On Monday, January 18, 2016 08:45:20 PM you wrote: > -------- > > In message <29659871.S9XTlaFu4r@linux>, Bruce Griffiths writes: > >To detect 100Hz modulation due to photocurrents in the LEDs the 150W > >incandescent bulb had to be placed within a few cm of the LEDs. > > Incandescent bulbs don't have much "hum" in their light output, > they're basically heating elements and they don't cool down nearly > fast enough. > > Try with fluorescent light instead, there's a reason people accuse > them of flickering. Its actually quite difficult to find low frequency operated fluorescent lamps here. I only have a small 6" one (sans phosphor so strictly not fluorescent) I assembled some years ago as a source of the mercury green line for an interferometer. I'll unearth it and setup an experiment using forward biased LEDs.
In any case obtaining an LED photocurrent of more than few microamp is very difficult. With a forward current of a few mA the resultant change in LED voltage will only be a few uV. Shielding the LED to ensure that such photocurrent induced modulation of the forward voltage drop is at the subnanovolt level is relatively simple. I used to test the suitability of photomultiplier housings by checking for light leaks with a 1 KW incandescent lamp using the photomultiplier as the light detector. Labyrinth seals with nested enclosures with everything painted matte black usually sufficed. Biggest problem was light leakage via the BNC/MHV connectors. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
