CHAPTER 3. TECHNOLOGY ASSESSMENT 

TABLE OF CONTENTS 

3.1 SPECIFICATIONS, TEST STANDARDS, AND PROCEDURES................................... 3-1 

3.2 LAMP METRICS ............................................................................................................... 3-3 

3.2.1 Lumens ................................................................................................................. 3-3 

3.2.2 Mean Lumens/Lamp Lumen Depreciation/Lumen Maintenance ........................ 3-3 

3.2.3 Color Rendering Index......................................................................................... 3-4 

3.2.4 Correlated Color Temperature ............................................................................. 3-5 

3.2.5 Efficacy ................................................................................................................ 3-5 

3.2.5.1 Visual Efficiency................................................................................. 3-5 

3.2.5.2 Moving Beyond the Limits .................................................................. 3-8 

3.2.6 Lamp Life............................................................................................................. 3-8 

3.3 MERCURY VAPOR LAMPS............................................................................................ 3-9 

3.3.1 Lamp Construction............................................................................................... 3-9 

3.3.2 Lamp Performance............................................................................................. 3-10 

3.3.3 Electrical Characteristics ................................................................................... 3-13 

3.4 HIGH-PRESSURE SODIUM LAMPS ............................................................................ 3-13 

3.4.1 Lamp Construction............................................................................................. 3-14 

3.4.2 Lamp Performance............................................................................................. 3-15 

3.4.3 Electrical Characteristics ................................................................................... 3-17 

3.5 METAL HALIDE LAMPS............................................................................................... 3-18 

3.5.1 Construction....................................................................................................... 3-19 

3.5.1.1 Probe-Start Quartz Metal Halide Lamps ........................................... 3-22 

3.5.1.2 Pulse-Start Quartz Metal Halide Lamps............................................ 3-24 

3.5.1.3 Pulse-Start Ceramic Metal Halide Lamps ......................................... 3-24 

3.5.2 Lamp Performance............................................................................................. 3-24 

3.5.2.1 Probe-Start Quartz Metal Halide Lamps ........................................... 3-26 

3.5.2.2 Pulse-Start Quartz Metal Halide Lamps............................................ 3-28 

3.5.2.3 Pulse-Start Ceramic Metal Halide Lamps ......................................... 3-29 

3.5.3 Electrical Characteristics ................................................................................... 3-30 

3.6 HAZARDOUS MATERIALS.......................................................................................... 3-30 

3.7 HIGH-INTENSITY DISCHARGE LAMP BALLASTS ................................................. 3-31 

3-i 
 

LIST OF TABLES 

Table 3.1.1 Documents Pertaining to High-Intensity Discharge Lamps ..................................... 3-1 

Table 3.2.1. Visual Efficiencies and Efficacies of Various Sources ........................................... 3-6 

Table 3.2.2. Sample Energy Output for High Intensity Discharge Lamps .................................. 3-6 

Table 3.2.3. Chromaticities and Maximum Spectral Efficiencies of Various Sources................ 3-7 

Table 3.2.4. Color Rendering Indexes and Spectral Efficiencies of High-Intensity Discharge 

Sources ................................................................................................................. 3-7 

Table 3.2.5. Probable Efficacy Limits by Color Correlated Temperature for Conventional 

High-Intensity Discharge Lamps ......................................................................... 3-8 

Table 3.3.1. Performance Summary of Mercury Vapor Lamps ................................................ 3-12 

Table 3.4.1. Performance Summary of High-Pressure Sodium Lamps..................................... 3-15 

Table 3.5.1. Performance Summary of Probe-Start Metal Halide Lamps................................. 3-27 

Table 3.5.2. Performance Summary of Quartz Pulse-Start Metal Halide Lamps ...................... 3-28 

Table 3.5.3. Performance Summary of Pulse-Start Ceramic Metal Halide Lamps ................... 3-29 

Table 3.6.1. Total Mercury Sold in Lamps................................................................................ 3-30 

Table 3.6.2. Total Mercury Sold by HID Lamp Type ............................................................... 3-31 

LIST OF FIGURES 

Figure 3.3.1. Mercury Vapor Lamp Construction ..................................................................... 3-10 

Figure 3.3.2. Spectral Power Distribution of Mercury Vapor Lamps (a) Without Phosphors 

and (b) With Phosphors ..................................................................................... 3-11 

Figure 3.3.3. Sample Power Flow of a Mercury Vapor Lamp .................................................. 3-13 

Figure 3.4.1. High-Pressure Sodium Lamp Construction .......................................................... 3-14 

Figure 3.4.2. Spectral Power Distribution*

 of High-Pressure Sodium Lamps........................... 3-16 

Figure 3.4.3. Sample Power Flow of a 400-Watt High-Pressure Sodium Lamp ....................... 3-17 

Figure 3.4.4. Trapezoid Boundary for High-Pressure Sodium Ballast Design.......................... 3-18 

Figure 3.5.1. Tin Halide............................................................................................................. 3-20 

Figure 3.5.2. Dysprosium Iodide ............................................................................................... 3-20 

Figure 3.5.3. Formed Arc-Tube Configuration for Horizontal MH Lamps............................... 3-21 

Figure 3.5.4. Offset Electrode Configuration for Horizontal MH Lamps ................................. 3-21 

Figure 3.5.5. Metal Halide Arc Tube with a Shroud ................................................................. 3-22 

Figure 3.5.6. Metal Halide Lamp Construction ......................................................................... 3-23 

Figure 3.5.7. Common Arc Tubes ............................................................................................. 3-23 

Figure 3.5.8. Spectral Power Distribution of Metal Halide Lamps (a) Without Phosphors and 

(b) With Phosphors ............................................................................................ 3-26 

3-ii 
 

 

CHAPTER 3. TECHNOLOGY ASSESSMENT 

High-intensity discharge (HID) lamps produce light by generating an electrical discharge 

between electrodes contained within an arc tube. By definition, HID lamps include mercury 

vapor (MV), high-pressure sodium (HPS), and metal halide (MH) lamps. HID lamps range from 

20 to 2000 watts (W). The lamps are often subdivided by power into low (less than 150), 

medium (from 150 to 500), and high (greater than 500) wattages. Because the electrical 

discharge exhibits a negative resistance, ballasts regulate this electrical discharge and prevent it 

from drawing excessive current that would lead to premature lamp failure. Therefore, HID lamps 

always operate with a ballast, which is typically external to the lamp and located within the 

luminaire. There are limited exceptions to this configuration, specifically self-ballasted (integral 

ballast) MV lamps and the MH parabolic aluminized reflector (PAR) lamps. 

The following discussion examines and summarizes current specifications, standards, and 

guidelines governing the classification, testing, and evaluation of HID lamps. Because this 

analysis considers lamps only, issues concerning the effects of ballasts on HID lamp 

performance are outside the scope of this analysis. However, the availability, capability, and 

functional relationship of ballasts and lamps are important for understanding the technology and 

its market. Therefore, as appropriate, ballasts and their characteristics are addressed in this 

section. 

3.1 SPECIFICATIONS, TEST STANDARDS, AND PROCEDURES 

The U.S. Department of Energy (DOE) reviewed available evaluations of the electrical 

and photometric properties of HID lamps and ballasts. Table 3.1.1 presents a list of industry 

standards publications pertaining to HID lighting systems. 

Table 3.1.1 Documents Pertaining to High-Intensity Discharge Lamps 

Source # Year Title 

ANSI* C78.1381 1998 American National Standard for Electric Lamps—70 W, M85 Double-Ended MH 

Lamps 

C78.380 2007 American National Standard for Electric Lamps-High-Intensity Discharge Lamps, 

Method of Designation 

C78.380a 2004 American National Standard for Electric Lamps-HID Lamps, Method of 

Designation (Amendment) 

C78.389 2004 

R2009 

American National Standard for Electric Lamps – High Intensity Discharge — 

Methods of Measuring Characteristics 

C78.40 1992 

R2003 

Specifications for Mercury Lamps 

C78.40a 1998 American National Standard for Specification for Mercury Lamps-Maximum 

Outline Drawing of Bulb BT56 

C78.42 2007 American National Standard for Electric Lamps-HPS Lamps 

C78.43 2007 American National Standards for Electric Lamps-Single-Ended MH Lamps 

C78.44 2008 American National Standards for Electric Lamps-Double-Ended MH Lamps 

C78.45 2007 American National Standard for Electric Lamps-Self-Ballasted Mercury Lamps 

C78.LL 3 2003 Procedures for HID Lamp Sample Preparation and the Toxicity Characteristics 

Leaching Procedure (TCLP) 

C81.62 2007 American National Standard for Electric Lampholders 

3-1 
 

 

 

 

 

 

 

Table 3.1.1 (continued) 

Source # Year Title 

ANSI* 

(contd.) 

C82.4 2002 American National Standard for Ballasts for HID and Low-Pressure Sodium (LPS) 

Lamps (Multiple-Supply Type) 

C82.6 2005 American National Standard for Lamp Ballasts – Ballasts for HID Lamps-Methods 

of Measurement 

C82.9 1996 American National Standard for HID and Low-Pressure Sodium (LPS) Lamps, 

Ballasts and Transformers—Definitions 

C82.14 2006 American National Standard for Lamp Ballasts-Low-Frequency Square Wave 

Electronic Ballasts-for MH Lamps 

IESNA** LM-31-95 1995 Photometric Testing of Roadway Luminaires Using Incandescent Filament and 

High Intensity Discharge Lamps 

LM-35-02 2002 Photometric Testing of Floodlights Using HID or Incandescent Filament Lamps 

LM-46-04 2004 IESNA Approved Method for Photometric Testing of Indoor Luminaires Using 

HID or Incandescent Filament Lamps 

LM-47-01 2001 IESNA Approved Method for Life-Testing of HID Lamps 

LM-51-00 2000 IESNA Approved Method for the Electrical and Photometric Measurements of 

High Intensity Discharge Lamps 

LM-61-06 2006 IESNA Approved Guide for Identifying Operating Factors Influencing Measured 

vs. Predicted Performance for Installed Outdoor HID Luminaires 

LM-73-04 2004 IESNA Guide for Photometric Testing of Entertainment Lighting Luminaires Using 

Incandescent Filament Lamps or High Intensity Discharge Lamps 

NEMA† LE 5B 1998 Procedure for Determining Luminaire Efficacy Ratings for HID Industrial 

Luminaires 

LSD 14 2002 Guidelines on the Application of Dimming to HID Lamps 

LSD 24 2003 Marking of Luminaire Codes on MH Lamps 

LSD 25 2008 Best Practices for MH Lighting Systems, Plus Questions and Answers about Lamp 

Ruptures in MH Lighting Systems 

LSD 31 2005 A Lighting Systems Division Information Bulletin: Changes to the 2005 NEC Will 

Impact Future MH Lamp Systems Options 

LSD 35 2006 ANSI Code Update to Include Letter “C” for Ceramic MH Lamps 

LSD 37 2008 Effects of EPAct 2005 on MV Lamp Ballasts and Lighting Systems: Frequently 

Asked Questions 

LSD 54 2010 The Strengths and Potentials of Metal Halide Lighting Systems 

* ANSI = American National Standards Institute. 

** IESNA=Illuminating Engineering Society of North America. 

† NEMA = National Electrical Manufacturers Association. 

Sources: NEMA website (http://www.nema.org), 2010; IESNA website (http://www.iesna.org), 2010. 

As the Secretariat for ANSI, NEMA publishes standards for lamps (C78), bulbs (C79), 

lamp bases and holders (C81), and ballasts (C82); standards for performing standardized tests to 

evaluate the energy efficiency of luminaires (LE); and general information documents (LSD) as 

part of its lighting-standards program.1

 Table 3.1.1 presents the ANSI standards specifically 

related to HID technology, excluding the more generally-applicable standards for bulbs (C79) 

and lamp bases and holders (C81). 

ANSI also publishes a nomenclature for the designation of HID lamps in its C78 

technical support documents. At a minimum, the designation code includes the class and 

electrical characteristics of the lamp. In addition, ANSI publishes a set of corresponding 

performance and physical characteristics specifications. The designations and specifications not 

only provide a system of identification, but also ensure a level of product commonality and 

interchangeability among manufacturers of HID lamps and ballasts. 

3-2 
 

 

 

 

IESNA is another organization promulgating standards for HID lamps and related 

technologies, including lighting measurement (LM) test procedure documents. IESNA LM-35­

02, LM-46-04, and LM-73-04 focus on testing luminaires using HID technology (as well as other 

light sources). IESNA LM-41-01 and LM-51-00 focus on life and electrical/photometric 

measurements of HID lamps, respectively. These publications build on ANSI standards to 

include procedures for both electrical measurements and photometric measurements by defining 

testing conditions, lamp stabilization, and other critical aspects to ensure consistency in the 

testing of lamp performance. Publications by IESNA reflect the consensus of industry 

stakeholders, including NEMA members. 

3.2 LAMP METRICS 

Lamp characteristics and performance are evaluated on a number of factors, in addition to 

lumen output. The following is a review of different metrics applicable to HID lamps. 

3.2.1 Lumens 

The lumen (lm) is the basic unit of light. The IESNA defines luminous flux as the time 

rate of flow of radiant energy, evaluated in terms of a standardized visual response2: 

ૠૡ૙ ࡰࡼࡿ ࣅࢊ Eq. 3-1 Φ = 683 × ׬ ሺࣅሻ ൈ ࢂ ሺࣅሻ ૜ૡ૙

Where: 

Φ = luminous flux (in lumens, lm). 

The value of 683 lumens per watt (lm/W) is a constant for the photopic luminous efficacy 

function. The equation essentially is the integral of the light source’s spectral content expressed 

as spectral power distribution (SPD) over the visible range of the electromagnetic spectrum 

weighted by the photopic luminous efficacy function. In practical terms, this equation expresses 

integrating the energy emitted by the light source across the visible light portion of the spectrum 

(380 to 780 nanometers [nm]) and multiplying by the visual efficacy function (a function 

weighting the different portions of the visible light spectrum by the different photoreceptors in 

the eye) times the constant 683 lm/W. The units cancel out to just lumens. 

3.2.2 Mean Lumens/Lamp Lumen Depreciation/Lumen Maintenance 

Lamp lumen depreciation (LLD) is also known as lumen maintenance. In use, a lamp 

loses light output over time. According to the IESNA, the LLD factor is “the fraction of the 

initial lumens produced at a specific time during the life of the lamp.”2

 The LLD value is used in 

lighting calculations to account for the reduction in output over the operating life of the lamp. 

Often the mean (also known as design) lumens are used for LLD. Mean lumens are published in 

the manufacturers’ catalogs and are measured at a certain point in time, typically a specific 

percentage of the lamp’s rated lifetime. 

3-3 
 

 

 

The IESNA does not define when to measure mean lumens; however, 70 percent of 

average rated life is the recommended criterion for lamp replacement for both group and spot 

relamping programs.2

 This value is usually not used in design calculations because it is difficult 

to determine from manufacturers’ data. Often, designers must build margins into their 

calculations and use the mean/design lumen value presented in the catalogs. 

The basis for mean lumens can vary among manufacturers, as shown in DOE’s survey of 

definitions from manufacturer catalogs: 

GE: “Mean Lumens – lamp light output at 40% of rated lamp life for (MH) lamps and 

50% of rated life for mercury and HPS lamps.”3 

OSRAM SYLVANIA: “Mean lumens are measured on ANSI reference circuits at rated 

wattage (HQI, LUMALUX Super and SOX lamp ratings are based on input voltage) at 

40% of average rated life except for those lamps with a “+” next to their life rating; these 

lamps are measured at 50% of average rated life. All measurements are based on ballast 

operation on systems with current crest factors of 1.8 or less. Higher current crest factors 

reduce values. In actual applications on constant wattage (CW) or constant-wattage 

autotransformer (CWA) ballasts, mean lumens may be higher than published ratings.”4 

Philips: “Approximate lumen output at 40% of lamp rated average life.”5 

USHIO: “Lumens, Mean: Average quantity of light output over the life of the lamp. High 

Pressure Sodium and incandescent lamps are measured for mean lumens at 50% of lamp 

life. Fluorescent and MH lamps are measured for mean lumens at 40% of rated lamp 

life.”6 

Venture (a manufacturer of only MH lamps): “Mean Lumens: Light output at 40% of 

rated life.”7 

Chapter 2, Market Assessment, discusses both draft legislation focusing on outdoor lighting and 

requirements related to mean lumens that are already in effect in California. The absence of an 

agreed-upon definition for mean lumens complicates any discussion of standards compliance or 

recommended relamping cycles and hinders comparisons of similar products from different 

manufacturers. 

3.2.3 Color Rendering Index 

The IESNA defines color rendering index (CRI) as “a measure of the degree of color 

shift objects undergo when illuminated by the light source as compared with those same objects 

when illuminated by a reference source of comparable color temperature.”2 In CRI calculation, 

14 samples are evaluated; however, the general CRI (Ra) is only an average of the first 8 

samples. Samples R1–R8 are not highly saturated and are pastel colors. R9 is an oft-cited color 

value because it is a deeply saturated red. The accurate rendering of this color is often desired in 

retail applications. Light emitted at the “red end” of the visual spectrum (above 700 nm) adds 

little to total lumen output, but can add important color qualities to the lamp. Incandescent and 

halogen lamps have R9 values of 100. The R9 value for HID lamps can be negative and is often 

0 because these sources do not emit significant light above 700 nm. 

3-4 
 

 

 

 

 

3.2.4 Correlated Color Temperature 

The IESNA defines correlated color temperature (CCT) as “the absolute temperature of a 

blackbody whose chromaticity most nearly resembles that of the light source.” Color temperature 

is a not a performance metric but rather characterizes the color appearance of a light source: 

“Color temperature is a specification of chromaticity only. It does not represent the SPD of the 

light source.”2

 Chromaticity (expressed as chromaticity coordinates, e.g., x and y) is a 

representation of the light source color calculated with by the standard observer and 

spectroradiometric measurements. 

3.2.5 Efficacy 

Efficacy (luminous efficacy) is defined by the IESNA as quotient of the total emitted 

luminous flux and the total lamp power. Expressed mathematically: 

η = luminous flux (lm) / lamp power (W) Eq. 3-2 

Where: 

η = luminous efficacy (in lumens per watt, lm/W). 

A 2001 paper by Nelson et al., “An Efficacy Analysis of HID Lamps,” examined the 

components of efficacy of HID lamps.8

 The paper was not entirely based on new research, but 

also on long-standing lighting science. The paper focused on aspects of efficacy irrespective of 

chromaticity and color rendering. The paper only examined lamp efficacy and excluded lighting 

system (i.e., ballasts and fixtures). The paper converted the mathematical efficacy function into 

the three components, rewritten as: 

η = ηvis × ηmax spectral × ηspectral × 683 lm/W Eq. 3-3 

Where: 

ηvis = visual efficiency, 

ηmax spectral = maximum spectral efficiency, 

ηspectral = spectral efficiency, and 

lm/W = lumens per watt. 

The value of 683 lm/W is both a constant and the absolute photopic luminous efficacy 

value. Therefore, as the different η values approach 1.0, the closer the efficacy is to 683 lm/W. 

3.2.5.1 Visual Efficiency 

The visual efficiency of a lamp is the quotient of the power radiated in the visible 

spectrum (380 to 780 nm) and the total lamp power. Table 3.2.1 is from Nelson et al.8 

3-5 
 

 

 

 

 

 

Table 3.2.1. Visual Efficiencies and Efficacies of Various Sources 

Lamp Type Pla* 

W 

ηvis η

lm/W 

High-Pressure Sodium 150 0.22 90 

400 0.31 124 

1000 0.33 135 

White High-Pressure Sodium 100 0.20 51 

Mercury Vapor 400 0.15 55 

Quartz Metal Halide–NaSc Pulse Start 400 0.35 110 

Quartz Metal Halide–NaTl In 400 0.24 80 

Ceramic Metal Halide–3000 K 100 0.35 98 

Ceramic Metal Halide–4000 K 100 0.38 95 

*Pla = Power of the lamp. 

The data in Table 3.2.1 reflect visual efficiencies ranging from 0.15 to 0.38. Newly 

developed (post-1990) HID lamps (pulse-start ceramic and quartz MH) have visual efficiencies 

above 0.35. As lamp power increases so does visual efficiency, as shown in the HPS data (150 

W/0.22, 400 W/0.31, 1000 W/0.33). Although related, changes in visual efficiency do not 

directly correlate to changes in efficacy. The white HPS lamp has a slightly lower efficacy than 

the mercury vapor, yet the HPS lamp has more visual efficiency, with values being virtually the 

same for the 150 W HPS (0.22) and the white HPS (0.20). The efficacy of the 150 W lamp is 

almost twice that of the 100 W white HPS lamp. 

Table 3.2.2 is excerpted from the IESNA Lighting Handbook, table 7-49.2

 Each of the 

HID lamps produces more infrared radiation (IR) than visible light. This distribution of energy 

directly affects the visual efficiency value of the lamp. If the HID lamps produced more energy 

in the visual light region of the electromagnetic spectrum, the visual efficiency values would be 

greater. 

Table 3.2.2. Sample Energy Output for High-Intensity Discharge Lamps 

Type of Energy 400 W 

% 

MV MH HPS 

Visible Light 14.6 20.6 25.5 

Infrared 46.6 31.9 37.2 

Ultraviolet 1.9 2.7 0.2 

Conduction-Convection 27.0 31.1 22.2 

Ballast 10.1 13.7 14.9 

Maximum Spectral Efficiency. Nelson et al. (2001) defined the maximum spectral 

efficiency a factor expressing the effect of the eye sensitivity curve for a given chromaticity. A 

given lamp’s location in color space factors into efficacy and that is the role of the maximum 

spectral efficiency. 

Nelson et al. provided the chromaticities maximum spectral efficiencies for the lamps 

that it provided the visual efficiency data for, which are shown in Table 3.2.3. The paper found 

(and supported by the data republished) that the maximum spectral efficiency varied from 0.70 to 

0.76 for HID lamps.8 

3-6 
 

 

 

 

 

 

 

 

 

 

 

 

Table 3.2.3. Chromaticities and Maximum Spectral Efficiencies of Various Sources 

Lamp Type Pla 

W 

x y CCT ηmax spectral 

High-Pressure 

Sodium 

150 0.521 0.423 2100 0.75 

400 0.521 0.413 2040 0.72 

1000 0.522 0.413 2040 0.72 

White HighPressure Sodium 100 0.461 0.405 2640 0.75 

Mercury Vapor 400 0.331 0.395 5680 0.73 

Quartz Metal 

Halide–NaSc Pulse 

Start 

400 0.374 0.394 4280 0.75 

Quartz Metal 

Halide–NaTl In 

400 0.390 0.398 3890 0.76 

Ceramic Metal 

Halide–3000 K 

400 0.368 0.368 4300 0.71 

Ceramic Metal 

Halide–4000 K 

100 0.433 0.388 2950 0.73 

High-Pressure 

Sodium 

100 0.372 0.366 4150 0.70 

Spectral Efficiency. The spectral efficiency is a measure of how well a given spectrum is 

distributed relative to the optimally efficient two-line spectrum for that chromaticity. There is a 

negative correlation with spectral efficiency. As spectral efficiency increases, CRI decreases. 

This is demonstrated in the high spectral values for HPS and MV (0.82 and 0.77, respectively) 

and the very low CRI values of 11 (HPS) and 17 (MV). In contrast, the high CRI values of 93 

and 89 from the HPS had lower spectral efficiency values (0.53 and 0.56, respectively; Table 

3.2.4). 

Table 3.2.4. Color Rendering Indexes and Spectral Efficiencies of High-Intensity Discharge 

Sources 

Lamp Type Pla 

W 

CRI ηmax spectral 

High-Pressure Sodium 150 11 0.82 

400 21 0.80 

1000 17 0.82 

White High-Pressure Sodium 100 84 0.50 

Mercury Vapor 400 17 0.77 

Quartz Metal Halide–NaSc Pulse Start 400 36 0.70 

Quartz Metal Halide–NaTl In 400 65 0.62 

Ceramic Metal Halide–3000 K 400 62 0.67 

Ceramic Metal Halide–4000 K 100 89 0.56 

High-Pressure Sodium 100 93 0.53 

Nelson et al. (2001) found that this negative relationship did exist and derived a function 

expressing the relationship of CRI and spectral efficiency for HID and LPS lamps. The function 

was a straight line with an R2

 value of 0.95 and is: ηspectral = 0.8461 – (0.0034 × CRI).8 

Potential Efficacy Limits. Nelson et al. hypothesized the possible efficacy limits for 

conventional HID lamps on the blackbody locus (BBL), based on their assumptions in the 2001 

paper.8 The authors assumed a visual efficiency value of 0.40. Based on the lamps they surveyed, 

a value 0.38 was the highest for HID lamps. In the discussion section of their paper, this value 

3-7 
 

 

 

 

was questioned. The authors defended their choice in that it represented a likely value for longlife, commercially available lamps with electrodes. The maximum spectral efficiency values 

were provided for the different chromaticities. Finally, a CRI of 80 was assumed, and using the 

function provided, the spectral efficiency values were derived. The authors chose a CRI 80 

because end users will be more concerned with color quality in the future. A CRI of 80 seems 

reasonable when reviewing other DOE lamp rules. Table 3.2.5 is a review of the probable 

efficacy limits for HID lamps that lie on the BBL and have a CRI of 80. In review, the efficacy 

ranges from 100 to 120 lm/W, depending on the lamp chromaticity. 

Table 3.2.5. Probable Efficacy Limits by Color Correlated Temperature for Conventional 

High-Intensity Discharge Lamps 

CCT ηvis ηmax spectral ηspectral η

lm/W 

2000 0.40 0.722 0.574 113 

2800 0.40 0.766 0.574 120 

3000 0.40 0.763 0.574 120 

4000 0.40 0.722 0.574 113 

5000 0.40 0.676 0.574 106 

6000 0.40 0.636 0.574 100 

3.2.5.2 Moving Beyond the Limits 

Nelson et al. hypothesized that improving the power balance could increase the visual 

efficiency. Of the three values in the efficacy function, this value was below 0.4. Also, as stated 

in Table 3.2.2, only 15 to 26 percent of the energy being used by HID lamps is in the visual light 

portion of the spectrum. Nelson et al. hypothesized that the “a” source, such as the sulfur lamp 

with a visual efficiency of 0.55 at 3000 kelvin (K) on the BBL and a CRI of 80, could have an 

efficacy of 170 lm/W.8 It should be stated that the sulfur lamp is no longer in production, but one 

reason that the lamp has a higher visual efficiency value is that it does not have electrodes. 

Nelson et al. hypothesized that spectral optimization would increase the spectral 

efficiency. As shown in Table 3.2.5, the spectral efficiency values are limited to 0.574 due to the 

CRI of 80. If the spectrum was more optimized and the CRI held constant, the spectral efficiency 

values could be 0.80, resulting in a 170 lm/W lamp. Nelson et al. point out that the measures 

could be used in conjunction, yielding in a possible 230 lm/W lamp. Finally, the authors note 

that “even after more than 50 years of HID lamp development, the task of achieving a lamp with 

a high luminous efficacy (say, greater than 150 lm/w [LPW]), high CRI and a chromaticity near 

the black body line will not be an easy one.”8 

3.2.6 Lamp Life 

The rated lamp life is defined when 50 percent of a sample group of lamps have failed. 

Rated lamp life is expressed in hours and varies with the method by which the ballast starts and 

operates the lamp. 

3-8 
3.3 MERCURY VAPOR LAMPS 

Introduced in the 1930s, mercury vapor was the first commercialized HID light source 

and remains fundamentally unchanged. Mercury vapor and fluorescent (FL) lamps are both MV 

discharge lamps, but FL lamps operate at low pressure and MV lamps operate at high pressure. 

One development in the movement toward efficient lighting was the invention of a 

self-ballasted MV lamp. This lamp originated as a longer-life substitute for the A-shaped general 

service incandescent lamp. By using a length of tungsten filament within the lamp structure to 

regulate current, these lamps function without ballasts. Although more efficient than 

incandescent lamps, these lamps are less efficacious than MV lamps with ballasts due to the 

resistive loss at the tungsten filament. 

Because of their low CRI (15 is typical), MV lamps are used primarily in spaces that are 

not frequently occupied by people. A phosphor coating is added to clear MV bulbs to obtain 

better CRI, but the improvement is marginal. Outdoor security, street, and landscape lighting are 

some of the applications for MV lamps, but higher performing MH and HPS lamps are replacing 

these. MV systems continue to maintain market share in some niche applications (e.g., the 

“security” or “barn” light—an arm-mounted luminaire typically used in residential applications) 

where long life and low initial cost are important. However, even in niche applications, MV is 

losing its advantage as other HID sources offer improved lifetime and initial cost. MV lamps are 

available in wattages from 50 to 1000. 

Mercury vapor lamps have applications aside from general illumination, including quality 

inspection, processing, scientific uses, reprographic (copy/duplication), fluorescent microscopy, 

and curing. The specific spectrum of MV lamps is beneficial to these applications. The selfballasted MV lamp has special niche because of its unique capability to directly replace highwattage incandescent lamps in standard mogul bases. Self-ballasted MV lamps are available in 

wattages between 100 and 400. Typical applications have included outdoor security lighting, 

area lighting, and some warehouse use. Although MV lamps offer modest energy savings over 

incandescent lamps, their more significant advantage over incandescent and other technologies is 

lamp lifetime, resulting in longer intervals between relamping. In recent years, the self-ballasted 

MV lamp has lost market share to integrally ballasted compact fluorescent lamps, integrally 

ballasted MH lamps, and even light-emitting diode replacement lamps. 

3.3.1 Lamp Construction 

In an MV lamp arc tube, an electric-current arc passes from the starting electrode to the 

main electrode. The initial arc strikes through the ionization of argon gas. Once the arc is 

established, its heat vaporizes the liquid mercury in the arc tube. The amount of mercury in the 

lamp essentially determines the final operating pressure, which is 200 to 400 kilopascals (kPa) 

(29 to 58 pounds per square inch) in the majority of lamps.2

 The arc tube construction is fused 

silica (quartz) that can operate at up to 1000 degrees Celsius (°C). 

An outer glass envelope (bulb) protects the arc tube and internal electrical connections 

from the environment. The bulb is usually in the shape of an ellipse and made of hard 

(borosilicate) glass, which absorbs most of the ultraviolet (UV) energy radiated by the discharge 

while allowing light to pass through. For lamps where UV emission is desired (e.g., germicidal 

3-9 
 

 

lamps), the bulb is made of other materials that allow transmission of UV energy.2 In coated MV 

lamps, the bulb is coated internally with a diffusing material to reduce source brightness of the 

lamp. This diffusing coating is usually a color-correcting phosphor that uses UV energy radiated 

by the arc tube to improve the lamp’s overall color-rendering properties, as in a fluorescent lamp. 

MV lamps are also available in a reflector lamp format. 

There are wires within the outer bulb that are suitable for high temperatures to conduct 

electricity to the arc tube and structural components to support the arc tube. The atmosphere in 

the outer bulb is usually a low-pressure gas (usually nitrogen) or, in rare cases, a vacuum.2 If the 

outer bulb breaks and the arc tube continue to operate, the lamp emits a significant amount of 

UV energy. Self-extinguishing lamps, designed to shut off the lamp should the outer bulb break, 

usually contain a tungsten filament in place of a portion of nickel wire that oxidizes quickly, 

opening the circuit. This separation renders the lamp inoperable. Figure 3.3.1 shows essential 

construction details typical of lamps with quartz inner-arc tubes within an outer envelope.2 

Nitrogen fill gas 

Main electrode Argon fill gas 

& mercury Quartz tube 

Main electrode Starting electrode 

Outer bulb 

Starting resistor 

Base 

Source: GE Lighting, High-Intensity Discharge Lamps Catalog, 2003. Reproduced with permission.9 

Figure 3.3.1. Mercury Vapor Lamp Construction 

3.3.2 Lamp Performance 

The pressure at which MV lamps operate has a significant effect on their characteristic 

SPD. As pressure increases, the emitted radiation shifts toward longer wavelengths (from UV to 

visible light) and the spectrum lines spread into wider bands. Within the visible region, the 

mercury spectrum consists of five principal lines (404.7, 435.8, 546.1, 577, and 579 nm), which 

result in greenish-blue light at efficacies of 30 to 65 lm/W, excluding ballast losses.a, 2 While the 

light source itself appears greenish-blue white, a deficiency of long-wavelength radiation distorts 

the perceived color of objects illuminated by that light source. Blue, green, and yellow are 

emphasized; orange and red appear brownish. MV lamps also emit radiation outside the visible 

region in the form of UV in the range of approximately 250 to 365 nm. These wavelengths do 

a

 Ballast loss – Power drawn by the ballast in addition to the rated lamp power used to operate the lamp. 

3-10 
not contribute to seeing, but are useful for non-illumination purposes (e.g., reprographic or 

germicidal applications). 

Clear MV lamps generally have a CRI value of approximately 15 and are not desirable 

for use where people will occupy the space. Phosphor-coated MV lamps convert some of the 

lamp’s UV radiation to visible light, as occurs with a FL lamp. The most widely used lamps of 

this type (designated “DX”) have a coating of vanadate phosphor that emits long-wavelength 

radiation (orange-red) where MV lamps are otherwise deficient, thus improving CRI.2 This 

phosphor may also blend with other phosphors to produce a cooler or warmer CCT between 

3200 and 7000 K. The phosphor coating can raise the CRI rating to 50. Figure 3.3.2 shows the 

SPDs of a clear lamp and coated lamp using these phosphors. 

H39KB-175 

0.80 

0.70 

) mens 0.60 00 lu

0.50 

for 1000

0.40 

5nm 

0.30 

s per 5

0.20 

tput (Watt 0.10 

0.00 

200 

Ou

300 400 

(a) 

500 

Wavelength (nm) 

600 700 800 

0.60 

H39KC-175/DX 

0.50 

0.40 

0.30 

0.20 

0.10 

0.00 

200 300 400 500 600 700 800 

Wavelength (nm) 

(b) 

Source: OSRAM SYLVANIA, 2003. Reproduced with permission.10 

Figure 3.3.2. Spectral Power Distribution of Mercury Vapor Lamps (a) Without Phosphors 

and (b) With Phosphors 

Output (Watts per 5nm for 1000 lumens) 

3-11 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Efficacies of self-ballasted MV lamps are slightly better than those of the incandescent 

lamps they replace. Typically, efficacies range between 15 to 25 lm/W. The spectrum consists of 

the line spectrum of mercury in addition to the blackbody radiation pattern from the incandescent 

component of the tungsten filament broadening the spectrum into long-wavelength range (red). 

Although the light in these wavelengths does not significantly increase total light output, it does 

increase the CRI of the source. The CCT ranges from 3300 to 4000 K, with a CRI of 50, 

depending on mercury pressure and phosphor coating used (if any). 

The light output from MV lamps decreases over the operating life of the lamp. Typically, 

lumen output depreciates about 25 percent from initial output level at 50 percent of its rated life. 

The depreciation in light output is a result of the bulb becoming darker because the cathode 

material evaporates through use and is deposited on the wall of the arc tube bulb. Typical rated 

life is 24,000 hours, but it is common for the lamp to continue operating long after its rated life. 

One of the major failure points for discharge lamps is that the cathode material eventually 

evaporates and fails to strike an arc. MV lamps are notorious for never burning out, but simply 

diminishing in output over time because the evaporating cathode material has to diffuse through 

mercury vapor, a very heavy gas at high pressure, thereby slowing the evaporation process. The 

lamp power remains constant as light output declines, meaning that the efficacy of the light 

source steadily decreases over time. 

To achieve the necessary high vapor pressures within the arc tube, MV lamps require a 

significant warm-up time of approximately 5 to 7 minutes. Re-strike times are about as long, 

requiring 5 to 7 minutes for the vapor pressure to reach the level where the arc can restart. 

Warm-up time for self-ballasted lamps is approximately 3 minutes, with a re-strike time of 

5 minutes. Table 3.3.1 summarizes the performance of common MV lamps. 

Table 3.3.1. Performance Summary of Mercury Vapor Lamps 

Lamp Power* 

W 

CRI CCT** 

K 

Initial 

Lumens 

Life 

hr 

Initial Efficacy 

at 100 hr† 

lm/W 

Mean Efficacy 

at 40–50% Life‡ 

lm/W 

50 Minimum 20 3200 1,050 6,000 22 13 

Median 45 4100 1,575 8,000 30 24 

Maximum 50 5700 1,900 24,000 40 33 

75 Minimum 20 3200 2,700 16,000 36 24 

Median 45 4100 2,700 18,000 36 30 

Maximum 50 5700 3,000 24,00 40 32 

100 Minimum 15 3200 1,100 6,000 11 8.3 

Median 40 4100 4,000 2,4000 40 26 

Maximum 60 7000 4,500 2,4000 45 37 

175 Minimum 15 3700 5,100 16,000 29 21 

Median 40 4300 7,800 24,000 45 39 

Maximum 50 6800 8,900 24,000 51 43 

250 Minimum 15 3200 3,200 12,000 13 11 

Median 43 4100 8,900 24,000 36 24 

Maximum 50 6700 13,700 24,000 55 45 

400 Minimum 15 3700 1,500 12,000 37.5 13.25 

Median 43 4000 21,000 24,000 53 36 

Maximum 50 6500 24,000 24,000 60 49 

1000 Minimum 15 3700 13,000 16,000 45 13 

Median 40 4100 45,200 24,000 58 45 

Maximum 50 6300 52,240 24,000 64 52 

3-12 
 

 

Table 3.3.1 (continued) 

* A minimum of three different manufacturers had to produce the type and similar wattage to have that wattage class 

listed in this table. 

** Correlated-color temperature is not a performance metric; the values are listed to show the range of available 

CCTs for the product. 

† Initial efficacy is initial lumens divided by the lamp rated power (the power use of the ballast is not factored into 

this table). 

‡ Mean efficacy is the mean lumen value provided by the manufacturer divided by the lamp rated power (the power 

use of the ballast is not factored into this table). Lumen depreciation still occurs after this point. 

3.3.3 Electrical Characteristics 

Because MV lamps have an additional electrode at one end of the arc tube to assist in 

lamp starting, they do not require a separate starter circuit. These lamps typically require an 

open-circuit voltage of approximately twice the operational lamp voltage to initiate and sustain 

the arc discharge. 

Figure 3.3.3 shows the energy balance from a typical 400-W MV lamp.11 Although this 

diagram dates from the mid-1970s and is for one lamp wattage, the diagram is representative of 

how the input power is used in this lamp type. The percentage values in parentheses are the 

portion of power for that input or output per rated lamp wattage. Typically, only 15 percent of 

the power used by the lamp is actually converted into visible radiation. The efficiency of the 

conversion of power into radiation increases with power. As shown in Figure 3.3.3, MV lamps 

produce equal or more energy in the IR region than in the visible light region. 

Figure 3.3.3. Sample Power Flow of a Mercury Vapor Lamp 

3.4 HIGH-PRESSURE SODIUM LAMPS 

HPS lamps were introduced in the 1960s, before the introduction of MH lamps. HPS 

lamps are currently the most efficacious HID light source, ranging from 38 to 150 lm/W, with 

typical efficacy being greater than 80 lm/W. These values are initial lamp efficacy (rated lamp 

3-13 
 

lumens/rated lamp power) and do not take in account any ballast losses. The 38 lm/W value is 

from a directional (reflector-type) lamp. This is an atypical lamp and its low efficacy is not 

representative of HPS lamps in general. Typical HPS lamps have low CCT (e.g., 2100 K) and 

low CRI (e.g., 22), but there are some enhanced-spectrum HPS lamps that have a higher CRI 

(and a higher CCT as a byproduct of the change in spectrum). 

HPS lamps are in use in public (e.g., outdoor roadway), commercial, and industrial 

sectors. Although HPS lamps are available in wattages from 35 to 1000; the most common 

wattages in these sectors range from 50 to 500. Typical applications include vehicular traffic 

areas (e.g., roadways and parking lots) and pedestrian areas (e.g., public-access areas, subways, 

and parks). HPS lamps are also used in commercial and industrial applications where color 

quality may not be critical (e.g., storage and loading areas, and corridors). Many of these 

applications overlap with MH applications, creating competition between the technologies for 

market share. 

3.4.1 Lamp Construction 

Figure 3.4.1 shows the basic construction of HPS lamps. Similar to MV lamps, they have 

an inner arc tube and an outer bulb. The arc tube is made of a ceramic material that contains 

electrodes, a sodium and mercury amalgam, and a small amount of xenon gas. No starter probe is 

present in the HPS arc tube, and a high-voltage, high-frequency pulse is used to ionize the 

starting gas. The high temperatures needed to vaporize sodium dictate the arc tube geometry and 

material. Further, the highly corrosive nature of sodium, especially at elevated temperature and 

pressure (700 °C/27 kPa [3.9 pounds per square inch]), precludes the use of certain materials 

(e.g., quartz). An amalgam reservoir inside the arc tube helps to stabilize pressure, similar to 

amalgam-based fluorescent lamps. This allows HPS lamps to operate in any physical orientation, 

simplifying stocking and installation.12 

Outerbulb 

Xenonfillgas, 

sodium& 

mercuryvapor 

Arctube 

mountstructure 

Vacuum 

Mainelectrode 

Ceramicarctube 

Mainelectrode 

Base 

Source: GE Lighting, High-Intensity Discharge Lamps Catalog, 2003. Reproduced with permission.9 

Figure 3.4.1. High-Pressure Sodium Lamp Construction 

3-14 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The lamp’s outer glass envelopes are typically elliptical in shape and are made of a hard 

glass that protects the arc tube from damage. Usually, an outer envelope contains a vacuum that 

reduces convection and heat losses from the arc tube to maintain high efficacy.12 

In some HPS lamps, an additional coil is wrapped around the outside of the ceramic arc 

tube to assist in starting the lamp.12 This coil is similar in function to the starting probe in probestart MH and MV lamps. This type of HPS lamp can directly replace MV lamps and operate on 

the same ballast without an ignitor. However, HPS retrofit lamps produce significantly more 

light for the same wattage. Therefore, to realize any energy savings, a lower-wattage HPS retrofit 

lamp should replace a higher-wattage MV lamp. 

3.4.2 Lamp Performance 

The high luminous efficacy of HPS lamps corresponds to the emittance of sodium in the 

yellow-orange portion of the visible spectrum, to which the human visual system responds most 

efficiently. The efficiency of HPS lamps is critically dependent on the specific vapor pressure of 

sodium in the arc tube. Any deviation from this optimum pressure results in reduced 

performance of the lamp. Notwithstanding, HPS lamps offer the highest efficacy of HID sources, 

achieving 64 lm/W for 35-W sources and up to 133 lm/W for 1000-W sources. HPS lamps of 

100 W or more have efficacies over 100 lm/W. Rated lifetimes of 24,000 hours are typical, with 

some long-life lamps rated at 40,000 hours. These lamps have an expected LLD value of 10 

percent at mean rated life. 

A historical perspective of how these values have changed in the 40 years since HPS 

lamps entered the market can be found in an IESNA “significant paper.” A 1965 publication in 

Illuminating Engineering stated that, with initial efficacy in excess of 100 lm/W, “10,000 hour 

lumen maintenance has been measured on laboratory test lamps at over 90 percent. Median life 

at the present time is in the 3,000- to 6,000-hour range. From an engineering viewpoint it is 

reasonable to expect that this can be increased as techniques for constructing the lamps are 

improved.”13 From the data in Table 3.4.1, it appears that the comment was true in that HPS 

lamp life has improved and efficacy somewhat improved. The historical perspective shows that, 

since the introduction of the HPS lamp to the market 40 years ago, the efficacy of the HPS lamp 

has increased 20 to 30 percent and HPS lamp life has significantly increased. 

Table 3.4.1. Performance Summary of High-Pressure Sodium Lamps 

Lamp Power* 

W 

CRI CCT** 

K 

Initial 

Lumens 

Life 

hr 

Initial Efficacy 

at 100 hr† 

lm/W 

Mean Efficacy 

at 40–50% life‡ 

lm/W 

35 Minimum 21 1,900 2,100 16,000 60 55 

Median 22 1,900 2,250 16,000 64 58 

Maximum 22 2,100 2,250 24,000 64 59 

50 Minimum 17 1,900 2,300 6,000 46 40 

Median 22 1,900 4,000 24,000 80 72 

Maximum 85 2,700 4,000 30,000 80 72 

70 Minimum 17 1,900 3,350 6,000 48 41 

Median 22 1,900 6,300 24,000 90 76 

Maximum 83 2,500 6,500 40,000 93 84 

100 Minimum 17 1,900 4,900 10,000 49 42 

Median 22 2,100 9,500 24,000 95 80 

Maximum 85 2,700 10,500 40,000 105 95 

3-15 
 

 

 

Table 3.4.1 (continued) 

150 Minimum 17 1,800 5,900 6,170 39 41 

Median 22 2,100 15,000 13,500 100 90 

Maximum 85 2,500 16,000 14,400 107 96 

200 Minimum 21 2,000 21,400 24,000 107 90 

Median 22 2,100 22,000 24,000 110 99 

Maximum 25 2,100 22,000 40,000 110 99 

250 Minimum 15 2,000 9,500 9,000 38 32 

Median 22 2,100 27,000 24,000 112 99 

Maximum 85 2,500 29,000 40,000 121 109 

400 Minimum 22 2,000 18,000 9,000 45 38 

Median 22 2,100 48,500 24,000 121 111 

Maximum 85 2,500 54,000 40,000 135 122 

1000 Minimum 21 2,000 125,000 15,000 125 112 

Median 22 2,100 138,750 24,000 139 126 

Maximum 25 2,100 146,000 40,000 146 136 

* A minimum of three different manufacturers had to produce the type and similar wattage to have that wattage class listed in this table. ** Correlated-color temperature is not a performance metric; the values are listed to show the range of available 

CCTs for the product. 

† Initial efficacy is initial lumens divided by the lamp rated power (the power use of the ballast is not factored into

this table).

‡ Mean efficacy is the mean lumen value provided by the manufacturer divided by the lamp rated power (the power 

use of the ballast is not factored into this table). Manufacturers select the time at which they provide the mean lumen data, which vary between 40 and 50 percent of rated life. Lumen depreciation still occurs after this point. Also, not 

all manufacturers publish mean lumen values, which can be higher than the initial efficacy values because the mean

lumens were not provided. This column is based on mean lumens published by manufacturers. 

Figure 3.4.2 shows the SPD for a typical HPS lamp. During warm-up, the lamp’s color 

appearance shifts from red to blue, before stabilizing at the characteristic yellow-white.2 A 

typical CCT value is 2100 K with a CRI of 22. Higher CCT values are possible at the cost of 

reduced efficacy and lifetime. The highest commercially available CCT is 2700 K with a CRI of 

85.14 Applying diffuse coatings does not significantly change the SPD of HPS lamps because 

most of the radiation emitted by the lamp is in the visible portion of the spectrum. 

LU400/ECO 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

300 400 500 600 700 800 

Wavelength (nm) 

Source: OSRAM SYLVANIA, 2003. Reproduced with permission.10 

* Same distribution for bare and coated lamps. 

Figure 3.4.2. Spectral Power Distribution* of High-Pressure Sodium Lamps Output (Watts per 5nm for 1000 lumens) 

3-16 
 

 

 

 

 

 

3.4.3 Electrical Characteristics 

Given their arc tube geometry and lack of starting probes, HPS lamps require an ignitor 

to generate the high-voltage pulse necessary to initiate the electrical arc across the electrodes. 

Once the ignitor initiates the arc, the cold lamp requires approximately 3 to 4 minutes of warmup time to attain full light output, with a typical re-strike time of 1 to 3 minutes. 

Figure 3.4.3 shows the energy balance from an example 400-W HPS lamp.11 Although 

this diagram dates from the mid-1970s and is for one lamp wattage, the diagram is representative 

of how the power is used. The percentage values in parentheses are the portion of power for that 

input or output per rated lamp wattage. Only 30 percent of the power used by the lamp is actually 

converted into visible radiation. The efficiency of the conversion of power into radiation 

increases with power. Very little lamp power (approximately 1 percent) is emitted in the UV 

range. Some power (20 percent) is emitted in the IR range; however, more power is emitted in 

the visible range. The values in Figure 3.4.3 are consistent in relationship to the energy output of 

an HPS lamp as listed in Table 3.2.2. 

Figure 3.4.3. Sample Power Flow of a 400-Watt High-Pressure Sodium Lamp 

Unlike a typical MV or MH lamp, where voltage remains relatively constant throughout its 

lifetime, the arc-tube voltage increases significantly during the operating life of HPS lamps. 

Sodium is lost over the operating lifetime of the lamp, and the arc voltage rises as the ratio of 

sodium to mercury changes. Although the voltage rises over life, the technology needs to operate a 

constant wattage. Therefore, HPS ballasts must compensate for the change in operating lamp 

voltage to maintain an acceptable average wattage. The lamp/ballast combination “constitutes a 

dynamic system in which the intrinsic voltage rise of an HPS lamp is either amplified or attenuated 

by the nature of the characteristic curve of the ballast on which the lamp is operated.”15 Figure 

3.4.4 illustrates the boundary conditions that restrict the performance of the lamp and the ballast to 

3-17 
 

 

 

 

certain acceptable limits. These boundary conditions, due to their shape on the graph, are referred 

to as the trapezoid-shaped boundaries. 16 HPS ballasts operate HPS lamps within this trapezoid for 

any input voltage within the designed range of the ballast. 

Source: NEMA, 2001. Reprinted by permission from ANSI C78.42-2001, HighPressure Sodium Lamps.

16 

Figure 3.4.4. Trapezoid Boundary for High-Pressure Sodium Ballast Design 

Toward the end of the lamp’s life, the lamp-operating voltage will rise to a level beyond 

the ballast’s capability to sustain the arc. At this point, the lamp will start, warm up to full 

brightness, and extinguish. The repeating of this sequence is known as cycling and signals endof-life for HPS lamps. If the lamp is then not replaced within a reasonable amount of time, 

premature failure of the ballast can occur. In the 1990s, the industry introduced non-cycling HPS 

lamps. Manufacturers increased the xenon pressure and added a starting strip on the arc tube to 

assist starting. They also reduced the mercury dose and included lead-free construction. This 

type of lamp operates on standard HPS ballasts. Non-cycling lamps, with lowered additive dose 

construction, do not have a voltage rise at end-of-life. Because sodium loss cannot be eliminated 

completely, the lamp will gradually become fully unsaturated in the useful operating regime at 

some point in life. As the lamp then ages, its operating point will begin to shift downward and to 

the left on the watts-volts plot.17 Other research in the 1990s found that a specific combination of 

mercury and sodium in the lamp to maintain mercury and sodium pressures led to a lamp in 

which the voltage did not significantly increase over life.18 Through the use of this specific 

relationship and changing the material of the emitter in the lamp, less sodium was lost and lumen 

maintenance was slightly improved. 

3.5 METAL HALIDE LAMPS 

Developed in the 1960s after HPS lamps, MH lamps offer an excellent combination of 

quality, performance, and flexibility for “white light” applications. The first lamps were probestart quartz (circa 1960), followed by pulse-start quartz (circa early 1990s) and then pulse-start 

ceramic (circa late 1990s). The sources provide a significant amount of light for the package. 

3-18 
 

Unlike MV and HPS lamps, MH lamps have many suitable uses in both interior applications and 

exterior applications. The lamps are available in a wide range of CCTs (2900 to 10000 K) and 

CRIs (65 to 90). The small physical dimensions and high intensity of the arc make it an ideal 

point source around which to create application-specific light distributions through precise 

optical design in reflector lamps and fixtures. MH lamps are used in public, commercial, 

industrial, and residential sectors. The lamps are even used in transportation activities like 

vehicle forward lighting and range in wattages from 20 to 2000. Low-wattage (below 150) lamps 

are used for floodlighting and recessed lighting. Very low-wattage MH lamps (20 to 60) can be 

found in exterior accent and landscape luminaires (both residential and commercial) and retail 

track lighting. Also, since around the year 2000, very low-wattage MH lamps can be found in 

automotive headlights. Medium-wattage MH lamps (150 to 500) typically are used in area (e.g., 

parking lot and pedestrian walkways), roadway, low-bay, and high-bay applications. Finally, 

high-wattage MH lamps are used in some parking lots, search lights, and stadium/sports lighting. 

Some manufacturers produce MH retrofit lamps capable of directly replacing other 

lamps. Some lamps are designed to replace MV lamps of similar wattage, and operate on the 

same MV ballasts. However, like HPS retrofit lamps, MH retrofit lamps produce significantly 

more lumens for the same wattage. For example, replacing a 400-W MV lamp with a 400-W MH 

retrofit lamp generates about twice the light of the original MV lamp. MH lamp manufacturers 

have also developed self-ballasted, very low-wattage (under 40 W) PAR38 lamps intended as 

direct replacement for higher wattage halogen and incandescent reflector lamps. These PAR38 

lamps are used in high-end retail applications and even grocery stores. 

3.5.1 Construction 

The standard MH lamp is similar to MV lamp technology; the lamp is essentially an MV 

lamp containing one or more metal halides (usually iodides) which vaporize in the lamp arc.19 

The added compounds broaden the MV spectrum, producing better color rendering and lamp 

efficacy in MH lamps. 

The use of metal halides presents two advantages. First, metal halides are more volatile at 

typical lamp operating temperatures than pure metals. This allows metals with desirable emission 

properties to be introduced into the arc at reasonable arc tube temperatures. Second, metal halides 

do not readily react with a fused silica arc tube, instead remaining in the arc. When the lamp attains 

full operating temperature, metal halides in the arc tube partially vaporize. As halide vapors 

approach the high-temperature central core of the discharge, they dissociate into halogen and 

metals, with the metals radiating their light spectrum. As halogen and metal atoms move near the 

cooler arc tube wall by diffusion and convection, they recombine, and the cycle repeats.20

 Figure 3.5.1 and Figure 3.5.2 compare and contrast power flow of two 400-W MH 

lamps. Although dated, the diagrams illustrate how different metal halides used in MH lamps 

affect SPD and overall lumen output.11 Figure 3.5.1 is a tin iodide (SnI) lamp and produces 

24,000 lumens, CCT of 4100 K, and a CRI of 91. In contrast, another lamp at the same wattage 

and type (MH) has very different output. Figure 3.5.2 is a dysprosium iodide (DyI) lamp and 

produces 32,400 lumens, CCT of 5250 K, and a CRI of 85. 

3-19 
 

 

 

Figure 3.5.1. Tin Halide Figure 3.5.2. Dysprosium Iodide 

MH lamp construction is similar to that of MV lamps. One significant difference is that 

arc tubes of MH lamps are usually smaller for equal wattages. The arc tube is typically made of 

either fused quartz or ceramic. MH arc tubes operate at a higher temperature and pressure than 

their MV counterparts. Quartz arc tubes typically use a white coating at their ends to increase 

temperature and vaporization of metal halides by trapping thermal energy inside the arc tube. 

Replacing quartz in the arc tube with ceramic materials enables the lamp to operate at even 

higher temperatures and pressures, resulting in improved efficacy, CRI, and color stability. 

An elliptical outer bulb, usually made of borosilicate glass, contains the arc tube. The 

bulb protects and buffers the arc tube and internal electrical connections from the environment. 

The outer envelope contains low-pressure inert gas (i.e., nitrogen) or a vacuum, which not only 

helps minimize the oxidation of internal components, but also provides a margin of safety 

against threat of arc tube rupture (also known as non-passive failure). The outer envelope also 

provides additional thermal buffering for a more stable arc temperature. The glass itself absorbs 

the majority of UV energy.20 

Manufacturers may coat the outer glass bulb with diffusing material. Usually, this is a 

phosphor coating that helps change emission spectra for small improvements in CRI. However, 

the primary purpose of the coating is to reduce source brightness of the lamp for glare control. 

The technology advantage of MH lamps is their capability to emit the desired spectra without the 

addition of a phosphor coating. Adding a diffuse coating to the lamp reduces the efficiency and 

effectiveness of luminaires with optics. 

The outer bulb contains wires suitable for high temperatures to conduct electricity to the 

arc tube and structural components to support the arc tube. There might be other components, 

including resistors, diodes, and bimetallic switches used to help start the arc discharge, as well as 

devices called “getters” to purify the atmosphere in the outer lamp. Most MH lamps use getters 

to control (reduce or eliminate) impurities that, if present in the outer jacket of MH lamps in 

sufficient concentrations, can compromise performance. 

3-20 
 

Like other lamps in the HID group, MH lamps typically have screw bases (medium or 

mogul) made from brass, nickel, or special alloys to minimize corrosion. A characteristic of MH 

arc tubes is that they can take different forms and can be made from different materials. 

In a horizontally operated MH lamp, the arc discharge bows away from the axis of the arc 

tube due to convection currents. The MH pool (liquid) moves to the center of the arc tube. The 

bowed arc moves farther from the metal halides than when the lamp is vertical, causing the metal 

halides to cool. This lowers the vapor pressure of MH chemicals and decreases the concentration 

of metals in the arc, resulting in loss of light. The bowed arc moves closer to the top of the arc 

tube wall, causing its temperature to increase. The higher heat loading on the arc-tube material 

can result in a decrease in life of approximately 25 percent. Therefore, manufacturers use 

additional shapes to compensate for this sensitivity in operating position. High-output lamps 

designed to operate horizontally use a special base and socket, such as the ANSI EP39 Mog 

position-oriented mogul base, to help ensure proper arc tube orientation and position. 

Figure 3.5.3 shows a bowed arc-tube shape that follows the natural bowing of the 

horizontal arc.20 

Note: POM means position oriented mogul. 

Source: OSRAM SYLVANIA, High Intensity Discharge Metalarc® Lamps, 1998.20 Reproduced with 

permission.10 

Figure 3.5.3. Formed Arc-Tube Configuration for Horizontal Metal Halide Lamps 

Figure 3.5.4 shows an asymmetric arc tube with offset electrodes. In this design, the 

electrodes are lower in the arc tube body, and the arc discharge bows to the center of the arc 

tube. 

Source: Philips, 2003. Reproduced with permission.21 

Figure 3.5.4. Offset Electrode Configuration for Horizontal Metal Halide Lamps 

Arc Tube

Main Electrode

Starter Electrode

Main Electrode

Arc Tube 

Main Electrode 

Starter Electrode 

Main Electrode 

3-21 
Some lamps use a transparent sleeve, called a shield or shroud, to surround the arc tube 

(Figure 3.5.5). The sleeves are useful as heat shields because they help the arc tube achieve a 

uniform temperature profile. Shrouds also prevent the outer jacket of the lamp from breaking in 

case of a violent arc-tube failure; however, shrouds are not the only method of protection (e.g., 

some new ceramic tubes have a wrapped wire instead of a sleeve). HID lamps with protective 

shrouds carry the ANSI O-rating, signifying that the lamps meet ANSI requirements for safe 

operation in an open-luminaire not equipped to protect against violent failure. To prevent user 

misapplication, the industry developed unique socket and base combinations in both medium 

bases and mogul bases for these open-luminaire lamps. 

Protective Shroud ective Shroud Arc Tube 

Source: Venture Lighting, 2003. Reproduced with permission.22 

Figure 3.5.5. Metal Halide Arc Tube with a Shroud 

Some applications, such as sports lighting, use MH lamps without outer jackets. Due to 

high levels of UV energy in their emission spectra, luminaires that operate with these lamps (no 

outer jackets) require a glass cover to absorb some of this harmful UV radiation. 

3.5.1.1 Probe-Start Quartz Metal Halide Lamps 

The first MH lamp was the probe-start lamp (Figure 3.5.6), where the arc tube is shaped 

into what is called the classic pinched body. These lamps require a starter electrode (or probe) in 

the arc tube. The lamp body must also contain a system that provides for cutting starting voltage 

after the lamp is started, typically with a bimetal switch. Continued application of high starting 

voltages can severely shorten lamp life. The location and type of bimetal switch can restrict the 

lamp operating position, as the bimetal must achieve a certain temperature to function. 

3-22 
Source: GE Lighting, High-Intensity Discharge Lamps Catalog, 2003. Reproduced with permission.9 

Quartz tube

Main electrode

Starting resistor

Argon fill gas,

metal halide

& mercury vapor

Nitrogen fill gas

Main electrode

Outer bulb

Starting electrode

Base

Quartz tube 

Main electrode 

Starting resistor 

Argon fill gas, 

metal halide 

& mercury vapor 

Nitrogen fill gas 

Main electrode 

Outer bulb 

Starting electrode 

Base 

Figure 3.5.6. Metal Halide Lamp Construction

 An evolutionary development of the probe-start lamp configuration is the formed-body 

arc tube. Manufacturers can mold arc tubes into unique shapes such as an ovoid (Figure 3.5.7), 

significantly improving performance. The contour of the formed-body arc-tube wall follows the 

shape of the arc, thereby allowing for a more uniform temperature profile for the arc tube. Also, 

formed-body arc tubes have much smaller pinch-seal areas. This allows MH chemicals to heat up 

more rapidly than those in conventional pinched-body arc tubes, resulting in a shorter warm-up 

time than pinched-body arc tubes of the same wattage. Probe-start MH lamps typically use 

pinch-seal designs (Figure 3.5.7) that have a starter electrode (or probe) to help initiate the 

breakdown of arc-tube gases. 

(a) Ovoid (b) Pinched-Body 

Source: Advanced Lighting Technologies Inc., 2003. Reproduced with permission.22 

Figure 3.5.7. Common Arc Tubes 

3-23 
 

 

3.5.1.2 Pulse-Start Quartz Metal Halide Lamps 

Thirty years after probe-start MH lamps entered the market, pulse-start MH (PMH) lamps 

were introduced. Pulse-start MH lamps are similar to probe-start; however, PMH lamps lack a 

starting probe in the arc tube. 

 Pulse-start MH lamps were the first to incorporate formed-body arc tubes, but this arctube shape is not exclusive to pulse-start configurations. Some manufacturers still use pinchedbody arc tubes in their PMH lamps.23 

Pulse-start MH lamps have a higher starting-gas fill pressure to decrease the starting time 

and minimize the transport of electrode material to the wall. These improvements extend life (up 

to 50 percent longer) and improve lumen maintenance (up to 33 percent) compared with 

traditional probe-start MH lamps. 

3.5.1.3 Pulse-Start Ceramic Metal Halide Lamps 

The most recent development in MH arc tube design incorporates the ceramic arc tube. 

Like formed-body arc tubes, this pulse-start technology lacks a starter probe. This arc tube 

represents the newest evolution in the development of MH lamps. The lamp performance and 

electrical-characteristic segments of this MH lamp chapter discuss the improvements in 

performance from these new shapes and materials. 

3.5.2 Lamp Performance 

Commercially available MH lamps have initial efficacies from 30 to 125 lm/W 

(excluding ballast losses). The lowest efficacy is related to a type of directional lamp and is not 

typical of the MH lamp family. Depending the on the type of MH lamp, the CRI ranges from 65 

to 90, far superior to virtually every other HID lamp (MV and HPS). This unique capability 

results from manufacturers’ ability to tailor the spectral outputs of the lamps. 

Metal halides are binary compounds consisting of halogen and metal elements. Halogens 

are a group of non-metals including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and 

astatine (At). Iodine in the form of ions (also known as iodide) is the most common halogen used 

in MH lamps. Bromine is the other halogen used, but less often than iodine. Metal halides are 

additive compounds, so nearly any metal can be combined with halogens. However, certain 

metals are not used because of toxicity, instability, or other problems with the metals at the 

required vapor pressures. Excluding those metals, roughly 50 different metals can still be used in 

MH lamps. Using two metals at a time, the number of possible combinations (not counting 

variations in concentration) is 1,225. The metals can be used three, four, or five at a time, giving 

19,600, 230,300, or 2,118,760 combinations.24 Although many possible combinations exist, 

metals are typically selected with strong emission lines in the desired portion of the spectrum. 

Typical metals used in MH lamps include indium (In), tin (Sn), and the rare earth (RE) 

elements which include scandium (Sc), yttrium (Y), and 15 lanthanoids: lanthanum (La), cerium 

(Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), 

gadodinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), 

ytterbium (Yb), and lutetium (Lu). 

3-24 
Other metals that have been explored are alkaline earth halides, a series of metals that 

comprise Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), 

strontium (Sr), barium (Ba), and radium (Ra). A 1976 study examining improving MH lamps 

found that: 

In many cases, e.g., sodium and the rare earth halides, an increase in vapour pressure will 

result in a higher luminous efficacy. In other cases, e.g., the alkaline earth halides, one 

could enhance the emission at certain wavelengths and thus substantially improve the 

colour rendering properties of the lamp.25 

Metal halides in these lamps have characteristic emissions that are spectrally selective. 

Some metals emit visible radiation in narrow spectral bands, generating specific colors to the eye 

(i.e., Na for yellow-orange, Tm for green, and In for blue). A 1985 study examining the spectral 

properties of MH lamps with rare earth iodides found that the spectra of the metal can be 

selectively used: 

This results in the possibility of optimizing the spectra for distinct applications. In 400 W, 

lamps the highest efficacies obtained were reached with Ce-Na and Pr-Na mixtures, η = 

110 to 115 lm/W [LPW]. The best colour rendering properties can be obtained with Tm 

and Dy (Ra>80).26 

Other metals such as tin, when introduced as halides, radiate predominantly as molecules, 

providing continuous band spectra across the visible spectrum. Various combinations of these 

halides can create a wide range of CCT and CRI for these lamps. 

Phosphor coatings also change the spectral emission of these lamps. Because phosphors 

convert shorter-wavelength radiation to longer-wavelength radiation, these phosphors effectively 

lower the CCT of lamps by approximately 300 K. Although a slight improvement in CRI may 

occur, the primary function of a phosphor coating of MH lamps is to create a more diffuse light 

source. These combinations of metals and their halides as well as phosphors (to a lesser extent) 

create an almost infinite palette of possibilities, giving MH lamps flexibility in light-output 

design unique to the HID sources. Figure 3.5.8 shows typical SPD plots for MH lamps with and 

without a phosphor coating. 

3-25 
 

MP100UMED 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

300 400 500 600 700 800 

Wavelength (nm) TR20014366 

(a) 

MP100/C/U/MED 

0.30

ns) 

0.25

0 lume 0.20 for 100

0.15

r 5nm for

0.10 

0.05 

Out

0.00

put (Watts pe

300 400 500 600 700 800 

Wavelength (nm) 204443b 

(b) 

Source: OSRAM Sylvania, 2003. Reproduced with permission.10 

Figure 3.5.8. Spectral Power Distribution of Metal Halide Lamps 

(a) Without Phosphors and (b) With Phosphors 

Because the physical operating orientation of the lamp affects performance, MH lamps 

are typically life-rated and lumen-rated in the vertical operating position. For example, MH 

lamps classified as universal orientation (able to operate in any orientation) achieve their rated 

performance in the vertical position. 

3.5.2.1 Probe-Start Quartz Metal Halide Lamps 

When operated to specifications, probe-start lamps have a rated life from 10,000 to 

20,000 hours with an average efficacy of 84 lm/W. The actual efficacy varies by both the lamp 

wattage and the lamp type (omni-directional lamps are more efficacious than directional lamps). 

The rated LLD is about 25 percent at 40 percent of rated life. 

Color quality is an important aspect of MH lamps. The average CRI for probe-start lamps 

is 76; actual values range as in Table 3.5.1). However, CRI only examines a sample of eight (R1­

R8) pastel color samples, atypical for some applications. Therefore, in addition to the CRI Output (Watts per 5nm for 1000 lumens) 

3-26 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

values, many MH lamp manufacturers are now reporting the R9 (deep red color) for 

specification in interior applications, especially retail. The R9 value of probe-start lamps is 

negative.27 Therefore, probe-start lamps have limited use in interior applications and are not 

practical for retail installations. Over life, the color shift among the same batch of MH lamps can 

be from 300 to 800 K.28 

Table 3.5.1. Performance Summary of Probe-Start Metal Halide Lamps 

Lamp Power* 

W 

CRI CCT** 

K 

Initial 

Lumens 

Life 

hr 

Initial Efficacy 

at 100 hr† 

lm/W 

Mean Efficacy 

at 40% Life‡ 

lm/W 

50 Minimum 70 2900 3,200 10,000 64 30 

Median 85 3500 3,525 10,000 71 46 

Maximum 92 4000 4,100 20,000 82 55 

70 Minimum 70 2900 2,610 3,200 37 43 

Median 92 4000 5,000 9,000 71 55 

Maximum 96 6500 6,200 20,000 89 66 

100 Minimum 65 2900 6,000 9,000 60 48 

Median 92 4000 8,400 15,000 80 59 

Maximum 96 6500 9,500 20,000 95 71 

150 Minimum 65 2800 5,400 2,800 36 48 

Median 95 3850 11,950 10,000 80 60 

Maximum 96 6500 14,000 20,000 93 70 

175 Minimum 55 3000 10,000 7,500 57 43 

Median 65 4000 13,600 10,000 78 50 

Maximum 75 10000 15,000 10,000 86 69 

250 Minimum 62 3000 17,500 7,500 70 38 

Median 65 4000 20,750 10,000 83 55 

Maximum 90 10000 23,000 20,000 92 78 

360 Minimum 60 3600 31,700 15,000 88 57 

Median 65 4000 36,000 20,000 100 65 

Maximum 80 4300 43,200 30,000 120 98 

400 Minimum 60 3000 25,000 8,000 63 44 

Median 65 4000 36,050 20,000 90 60 

Maximum 90 10000 43,000 20,000 108 84 

1000 Minimum 65 3200 72,000 6,000 80 52 

Median 65 3700 110,000 12,000 110 86 

Maximum 72 5500 120,000 18,000 120 96 

1500 Minimum 60 3400 125,000 3,000 83 67 

Median 65 4000 163,000 3,000 109 93 

Maximum 92 5500 170,000 6,000 113 102 

* A minimum of three different manufacturers had to produce the type and similar wattage to have that wattage class 

listed in this table. 

** Correlated-color temperature is not a performance metric; the values are listed to show the range of available 

CCTs for the product. 

† Initial efficacy is initial lumens divided by the lamp rated power (the power use of the ballast is not factored into 

this table). 

‡ Mean efficacy is the mean lumen value provided by the manufacturer divided by the lamp rated power (the power 

use of the ballast is not factored into this table). Manufacturers select the time at which they provide the mean lumen 

data, which vary between 40 and 50 percent of rated life. Lumen depreciation still occurs after this point. Also, not 

all manufacturers publish mean lumen values. The mean efficacy values can be higher than the initial efficacy 

values because the mean lumens were not provided, and this column is based on mean lumens. 

3-27 
 

 

 

 

3.5.2.2 Pulse-Start Quartz Metal Halide Lamps 

When operated to specifications, the rated life of pulse-start MH lamps is 15,000 to 

30,000 hours with efficacies in excess of 100 lm/W. The LLD is about 25 percent at 40 percent 

of rated life. Table 3.5.2 summarizes the performance of PMH sources. 

Table 3.5.2. Performance Summary of Quartz Pulse-Start Metal Halide Lamps 

Lamp Power* 

W 

CRI CCT** 

K 

Initial 

Lumens 

Life 

hr 

Initial 

Efficacy 

at 100 hr† 

lm/W 

Mean 

Efficacy 

at 40 % Life‡ 

lm/W 

50 Minimum 60 2900 2,900 10,000 58 30 

Median 70 3300 3,300 10,000 66 41 

Maximum 92 4000 4,100 20,000 82 55 

70 Minimum 65 2800 2,610 3,200 64 40 

Median 82 3500 5,200 12,000 74 54 

Maximum 96 6500 7,400 20,000 106 79 

100 Minimum 65 2700 5,800 7,500 58 48 

Median 73 3200 8,500 15,000 85 58 

Maximum 92 4200 9,500 20,000 95 72 

150 Minimum 60 2800 5,400 2,800 73 55 

Median 85 3550 12,500 12,000 83 64 

Maximum 96 6500 15,000 20,000 100 75 

175 Minimum 62 3200 13,000 10,000 74 57 

Median 65 4000 16,000 15,000 93 71 

Maximum 75 4200 17,500 15,000 100 80 

250 Minimum 60 3000 16,500 10,000 66 52 

Median 70 4000 22,500 15,000 90 69 

Maximum 94 6500 26,000 20,000 104 80 

320 Minimum 62 3200 22,500 10,000 70 28 

Median 70 4000 30,000 20,000 94 72 

Maximum 90 5000 34,000 20,000 106 84 

350 Minimum 62 3200 25,000 10,000 88 57 

Median 67 4000 34,500 20,000 99 74 

Maximum 90 5000 51,628 30,000 120 98 

400 Minimum 60 3600 27,000 10,000 68 39 

Median 65 4000 39,850 20,000 100 75 

Maximum 90 6500 44,000 20,000 110 90 

1000 Minimum 65 3400 80,000 5,000 80 64 

Median 65 3900 110,000 12,000 110 88 

Maximum 92 5500 120,000 15,000 120 96 

* A minimum of three different manufacturers had to produce the type and similar wattage to have that wattage class 

listed in this table. 

** Correlated-color temperature is not a performance metric; the values are listed to show the range of available 

CCTs for the product. 

† Initial efficacy is initial lumens divided by the lamp rated power (the power use of the ballast is not factored into 

this table). 

‡ Mean efficacy is the mean lumen value provided by the manufacturer divided by the lamp rated power (the power 

use of the ballast is not factored into this table). Manufacturers select the time at which they provide the mean lumen 

data, which vary between 40 and 50 percent of rated life. Lumen depreciation still occurs after this point. Also, not 

all manufacturers publish mean lumen values. The mean efficacy values can be higher than the initial efficacy 

values because the mean lumens were not provided, and this column is based on mean lumens. 

3-28 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.5.2.3 Pulse-Start Ceramic Metal Halide Lamps 

Advancements in arc tube materials led to the development of the ceramic arc tube. This 

material allows MH lamps to operate at even higher temperatures and vapor pressures. The 

technology is currently available only in wattages up to 400. Improvements in ceramic arc-tube 

design will soon make higher-power versions available. When operated to specifications, 

ceramic metal halide (CMH) lamps have a rated life of 6,000 to 20,000 hours with an efficacy of 

approximately 88 lm/W. The LLD improves over quartz MH lamps to about 20 percent at 

40 percent of rated life. CMH lamps also have excellent CRI with an average CRI of 88. Typical 

R9 values are positive but very low. 

Recent advances in CMH lamp design allow for high CRI (90), good R9 (over 40), 

greater efficacy, and improved lumen maintenance. These new CMH lamps, currently produced 

by Philips, are medium wattage (315 and 210) and have an efficacy over 120 lm/W. In contrast, 

other similar wattage CMH or PMH lamps are between 90 and 115 lm/W. The lumen output of 

these new lamps is 90 percent at 40 percent of rated life; in contrast to typical 80 percent for 

CMH, 75 percent for PMH, and 70 percent for MH. The developers of this new CMH lamp 

attribute the performance enhancements to operating the lamp on an electronic ballast; using new 

chemical additives (presumably different metal halides); and optimized arc tube shape.27 

Table 3.5.3 summarizes the performance of CMH lamps. 

Table 3.5.3. Performance Summary of Pulse-Start Ceramic Metal Halide Lamps 

Lamp Power* 

W 

CRI CCT** 

K 

Initial 

Lumens 

Life 

hr 

Initial Efficacy 

at 100 hr† 

lm/W 

Mean Efficacy 

at 40–50% Life‡ 

lm/W 

50 Minimum 81 2900 1,400 6,000 72 49 

Median 85 3000 2,225 10,000 76 52 

Maximum 92 4200 3,500 15,000 82 57 

70 Minimum 80 2900 2,850 9,000 51 37 

Median 88 3000 5,800 12,000 81 61 

Maximum 95 4300 7,300 24,000 104 93 

100 Minimum 81 3000 5,700 10,000 57 40 

Median 85 3000 8,200 12,500 82 62 

Maximum 93 4100 9,500 24,000 95 72 

150 Minimum 80 2800 9,100 5,000 61 55 

Median 90 3000 12,800 10,000 85 63 

Maximum 96 5500 15,500 24,000 103 83 

250 Minimum 85 3000 20,750 12,000 83 66 

Median 90 4050 22,500 20,000 90 73 

Maximum 94 4200 25,000 24,000 115 103 

400 Minimum 85 3000 34,800 15,000 87 70 

Median 90 4000 38,000 20,000 95 78 

Maximum 90 4200 41,000 20,000 102 82 

* A minimum of three different manufacturers had to produce the type and similar wattage to have that wattage class

listed in this table. ** Correlated-color temperature is not a performance metric; the values are listed to show the range of available 

CCTs for the product. 

† Initial efficacy is initial lumens divided by the lamp rated power (the power use of the ballast is not factored into

this table).

‡ Mean efficacy is the mean lumen value provided by the manufacturer divided by the lamp rated power (the power 

use of the ballast is not factored into this table). Manufacturers select the time at which they provide the mean lumen data, which vary between 40 and 50 percent of rated life. Lumen depreciation still occurs after this point. Also, not 

all manufacturers publish mean lumen values. The mean efficacy values can be higher than the initial efficacy

values because the mean lumens were not provided, and this column is based on mean lumens. 

3-29 
3.5.3 Electrical Characteristics 

The additional electrode located at one end of the arc tube in probe-start MH lamps 

allows operation without an ignitor circuit, making it possible for MH lamps to share the same 

ballast with MV lamps, within limits. However, MH ballasts typically have more rigorous 

operating requirements than MV ballasts. Thus, MV lamps can operate universally on similar 

wattage probe-start MH ballasts, but the opposite is true only with specially designed MH lamps. 

Lamp manufacturers took advantage of this and produced MH lamps that could operate on MV 

lamp ballasts. However, replacement raises issues of economy and utility, in addition to 

technological issues. The engineering analysis (chapter 4) of this document addresses these 

issues. 

Pulse-start MH lamps lack the secondary electrode found in probe-start MH lamps, 

resulting in different electrical requirements and performance. Using an ignitor, a high-voltage 

pulse (typically in excess of 3 kilovolts) is applied directly across the main electrodes to initiate 

the arc, resulting in faster starting and re-strike times than for probe-start MH lamps. The warmup and re-strike times are 2 minutes and 3 to 4 minutes, respectively. That is an improvement 

over the typical probe-start MH warm-up time of 4 minutes and a re-strike time of 15 to 20 

minutes; these results are also better than those of typical MV and HPS lamps. 

3.6 HAZARDOUS MATERIALS 

Mercury is a double-sided issue in the lighting industry. Although HID lamps are more 

efficacious than halogen/incandescent (mercury free) lamps, mercury is needed in most vapor 

discharge sources (both low and high pressure). However, use of these sources displaces more 

mercury released in energy production, so it still is beneficial to use a discharge source over 

incandescent/halogen. Amount of mercury in an HID source varies by lamp type and wattage. 

Table 3.6.1 is from a 2008 report about trends in mercury use in products.29 In both 2001 

and 2004, lamps represented about 8 percent of the total use of mercury in products. Overall 

mercury usage in lamps decreased by roughly 6 percent between 2001 and 2004. The total use of 

mercury in HID lamps increased by 15 percent, whereas use by fluorescent lamps decreased by 

14 percent between 2001 and 2004. The reason total mercury usage was relatively flat, while 

these two lamp types changed significantly, is that fluorescent lamps have been designed to use 

less mercury and more HID lamps were specified between the 2 years. Table 3.6.2 breaks down 

the mercury sold by HID lamp type. The vast majority of mercury usage in HID lamps is in the 

MH family. 

Table 3.6.1. Total Mercury Sold in Lamps 

All Lamps Total Mercury Weight 

lb (kg) 

2001 2004 

Fluorescent 16,657 (7,555.48) 14,372 (6,519) 

High Intensity Discharge 2,749 (1,246.93) 3,156 (1,431.54) 

Compact Fluorescent 877 (397.80) 1,479 (670.86) 

Neon 1,103 (500.31) 1,070 (485.34) 

Short Arc 10 (4.54) 17 (7.71) 

Miscellaneous 42 (19.05) 24 (10.89) 

Total 21,438 (9,724.11) 20,118 (9,125.37) 

3-30 
 

 

Table 3.6.2. Total Mercury Sold by High-Intensity Discharge Lamp Type 

Lamp Type 2001 Total Mercury 

Sold by Weight 

lb (kg) 

Portion of 

total HID 

% 

2004 Total Mercury 

Sold by Weight 

lb (kg) 

Portion of 

total HID 

% 

MH 2,145 (972.95) 78 2,426 (1100.42) 77 

Ceramic MH N/A 0 31 (14.06) 1 

HPS 401 (181.89) 15 453 (205.47) 14 

MV 203 (92.08) 7 213 (96.62) 7 

Total 2,749 -- 3,156 --

Mercury is integral to the three lamp types, though more for some than others. HPS 

lamps have been designed with low mercury and even no mercury content (labeled as such in 

catalogs). The typical amount of mercury for HPS lamps from 35 to 1000 W is between 10 and 

50 milligrams (mg). By definition, MV lamps must contain mercury. The typical mercury 

content in MV lamps from 50 to 1000 W is between 50 and 150 mg. Because MH technology is 

related to MV lamps, mercury plays a vital role in these lamps. The typical mercury content in 

MH lamps from 39 to 50 W is between 1 to 10 mg; 70 to 250 W is between 5 to 50 mg; 350 to 

400 W is between 30 to 100 mg; and 400 to 2000 W is between 100 to 150 mg. 

In response to reducing mercury in products, mercury-free HID lamps have been 

investigated. A 2007 research paper considered replacing mercury with noble gases. Noble gases 

include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). The study 

experimented with Ne, Ar, and Xe. “The presented results emphasize Ar and Xe as proper Hg 

substitute candidates.”30 

Lead is sometimes present in HID lamps as solder for the coupling. A toxicity 

characteristics leaching procedure test on HID lamps classifies them as hazardous waste for 

mercury and lead. Therefore, they are subject to the Universal Waste Rule published by the U.S. 

Environmental Protection Agency (EPA) on July 6, 1999.31 State and local regulations will vary 

on their disposal, but recycling is recommended. 

A small percentage of MH lamps contain the radioactive isotope krypton 85. The MH 

lamps that contain this radioactive isotope are primarily used in special applications of theatrical 

and film luminaires. 

3.7 HIGH-INTENSITY DISCHARGE LAMP BALLASTS 

High-intensity discharge lamp ballasts apply sufficient voltage for lamp ignition, regulate 

the operating current, and essentially relight the lamp at each one-half cycle of the voltage. A 

1983 paper focusing on the relationship between HPS lamp voltage rise and the ballast 

summarized the relationship: “A lamp and ballast cannot be considered separate elements but 

each contributes to a dynamic system influencing each other in achieving total system 

performance.”15 Although this quote was in relation to HPS lamps, it is applicable to HID lamps 

in general. For HPS and PMH lamps, an additional ignitor circuit generates the high-voltage 

starting pulse necessary to initiate the arc discharge. Typical input voltages for HID lighting 

systems are 120, 208, 240, 277, and 480 volts. 

3-31 
 

 

 

 

 

 

 

There are two types of HID ballasts: magnetic and electronic. The majority of ballasts 

sold for HID lamps are magnetic, also known as core-and-coil. The ballasts operate at 60 hertz 

(Hz). Within the magnetic HID ballast family, there are seven sub-types of ballasts: (1) highreactance autotransformer; (2) reactor-normal power factor; (3) reactor-high power factor; (4) 

regulated-lag, also known as magnetically regulated; (5) constant-wattage autotransformer 

(CWA); (6) constant-wattage isolated (CWI); and (7) super constant-wattage autotransformer 

(SCWA). CWA has become the most popular HID ballast for lamp power levels above 150 W.32 

Ballast efficiency varies with rated lamp power, less ballast losses occur as the rated power 

increases.b 

The other major type of ballast is electronic; currently, electronic ballasts only exist for 

pulse-start lamps. Within the electronic HID ballast category, there are only two types: low 

frequency (less than or equal to 400 Hz) and high frequency (equal to or above 100 kilohertz 

[kHz]). Most electronic HID ballasts are for MH lamps, with a small portion for HPS lamps, and 

no electronic ballasts for MV lamps. A 1990 paper comparing some of the first electronic HID 

ballast with conventional ballasts found that when electronic ballasts for high-pressure lamps 

will be different than for electronic ballasts for low-pressure discharge lamps. For electronic 

ballasts, “more sophisticated, forms of generators for lamp operation must be used than in the 

field of low-pressure discharge lamps.”33 Unlike electronic ballasts for FL lamps, HID electronic 

ballasts do not always make the lamp-ballast system more efficient. In 2006, the Lighting 

Research Center (LRC) compared 70-W MH lamps from various manufacturers operating on 

both magnetic and electronic ballasts by different manufacturers. The LRC study found that 

ballast efficiency was directly affected by the type of ballast: “Because of design and 

manufacturing practicalities, the ballast efficiency of magnetic ballasts is approximately 10 

percent lower than that of electronic ballasts.”34 There are some system (lamp plus ballast) 

efficiency gains from converting from magnetic to electronic HID ballasts, but there are other 

electrical issues associated with electronic HID ballasts that affect HID lamps. During the public 

meeting for the framework document for the MH lamp fixture energy conservation standard, the 

disadvantages and advantages of electronic HID ballasts were discussed. A comment from the 

meeting sums up the issue of electronic HID ballasts: “Some electronic ballasts do improve lamp 

maintenance and lamp life, others do not; as a matter of fact, some electronic ballasts can 

decrease lamp life.”35 

Long-rated operating lifetimes are one of the desirable features of HID lamps, compared 

with other sources. Electronic ballasts can both start and operate a lamp more “gently” than a 

magnetic ballast, with positive benefits in the lamp performance. A study from the mid-1990s 

found electronic ballasts can extend lamp life once other electrical issues are addressed: “[W]ith 

attention paid to the proper features of the electronic ballast, namely high extinguishing 

resistance, it can be concluded that lamp service life with electronic ballasts will be 1.5 to 2.0 

times longer than with conventional ballasts.”36 

One of the principal disadvantages of electronic ballasts is that the lamps operate at high 

frequency and this creates acoustic resonance. The LRC study comparing 70-W lamps operating 

on electronic ballasts describes the negative issue of acoustic resonance: “At frequencies above 

4 kHz, standing pressure sound waves (acoustic resonances) build inside the lamp’s arc tube, 

which can lead to visible distortions and instability of the electrical discharge, light flickering, 

b

 Ballast efficiency – the ratio of lamp rated power/ballast input power (Pout/Pin). 

3-32 
 

 

and possible cracking of the tube.”34 As stated earlier, lamp life can be extended via the use of an 

electronic ballast but can also be cut short if special precautions in either the ballast or lamp 

design are not used. 

Ballast design is not the purview of this document. Therefore, only aspects of the lamp 

that directly affect acoustic resonance are reviewed here, specifically, arc tube size and 

geometry. Pressure waves are created in the lamp when the resonant frequency is close to the 

operating frequency. These pressure waves move through the lamp, distorting the arc tube path, 

which causes flicker and, in extreme cases, arc contact with the tube wall. If the arc touches the 

tube wall, the arc tube can crack. A cracked arc tube seriously affects the lamp and can lead to 

non-passive failure (i.e., rupture) of the arc tube and bulb wall. 

Lamp Current Crest Factor (LCCF)c is an aspect of either magnetic or electronic ballasts 

that can affect both the HID lamp life and lumen maintenance. Many within the lighting industry 

consider lamp life and lumen deprecation the primary performance metrics of a lamp-ballast 

system.32 The lamp electrodes can be damaged by high LCCFs, which directly affects lumen 

maintenance and lamp life. LCCF values can range from 1.0 to infinity; however, ANSI specifies 

maximum LCCF values. For example, ANSI C78.43-2007 covers single-ended MH lamps from 

39 to 1650 W and sets a maximum LCCF of 1.8 for 39- to 1650-W MH lamps.37 A 2008 paper 

comparing the effects on lamp life and lumen depreciation for two different types of ballasts for 

400-W MH lamps articulated the value of an LCCF limit: “The rationale for placing an upper 

limit upon the LCCF is to prevent the lamp current from falling to an unsuitably low value for a 

significant period of time on a half-cycle basis.”32 Lower LCCF values are better for the lamp 

electrode and thus are better for the lamp life and lumen maintenance. The LRC study articulated 

the waveform and LCCF issues of magnetic and electronic ballasts in their comparison: “An 

ideal sinusoidal waveform (and therefore, a magnetic ballast) cannot have an LCCF below 1.4. 

Most magnetic ballasts have LCCFs ranging from 1.5 to 1.7. The square current waveform of an 

electronic ballast allows the LCCF to approach 1.0.”34 

c

 Lamp Current Crest Factor (LCCF) – the ratio of the peak lamp current to the root-mean-square value of the lamp 

current. 

3-33 
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