Theatre Design & Technology - Summer 1982 - 24

Part 2: The Effects of Output Control Upon Light
Color and Lamp Color Rendition

This part of the discussion deals exclusively with the light
color of lamps with respect to the control of their power input.
What is varied in output control? The spectral distribution of
energy within the visable range of from 400 to 700 mm.
The primary difference between incandescent lamps and
discharge lamps is that the former operates continuously and
the latter noncontinuously (line and band spectra respectively). In the case of incandescent lamps variations in the
spectrum occur in accordance with particular, known physical
laws. In the case of discharge lamps no uniform statement can
be made. There is too great a difference with respect to the
technology and the physical characteristics of the respective
types of lamps involved.
Before explaining the individual illustrations a review of
some terms seems in order.
1. Color Temperature of the Selective Radiator
The true temperature of a full radiator in degrees Kelvin:
0° Kelvin = Absolute zero point
0° Kelvin = -273°C
The tungsten filament of an incandescent lamp can, with a
reasonable degree of accuracy, be considered a full radiator.
Measurement of the color temperature of an incandescent
lamp is possible with standard temperature gauges calibrated
in ° C. A measured value of + 273 ° C gives the color temperature in degrees Kelvin. The start of the visable range is at
527°C = 800 degrees Kelvin.
2. Color Location
The color location of a lamp characterizes the light color of
a lamp. Color location is represented in three dimensions by
means of three color coordinates: x; y; and z. The sum of the
three coordinates x + y + z = 1. A representation of x and y
is usually sufficient since z is derived from the difference from
1. Color location is thus an arbitrarily chosen representation.
3. Spectral Distribution of Energy
The spectral distribution of energy characterizes the emitted energy of a light source within the visible spectrum from
400 nm (violet) to 700 nm (red).
1 nm = 10- 9 m = 10- 6 mm
500 nm = 5
250

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150

~ 100

350

1/:

2,500 mm .

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5
10,000 mm

x 10- 4 mm

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100

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Fluorescent
Tube
Warm Hue

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400

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600

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700

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Spectral Distribution of Energy of A Fluorescent Tube
No continuous spectrum with the composition consisting of
the mercury curve and the continuum of the luminescent material.
Control: there is practically no variation in the spectral distribution of energy, since during such control only the
excitation energy in the ultraviolet range is varied.

The Spectral Distribution of Energy of Additives of Halogen-Metal Vapor Systems
Known additives include natrium, thallium, indium, lithium,
dysprosium, thulium, and holmium.
Natrium, thallium, indium, and lithium have line spectra
while thulium, dysprosium, and holmium have quasi-continuous spectra.
Excitation conditions vary among the individual additives
depending upon the given temperature or power input. Output
control results in great variation in light color.
There is no uniformity with respect to the different types of
lamps.
Prerequisites include special lamps for film, theater, television, quasi-continuum, high-pressure.
Lamps with varying additives are available within the commercial market. Deviations in spectral distribution of energy is

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High-Pressure Output in:

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560

Incandescent Lamp

600

700

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Spectral Distribution of Energy of An Incandescent Lamp
Continuous spectrum resulting in a greater proportion of
red and a lesser proportion of blue.
Control: positive power input = higher color temperature and
a relatively greater proportion of blue
negative power input = lower color temperature and
a relatively lower proportion of red.

Spectral Distribution of Mercury High-Pressure Vapor Lamp
with Iodide Additives

Table of Contents for the Digital Edition of Theatre Design & Technology - Summer 1982