American Cinematographer - April 2018 - 22

also be substantial. Electrical usage -
generator fuel or kilowatt-hours charged
- decreases; air conditioning costs are
reduced, as there's no need to combat the
heat generated from incandescent sources;
the expendables budget goes down, since
Field Guide
Power Consumption and
Alternate Light Sources
Traditional tungsten fixtures are incandescent sources of light - incandescent
meaning "light from heat." In order for an
incandescent source to produce light, electricity passes through the tungsten filament,
which resists the electrical flow of electrons;
the friction of that resistance in turn causes
the element to heat up until it eventually gets
hot enough to glow.
This process produces beautiful light,
but at the cost of considerable energy being
lost to the generation of heat - 70-80
percent of the energy used by a tungsten
light bulb is lost to heat. A naturally occurring
metal, tungsten is a very brittle substance
with the highest melting point of non-alloyed
metals, and the second highest melting point
of all elements on the periodic table:
3,422°C, or 6,192°F. This makes it the perfect
source of incandescence, as the standard
tungsten filament can heat up to temperatures of more than 5,000°F. That's super hot
- and it results in the expenditure of a lot of
energy, which means it takes more electricity
to produce a given amount of light from a
tungsten fixture than it does from other
sources of light.
Fluorescent lighting, for example,
requires significantly less energy. Instead of
"light from heat," it's produced by means of
an arc of electricity that excites mercury mole-

color-tunable LEDs do away with the need
for colored lighting gels; the crew saves
time, since no one needs to climb into the
perms to scrim a fixture or swap out a gel;
and pre-rigging time and hardware requirements are mitigated thanks to lighter-

weight fixtures and simpler DMX cabling. It
all adds up very quickly.
LED technology continues to evolve.
It is not yet a perfect medium - but it is
certainly a lighting solution that is here to
●
stay.

cules suspended in gas inside the tube; the
excited mercury then strikes phosphors that
coat the inside of the tube and creates light,
aka fluorescence. The greater the surface
area of the fluorescent tube, the brighter the
source of light. This is why compact fluorescent bulbs have those tight curls to them:
Those curls create more overall surface area
and, therefore, a brighter output. Although
fluorescent fixtures require a ballast to regulate the arc of electricity inside the tube, they
need relatively low electrical current to function - about 60-70 percent less electricity
than a tungsten lamp with an equivalent
brightness.
LED fixtures are even more efficient in
their electrical usage per lumen. The movement of the electrons within the light-emitting diode creates its own light, with little to
no wasted energy. This efficiency means that
for the equivalent output of a tungsten bulb,
an LED fixture uses up to 80 percent less
energy.
One of the woes of location shooting,
especially on small productions where you
can't afford a generator or a qualified electrician to tap into existing power, is being
limited to wall-socket power in the 15-amp
or, at most, 20-amp variety. (See Shot Craft,
"Keeping the Lights On," AC March '18.)
This limits you to, at most, a 2,000-watt
fixture - which is definitely pushing the
limits of safety. In the HMI world, you're
limited to a 1,200-watt fixture or perhaps the
1,800-watt Arri M18, which was specifically

designed to be the most HMI output you can
get on 20-amp "household" power. Where
you get the most bang for your buck - the
highest output with the lowest energy
consumption - is with fluorescent and LED
fixtures.
Energy in this sense is wattage. If we
recall the "West Virginia" law - watts =
volts x amps - we can see that while voltage
remains a constant, if we reduce the
wattage, we also reduce the amperage.
If a 100-watt tungsten bulb produces
approximately 1,600 lumens of illumination,
it also consumes 1 amp of electricity (assuming a 100-volt system). If a 1,600-lumen fluorescent fixture only requires 25 watts of
power, then it only consumes .25 amps. The
same 1,600 lumens can be produced by an
LED fixture at 15 watts, which is only .15
amps. So we're using significantly less electricity for the same general amount of light.
Scaling this up, imagine that you're
lighting a scene where you would normally
use a 2K tungsten soft light - that's 20 amps
of electricity. The same brightness of light
from a fluorescent fixture requires only 750
watts, or 7.5 amps. With LEDs that's about
400 watts, or 4 amps.
You can quickly see how utilizing alternate power sources not only saves electricity,
but allows you to light brighter scenes with
available power.
- JH

From left: A Mole-Richardson 2K tungsten Fresnel, an Arri M18 1.8K HMI, a Kino Flo 2' 4Bank fluorescent fixture, and LiteGear LiteMat LED units.

April 2018

American Cinematographer

Table of Contents for the Digital Edition of American Cinematographer - April 2018