www.lightingandsoundamerica.com • January 2012 • 69
dims down—particularly at the bottom end—but Chauvet
avoids that issue well in the Legend 412.
I measured the PWM frequency at 1kHz, which should
be high enough to avoid flicker problems in most applica-
tions.
As a sidebar, I was asked recently how I measure the
PWM frequency of LED luminaires. I try to make all my
measurements as non-invasive as possible, and don’t want
to go poking around with voltage probes on unknown cir-
cuit boards. In this case, I use a small photovoltaic solar
cell connected to an oscilloscope, which, when placed in
the output beam, clearly shows the rapid fluctuations in
light output from the PWM pulses. Figure 10 is the curve
from the Legend 412 when it is dimmed down to about
50%; it shows a solid 1kHz PWM signal.
The dimmer curve itself is almost perfectly straight, and
matches a linear dim curve very well (Figure 11). Overall, I
feel that Chauvet has done an impressive job with both the
dimming smoothness and control. Controlling it with a man-
ual fader, the dimming felt natural and organic.
Finally, the unit has a dedicated strobe channel, with
the normal varied strobe options, including ramp and
snap strobes. I measured a possible strobe range (using
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Figure 10: PWM measurement
40%
50%
60%
70%
80%
90%
100%
Output
Dimmer Curve
Le
end 412
S
uare Law
Lin ear
Chauvet Legend 412
11/27/2011
0%
10%
20%
30%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
DMX Input
Figure 11: Dimmer curve
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