Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

stroboscopic fillament

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