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The Lamp Section of the National Electrical Manufacturers Association proposes the following definition for "colored" lamps. There are several colors such as fluorescent cool green and incandescent jewelers blue. that..are_ sold Jn. particular. niche:- markets,,--We propose that these lamps and similar future niche market designs be excluded in a similar fashion to the cold temperature fluorescent lamps i.e. they would be clearly marked and marketed for use only in a particular well defined application. Proposed Definition of Colored Lamp
The excitation purity of a "colored" source; pe, is defined as the ratio NC/ND of two collinear distances on the chromaticity diagram of the CIE 1931 or 1964 standard colorimetric systems (Ref 1).. NC is the distance between the point C representing the color stimulus of the lamp being considered and the point N which represents the specified reference (or achromatic) stimulus. ND is the distance between the point D on the spectrum locus at the domir ant'wavelength of the color stimulus of the lamp being considered and the point N which represents the specified reference (or achromatic) stimulus. This definition leads to the following expressions for pe:

P. = (Y-Yn)/(Yd-Yn) or pe = (X-Xn)/(xd-xn)
where (x,y), (xn,yn) and (Xd,Yd) are the x,y chromaticity coordinates of the points C, N and D, respectively. These equations are equivalent; however, the equation with the larger numerator gives greater precision.
Dominant wavelength of a color stimulus is the wavelength of the monochromatic stimulus that, when additively mixed in suitable proportion to the specified reference stimulus, matches the color stimulus of the lamp being considered.
It is proposed that the excitation purity, Pe, based on the 1931 CIE color space, be used to define a "colored" lamp.
Figure 1 is a diagram of the 1931 CIE color space. The point N is chosen as the color stimulus of an equi energy source i.e. a source with equal energy at all wavelengths. Points indicating the color stimulus of currently produced lamps which should be defined as "colored" are plotted. The excitation purity for each plotted lamp chromaticity is included in Table 1. From Figure 1 it is evident that a value greater than 50% for the excitation purity would be a reasonable lower limiting value defining a "colored" lamp. This is defined as area A - Saturated Colored Lamps in Figure 2. Lamps whose pe value falls within the area defined as B - Pastel Colored Lamps and C - White Lamps produce non-colored light with the exception of some niche marketed products which fall within area B. The advantage of this definition is that a single definition suffices for all colors. With the establishment of the 50% excitation purity area. all that remains is a single plot of the x and y chromaticity coordinate point to determine if the lamp is colored.
Reference 1 CIE 15.2 (1986) Colorimetry 2nd ed.

## 1931 CIE Diagam with Loci for Excitation Purity based on an Equi Energy Source

M M. • F I Gw • fl..ew.. r4..L.r Rid PAR Mod



## 0.0 0.2 0.4 0.6 0.8 1.0 0.75, Equi Energy Source

0.50, Equi Energy Source 

## 1931 CIE Diagram illustrating Locations of
Colored Sources'



# xI iHjure 2 - 1931 CIE Diagram Defining Regions of Colored and.Non-Colored :: Light



## 0. r"°' A - Saturated Colored Lamp. exempt from EPAC standard. B - Pastel Colored. Lamp -;must meet EPAC standard or`: be marked and marketed for a specific application. C - White Lamp - must meet EPAC standard. 

## Q.6

C

0,0



## 0.0 0.2 0.4 0,6 0.8



# x Note: The distance about-the black body-.locus (area C) to be dete:rmined.Table 1. Excitation Purities of Current "Colored" Sources

Summary of Excitation Purities of :."Colored" Lamps.for. Equi Energy .Source ..:.

PAR Blue Dichroic Amber Dichroic Blue Dichroic Green Dichroic Red Dichroic Yellow Green Lt. Blue Pink Red Yellow Pe 0.773 0:991 0.882 0.748 0.975 0.913 '0.591 0.357 0.655 0.948 0.960

Fluorescent Cool Green 0.122 Gro Lux 0.360C Blue 0.596 Green 0.704 Pink 0.649 Gold 0.992

Incandescent Bug Yellow 0.981 Green Ceramic - 0.421 Standard Blue 0.154 Red Ceramic 40W 0.957 Red Ceramic 60W 0.972 Soft Pink - Ferro 0.957 Bug Yellow - Ferro 0.852Method of Determination of the Excitation Purity (pe) for a Lamp

Determine the CIE 1931 2° chromaticity coordinates (x,y) for the lamp at the selected operating conditions. This can be done by any of the accepted methods ,such as tristim.ulus'colorimeter or. spectral measurement and 'baldi latlohi :.. The' accuracy 'of the °cfefetm iriation" of' the 'e-ccfetiori :puritjt is dependent upon the accuracy of the determination of the chromaticity coordinates. Refer to.appropriate I.ES LM's and CIE documents for direction in 'determining chromaticity.
2. Plot the lamp 'chromaticity point on the 1931 CIE diagram.
3. Plot the reference source chromaticity on the C.IE diagram. For the equienergy source, the coordinates are (xn,yn) with values (0.3333, 0.3333).
4. Draw a line through the lamp chromaticity point (x,y) and the equi-energy source chromaticity point (xn,yn) so that it intersects the locus of the spectrum colors (the actual CIE curve). This point of intersection defines the dominant wavelength. Note that identification of the dominant wavelength is not necessary; only the chromaticity coordinates of the dominant wavelength (Xd,yd) are required.
5. Read the chromaticity coordinates at the dominant wavelength (xd,yd) from the diagram.
6. Use the following equations to determine the excitation purity, pe:

P. = (Y-Yn)/(Yd-Yn) or P. = (x-xn) /(xd-xn) Both equations should give the same result. Use the equation with the larger numerator for better precision.
e.g. The integrated light from a PAR larnp with blue coating was measured with a spectroradiometer. The calculated lamp chromaticity. (x,y) is 0.1310, 0.2233. Using the equi-energy reference, (xn,yn) are 0.3333, 0.3333. The chromaticity coordinates of the dominant wavelength (Xd,Yd), taken at the intersection described in 4, above, are 0.080, 0.1950. Calculation using pe = (Y-Yn)/(Yd-Yn) yields a value of 0.796; calculation using Pe = (X-xn)/(xd-xn) yields a value of 0.798.NOTE:

The previously proposed definition of a colored lamp will assign normal clear and diffuse coated incandescent lamps as colored sources if their color temperature ranges from slightly above a 2856K CCT to lower CCT's. This is inherent in the proposed color definition and cannot be readily corrected by redefining the limit for the excitation purity.
For example a 2856K blackbody source with the equi-energy source as the reference will have a calculated excitation purity of 0.595. If the excitation purity value above which lamps are defined as colored is 0.50 then this source would be considered a colored source. If the excitation purity limit is changed to include this 2856K source within the limit then lower CCT incandescent lamps would still remain outside of the limit. Clearly, there is no sharp limit between colored and white light sources. To resolve this problem the limit on excitation purity is relaxed within the range defined by area C around the black body locus.

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