Theatre Design & Technology - Spring 1979 - 25

w-o'ff-Technical Reports

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Fred_M_,

Using Photometric Data Sheets
by Robert Bullock
placement and aiming of lights. To a lighting designer it is a link
between the ideal and the realities imposed by the limitations of the
theatre building.
Data sheets iilustrate instruments positioned in zero degrees, or
perpendicular to the working plane. In the resulting cone of light the
field angle, the beam angle, and illumination values are indicated. In
the cone of light the beam angle is where the candlepower is 50
percent of maximum candlepower and the field angle is where the
candlepower is 10 percent of the maximum candlepower. When a
lighting instrument is hung at zero degrees, a circular beam pattern
results; when a lighting instrument is hung at an angle, however, the
cone of light creates an oval beam pattern. In actual plotting of the
beam, only the height of the instrument, the angle at which it is hung
(or horizontal distance of the instrument to the center of the area to
be lighted), the field angle and the beam angle of the instrument are
needed. The height and the angle of focus depend on the auditorium
and the demands of the production, and the field angle, beam angle
are indicated on manufacturers' data sheets. In Figure 1 the beam is
divided into the point of focus (A) and zero degree positioning (B) for
explanatory purposes. Plotting to scale, the lighting instrument is

A joint study done by the Illuminating Engineering Society and the
Society of Motion Picture and Television Engineers was initiated in
1958 by IES and their report, Recommended Practice lor Reporting
Photometric Perlormance 01 Incandescent Filament Lighting Units
Used in Theatre and Television Production, was published in lIfumination Engineering, September 1958. The study set minimum requirements for data included in photometric reports (data sheets)
and suggested a standardized vocabulary and format for such reports, but how the information was presented was left to the manufacturer. Section 5 of the report pertained to the presentation of
photometric information and included a Candlepower Distribution
Curve, and Illumination Curve (and throw distance), Conversion Factors, Field and Field Angle, Beam and Beam Angle.
Stage lighting manufacturers provide data sheets for individual
instruments purchased but these invaluable sheets are usually filed
away or discarded. Photometric data is most commonly found in
distributors' lighting catalogs and brochures, but often this information is not specific enough to be used in designing a lighting plot; it is
not intended for this. The information contained on data sheets is
more complete and can be used to determine more accurately the

B

POSITIONED INSTRUMENT
POINT OF fOCUS-

O· POSITION

45'

-5.5'

BE A'" M.GLE

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Idted 10

~b:PI.ilne I,lled

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M.""~llt,n be'OO't
\1"~,"9 lIoo, p~ne

10 l.ho.-

0" be''''p,llle,"
"'ote O·."'ete' ., .I1W)
CGmpulf'd ,,'fll diOlol

,heel guIde nu...be,

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l.UI

e

i= 1'-0

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Figure 1: BEAM COMPUTATION

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1000W 12' ELLIPSOIDAL

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A Point

of focus: establishes
long axis of elliptical pattern

/

B 0'

Positioning: establishes
short axis of elliptical pattern

C Plan

of elliptical beam
pattern

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IY'

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I

,

(~l/
\~I
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SHORT AXIS
t~'-.(

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LONG AXIS

10'-·'

C

Robert Bullock is completing an MFA in stage design and a BFA in product/graphic design.
Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1979
