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Re: [Phys-l] Hewitt's three answers




On 2012, Mar 29, , at 08:37, William Maddox wrote:

From: WC Maddox

The day before I read about this in Physics Teacher I constructed a circuit
for another purpose which detected this variation in brightness of
fluorescent and incandescent lights. It use a solar cell and a National
Instruments DAQ. The voltage variation was displayed on a LabVIEW
simulation of a voltage meter.

Using the overhead fluorescent lights the voltage varied between 0.215 and
0.235 volts with peaks appearing with a frequency of 120 HZ.
Using a 25 W incandescent bulb the voltage varied between 0.265 and 0.285
volts with frequency of 120 Hz.


One can't conclude much because of the phosphor -- one is likely measuring the decay of the phosphor not the decay in the discharges luminescence. I suggest using a phosphorless lamp (danger UV). Also "look" at the supply. And a neon -- either an ne-2 or a decorative lamp. Try also a CFL -- look at its supply wave form too.

bc to busy to try his Na lamp.

p.s. be aware of the limitations of your light detector.