandescent. MFE Mine face equipment. 

'Cabling only, luminaries are explosion-proof. 

'Power supply transforms machine power to 25 to 30 V ac and subsequently conditions this power to 13 to 16 V dc by a solid-state filter-rectifier unit. This power 

is distributed through 2 solid-state control circuits (channels), which provide intrinsically safe 12-V dc power to integral, inverter-ballasted luminaries. Each control 

channel incorporates redundant circuits to limit output power to 12 V per 100 A, including an electronic current limiter, overvoltage crowbar circuit, and output fusing. 

The current limit restricts the number of luminaires that can be connected to each distribution channel. 

3Power supply utilizes the same control circuitry as ac power supply. Machine power is inverted to high-frequency ac power, transformed to 12 to 16 V ac, then 

inverted to dc power for the control channels. A transient suppressor unit protects the power-conditioning system. Resistors are installed to maintain system input 

voltage at the lower end of the design range for the system and the transient supressor is designed to suppress voltage peaks above the upper end of the voltage 

design range. 

AC power supply is utilized with power obtained from a hydraulically driven alternator with provision for flow control to maintain constant voltage for variation in 

engine rotational speed. 

NOTE:-No entry in a ballast column indicates the category is not applicable. 

Table B-12.-Ocenco Inc. luminalre specifications 

Model 

30M 1513M 16M AR-150 

Lamp: 

Type .................. fl ............ fl ............ fI ............ inc. 

Number ................. 1 ........... 1 ........... 2 ........... 1. 

Designation ............... F30T12 ........ F15T12 ........ F8T5 ......... 150 W A-23 

or PS-25. 

Circuit design: 

Internal to luminaire .......... XP . ; ......... XP ........... XP ........... XP 

Leads to luminatre ........... IS ........... IS ........... IS ........... XP. 

Guardstandard .............. No ........... No ........... No ........... No. 

Optional guard available ......... Yes .......... Yes .......... Yes .......... Special order. 

Dimensions, in: 

With guard: 

Height ................ 5 ........... 5 ........... 5 ........... NAP. 

Width ................. 6 ........... 6 ........... 6 ........... NAP. 

Length ................ 40 ........... 28 ........... 16 ........... NAP. 

Without guard: 

Height ................ 3 ........... 3 ........... 3 ........... 6. 

Width ................. 3 ........... 3 ........... 3 ........... 9-112. 

Length ................ 40 ........... 28 ........... 14 ........... 10-112. 

Weight, Ib: 

Withguard ............... 33 ........... 27 ........... 9 ........... NAP. 

Withoutguard ............. 8 ........... 7 ........... 4 ........... 40. 

Materials: 

Lens .................. Polycarbonate. Polycarbonate. Polycarbonate. Tempered glass 

Housing .................. do .......... do .......... do ....... Steel. 

Guard .................. Steel ......... Steel ......... Steel ......... NAP. 

Integral ballast .............. Yes .......... Yes .......... Yes .......... No. 

Ballast: 

Sol~dstate ............... Yes .......... Yes .......... Yes .......... NAP. 

Coreandcoil .............. No ........... No ........... No ........... NAP. 

Input voltage ...... V dc .. 12 ........... 12 ........... 12 ........... NAP. 

Potted ................. Yes .......... Yes .......... No ........... NAP. 

Packing glands: 

Singleordual ............. NAp .......... NAp .......... NAp .......... Dual. 

Threaded or sl~p-fit ........... NAp .......... NAp .......... NAp .......... Threaded. 

Clamp or tubing ............ NAp .......... NAp .......... NAp .......... Tubing. 

Connection integral to lumina~re. ..... No ........... No ........... No ........... No. 

Pigtail integral to luminaire. ........ Yes .......... Yes .......... Yes .......... No. 

Separate XP connector supplied .. , .. No ........... No ........... No ........... No. 

Lamp cartridge: 

Util~zed ................. No ........... No ........... Yes .......... No. 

Connection type ............ NAp .......... NAp .......... Plug .......... NAP. 

Primary application ............ MFE and longwall. .. MFE and longwall. .. MFE and longwall. .. MFE. 

Ac or dc machine power ......... Both .......... Both .......... Both .......... Both. 

Figure ................... 8-11 .......... B-11 .......... 8-12 .......... 8-13, 

fl Fluorescent. 

inc Incandescent 

IS Intrinsically safe 

NAp Not applicable. 
Figure B-12.-Ocenco Inc. model 16M luminaire. 

Figure B-13.--0cenco Inc. model AR-150 luminaire. 
XP Ballasts 

Application or Lamp type Model Description 

IS Standard Solid state Integral Remote 

MFE, ac ....... XP X X VHO fl ....... i : ::::::: I None. 

MFE, ac ....... XP X X HPS ........ 14812D Do. 

MFE, ac ....... XP inc ......... 14812D Do. 

MFE, dc ....... XP inc ......... 14812D Do 

fl Fluorescent. IS Intrinsically safe. 

HPS High-pressure sodium. MFE Mine face equipment 

inc Incandescent. VHO Very-high output. 

NOTE.-No entry in a ballast column indicates the category is not applicable. 

Figure B-14.-Service Machine Co. model D513 luminaire. 
Figure B-15.-West Virginia Armature Co. model 184W24 and 18400-18 luminaires. 

Flgure B-16.-West Virglnla Armature Co. model 1481 2D Iuminaire. 
LONGWALL ILLUMINATION SYSTEMS 

Important descriptive information is presented below 

for the various illumination systems approved for use on 

longwalls. Figures B-17 and B-18 show a "typical" layout 

and interconnections for each of the manufacturer's systems. As indicated in the figures, all systems utilize a 

power center (typically a transformer with overcurrent, 

short circuit, and ground fault protection, along with 

ground monitoring) to provide 120-V, three-phase ac power 

for distribution along the face. The 120-V, three-phase 

power is connected to intermediate power-conditioning or 

distribution units that subsequently deliver power to the 

luminaires. As outlined in chapter 4, system interconnection is important on longwall lighting systems. With 

respect to the power supply or distribution box, there are 

three basic categories utilized on these systems, as follows: 

1. Separate cable to each luminaire with intermediate 

connector(s). 

2. Cable is feed-through connected to string of dualglanded luminaires. Intermediate connectors utilized. 

3. Junction boxes are installed on the feeder line for 

each luminaire. A cable with line-installed connector runs 

from each junction box to each luminaire. 

A functional description of four of the manufacturer's 

systems follows: 

Ocenco (fig. B-17).-The main power is transformed, 

rectified, and filtered to 13 to 16 V dc, which is fed to each 

of two identical control circuits or channels that provide 

intrinsically safe 12-V dc power to the luminaires. Each 

channel limits power output to 12 V at 10 A and insures 

that intrinsically safe conditions are maintained in the 

event of failure. The current limit restricts the number of 

lamps that may be driven to 10 integrally ballasted model 

1513M or 8 model 30 luminaires per power conditioning 

unit. Type 3 interconnection is utilized between the power 

supplies and luminaires. 

Ocenco Face Support Line 

Service Machine Face Support Line I 

Legend 

X/P Connector 0 Non-X/P J-Box 

System Power Center 0 Non-x/P Connector Integrally Ballasted 

Fluorescent Luminaire 

[XI Power Conditioning Unit = 120v, 34 Line 

- o Fluorescent Luminaire I. S. Line 

Flgure B-17.-lnstallatlon and wlrlng schematlcs for lntrlnslcally safe fluorescent systems on a typlcal coal mlne longwall face. 
Mdunkin wg. B-IS).-To maintain load balance, distribution units are connected across alternate phases of 

the main feed-through line. Two 120-V, single-phase feeder 

lines originate at the distribution box and provide power 

for up to 10 feed-through model integrally ballasted 100130 

luminaires per line, or a maximum of 20 lamps per distribution unit. An intrinsically safe interlock unit is provided for connector deadfacing and ground-fault protection. 

To offset line losses, an autotransformer voltage boost is 

used in distribution units distant from the system power 

center. Type 2 interconnection is utilized between the distribution boxes and luminaires. 

Mine Safety Appliances Cfig. B -1 8).-Two branch feed 

lines originate at the distribution unit by connecting across 

phases of the main feed-through and provide 120-V, singlephase power to a maximum of 12 feed-through model 

LX2401 luminaires per line for a maximum of 24 per distribution unit. To maintain load balance, the branch phase 

connections alternate between phases along the face. A 

different unit with a pilot system is provided for meeting 

the Commonwealth of Pennsylvania deadfacing requirements. Type 2 interconnection is utilized between the distribution boxes and luminaires. 

National Mine Service (fig. B-IS).-Distribution units 

are connected across alternate phases of the main feedthrough line. Five feeder lines originate at each distribution box with each line supplying 120 V, single-phase power 

to a single luminaire for a total of five luminaires per 

distribution unit. Three different distribution units are 

available, providing options concerning pilot circuit configurations. One unit provides no provision for a pilot circuit and basically consists of a terminal board in an 

explosion-proof enclosure. A second unit provides a pilot 

circuit to each luminaire with a single relay at the distribution box. The third option provides a separate pilot circuit and relay for each luminaire, enabling decoupling of 

one luminaire while maintaining the operation of the 

remaining luminaires on the distribution unit. Type 1 

interconnection is utilized between the distribution boxes 

and luminaires. 

Mc Junkin Face Support Line 

Leg A2 .-A Leg B1 - 

A I 

MSA 

B 

Face Support Line 

Leg A2 --A Leg B2 

National 

Legend Fl X/P Connector r( Dual-glanded, Integrally Ballasted 

system power center 

= Fluorescent Luminaire 120v, 3@ Line n U Single-glanded, Integrally Ballasted 

Power Distribution Box - 120v, 10 Line Fluorescent Luminaire 

Flgure B-18.-lnstallatlon and wlrlng schematlcsfor explosion-proof fluorescent systems on a typlcal coal mlne longwall face.