Theatre Design & Technology - Oct 1973 - 19

As much as possible, the entire testing procedure was
kept to what would be a normal handling of color media.
Each sample was cut from its sheet under normal room
light conditions. At no time throughout the testing were
the media deliberately kept away from that light which
would strike it during normal stage handling.
The choice of instrument type allowed for a reasonably
strict test. Though spotlights of over 500 watts are often
used in stage lighting, such instruments are not always
burned at full capacity. In addition, the spot focus at
which the instruments were set allowed for a concentration of light closer to the center of the color medium.
Exposure time for each section of the trial was
determined by an approximation to normal time used for
most theatres. At the beginning of the test, the color
samples were burned for three five hour intervals to
simulate burning time of some pretechnical and technical
rehearsals. After that, ten three hour burning periods
were run, as would happen with dress rehearsals and performances, for a total of forty five hours exposure time.
(The Gaiser-Rootes study used nine three hour periods).
Between each of the th irteen trial periods, enough time
was left for the instruments to cool completely. This cooling period assured that there wou Id be no cumulative
effect of the heat in an instrument, since the type of
instrument used rises quickly to its maximum temperature
and retains heat for a time after it has been shut down.
The choice of time intervals for exposure again gives a
stringent test, as particular instruments usually do not
burn at full capacity for the entire elapsed running time
of a particular performance.
At the end of each exposure period, samples of each
tested color were taken. The samples were one-half inch
square, and each sample fell on the circumference of a
circle one-and-one-half inches from the center of each
color medium frame. An additional sample was taken
from the axis of each sheet at the end of the test. To
prevent heat loss through the openings left by the removed
samples, these openings were patched with a new piece of
equal size taken from the original sheets of color medium
using ordinary transparent tape. It had been found in the
Gaiser-Rootes tests that with this method of replacement
the effect did not differ from the effect on an uncut sheet.
After each sample was taken, it was put in a light-tight
envelope until the time that it was inserted into the recording spectrophotometer. Each sample was separately
placed in a Bausch and Lomb Spectronic 505. This
particular machine uses a tungsten source and measures
spectral transmittance with an accuracy factor of ±-0.5%,
and a repeatability factor of '±'0.3%. It records the spectral
transmittance curves with the horizontal reference being
the visible wavelengths measured in nanometers (millimicrons). and the vertical reference being the percentage
of spectral transmittance of light.

specific results: 1) a comparison of the specific variations
in the same color area of the different brands tested, 2)
a comparison of the effects of light at the center of the
color medium with a point one-and-one-half inches from
the center, 3) a comparison of the color stability of the
two newly-marketed products with the control product
for the twenty-seven hours used as a maximum time in the
Gaiser-Rootes experiments, and extended to forty-five
hours to help determine the supposed further stability of
the new media in relation to the media previously tested,
and 4) a comparison of the spectral transmittance curves
of each color at specific exposure times against the
spectral transmittance curves of zero exposure time to
reveal any significant changes in transmission over the
entire testing period.
The carefu I and consistent use of normal stage procedures and the use of like instruments, combined with
the incident light and voltage readings taken during the
experiment were in conformity with the purpose of the
testing procedure used in the first study. That study
attempted to stabilize all the possible variables that
account for or contribute to color medium burnout. The
'±'0.5% accuracy of the spectrophotometer, the '±'3%
voltage fluctuation plus other unavoidable deviations,
such as operator variations and variable usage results in
lamps and instruments need to be brought into the "range
of error" factor. Gaiser and Rootes estimated that a
difference of 10% in perceived luminance "under the
masking complexities of a normal production in the
theatre . . . might well pass unnoticed" by the human
eye (p. 8). Possible variations in this experiment are well
within that estimate. In conformity with the previous
test, discussion of results will take that 10% factor as a
minimum variation in considering change in percentage of
transmittance of spectral energy.

II
Specific study of the samples taken during exposure
of the color media included a visual examination of the
exposed color sheets as well as the comparisons of spectral
transmittance curves mentioned above. All resu Its except
that visual examination are shown in the series of graphs
included in this study.
Figure B
Spectral
energy distribution of
a 500 watt
incandescent
lamp

,... .."

, ...... ,
___"

.......,......0"
$0

Ilotrt

-.,

,,_

/
/
/

The following comparisons, then, were examined for

THEATRE DESIGN AND TECHNOLOGY

OCTOBER. 1973

Table of Contents for the Digital Edition of Theatre Design & Technology - Oct 1973