[JD]

Originally Posted by Radiant

Thanks for the rundown JD!

Is the magnetic ballast "blink" perceptible to the human eye? What about to NTSC video cameras? I've heard that that it is, thus we selected electronic ballast units. But at 120 Hz, shouldn't that be so fast as to be imperceptible?

Not too perceivable to the human eye, but to a TV camera (NTSC) which has a vertical rate of 59.94hz, a beat pattern which appears as a flicker can occur. There are some ways around this, such as using a low read rate from the CCD, but that has the same effect as a slow shutter (in fact, some refer to it as the shutter speed) in that you will end up with blur on fast moving objects. Unlike analog cameras, where the vertical read rate is fixed at the sync gen's vertical frequency, digital cameras can read the CCD at any rate, and the output only becomes fixed at the NTSC encoder, so they usually do not have a problem that cannot be worked around.

Same kind of effect as someone trying to film a TV monitor with an older analog camera, or too high a shutter speed.

EDIT: Generally, if the lamps are young, there is a bit of persistence in the glowing of the arc gas and you may not notice any flicker. As the lamps get old, they get a bit like old florescent lamps where there is a distinct "black" period in the ac cycle and it will be more problematic to the camera. Solid state ballasts generally output at 40khz to 300khz dependant on the application and load/line conditions. Because of that, there is no perceived flicker outside of what may be caused by debris in the arc tube.