American Cinematographer - April 2018 - 20

An LED incorporates a semiconductor that's been "doped" to have a positive region and a negative
region. When a current is applied, electrons pass from the negative side to the positive side, where they
release energy in the form of a photon, which in turn emits light.

Deep Focus
The Need for Lumens
For years, cinematographers, gaffers
and electricians have identified lighting by
wattage. "I need a 650 over here and a 1K
there, and give me a 5K outside that
window." That's a 650-, 1,000- and 5,000watt fixture, respectively. Lighting professionals know, intuitively, what kind of illumination levels we'll get from a specific wattage
tungsten fixture.
When HMI came on the scene, we
continued to identify the sources by their
wattage - for example, 1.2K, 4K and 12K
HMIs. We did this even though, per watt,
HMIs are substantially brighter than their
tungsten counterparts. But this was a conceit
that everyone understood and mentally
accounted for. If you needed the output of a
5K tungsten from an HMI, you knew to ask
for a 1.2K instead.
With the arrival of fluorescent fixtures
for motion-picture lighting, the correlation
between wattage and output was suddenly
very different. A 23-watt tube puts out how
much light? So, instead, we started identifying fluorescent units by the length and
number of tubes in the fixture. As in, "Give
me a four-by-four over there and a two-foot
four-bank in the corner."
And now LEDs are here, and wattage
has been flung even farther out the window
in terms of being a useful descriptor. No one
really knows quite how to identify these
fixtures.
What is required is a change in our
thinking - a move away from wattage to a
universal terminology that remains consistent
20

April 2018

across all types of lighting fixtures: lumens.
The lumen is an English measurement of
brightness that is exactly equal to the footcandle, defined as the amount of illumination produced by one candle at a distance of
1'. It is a consistent form of intensity
measurement, regardless of the light source
or its power consumption.
Lumens have already begun to take
hold on the consumer level. Consumer packaging for all types of luminaires feature the
actual wattage of the lamp, the equivalent
wattage in a standard tungsten lamp, and
the lumen output. It's that last part that we
need to adopt in motion-picture lighting.
While some manufacturers of
motion-picture lighting equipment have
started to incorporate this in their specs and
photometrics, overall our industry has been
slow to change. This change is necessary,
though, as wattage has become both
outdated and, frankly, inadequate for identifying a fixture's lighting output. Wattage only
describes the amount of energy necessary -
the product of amperage and voltage - to
power a light source. HMI, fluorescent, LED

American Cinematographer

increasing in brightness and decreasing in
cost. In little over a decade, we have gone
from small onboard LED fixtures that
sit atop the camera, providing a bit of fill,
to units that can match the output of
a nine-light Maxi-Brute. Features such
as Independence Day: Resurgence,
photographed by Markus Förderer, BVK (AC
July '16), and Rogue One: A Star Wars
Story, shot by Greig Fraser, ASC, ACS (AC
Feb. '17), made extensive use of multicolored LED fixtures, which allowed the cinematographers to alter the color and intensity of those lights nearly instantaneously.
The savings to the production can
and plasma lighting fixtures have substantially lower wattage ratings for substantially
higher light outputs than tungsten bulbs.
So we need to learn to say, "I need
7,000 lumens here and 1,000 lumens
there." In truth, it's a return to old-school
methods of communication. Cinematographers used to regularly ask gaffers for a
certain footcandle level in a given portion of
a scene. Everything old is new again.
Of course, as noted, the lumen, or
footcandle, is an English system of measurement. The metric measurement is the lux; 1
lux is equal to 1 lumen over a 1-square-meter
area. It's almost the same thing, except that
1 square meter is equal to 10.76 square feet.
So:
1 lux = .09 footcandles or lumens
By way of example, the chart below
compares various lumen outputs and the
relative wattage equivalents of consumer
incandescent bulbs, CFLs and LEDs.

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