May Issue - Stage Directions Magazine

Why the Difference?
There has been much gnashing of teeth and pounding of
café tables and bars over why these differences have arisen. The
fixed focus fanatics base their fervor on the higher output and
sharper focus possible with the simpler optics of their favored
fixture. The zoom focus acolytes believe that the additional
flexibility offered by the wider range of beam angles justifies
the marginal light loss, the higher weight and higher price of
their choice. One particularly hurtful (but valid) comment from
the fixed beam camp is that, in many installations, the front-ofhouse
rig is immutable because of a venue’s structure, and so
nullifies any possible benefit from zoom optics.
There may be other, less clearly identified forces at work,
however. In most of the world, a luminaire is seen as a long-term
investment that may not be replaced for 15 to 25 years, so buying
the most flexible unit possible is seen as a measure of futureproofing
the investment. Equipment upgrade and replacement
cycles tend to be much shorter than this in the U.S., particularly
when the inventory belongs to a commercial enterprise.
In the same way that continental drift has separated the continents
and allowed differing evolutionary paths for related species
of animals and plants; so, too, has supply voltage difference
isolated the two branches of luminaire development. Ohm’s
law makes it quite clear that if you halve the voltage to a device
(230V to 110V), you will need twice the current to produce the
same amount of power (approximately 4 amps per kilowatt at
230V and 8 amps per kilowatt at 110V).
What Ohm’s law doesn’t tell you is that a 100V+ lamp is
almost 10 percent more efficient than
its 200V+ equivalent, due to increased
heating efficiencies in the heavier filament.
It also neglects to mention that
the thinner filament is much more fragile
or that the insulation required for
200V+ devices is substantially heavier
and more expensive than that required
for 100V+. There may be 200V+ and
100V+ versions of many lamps, but they
are by no means equivalents in terms of
filament size, robustness or efficiency.
It was only quite recently, when voltage-independent
switching power supplies
became standard on some moving
lights, that it was possible to make a
luminaire that would work wherever in
the world it was plugged in.
The Altman 360Q probably didn’t
make it in the 200V+ regions because
there was no decent lamp available for
it and because it came with 110V insulation
that could not be approved by
electrical authorities. Similarly, CCT was
so busy building Silhouette luminaires
to run at 200V+ that no effort was made
to develop a 100V+ version. Even in this
time of galloping globalization, only a
handful of theatrical luminaire manufacturers
set out to build products that
can work across the entire voltage and
regulatory spectrum.
While one evolutionary branch of the
plano convex spot may have become the Fresnel spot in most
of the world, in Europe in the early 1980s, Fresnel lens technology
was used to craft a hybrid lens. This is a kind of back-cross
between the original ground and polished plano-convex lens
and the molded Fresnel lens. Variously known as a prism convex
or pebble convex lens, this variation has some knobby features
molded onto what was previously the flat surface of the PC lens.
The intention is to remove the unevenness of the original PC’s
beam without losing its sharp focus. The result lies somewhere
between an ellipsoidal and a Fresnel spot. Some less charitable
critics of the result have observed that it combines the worst
characteristics of both. While many LDs will use this luminaire
for specific applications, such as tight stage pools, their use in
the professional industry is not widespread. Nevertheless, most
200V+ theatrical Fresnel manufacturers also offer a PC variant
of their products.
Nigel Levings, the 2003 Tony Award-winning lighting designer
(La Boheme) who works in venues and productions on both
sides of the Atlantic, gets to have the final to say on the subject.
“From time to time, I have been forced to use PCs in repertory
rigs, but I don’t like them much, “ he admits. “I see them as a lazy
substitute for those who can’t calculate beam coverage. My rigs
these days are mostly S4 fixed beam profiles (ERS) with various
frosts and PAR cans.” I guess that this argument will probably
continue in the bar after tonight’s show.
Andy Ciddor has been involved in lighting for nearly four decades
as a practitioner, teacher and technical writer.
www.stage-directions.com • May 2007 17