# Theatre Design & Technology - Oct 1972 - 24

```colors would be identified by their wavelength listed in
nanometers. 3
The term "white" source has been used above. It has
been recognized that with different sources of light (various incandescents or carbon arcs) a particular color media
will produce a different color with respect to each separate source of light. Because of this the C.I.E. has defined
a series of sources. "Source A is an incandescent lamp
operated at a color temperature of 2854°K. Source B is
obtained by using the same lamp in combination with a
two-cell David-Gibson liquid filter designed to give a color
0
temperature of about 5000 K (representative of noon
sunlight). Source C is obtained similarly and results in a
sou rce of correlated color temperature of about 6800° K
(representative of average daylight such as that from a
completely overcast sky"4 Due to the fact that Source A
is the most common source color temperature used in the
performing arts trades, it is recommended that Source A
be used for the purpose of this color code.
The mathematics utilized in this system involves using
the X,Y,Z values of a color calculated from the spectral
composition of the radiant energy of the light source (or
color specimen). Using these values, two calculations must
be made, one of which is small x and the other small y.
(Small z could also be calculated but is not used; however,
the sum of the three values must equal unity). Small x
designates the total percentage of X (red) and is found by
dividing the X value by the sum of X, Y, and Z Values.
Small y is found similarly. With these two values, a point
on the chart can be plotted for the color that has been
tested (Figure 2). A line can then be drawn from the point
on the chart designated as the Iight sou rce th rough the
color specimen's plotted point and intersecting on the
curve indicates the dominant wavelength 5 of the color
that has been tested. This is known as the dominant wavelength only if the unknown color is plotted between the
source and the spectrum. If the light source is located
between the unknown color specimen's plotted point and
the intersection on the cu rve, the color falls in the open
end of the curve and is not in the spectrum (Figure 3).
Such a color, i.e. magenta or purple, cannot be assigned its
own wavelength since, although visible, it does not fall in
the spectrum. The complement of such a color is within
the spectrum and therefore such a color may be described
by the complementary wavelength. This may be found by
extending the line until it intersects the curve.
Purity of color is that amount of hue 6 in a color
tested. It is a term used in the color sciences and does
point out the nature of pastel shades. In a sense it is
related to, but is not the same as transmission. For this
reason, it is recommended that mention of it in this proposed coding system be eliminated.
The writer of this paper recommends that a definite
procedure be adopted as a standard:
1) Tests be made by an independent color testing
laboratory using Source A preferably with a spectral

24

distribution chart and the values of X,Y,Z and the
transmission factor furnished, or, allow the manufacturers, at their option, to supply at no charge
equal information. Manufacturers can be requested
to furnish typical samples for testing.
2) A sample uniform work sheet be adopted similar to
the one included.

.,

575

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.,.. t. .511:>
.7

.,

i

!"-

.

:3 \
.@ ~ ~
i
'2 t ~~
I

.0

---

.

""""'\

.5

.'

--_.'

!

"-

\

. I . .t

--

1\.7Ig()

.,.V ......... 1

I~ ~ V

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.-

J

I

3 ..., . S' * c *., I * '8' * '1
)(

Figure 2.
Line drawn from Source A through point (x
y = _34) crossing curve at :\488.

.26,

J.
.S-H-+--+---Poo.:-+--~+-~-+---;

'I;'

-'--j+-+--+----i--+-:"o.:-!:=-~.-----_+_-__j

.34---\-+--+-----:.-t-f----3'oc-'lr-::=~_j
=--~c..:..=.+_j
I

------10-----1

.C .'1 .'a .~
Figure 3.
Source is between point (x = .52, y = .37) and curve;
therefore color is in open end (not in spectrum). Identified
by use of complementary :\ found by extending line until
it crosses curve. [C506]
30 ne nanometer
1 X 1O-- 6 mm.

(nm)

is

1/1.000,000

millimeter

or

4Nimeroff, I., COLORIMETRY: National Bureau of Standards
Monograph 104, p. 9, January 1968.
5The dominant wavelength is the color that the human eye
recognizes (it might be termed the mean average wavelength of
light the eye recognizes).
6Hue is that quality of color which we describe by the words
red, yellow, etc.

~ THEATRE DESIGN AND TECHNOLOGY

OCTOBER, 1972

```

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