Theatre Design & Technology - Oct 1972 - 26

IMPROVING THE PERFORMANCE
oF LAM POI MMER st
GEORGE A. KAPPENHAGEN, Hub Electric Co.

Use of integrated circuits and feedback technology provides easy, accurate, and stable control of the light output
from incandescent lamps.
Dimming control for incandescent lamps has been
steadily improved through the years and its applications
broadened. The latest improvement is a dimmer that compares actual Iight output with desi red output and makes
the required correction to regulate light level accurately
over all levels from full bright to fully dimmed.
The original application for dimmers, and still a large
one, is in complex switch boards for theater stage lighting.
A large installation has several hundred dimmers with
sophisticated programming. More and more smaller installations appear as high schools and colleges build new stage
faci Iities or upgrade ex isti ng ones. In any theater, accu rate
light regulation is important because visual effects constitute a large part of a performance.
Light levels also are important in television and photographic studios. The response of the camera to light is
quite specific and does not adapt like the human eye; for
good pictures, light levels must be easily adjustable and
remain set where they are supposed to be.
Intensive-care areas in hospitals have dimmers to dim
the lighting at night. It is important that the area not get
too dark due to drop in line voltage or to normal temperature rise in the dimmer. Other applications are in conference rooms and demonstration areas, where special lighting effects are often advantageous.

volt.
Loading also causes line voltage changes. All of the
wiring, reactors, transformers, and so on have resistance.
When only a few lamps are on, a small current flows and
the voltage drop across this resistance is quite low. When
all the lamps are on, however, a very large current flows
and the voltage drop across the resistance is very high.
Consequently, lamp voltage tends to fluctuate. The new
dimmer typically allows only a 0.5-volt total change from
full lamp load to minimum lamp load.
Temperature changes tend to cause drift in control circuits. Most dimmers do not always track with each other
(dim their lamps uniformly and together). The reason is
that one may be hot and another cold; the lamp voltage
changes, in turn, and different lamps supposedly at the
same light level are actually at different levels. Drift is
especially a problem at low light levels, where it is very
obvious. Dimmer racks give off heat of their own and are
usually tucked away in out of the way places that are not
air conditioned. The new dimmers are so designed that
they are thermally stable.

Development
In the early days of lighting control, dimmers were
variable autotransformers. They provided smooth flicker-

Dimmer Requirements
Dimmers have to overcome three main adverse effects - fluctuations in line voltage, loading, and temperature.

less control at low cost and are still suppl ied for small

Line voltage can vary considerably in the far reaches of
a power system. The variations cause light level to fluctuate, and a high line voltage in the full-bright control posi-

26

tion causes lamps to run over rated wattage and burn out
quickly. Hub Electric Company's new dimmer can take a
line voltage change of ± 10 volts and typically allow a
change of only ± 0.1 volt at the load. For a ± 20-volt
change, which is very rare, typical regulation is ± 0.25

tThis article appeared in the July 1972 issue of the Westinghouse
Engineer and is reprinted here with their permission. Ed.

rnrrc::J

THEATRE DESIGN AND TECHNOLOGY

OCTOBER, 1972



Table of Contents for the Digital Edition of Theatre Design & Technology - Oct 1972

Contents
Theatre Design & Technology - Oct 1972 - 1
Theatre Design & Technology - Oct 1972 - 2
Theatre Design & Technology - Oct 1972 - 3
Theatre Design & Technology - Oct 1972 - Contents
Theatre Design & Technology - Oct 1972 - 5
Theatre Design & Technology - Oct 1972 - 6
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