Most self contained, medium base compact fluorescent lights are designed to function at a particular input voltage, and if the voltage varies too much from optimal, they can self destruct, and possibly cause problems with the circuit that they are fed from. They are not simple resistance lights as are standard, and even halogen cycle bulbs (for the most part).
Fluorescent bulbs require much higher voltage than standard line voltage to fire, and once lit, they require external current limiting to keep them from becoming a pyrotechnic device. That is the function of a fluorescent ballast. Self contained bulbs of the type (CFL bulbs) have built in ballast devices, but they are not designed to modulate light output to varying input voltage. They are only designed to safely fire the bulb, and keep it stable within a narrow input voltage range.
The typical lights used as modeling lamps contain thin coils of tungsten wire that respond to applied voltage by getting hot enough to glow. They are tuned to glow at a certain color temp at a certain voltage. Exceed that voltage by too much of a margin, and the tungsten wire melts, resulting in an open circuit failure. As you lower the voltage, the light output, and color temp drops until there isn't enough voltage to make it glow anymore. A halogen light is pretty much the same, but at it's design output, it can be driven much brighter, and last much longer than a regular tungsten light, because of the magic of the "halogen cycle". Sweet. They make great modeling lights, as their relative output can be easily made proportionate to input voltage. Color temp will vary, but relative brightness is pretty reliable.
In essence, resistance lighting, and fluorescent lighting are really two different animals, but demand, combined with digital chip technology has made a few voltage dimable ballasts available for regular fluorescent tubes (about $95 ea, wholesale), and a few fairly expensive voltage dimable self contained spiral tube bulbs available as well. So far, they are still expensive, and not very linear in response. I'm sure that will change in time, but right now, the problem with using a CFL bulb as a modeling light goes far beyond simple RFI.
Voyager
|