John Sohl made some measurements and posted them on a web page. I have
done the same. My results can be found at
www.bluffton.edu/~edmistonm/light.bulb.pdf
My results are similar to John's but different.
(1) I don't understand the oscillations in John's plots. If the time
scales are correct, the oscillation period is about 200 ms giving a
frequency of about 5 Hz. This might seem to be a vibrating filament
except John's fluorescent bulb also showed the 5-Hz behavior. That
makes me think his time scale is incorrect.
My filament clealry showed 120-Hz oscillations in light output caused by
the 60-Hz AC power. The magnitude of these oscillations is considerably
more than I would have guessed. I wasn't sure they would be visible at
all, but they amounted to about 18% of the average light output.
(2) John saw his bulbs heat faster than they cooled during turn-on
versus turn-off. I saw the opposite in terms of overall behavior.
However, in the 120-Hz oscillations I observed the cool-down was
noticeably slower than the warm-up.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
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