Theatre Design & Technology - Oct 1966 - 20

The control curve of a remote-controlled dimmer is the
characteristic of most interest to the operator and the
lighting designer. It is the one part of a functional design
that anyone can evaluate. Certainly, for convenient and
effective operation the nature of the curve should meet
the operator's expectations.
It would seem that the ideal control characteristic for
theal1"ical useage would be to have the property that equal
increments at the control give equal changes in the perceived light level. At this time there is no official standard which describes such an ideal.
It has been claimed that the so called "square law"
curve is close to the ideal characteristic. Whether this
is true or not is beyond the scope of this test series.
The fact is that present practice uses the "square law"
curve as the standard called out in manufacturers specifications. All of the dimmers tested had curves to "square
law". "Square law" control requires that the percentage
of full light output of any incandescent lamp be the
square of the control setting with the normal range of
zero to ten. All the dimmers tested were either factory
adjusted and sealed, or adjusted to optimum setting by
a representative of the factory.

Close physical inspection of the units revealed several
distinct levels of manufacture and workmanship quality.
Mechanical convenience varied widely also. Curve adjustments could be made without removing covers, screws
or hardware on only one unit, another required sliding
open small panels, and the three remaining designs were
either sealed or very clumsy to adjust.
One instruction manual was well done and complete, all
that it should be; another was in error, ambiguous and
incomplete. The three remaining dimmers carne without
any instructions at all.
There is wide variation in the heat-sinking on the various
units. The radiating surface per SCR ran in a range from
312 sq. in. down to 37.5 square inches. (The unit with
a small sink required forced air for safe operation. If a
power failure occurred removing all power from the
system, the heat energy stored in the SCR's and sinks
could destroy the SCR before power to the system returned.)
Several units required fans either in the dimmer package
or in the rack to provide adequate cooling. The reliability of such an approach is inferior to a system designed
for convection cooling.

The center of black band on the Figure 12 indicates a Admittedly these results are preliminary. No measurement
true square law response. The band width represents a of thermal drift was attempted nor was the very interesttolerance of
5 %. The use of a log-log chart allows a ing question regarding manufacturing consistency investigated.
straight line to represent this curve.
In summary I think it can be said that as an industry,
The best fit and the two extremes are displayed. Only
theatrical dimmer manufacturers are not routinely betterone dimmer stayed close to proper curve. The dimmer
ing, and in some cases, not even meeting their published
whose response is represented by the upper curve did
spec ificat ions.
not respond as rapidly as required by the "square law"
at settings near full nor at the low end of the control It seems evident that a buyer of a dimming system should
callout detailed performance specifications and plan on an
scale.
extensive inspection procedure on delivery.
The lower line represents the dimmer which showed
the least useable curve of any unit tested. The curve Another feature of our experience with these tests is
followed "square law" control over the 6 to 10 range. the wide variation we encountered in the way the speciBelow a setting of 3, the light output is nil.
fications are written. A standardized specification format
would be of advantage to those interested in dimming
systems. Such a format should include the line and load
tran~ients and some realistic evaluation of the lamp noise
produced by the dimmer.

±

Vout (RMS)

Vline

1.-------------------=:;;00-..
.9
.8

It is also evident from these tests that the variation between designs is smallHthe customer who buys the most
expensive dimmer available gets nearly the same product
as the man who buys the cheapest. In neither case is
the dimmer as complete, as functional nor as reliable as
it is presently possible to design and manufacture.

.7

.6

The modern theatre exists in a cultural matrix of extremely high scientific and engineering sophistication. We
have available to us the fruits of the scientific and
engineering efforts which mark the twentieth century.
The future advance of the craft of theatre cannot depend
on repeating blindly the practices of the past, but should
aim instead towards constructive and effective use of the
skills and knowledge of our times.

.2

2

Fig. 12:

20

Beyond the question of specified performance, present
SCR dimming equipment is far from as effective or as
useful as it could be. The "state of the art" often seems
to be ignored as far as line voltage regulation, construction practices and ther'llal control are concerned .

3
SETTING

4

5

6

7

8

9 10

Dimmer Response.

I USITT I

THEATRE DESIGN AND TECHNOLOGY



Table of Contents for the Digital Edition of Theatre Design & Technology - Oct 1966

Contents
Theatre Design & Technology - Oct 1966 - 1
Theatre Design & Technology - Oct 1966 - 2
Theatre Design & Technology - Oct 1966 - 3
Theatre Design & Technology - Oct 1966 - Contents
Theatre Design & Technology - Oct 1966 - 5
Theatre Design & Technology - Oct 1966 - 6
Theatre Design & Technology - Oct 1966 - 7
Theatre Design & Technology - Oct 1966 - 8
Theatre Design & Technology - Oct 1966 - 9
Theatre Design & Technology - Oct 1966 - 10
Theatre Design & Technology - Oct 1966 - 11
Theatre Design & Technology - Oct 1966 - 12
Theatre Design & Technology - Oct 1966 - 13
Theatre Design & Technology - Oct 1966 - 14
Theatre Design & Technology - Oct 1966 - 15
Theatre Design & Technology - Oct 1966 - 16
Theatre Design & Technology - Oct 1966 - 17
Theatre Design & Technology - Oct 1966 - 18
Theatre Design & Technology - Oct 1966 - 19
Theatre Design & Technology - Oct 1966 - 20
Theatre Design & Technology - Oct 1966 - 21
Theatre Design & Technology - Oct 1966 - 22
Theatre Design & Technology - Oct 1966 - 23
Theatre Design & Technology - Oct 1966 - 24
Theatre Design & Technology - Oct 1966 - 25
Theatre Design & Technology - Oct 1966 - 26
Theatre Design & Technology - Oct 1966 - 27
Theatre Design & Technology - Oct 1966 - 28
Theatre Design & Technology - Oct 1966 - 29
Theatre Design & Technology - Oct 1966 - 30
Theatre Design & Technology - Oct 1966 - 31
Theatre Design & Technology - Oct 1966 - 32
Theatre Design & Technology - Oct 1966 - 33
Theatre Design & Technology - Oct 1966 - 34
Theatre Design & Technology - Oct 1966 - 35
Theatre Design & Technology - Oct 1966 - 36
Theatre Design & Technology - Oct 1966 - 37
Theatre Design & Technology - Oct 1966 - 38
Theatre Design & Technology - Oct 1966 - 39
Theatre Design & Technology - Oct 1966 - 40
Theatre Design & Technology - Oct 1966 - 41
Theatre Design & Technology - Oct 1966 - 42
Theatre Design & Technology - Oct 1966 - 43
Theatre Design & Technology - Oct 1966 - 44
Theatre Design & Technology - Oct 1966 - 45
Theatre Design & Technology - Oct 1966 - 46
Theatre Design & Technology - Oct 1966 - 47
Theatre Design & Technology - Oct 1966 - 48
Theatre Design & Technology - Oct 1966 - 49
Theatre Design & Technology - Oct 1966 - 50
Theatre Design & Technology - Oct 1966 - 51
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Theatre Design & Technology - Oct 1966 - 53
Theatre Design & Technology - Oct 1966 - 54
Theatre Design & Technology - Oct 1966 - 55
Theatre Design & Technology - Oct 1966 - 56
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