Electronic ballasts for fluorescent lighting

[LAsludge]

Question: are all electronic ballast equal? I guess not but maybe someone here can tell me what's going on with my setup.

In my work I shoot high frame rate digital video up to 1000 frames per second. At this framerate flickering can ruin my work. Ordinary fluorescents with magnetic ballasts are useless to me as they have a 120 hertz flicker. New fluorescents with electronic ballasts switch at about 30KHz and theoritically work perfectly. I bought some lamps with dimmable electronic ballasts and I was very pleased with their constant light output.

Dimming is not a feature I need so I bought some more fluorescents lamps with fixed output electronic ballasts. Unfortunately my new lamps do not give me a constant output. They varies in output intensity by 5-10% over a 5-10 second period. I also see a small color shift. The effect is noticable and makes the work useless.

The lamps are identical in all respects except some ballasts are dimmable and others are not. A side by side comparision shows the dimmable ballast output is rock steady while the output of the fixed electronic ballasts "floats". A voltmeter on the building AC power shows a constant 116 VAC and the current draw looks the same for both. I don't get it.

My question is what's going on and how can I fix it? The dimmable lamps cost almost twice as much and I'd rather try to get the constant output lamps to work correctly and save several thousand dollars.

Any thoughts anyone?

 

[itsmoked]

Are they drifting enough to see with just your eyes?

I'm not envisioning any obvious mechanism for the ballast to drift with the period you're describing.

All fluorescent lights take a while to "burn in". Have yours had time yet? I'd run them continuously for a few days and see if the drift changes or stops.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[VTer]

Fluorescent lamps have a so called negative electrical resistance. That is, once an arc is struck across the lamp, the ionized mercury vapor becomes increasingly more conductive, and thus more current will flow until the lamp burns out. For this reason, fluorescent lamps requires a ballast, which serves both as a transformer to boost the voltage at the lamp terminals and as a choke to limit the maximum flow of current. Thus the lamp output will always vary slightly.

Now electronic dimmable ballast is generally more efficient than the non dimmable one, and furthermore can substantially reduce lamp flicker. Another important factor to know is that fluorescent lamp efficiency increases with frequency so my advice is to look into ballast with higher output frequencies (better efficiency) or stick with the dimmable ballast which seems to work for you already. Either way I assume the cost will even out for either one for your application requirements.


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