Evaluation of Visual Performance when Using 

Incandescent, Fluorescent, and LED Machine Lights 

in Mesopic Conditions 

M.A. Reyes 

S. Gallagher, Ph.D. 

J. Sammarco, Ph.D.
 

National Institute for Occupational Safety and Health
 

Abstract - This experiment investigated the effects of 

different machine mounted area lighting technologies on 

visual performance. The primary objective was to conduct a 

comparative evaluation of the lighting technologies based on 

the visual performance of thirty-six human subjects in a 

simulated underground mine environment. Incandescent 

(Incand), fluorescent (Fluor), and light-emitting diode (LED) 

technologies were used to create four lighting combinations. 

Visual performance was quantified for the detection of 

movement in the peripheral field of view and the 

identification of ground hazards. Measurements were made 

of the speed [response time measured in milliseconds (ms)], 

the accuracy (the number of targets and objects missed), and 

the subjective discomfort rating of the glare experienced for 

each lighting combination. A secondary objective explored 

the effects of aging on visual performance. The results 

indicate that lighting combinations which consisted of LED 

area lights significantly improved visual performance for the 

detection of hazards found in the peripheral field of view, as 

well as those found on the ground. They furthermore, 

indicate that age plays a significant role in visual 

performance. 

I. INTRODUCTION 

The Illuminating Engineering Society of North America 

reports that the coal mine face is the most difficult lighting 

environment in the world [1]. Given the limitations of 

illumination produced by a miner’s cap lamp, identifying 

potential hazards in a working area can often prove extremely 

difficult. Reduced levels of light around mining machinery can 

impair a miner’s ability to judge the speed or direction of a 

machine. Coupled with the fact that machines such as continuous 

miners have deceptively quick rates of travel, a miner is exposed 

to extreme conditions in which illumination plays a critical role 

in their ability to perform their jobs safely. According to MSHA, 

a total of 144 fatal accidents, attributed to moving mining 

machinery, were reported in underground coal mines from 2001 

to 2007. Twenty-five of those were attributed to accidents that 

involved continuous miners. MSHA also reports that 11% of losttime injuries reported from 2002 to 2006 were attributed to those 

caused by machinery. In addition to pinning and striking 

accidents, the 2nd highest cause of lost-time injuries is slip or fall 

of a person. MSHA records indicate that slip or fall of person 

lost-time injuries account for 17.4% of the reported cases from 

2002 to 2006. Increasing light levels around the perimeter of 

machines may potentially improve visual recognition of these 

hazards and, consequently, reduce the number of injuries and 

fatalities in the mining industry. However, when increasing light 

levels, glare becomes a significant aspect to consider as it may 

negatively affect a miner’s vision and ability to detect hazards. 

Accordingly, mine illumination systems must be properly 

designed to limit the effects of glare in order to efficiently 

illuminate an area and improve safety. 

The main objective of the NIOSH research outlined in this 

paper was to explore the existence of visual performance 

improvements through the implementation of different machine 

mounted, lighting systems. The visual performance of thirty-six 

human subjects was evaluated and compared for four different 

lighting conditions that consisted of incandescent lights alone, a 

combination of incandescent and LED lights, fluorescent lights 

alone, and a combination of fluorescent and LED lights. A 

secondary objective was to determine the role of aging on visual 

performance and the benefits of using one lighting mode over 

another. Physiological changes that occur as a person age include 

reduced pupil size, cloudier lenses, and reduction in the amount 

of photoreceptors that play a dominant role in low level lighting, 

all have a significant impact on visual performance as light levels 

decrease. Because the physiology of the human eye is such that 

visual performance degrades as a person ages, implementation of 

lighting systems that can account for that degradation is critical. 

II. METHODOLOGY 

A. Overview 

Pursuant to the ethics guidelines established by the human 

subject review board, subjects were first informed about their 

rights and were given a detailed description of what each 

experiment would consist of. Subjects were given 15 minutes to 

allow for their vision to adapt to the darkened environment in 

which the experiment was going to be administered. Each subject 

was seated on the observation station (Fig. 1) before proper 

adjustments were made to ensure each subject had the same eye 

height from the floor. Ear protection was then adjusted, as 

needed, depending on the experiment being administered. Eye 

protection was provided to each subject to further simulate proper 

personal protective equipment worn in underground mine 

environments. Various measures were implemented in each study 

to prevent learned behavior from impacting validity of results. 

This was done by the introduction of varied sequences and 

counterbalancing of tests that varied between subjects. Each 

study consisted of a practice session to allow the subjects to 

familiarize themselves with the different control systems and 

procedures. After the completion of the practice session, each 

subject was asked if there were any questions and they were 
addressed prior to commencing the actual test. 

This experiment consisted of three different studies designed 

to evaluate machine mounted, area lighting technologies. The 

first study was designed to quantify a subject’s visual 

performance in detecting movement in their peripheral field of 

view. This is important for avoiding pinning and striking 

accidents. The second study was designed to quantify a subject’s 

visual performance in detecting trip hazards located in their 

forward field of view. The third study was designed to obtain a 

subjective discomfort rating of the light sources used, as observed 

from two different points of view. The reaction times in detecting 

each hazard and the accuracy in which targets and objects were 

identified was recorded and documented as outlined in this paper. 

B.	 Setting 

1) Human Performance Research Mine: The experiment 

was conducted at the NIOSH Pittsburgh Research Laboratory in 

the Human Performance Research Mine (HPRM). The HPRM 

measures 21.25 meters (m) by 8.45 m and has a roof height of 

4.67 meters. The dimensions were selected to provide space 

consideration for large pieces of mining machinery and the data 

acquisition and control (DAC) systems required to conduct 

ongoing research efforts at NIOSH. The interior of the facility 

was painted a flat black color to closely match the color and 

reflectivity found in an underground mine setting. Proper labeling 

of exits and escape ways were among the safety precautions 

implemented to create an environment suitable for human subject 

testing. 

2) Observation Station: NIOSH personnel designed and 

constructed the observation station, depicted in Fig. 1, to ensure 

each subject was tested from a fixed position.

Figure 1. Observation Station 

 This was 

developed in efforts to create a method of observation that was 

consistent for each of the thirty-six subjects tested, thus 

eliminating the possibility of confounding data due to variations 

in the subjects’ point of view. This also allowed subjects to 

complete multiple studies, while remaining seated, to prevent 

being exposed to unnecessary risks in having to walk through a 

darkened facility to go from one study to the next. 

Electronic actuators were installed to raise and lower the seat, as 

much as twenty centimeters (cm), for the purpose of adjusting 

each subject’s eye to a height of 165.1 cm. This height is 

equivalent to the 50th percentile standing male [2]. 

Subjects were required to wear a, rigidly mounted, hardhat 

to accommodate for variations in torso heights and to maintain a 

consistent head and cap lamp position. The helmet was equipped 

with ear protection that each subject was required to wear during 

testing. The observation station and all of its components were 

painted flat black to minimize any distractions or reflection of 

any light during the testing phase. 

C.	 Light Sources 

Area lights were installed on a continuous miner and were 

used to create four different lighting modes. These lighting 

modes were made up of a single light source or a combination of 

two lighting technologies that consisted of incandescent, 

fluorescent, or LED lights. While testing occurred on one side of 

the machine, lights were installed on both sides to closely 

simulate normal operation. The following four modes were used 

in each of the three studies: 

1) Incandescent and LED machine lights: This lighting 

mode consisted of the incandescent area lights commonly 

installed on continuous miners with the addition of LED strips 

installed around the perimeter of the machine. The locations of 

these LED area lights are depicted by the rectangular bars on 

both sides and the rear of the continuous miner as shown in Fig 2. 

Figure 2. Light source locations 

2) Incandescent machine lights alone: Incandescent 

lighting mode consisted of the area lights commonly installed on 

continuous miners. The location of these lights is depicted by the 

rectangular shapes around the middle of the machine in Fig 2. 

3) Fluorescent machine lights alone: Fluorescent lighting 

mode consisted of area lights installed on some continuous 

miners. These lights consist of two fluorescent bulbs encased in a 

hardened steel frame. The location of these lights is depicted by 

the octagonal shapes around the middle of the machine in Fig 2. 

4) Fluorescent and LED machine lights: This lighting 

mode consisted of the Fluorescent area lights previously 

mentioned for lighting mode 3 with the addition of the LED 

strips installed around the perimeter of the machine. The 

locations of these LED area lights are depicted by the rectangular 

bars on both sides and the rear of the continuous miner as shown 

in Fig 2. 
D.	 Subjects 

A total of thirty-six subjects were recruited from NIOSH 

personnel. Twenty-six males and ten females were selected based 

on their vision screening examination results performed by the 

NIOSH medical staff. Each subject underwent extensive 

screening for distance visual acuity, contrast sensitivity, color 

vision deficiency, and peripheral vision capabilities. Because one 

of the objectives of this experiment was to explore the visual 

performance, with respect to aging, three age groups were 

designated to accommodate age groups representative of the 

mining industry. Twelve subjects were recruited for each of the 

age groups: group A was for subjects ages 18 to 25, group B was 

for subjects ages 40 to 50, and group C was for subjects 51 and 

above. The average age of the subjects tested was 42 years which 

was closely representative of the average age for a miner in the 

United States, which is approximately 43 years of age [3]. 

III.	 EXPERIMENT 

A.	 Peripheral Motion Detection Study 

1) Experimental Layout: The experimental layout for this 

study is depicted in Fig 3. 

Figure 3. Experimental layout for Study 1: Peripheral Motion 

Detection. (Figure not to scale.) 

The system used for this study 

consisted of four major components operated by a data 

acquisition and control system. The main components of the 

DAC were a microcontroller, a flip-dot matrix, three circular 

targets connected to dc-powered motors, and a mouse. The 

system’s input was controlled by each subject in the form of an 

electrical signal sent to the microcontroller when the mouse 

button was depressed. A depressed mouse button initiated the test 

sequence. The microcontroller was programmed with software 

developed to activate the flip-dot matrix, as well as control the 

sequence and duration of the circular target’s rotation. This flipdot matrix was used as a visual target to draw the subject’s focus 

and fix their eye orientation to the center. This panel was located 

in the subject’s forward field of view, at zero degrees, to ensure 

that each subject used their peripheral vision to detect the motion 

of the circular targets as opposed to using direct line of sight. 

The control system accessed one of four different software 

versions compiled to vary the sequence in which the three 

circular targets were activated. The targets measured a total of 

120 millimeters (mm) in diameter and were painted white with a 

single black line across the center. The circular targets, 

positioned at -50°, -40°, and 20° off-axis, were rotated by dc 

motors mounted on tripods. Because the dc motors emitted noise 

that could have confounded the results, it was necessary to mask 

the noise by using ear protection and playing sounds of mining 

equipment in operation in the background. This eliminated a 

subject’s ability to use the auditory cues to identify which target 

was activated. The data acquisition process consisted of a timestamped spreadsheet macro, which recorded all the pertinent data 

such as the lighting mode used, the software version used, the 

sequence in which the targets were rotated, and the subject’s 

reaction time in detecting movement. 

2) Illuminance Measurements: Illuminance measurements 

were recorded for the three circular targets as illuminated by each 

of the four lighting modes. The lights were left on for ten minutes 

prior to taking light measurements to allow each light source to 

stabilize. For each target, three spot measurements were made 

using the Konica Minolta T-10 Illuminance Meter. The meter’s 

sensor was attached flat against the circular target in each of 

three positions: top, middle, and bottom. The average 

illuminance measurements are recorded in Table 1. 

TABLE I. AVERAGE TARGET ILLUMINANCE IN LUX. 

Target Position 

(degrees) 

Incandescent & LED Incandescent Fluorescent Fluorescent & LED 

20 2.89 2.62 2.76 3.00 

-40 1.96 1.50 2.11 2.58 

-50 2.30 1.26 2.57 3.69 

3) Procedures: This study consisted of five different 

trials, one of which was a practice session. Subjects were given 

instruction on the operations of the test apparatus before the 

practice session was initiated. The subjects were instructed to 

keep their eyes focused on the flip-dot matrix target in front of 

them during the duration of the study. They were handed a 

computer mouse and were briefed on its operation. Holding 

down the left mouse button initiated the test. The subjects were 

to release the depressed mouse button to indicate when they saw 

a circular target rotate. Reaction time was measured as the time 

elapsed from the time the circular target was initially activated to 

the time the subject released the depressed mouse button. A 

reaction time of 4.2 seconds or above would be recorded as a 

missed target. The remaining four trials were the actual test 

which consisted of the variation of the four lighting mode. 
4) Result: Peripheral motion data was examined using a 

split-split plot design, with subjects as the replication factor, 

AGEGROUP as the main plot factor, LIGHTING was the split 

plot factor and ANGLE was the split-split plot factor. Initial 

analysis of variance of the time to detection of the stimulus was 

performed but the plot of residuals versus fitted values were 

found to have a non-linear trend, thus the analysis reported 

employed a natural log transformation of the original time data. 

This transformation resulted in greatly improved behavior of the 

residuals. Alpha levels were set at 0.05. 

Analysis using the log transformed data demonstrated 

significant main effects due to AGEGROUP (F 2,22 = 5.19, p < 

0.05) and ANGLE (F 2,264 = 224.19, p < 0.001). None of the other 

factors were found to be statistically significant; however, a trend 

was observed for both LIGHTING (F 3,99 = 2.20, p = 0.09) and 

the AGE*LIGHTING interaction (F 6,99 = 1.98, p = 0.08). Fig. 4 

displays the effect of AGEGROUP on detection time using 

retransformed (i.e., original scale) data.

Figure 4. Effects of age group on time. 

 The Dunn-Sidak multiple 

comparison test for the AGEGROUP effect indicated that only 

the Young and Older Age Groups differed significantly from one 

another (p < 0.05). The same post hoc test was used for the 

ANGLE effect and results showed that detection time was 

significantly different for each angle studied, as depicted by Fig. 

5. 

Figure 5. Stimulus detection by target angle. 

B.	 Trip & Fall Study 

1) Experimental Layout: The general layout for this study 

is depicted by Fig. 6. 

Figure 6. Experimental layout for Study 2: Trip and Fall Hazard 

Detection. (Figure not to scale.) 

A motorized curtain was installed .91 m in 

front of the observation station to prevent the subject from 

gaining an advantage of knowing the location of the objects while 

the researcher set the different pattern locations on the ground. 

Two location distances were established for this experiment: 

near-field 1.8288 meters (m), about the distance of two strides for 

the average male, and far-field 2.7432 m which is a more 

common visual attention location for a walking person. Each 

object was 6.4 cm long with a 3.3 cm outer diameter. The objects 

were painted a dark color such that they would have a very low 

contrast (-0.11 to 0.09) and a reflectivity very similar to that of 

objects found in an underground mining environment. Because 

the objects were hard to detect, NIOSH personnel designed the 

objects to house battery-powered infrared LEDs to illuminate 

themselves when observed through a video camera’s night mode 

but still remain difficult to detect by the subject’s eyes. 

The electrically powered curtain was connected to a timer 

circuit programmed to open and shut the curtain after ten 

seconds. The ten second span was visually displayed using a red 

LED, for curtain closed, and a green LED, for curtain opened. 

Each sequence was video recorded and post processed to 

determine the amount of time it took to find each object. The 

timing was calculated as the time elapsed from the instant the 

timer circuit switched from a red LED to a green LED, to the 

instant the subject identified and pointed at each target with a 

laser pointer. A total of 11 object pattern location combinations 

were used in which the number of objects varied from two to 

four and the locations of the objects varied from near field, to far 

field, to a combination of both. 

2) Illuminance Measurements: Light intensity 

measurements were recorded for each of the six possible object 

locations as illuminated by each of the four lighting modes. The 

lights were left on for ten minutes prior to taking light 

measurements to allow each light source to stabilize. The 

intensity measurements were made using the Konica Minolta T10 Illuminance Meter. A single spot check was performed on 

each object by placing the meter’s sensor flat against the cylinder 

while facing the observation station. The average illuminance 

measurements are recorded in Table 2. 
TABLE II. TRIP AND FALL OBJECT ILLUMINANCES IN LUX 

Incandescent & LED Incandescent Fluorescent Fluorescent & LED 

Object 1 2.93 0.87 0.85 2.41 

Object 2 4.81 1.04 1.12 5.14 

Object 3 5.76 0.86 0.94 5.82 

Object 4 1.72 0.84 0.88 1.59 

Object 5 1.93 0.87 1.04 2.03 

Object 6 1.6 0.75 0.96 1.78 

3) Procedures: The procedure was to close the black, 

electrically powered, curtain and arrange objects according to the 

corresponding object patterns selected for each subject. The 

subjects were instructed to point at each object using a laser 

pointer and count it, out loud. When the subject was ready, the 

curtain was opened. A video camera was pointed at the ground 

which included a shot of the timer circuit. The purpose for this 

positioning was to identify the instant the timer circuit started, 

signified by the illumination of a green LED, to the instant the 

subject identified and pointed at a particular object on the ground. 

Two researchers determined an object was detected the instant 

the subject pointed the laser-pointer at the target and confirmed it 

audibly by counting. The curtain automatically closed after ten 

seconds and the next object pattern combination was prepared. 

Each lighting mode trial consisted of four different object 

patterns. The time to find each object and the time to complete all 

four trials for a given lighting condition was recorded. NIOSH 

personnel used video editing software to identify specific frames 

in which the subjects identified the objects and the corresponding 

time stamps associated with each object. 

4) Results: Independent variables for this experiment 

consisted of AGEGROUP (3 levels) and LIGHTING conditions 

(4 levels). The three levels of AGEGROUP were Young (ages 18 

to 25), Middle-Age (ages 40 to 50), and Older (ages 51 and 

older). Twelve subjects were recruited for each age group for a 

total of 36 subjects. The four lighting conditions were: (1) 

incandescent and LED machine lights, (2) incandescent machine 

lights alone, (3) fluorescent machine lights alone, and (4) 

fluorescent and LED machine lights. In addition, the subject wore 

a hardhat fitted with an incandescent cap lamp for all trials. The 

dependent variable was the total time (in seconds) it took for the 

subject to locate all objects on the floor in front of them. 

A split-plot experimental design was used to analyze the 

data. Subjects were treated as the replication (whole-plot) 

variable, with AGEGROUP as the whole-plot factor and 

LIGHTING (randomized on a within subjects basis) constituted 

the split-plot factor. Alpha levels were set at 0.05. 

Detection time of the floor objects was found to be 

significantly affected by the main effects of both AGEGROUP 

and LIGHTING. The interaction of AGEGROUP and 

LIGHTING was not significant (F 6, 99 = 0.54, p > 0.05). The 

sections below provide additional detail regarding the significant 

main effects. 

a) Age Group: Fig. 7 illustrates the influence of 

AGEGROUP on the time required to locate the floor objects. 

20 

15 

Young Middle Older 

Time (s) 10 

5 

0 

Age Group 

Figure 7. Effects of age group on time. 

Age 

Group was a significant factor in the ANOVA (F 2,22 = 3.48, p < 

0.05). A post hoc Dunn-Sidak pairwise comparison test indicated 

a significant difference between the Young age group and the two 

older age groups in terms of the time taken to detect objects, with 

younger subjects detecting objects approximately 3 seconds 

faster than the older age groups on average. No differences in 

detection times were present between the Middle age and Older 

age groups (p > 0.05). 

b) Lighting Conditions: Differences in LIGHTING also 

influenced the time to detect floor objects (F 3,99 = 6.92, p < 
0.001). Fig. 8 provides the detection time of the floor objects 

under each of the four lighting conditions.

Figure 8. Effects of lighting mode on time. 

 Dunn-Sidak post hoc 

analysis indicated that the two lighting conditions that consisted 

of LED lighting as the auxiliary source (the incandescent and 

LED and the fluorescent and LED conditions) resulted in 

detection times that were significantly faster (by approximately 

one second) than times achieved with the other two lighting 

modes (incandescent machine lights and fluorescent lights alone). 

There was no significant difference in detection time between 

these pairs of lighting conditions (p > 0.05) 

C. Discomfort Glare Study 

1) Experimental Layout: The experimental layout for the 

glare experiment is depicted in Fig. 9.

Figure 9. Experimental layout for Study 3: Discomfort glare. 

(Figure not to scale.) 

 The De Boers scale was 

used to obtain a subjective rating on the degree of discomfort 

experienced by subjects when exposed to the glare produced by 

each lighting mode. The De Boer’s scale is a 9-point subjective 

scale where a rating of 1 was considered “unbearable” and a 

rating of 9 considered “just noticeable”. This scale was printed 

and mounted onto the machine where the subject would be asked 

to focus their attention to. Two positions were selected for this 

study based on the positions that a continuous miner operator 

would generally stand during normal operations. Position #1 was 

towards the rear corner of the machine at a distance of 1.2192 m. 

Position #2 was located diagonally of the rear corner of the 

machine at a distance of 2.7262 m. 

2) Procedures: The subjects were instructed to stand at 

Position #1 which was notably marked to ensure that each subject 

had the same point of view. They were warned not to look 

directly at the light sources to prevent impairing their vision prior 

to starting the study. They were instead instructed to look directly 

at the De Boer scale where the ratings were listed. Each of the 

lighting modes was then turned on, giving ample time for the 

light sources to stabilize prior to asking the subjects to rate the 

discomfort glare experienced. After going through the four 

different lighting modes, the subjects were then walked to 

Position #2 where the process was repeated. NIOSH personnel 

noted the rating and recorded any comments made. 

3) Results: Subjective discomfort glare ratings were 

obtained using the De Boer scale (reference). A split-split plot 

experimental design was again employed, using subjects as the 

replication factor, AGEGROUP as the main plot factor, 

LIGHTING was the split plot factor and POSITION was the 

split-split plot factor. It was assumed for the purposes of the 

analysis that the De Boer rating values represented equal 

gradations on the scale [4]. The interval difference between two, 

discomfort glare, ordinal ranks was considered to be of the same 

order of magnitude. Accordingly, the use of parametric 

techniques to perform the analysis can be employed [5]. Alpha 

levels were set at 0.05. 

The ANOVA indicated the presence of an interaction 

between LIGHTING and POSITION (F3,132 = 22.19, p < 0.001). 

This interaction is depicted in Fig. 10 below. 

Figure 10. Glare ratings by lighting and position. 

As can be seen from 

this figure, glare ratings were higher for the incandescent lighting 

condition when positioned behind the machine, while glare rating 

for lighting conditions involving fluorescent lights were higher 

when position next to the machine. Fluorescent lighting 

conditions were generally associated with lower ratings of glare 

than incandescent conditions, and conditions using LEDs tended 

to have slightly greater glare ratings. 

VI. DISCUSSION 

Overall, the results indicate that age played a significant 

factor in visual performance as the younger age group produced 

average detection times that were as much as 27% and 18% faster 

than the older age group for the peripheral motion and tripping 

hazard studies, respectively. The results for both studies further 

indicated that lighting conditions also played a significant factor 

in visual performance. The lighting condition which consisted of 

both fluorescent and LED lights resulted in the fastest detection 

times for the peripheral motion study where the average detection 
times were between 12% and 14% faster than the other lighting 

conditions. The combination of fluorescent and LED lights 

provides more of the shorter wavelengths of visible light than any 

of the other lighting conditions. Prior NIOSH research indicated 

that lighting characterized by having more of the short 

wavelengths of visible light improved visual performance for 

peripheral motion detection (Sammarco, J. et al., 2008). This 

combination also provided the greatest average target 

illumination (Table 1). Thus, the superior peripheral motion 

detection visual performance is likely to be result of a 

combination of increased illuminance and having more of the 

short wavelengths of visible light. The lighting condition which 

consisted of incandescent and LED lights resulted in the fastest 

detection times for the tripping hazard study where detection 

times were between 6% and 7% faster than lighting conditions 

that did not include LED lights. However, the difference in 

average detection times between the lighting combination of 

incandescent and LED lights and the combination of fluorescent 

and LED lights was not statistically significant in the tripping 

hazard study. A given lighting combination did not consistently 

give greater target illuminances in this study as was the case for 

the peripheral motion detection study. The lighting combination 

of incandescent and LED lights and the combination of 

fluorescent and LED lights did provide much more target 

illumination compared to using only the incandescent or 

fluorescent area lights. Thus, the superior trip detection visual 

performance is likely to be result of increased illuminance and 

having more of the short wavelengths of visible light. 

The results of the comparative analysis conducted between 

lighting modes that consisted of LED lighting and those that did 

not, provide important data for improving the design of lighting 

systems to improve mine illumination and, consequently, 

improve a miner’s ability to perform their job safely. By 

increasing light levels, a miner can more easily detect moving 

hazards in his peripheral and forward fields of view and 

ultimately reduce his exposure to risks associated with pinning 

and striking and trip and fall injuries. 

The implications of this paper focus on the concept that 

using LED lighting as an auxiliary source to increase illumination 

is noteworthy. As past NIOSH research has shown, the use of 

spectral power distributions having more of the short 

wavelengths of visible light, as afforded by the use of cool white 

LED cap lamps can improve visual performance in mesopic 

conditions [6]. It is with these benefits in mind that the research 

described in this paper indicates that the use of LED lights, as an 

auxiliary source of area lighting, would improve the visual 

performance of miners working around the perimeter of a 

machine. Future design considerations for lighting systems can 

be influenced by this concept but there are caveats to be noted. 

Perhaps more important than increasing illuminance levels 

around the machine is the lighting technology used, the location 

of the light sources and the direction in which the light is emitted. 

The results from the discomfort glare study indicate that the 

fluorescent machine lights generally had De Boer ratings 

associated with higher levels of discomfort glare. This may be 

attributed to elevated illuminance levels that the light source was 

producing. The results also indicated that lighting conditions that 

consisted of LED machine lights had De Boer ratings associated 

with the least amount of discomfort glare, when experienced 

from position #1. While these results were expected, they did not 

hold true for all LED lighting combinations, when viewed from 

position #2. The results indicate that incandescent lights alone 

resulted in lower levels of discomfort glare when compared to the 

fluorescent and LED lighting combination. This may be 

attributed to the way in which the light was being directed as the 

Fluorescent light was mounted in such a way that emitted light 

back toward the area where a continuous miner operator would 

normally be standing (position #2). An important consideration 

in designing machine mounted lights is the application of optics 

and shields to direct the light where needed, rather than emit it in 

every direction, to reduce glare. This is especially important with 

light sources that are capable of producing illuminances that can 

impair a miner’s vision enough to drastically reduce their ability 

to perform their job safely. 

Another consideration is that of maintenance. Because this 

particular experiment only explored the use of LED lights as 

auxiliary lights, it is not within the scope of this paper to declare 

that LED area lights will produce vast improvements on visual 

performance in favor of other lighting technologies. However, 

past research exploring the power consumption and durability of 

LED lights, which generally translate to lower maintenance 

requirements, affords NIOSH personnel the ability to make the 

recommendation to consider the design and implementation of 

lighting systems using LED technologies. All things considered, 

the benefits of using LED area lights as auxiliary sources in 

existing lighting systems can result in improved illumination 

methods underground and increase mine safety and health. 

V. ACKNOWLEDGMENTS 

The studies in this paper were conducted with the assistance 

from J. Bartels, T. Lutz, A. Mayton, M. Nelson, A. Cook, J. 

Srednicki and D. McGraw, of NIOSH PRL. Vision testing of 

subjects was conducted by M.A. Rossi R.N. Figures and three 

dimensional models of experimental layouts were created by D. 

Beshero. 

VI. REFERENCES 

[1] Illuminating Engineering Society of North America (IENSA), 

1993. Lighting Handbook: Reference and Application 8th 

Edition. 

[2] USDOT, FAA, (2003), "Human Factors Design Standard 

(HFDS)", Report # DOT/FAA/CT-03/05 HF-STD-001. 

[3] U.S. Bureau of Labor Statistics (BLS), 2008b. Mining 

Employment. Available from 

http://www.bls.gov/oco/cg/cgs004.htm#emply 

[4] Snedecor GW and Cochran WG, 1989. Statistical Methods. 

8th ed. Iowa State University Press, Ames. 

[5] Velleman, P.F. & Wilkinson, L. (1993). Nominal, ordinal, 

interval, and ratio typologies are misleading. The American 

Statistician, 47 (1), 65-72. 

[6] Sammarco, J; Reyes, M.; Gallagher, S. [2009]. Do LightEmitting Diode Cap Lamps Enable Improvements in Miner 

Safety? In: Proceedings of the Society for Mining, Metallurgy, 

and Exploration 111th Annual Meeting. Denver, CO. February 

2009.