t^- /04

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.

EE-RM-94-220-IF COMMENT 10D
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'

x

EE-RM-94-220-IF COMMENT 10D
I 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.

EE-RM-94-220-IF COMMENT 10D
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 0.852

EE-RM-94-220-IF COMMENT 10D
Method 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.

EE-RM-94-220-IF COMMENT 10D
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.

6

EE-RM-94-220-IF COMMENT 10D