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[Phys-L] Lamp on-off behavior



Hi All:

I made a bunch of measurements on various lamps and have posted the
results at:
http://planet.weber.edu/physics/Lamp-On-Off.xls

Bottom line: Lamps do not flash when turned on.

You can clearly see that the LED turns on and off as fast as the
detection system can respond. The two incandescent bulbs (halogen and
normal) have clear ramp up and ramp down behavior but no overshoot. The
incandescent bulbs heat up faster then they cool down. (No surprise
there.)

Several comments on the data collection:
1. The fastest I could get that particular computer to run with LabVIEW
and without messing with direct memory access (DMA) was about 60 Hz.
That was not really stable, but 50 Hz was very uniform and also not an
integer ratio of 60 Hz line frequency. Thus, all data was collected at
50 Hz. There are serious Nyquist issues at that data rate but you can
still see hints of line frequency noise. (The 60 Hz measurements were
not significantly different.) Maybe someday I'll break down and figure
out DMA programming and repeat the experiment.

2. I turned the lamps on and off by hand but with everything clamped
down to eliminate movement.

3. The bulbs were imaged through a ground glass to remove any evidence
of hot spots in the filaments. In practice, the results were completely
the same without the ground glass anyway.

4. The units for irradiance are arbitrary. The peak values were
adjusted so as to not saturate the photodiode.

5. The IR photodiode gave the same results for the incandescent lamps
as the visible photodiode as expected but with ever so slightly longer
of a cooling curve. Only one measurement was made this way, so that data
is not extensive.

6. The 25 W bulb was the same as the 40 W bulb. I didn't have a higher
power bulb at immediately at hand.

So, there you have it. Bulbs don't flash.

John


- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
John E. Sohl, Ph.D.
Professor of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508

voice: (801) 626-7907, fax: (801) 626-7445
e-mail: jsohl@weber.edu
web: http://physics.weber.edu/sohl/
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