Given that it's possible to detect modulation from spacecraft beyond the orbit of Pluto, it should come as no surprise that it's possible to detect filament-current changes. But that's not what a television camera is designed to do. It integrates light over a period that is a substantial fraction of (or, in the case of a 25-frame camera looking at a 60 Hz bulb, a period greater than) the filament-current period. And the filament current drops below 50% for only 1/3 of each sinusoidal cycle -- and that in two sub-periods per cycle. And, even then, there's a thermal "flywheel" effect. If the mismatching of camera frame rate and incandescent lighting power frequency were really a problem, then it would be a problem even for NTSC in a 60 Hz environment due to the mismatch of 60 Hz and 29.97 frames per second. It would also be a problem for motion-picture film cameras, especially when they shoot slow motion. And a still camera shooting at, say, 1/200 of a second would be expected to deliver wildly different exposures under AC incandescent lighting, depending on the part of the power cycle during which the exposure took place. Well, out with your still cameras! Shoot! Are the exposures wildly different? Try 1/500 of a second. Got any wildly differing exposures yet? I have been involved in many projects where NTSC cameras were used in 50 Hz countries and 25-fps cameras were used in 60 Hz countries. In all cases, low-frequency fluorescent and arc lights were problematic. In no cases were incandescent lights a problem. TTFN, Mark Craig Birkmaier wrote: >At 8:58 AM +0200 9/13/04, jeroen.stessen@xxxxxxxxxxx wrote: > > >>I'd say that Doug is right. I remember long time ago a hobby >>project (in a magazine) where a lamp was used to carry speech >>over a distance, by modulating the filament current. While it >>may take a long time for a filament to cool off completely, >>initially the cooling goes very fast. It has to do with the >>radiated power being proportional to the FOURTH power of the >>temperature. Thin white hot metal will cool very quickly ! >> >> > >YUP. > >We are talking about the ability to perceive the modulation in >intensity of the "flickering" light source. > >Regards >Craig > > >---------------------------------------------------------------------- >You can UNSUBSCRIBE from the OpenDTV list in two ways: > >- Using the UNSUBSCRIBE command in your user configuration settings at >FreeLists.org > >- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word >unsubscribe in the subject line. > > > > ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.