5C-i 

APPENDIX 5C. MODIFIED-SPECTRUM INCANDESCENT REFLECTOR LAMPS 

TABLE OF CONTENTS 

5C.1 INTRODUCTION .........................................................................................................5C-1 

5C.2 BACKGROUND ...........................................................................................................5C-1 

5C.2.1 Spectral Power Distribution and Commonly Used Color Properties...........5C-1 

5C.2.2 Methods of Modifying Spectral Power Distributions..................................5C-4 

5C.3 APPLICATION OF “MODIFIED-SPECTRUM” DEFINITION TO IRL ...................5C-4 

5C.3.1 Color Requirements .....................................................................................5C-5 

5C.3.2 Black Body Locus Requirements.................................................................5C-5 

5C.3.3 MacAdam Step Requirements .....................................................................5C-6 

5C.4 METHODOLOGY ........................................................................................................5C-7 

5C.5 ANALYTICAL RESULTS .........................................................................................5C-10 

5C.6 SELECTION OF FINAL SCALING FACTOR..........................................................5C-12 

REFERENCES ........................................................................................................................5C-13 

LIST OF FIGURES 

Figure 5C.1: Spectral Power Distribution of Two IRL Tested By DOE...................................5C-2 

Figure 5C.2: The CIE 1931 Chromaticity Diagram...................................................................5C-3 

Figure 5C.3: Combined Black Body Locus and Color Requirements of the “ModifiedSpectrum” Definition...................................................................................5C-6 

Figure 5C.4: Example of IRL That Meet the Definition of "Modified-Spectrum” ..................5C-8 

Figure 5C.5: Transmittance of a Specific Modified-Spectrum Lamp Cover Glass Relative 

to the Standard-Spectrum Transmittance...................................................5C-10 

Figure 5C.6: Comparison of Standard Spectrum and Modified-Spectrum IRL Efficacy 

Requirements .............................................................................................5C-12 

LIST OF TABLES 

Table 5C.1: Test Results for Purchased PAR IRL Models Advertised as ModifiedSpectrum Lamps ........................................................................................5C-11 

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APPENDIX 5C. MODIFIED-SPECTRUM INCANDESCENT REFLECTOR LAMPS 

5C.1 INTRODUCTION 

 A modified-spectrum incandescent lamp is an incandescent lamp with special coatings or 

other features that modify the wavelengths of light that exit the lamp, changing the perceived 

color of the lamp’s light. The definition of “modified-spectrum” in the Energy Policy and 

Conservation Act (EPCA) as amended by the Energy Independence and Security Act of 2007 

(EISA 2007) applies to general service incandescent lamps (GSIL) that are noticeably different 

in color than unmodified (or standard-spectrum) GSIL, with specific additional color 

requirements. Some incandescent reflector lamps (IRL) are also sold with features that modify 

their spectrums, and DOE believes that such IRL provide a unique utility to users. For example, 

a number of these lamps are advertised as being able to reproduce the spectrum of natural 

daylight. 

 The features that modify the spectrums of incandescent lamps usually reduce the 

efficacies of the lamps. Thus, DOE is creating a modified-spectrum IRL product class and 

setting standards for these lamps by scaling efficacy requirements from the standard spectrum 

IRL product classes. As discussed in chapter 3, Market and Technology Assessment, DOE used 

the EPCA “modified-spectrum” definition to determine what lamps would be included in this 

product class. DOE believes that the definition of “modified-spectrum” was created for GSIL, as 

the EPCA definition requires the testing of clear lamps as a reference for spectrum comparison, 

but IRL are not clear lamps due to their reflective coating. This appendix describes how DOE 

adopted the EPCA definition of “modified-spectrum” for IRL and developed the factor used to 

set the efficacy requirements for the modified-spectrum IRL product class. In particular, DOE 

tested IRL advertised as “modified-spectrum” by using similar standard-spectrum IRL as 

references for spectrum comparison. 

5C.2 BACKGROUND 

 Objects absorb, reflect, and radiate a form of energy known as electromagnetic radiation, 

which can be visualized as waves of energy that travel through open space. Different 

wavelengths of electromagnetic radiation have different common names; for example, radio 

waves have wavelengths ranging from millimeters to hundreds of thousands of kilometers, and 

visible light has wavelengths roughly between 380 and 750 nanometers (nm). Various 

wavelengths of visible light are perceived as various colors by humans. 

5C.2.1 Spectral Power Distribution and Commonly Used Color Properties 

 Some portion of the electromagnetic radiation emitted by lamps exists in the spectrum of 

visible light. Most lamps emit multiple wavelengths of light simultaneously, and the radiant 

power (energy radiated per unit time) of each wavelength can be plotted as a spectral power 

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5C-2 

distribution (SPD).1 Example SPDs is shown in Figure 5C.1 for a specific standard-spectrum 

IRL and a specific modified-spectrum IRL tested by DOE for this rulemaking. 

350 400 450 500 550 600 650 700 750 800

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

Wavelength (nm)

Spectral Power (W/nm)

Modified spectrum

Standard spectrum

Figure 5C.1: Spectral Power Distribution of Two IRL Tested By DOE 

 The measurement of a lamp’s SPD allows the characterization of the lamp’s perceived 

light color. Three color properties in particular are commonly computed for lamps based on the 

SPD. One is the chromaticity, which refers to the color of the lamp’s light as mapped onto a 

chromaticity diagram such as the CIE 1931 chromaticity diagrama shown in Figure 5C.2.2 

Subtle differences in color can be quantified using MacAdam steps, named after David 

MacAdam, who studied color perception in the 1940s.3 A MacAdam step is an ellipse that 

encircles a region of points on the chromaticity diagram that appear to be indistinguishable to 

most humans (in other words, they appear to be the same color). Points further than a distance of 

three MacAdam steps from any reference color point are generally perceived as being different 

in color than the reference point. 

 

a

 This particular figure is the chromaticity diagram for the CIE 1931 color space, created by the Commission 

Internationale de l’Eclairage (International Commission on Illumination, or CIE) in 1931. The colors on the outer 

curved boundary are composed of single wavelengths of electromagnetic radiation, with wavelengths indicated by 

the numbers. All colors inside the space are composed of a distribution of wavelengths of various powers. 

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Figure 5C.2: The CIE 1931 Chromaticity Diagram 

 The curved line in the center of Figure 5C.2 is known as the black body locus and 

represents the perceived light color emitted by a black body heated to the indicated temperature 

(in Kelvin). In the field of physics, a black body is a theoretical object that is considered to be 

the simplest emitter of electromagnetic radiation. It absorbs all electromagnetic radiation falling 

onto it (and thus reflects no radiation), and wavelengths of the radiation emitted by the body are 

related only to its temperature. Black bodies are so named because at room temperature they 

emit mostly infrared radiation, which has a lower frequency and longer wavelength than visible 

light. Because they reflect no radiation, they would appear black. As the temperature of a black 

body increases, its emitted radiation increases in frequency while shortening in wavelength and 

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5C-4 

begins to be perceived as visible light. Any object hot enough to emit visible light is said to 

incandesce, and the phenomenon of visible light emission due to high temperature is known as 

incandescence. 

 A lamp’s correlated color temperature (CCT) is another commonly computed color 

property and is based on the behavior of black bodies. The CCT of a lamp is the temperature of 

a black body that produces roughly the same spectral power distribution of light (and thus 

roughly the same perceived color). Incandescent lamps produce light when electric current is 

sent through the filament inside the lamp, causing the filament to heat up and incandesce. The 

SPD generated by incandescent lamps is similar to the SPD generated by a black body; thus, the 

temperature of the heated filament is near the CCT of the lamp. Many IRL have a CCT between 

2,700K and 3,000 K. 

 The color rendering index (CRI) of a lamp is also commonly computed and refers to how 

closely the perceived color of an object illuminated by that lamp matches the perceived color of 

the same object in daylight or black body radiation. The CRI ranges from 0 to 100; lamps with 

high CRIs illuminate objects such that humans perceive colors similar to what would be 

perceived if those objects were illuminated by daylight. Most incandescent lamps without 

modified spectrums have a CRI near 100. 

5C.2.2 Methods of Modifying Spectral Power Distributions 

 Though the visible spectrum contains green and other colors, the spectral power 

distributions that can be generated by incandescence are such that incandescing objects can only 

produce a narrow subset of all of the colors that the human eye can perceive. To produce colors 

that are distant from the black body locus, the SPD of an incandescent object’s radiation must be 

modified in some way. 

 Various methods are used to modify the SPD of incandescent reflector lamps. Some 

methods utilize specific chemicals, such as neodymium, that are introduced into the cover glass 

of the lamp. Other methods rely on layers of material that are sandwiched into the cover glass or 

coatings that are applied to the outside or inside faces of the glass. The compounds, layers, or 

coatings used to modify the SPD operate by reducing the power of specific wavelengths of light; 

thus, they act as selective filters. Because the total light output of the IRL is reduced, IRL with 

modified spectrums are less efficacious than standard-spectrum IRL of the same filament, bulb 

shape, rated voltage, and rated wattage. 

5C.3 APPLICATION OF “MODIFIED-SPECTRUM” DEFINITION TO IRL 

 The Energy Policy and Conservation Act (EPCA), as amended by the Energy 

Independence and Security Act of 2007 (EISA 2007), defines “modified-spectrum” as follows 

(42 U.S.C. 6291(30)(W)): 

“The term ‘modified-spectrum’ means, with respect to an incandescent lamp, an incandescent 

lamp that— 

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5C-5 

 (i) is not a colored incandescent lamp; and 

 (ii) when operated at the rated voltage and wattage of the incandescent lamp— 

(I) has a color point with (x,y) chromaticity coordinates on the Commission 

Internationale de l’Eclairage (C.I.E.) 1931 chromaticity diagram that lies below 

the black-body locus; and 

(II) has a color point with (x,y) chromaticity coordinates on the C.I.E. 1931 

chromaticity diagram that lies at least 4 MacAdam steps (as referenced in IESNA 

LM16) distant from the color point of a clear lamp with the same filament and 

bulb shape, operated at the same rated voltage and wattage.” 

 The following sections will address each component of the definition in turn as it relates 

to modified-spectrum IRL. 

5C.3.1 Color Requirements 

 The “modified-spectrum” definition requires that the modified-spectrum lamp meet 

specific color requirements; namely, that it not be a “colored incandescent lamp.” (42 U.S.C. 

6291(30)(W)(i)) The amended EPCA defines “colored incandescent lamp” as follows (42 

U.S.C. 6291(30)(EE)): 

“The term ‘colored incandescent lamp’ means an incandescent lamp designated and marketed as 

a colored lamp that has— 

(i) a color rendering index of less than 50, as determined according to the test method 

given in C.I.E. publication 13.3–1995; or 

(ii) a correlated color temperature of less than 2,500K, or greater than 4,600K, where 

correlated temperature is computed according to the Journal of Optical Society of 

America, Vol. 58, pages 1528–1595 (1986).”b

Most IRL with unmodified spectrums have a CRI near ideal (100) and a CCT between 

2700 K and 3,000 K. Colored incandescent lamps are lamps that have been modified, using 

coatings or other methods, so that they produce light that is perceived as blue, red, green, or 

other colors. These lamps are used for aesthetic or artistic effects and thus are not meant to 

reproduce object colors accurately. 

5C.3.2 Black Body Locus Requirements 

 The “modified-spectrum” definition also requires that a modified-spectrum incandescent 

lamp produce a perceived color with a “color point . . . that lies below the black-body locus” on 

the CIE 1931 chromaticity diagram when operated at its rated voltage and wattage. (42 U.S.C. 

6291(30)(W)(ii)(I)) The chromaticity diagram and black-body locus are shown in Figure 5C.3 

along with red straight lines indicating color requirements. The combined color and black body 

 

b

 Note that EISA 2007 included “1986” as the year of publication of the article. However, 1986 is the incorrect year 

for the Journal of Optical Society of America reference; the correct year is 1968. 

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5C-6 

locus requirements of the “modified-spectrum” definition exclude all lamps with color points 

outside of the dark grey area in the figure. 

1931 CIE Chromaticity Diagram

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

x

y

Figure 5C.3: Combined Black Body Locus and Color Requirements of the “ModifiedSpectrum” Definition 

5C.3.3 MacAdam Step Requirements 

 Finally, the “modified-spectrum” definition requires that a modified-spectrum 

incandescent lamp have a color point that “lies at least 4 MacAdam steps . . . distant from the 

color point of a clear lamp with the same filament and bulb shape, operated at the same rated 

voltage and wattage.” (42 U.S.C. 6291(30)(W)(ii)(II)) Requiring the color point to be “at least 4 

MacAdam steps . . . distant from the color point of a clear lamp” ensures that modified-spectrum 

lamps will be noticeably different in color compared to similar clear lamps. 

 Applying the definition of “modified-spectrum” requires comparing the color point of the 

IRL in question to the color point of a clear lamp. IRL, however, are not clear lamps because 

they have reflectors; IRL also commonly have frosted or textured faces. In order to apply the 

definition of “modified-spectrum,” DOE developed a normalization method to model a clear 

lamp. This method is discussed in the section below. 

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5C-7 

5C.4 METHODOLOGY 

 In order to explore the efficacy differences between standard-spectrum and modifiedspectrum IRL, DOE paired commercially available standard-spectrum IRL with available IRL in 

the same product line that were advertised as modified-spectrum versions (for example, IRL 

advertised as “daylight” or “full-spectrum” lamps). First, DOE surveyed the market of 

commercially available IRL. DOE then selected lamp models that could be identified as 

modified-spectrum based on the manufacturers’ catalogs or marketing literature. Standardspectrum lamp models were paired with the modified-spectrum lamps such that they had the 

same bulb shape, the same rated life, the same rated voltage and wattage, and the same class of 

filament shape. All lamps had a rated voltage of 120V. 

 In total, DOE purchased eight pairs of parabolic aluminized reflector (PAR) lamps.c 

Seven pairs consisted of halogen lamps, and one pair consisted of halogen infrared (HIR) lamps. 

Each pair contained three samples of an IRL model advertised as modified-spectrum along with 

three samples of a corresponding standard-spectrum IRL model in the same product line. 

Halogen and HIR lamps were selected because the IRL design options that meet the proposed 

IRL standards in this rulemaking consist of both halogen and HIR technologies. Non-halogen 

incandescent lamps were not selected, as these non-halogen IRL have significantly different 

radiation spectra over wavelengths contributing to the calculation of lumens (in general their 

light outputs are shifted toward lower wavelengths) than HIR and halogen sources. Therefore, it 

is likely that the resulting scaling factor based on these lamps would be significantly different 

than for halogen sources. Because non-halogen IRL (representing the IRL lamp types exempted 

from standards) are not regulated in this rulemaking, DOE believes that it would be inappropriate 

to include such lamps in its scaling factor analysis. Therefore, DOE considered only halogen 

and HIR IRL for the computation of the modified-spectrum IRL scaling factor. Though DOE 

could not purchase and test all modified-spectrum PAR lamps on the market due to time and 

resource constraints, DOE believes that the eight purchased pairs are representative of the 

market. 

 DOE measured and recorded the SPDs of the standard-spectrum IRL samples in each 

pair, in accordance with the guidelines in 10 CFR Appendix R to Subpart B of Part 430 for 

incandescent lamps. Using the same guidelines, DOE also measured and recorded the SPDs of 

the samples of lamps advertised as modified-spectrum IRL in each pair. The SPDs allowed DOE 

to compute color properties of all of the lamps. To determine if the IRL advertised as modifiedspectrum satisfied the black body locus and color requirements of the “modified-spectrum” 

definition, DOE observed whether the color points of the lamps were located inside the dark grey 

area of the CIE 1931 chromaticity diagram shown in Figure 5C.3. Lamps with color points 

outside of this area were recorded as not meeting the definition. 

 To determine if the IRL satisfying the black body locus and color requirements had color 

points located at least four MacAdam steps away from the paired standard-spectrum IRL, DOE 

computed the average color point of the three standard-spectrum IRL in a pair and used this color 

 

c

 Other IRL bulb shapes, such as BR and R shapes, are not covered by the standards proposed in this rulemaking. 

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5C-8 

point as the center of the MacAdam steps. DOE then plotted an ellipse representing a distance of 

four MacAdam steps away from this center reference point and observed whether the lamps 

advertised as modified-spectrum IRL had color points outside of this ellipse. Lamps with color 

points inside the ellipse were recorded as not meeting the “modified-spectrum” definition. 

Figure 5C.4 shows a magnification of the CIE 1931 chromaticity diagram with an 

example of three IRL samples that meet the definition of “modified-spectrum.” The color points 

of the three standard-spectrum and three modified-spectrum IRL samples in this pair are shown 

as blue dots in the figure. The modified-spectrum IRL have color points located below the black 

body locus, shown in black. In addition, they meet the color requirements bounded by the red 

straight line at the right (the left bound is located outside of the area shown by the figure). 

Finally, their color points meet the MacAdam step requirement established by the three 

corresponding standard-spectrum lamps located in the center of the red ellipse, which represents 

a distance of four MacAdam steps from the average color point of the standard-spectrum IRL. 

Figure 5C.4: Example of IRL That Meet the Definition of "Modified-Spectrum” 

 Once DOE determined which lamps advertised as modified-spectrum met the definition 

of “modified-spectrum,” DOE then computed the reduction in light output in comparison with 

the corresponding standard-spectrum lamps. In order to do this, DOE first had to account for 

lamp physical variations apart from spectrum-modifying features (such as physical variations in 

filament shape and resistance, bulb shape, cover glass thickness, chemical additives, etc.). 

Because DOE could not assume that any lamp pair purchased represented identical lamps (with 

the exception of the modified spectrum), the recorded SPDs represented the effects of these other 

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5C-9 

physical variations in addition to the spectrum-modifying features. DOE assumed that these 

other variations are spectrally neutral; that is, they do not affect the color points of the lamps, but 

they do affect the lumen output. Based on this assumption, DOE developed a methodology to 

isolate the effects of spectrum modification in order to determine the reduction in lumen output 

caused by spectrum-modifying features alone. The method also assumes that spectrum 

modification is achieved through the usage of neodymium in the cover glass of a modifiedspectrum lamp. The methodology utilizes the equation shown below in Eq. 5C.1: 

MNS R =

β α Eq. 5C.1

where α is a scaling factor accounting for physical variations apart from spectrum-modifying 

features, SR is the average of the recorded SPDs for the three standard-spectrum IRL samples in a 

lamp pair, N is the transmittance of the glass covering the face of the modified-spectrum lamp, β

is a scaling factor representing variations in the cover glass thickness, and M is the resulting 

estimation of the modified-spectrum SPD with spectrum-modifying features isolated. 

Transmittance is the fraction of light (at a specific wavelength) hitting an object that 

travels through the object and can be measured on the other side. To determine N, DOE 

removed the cover glass from a modified-spectrum lamp sample and measured the transmittance 

between the wavelengths of 380 nm and 780 nm. This was also done for a sample of the 

corresponding standard-spectrum lamp model. The cover glass transmittance for a specific 

modified-spectrum lamp tested by DOE is shown relative to the corresponding standardspectrum lamp transmittance in Figure 5C.5. Sharp dips in the plot clearly indicate which light 

wavelengths are absorbed by the cover glass. Note, however, that the modified-spectrum 

transmittance in the figure is greater than the standard-spectrum transmittance for certain 

wavelengths (most visibly between 380 nm and 410 nm), indicating the presence of other 

physical variations apart from spectrum-modifying features. 

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350 400 450 500 550 600 650 700 750 800

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

Wavelength (nm)

Spectral Transmittance

Figure 5C.5: Transmittance of a Specific Modified-Spectrum Lamp Cover Glass Relative 

to the Standard-Spectrum Transmittance 

 To compute α and β and thus take into account these variations, DOE used the average of 

the recorded SPDs for the three modified-spectrum lamps in a lamp pair as MR in Eq. 5C.2: 

R = MNS R

β α Eq. 5C.2

Because SR, N, and MR are measured data, DOE was able to compute α and β. These factors 

were then used as input to Eq. 5C.1 to derive M, the estimated modified-spectrum SPD with 

spectrum-modifying effects isolated. Using M, DOE calculated the lumen output reduction due 

to spectrum modification. 

5C.5 ANALYTICAL RESULTS 

 Out of the eight purchased PAR lamp models advertised as modified-spectrum, two 

models met the definition. The average light output reductions for these lamps (due to the 

efficacy reductions caused by the features that modify the spectrum) are shown in Table 5C.1. 

When isolating the effects of spectrum-modifying features for lamp model “C,” DOE determined 

the scaling factors for Eq. 5C.1 to be α=1.007 and β=1.1169. For lamp model “D,” DOE 

determined the factors to be α=1.1473 and β=1.0623.

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Table 5C.1: Test Results for Purchased PAR IRL Models Advertised as Modified-Spectrum Lamps 

Lamp 

Model 

Name 

Rated 

Wattage 

[W] 

Shape 

and 

Diameter 

Rated 

Voltage 

[V] 

Rated 

Lifetime 

[hours] 

Meets Color 

Requirement? 

Meets Black 

Body Locus 

Requirement? 

Meets 

MacAdam Step 

Requirement? 

Meets 

Complete 

"Modified 

Spectrum" 

Definition? 

Average L

Outpu

Reduction 

Modifi

Spectru

A 50 PAR20 120 2500 Yes Yes No No N/A 

B 75 PAR30 120 3000 Yes Yes No No N/A C 75 PAR38 120 2500 Yes Yes No No N/A 

D 50 PAR20 120 2500 Yes Yes Yes Yes 19% 

E 50 PAR38 120 3000 Yes Yes Yes Yes 19% 

F 50 PAR20 120 3000 Yes No Yes No N/A 

G 75 PAR30 120 3000 Yes No No No N/A H 75 PAR38 120 3000 Yes No No No N/A 

Average light output reduction for all modified spectrum PAR lamps: 19% 

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5C.6 SELECTION OF FINAL SCALING FACTOR 

 Because DOE is only developing standards for IRL with the PAR shape in this 

rulemaking, DOE used the light output reduction for the two purchased PAR lamp models, “D” 

and “E,” that met the definition of “modified-spectrum.” These models both had an average 

light output reduction of 19% in comparison to their corresponding standard spectrum IRL. 

Thus, DOE used 19% as the final scaling factor reduction to establish the efficacy requirements 

for the modified-spectrum IRL product class based on the standard spectrum IRL requirements. 

 A comparison of the efficacy requirements for standard spectrum and modified-spectrum 

IRL is shown in Figure 5C.6. The IRL standard that currently exists in EPCA is shown as the 

dotted stair-step line labeled “Baseline EPCA.” Note that the smoothed lines for the modified 

spectrum efficiency levels (ELs) 1 and 2 have been raised in some areas so that the EPCA 

standard is met. This is because DOE “may not prescribe any amended standard which increases 

the maximum allowable energy use . . . or decreases the minimum required energy efficiency, of 

a covered product.” (42 U.S.C. 6295(o)(1)) 

Baseline

EPCA

EL 1

EL 2

EL4

EL 3

EL5

9.0

11.0

13.0

15.0

17.0

19.0

21.0

23.0

20 30 40 50 60 70 80 90 100 110

Lamp Power (W)

Lamp Efficacy (lm/W)

Mod EL1

Mod EL2

Mod EL3

Mod EL4

Mod EL5

Figure 5C.6: Comparison of Standard Spectrum and Modified-Spectrum IRL Efficacy 

Requirements 

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REFERENCES 

 

1

 Rea, Mark S., ed. The IESNA Lighting Handbook: Reference & Application, 9th Edition. 

2000. The Illuminating Engineering Society of America: New York, New York. 

2

 International Energy Agency. Light’s Labour’s Lost: Policies for Energy-efficient Lighting. 

OECD/IEA, 2006. 

3

 D. L. MacAdam, "Visual Sensitivities to Color Differences in Daylight," J. Opt. Soc. Am. 32, 

247-273 (1942). 

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