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Light on the Subject
16-bit resolution for dimming LEDs provides a smoother dimming curve, as the “steps” between each level is less noticeable.
The 65,536 Steps
But problems like this spell opportunity to some.
Some manufacturers of LED luminaires have figured out
how to get around this problem. How do they do it?
Pythagoras said that all things are number. In this
case, numbers transmitted by a lighting console translate
to a dimmer level. The typical dimmer is controlled
by a single channel of DMX, which is eight bits long,
yielding 256 possible dimmer levels. These dimmer
levels are converted to pulses of electrical current at a
fixed frequency. The width of the pulse is proportional
to the dimmer level and determines the perceived light
output of the LED. This is called “pulsewidth
modulation.” The frequency of
the pulses, known as the “frame rate,”
varies by manufacturer, but it typically
range from 1000 Hz to tens of thousands
of hertz.
This scheme is effective but it has its
drawbacks. When the dimming level of
an LED changes in increments of 256
steps between 0 and full, it looks like
the intensity is climbing a stair case—
each step is distinctly discernable.
How can you smooth out the dimming
curve without reinventing the wheel?
The answer is to increase the dimming
resolution. By using 16-bits
instead of 8-bits for control of a single
dimmer, the number of dimming steps
can be increased from 256 to 65,536.
That’s because for every step of an
20 October 2010 • www.stage-directions.com