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On February 1 Leigh Palmer wrote:
I tipped a 300 watt tungsten halogen "torchiere" lamp (cheap at
the mall) over on its side to illuminate the top .. the
instantaneous lamp temperature varied. My 1/10,000 second shutter
speed reveals clearly the appreciable variation in the tungsten
filament temperature. Even this incandescent source has a small
stroboscopic effect, something that was certainly a big surprise
to me. The effect would be greater for a tungsten halogen lamp
than it would be for a conventional nitrogen filled bulb because
the peak temperature of the former is greater, and it cools
faster.
Very surprising. The time interval between the peaks of I^2 (at 60
Hz) is only 1/120 s. And this is sufficient to overcome the "thermal
inertia" of a tungsten fillament. Amazing. How thin must the
fillament (a black body source) be to make this possible?
Ludwik Kowalski