Is it possible that the florescent black lights are the problem with epileptics?  Florescent lights are actually flashing on and off (although very rapidly)and strobe lights can initiate epileptic seizures.  Possibly the incandescent versions would prevent this reaction?  Good point even if this isn't an answer.

Marty

Oh, I didn't know that... I'll have to remember it for any shows I do!

The same thing could happen with an electronic theatrical dimmer that is out of calibration.  You probably wouldn't notice the flicker unless the lights were at low brightness.

Marty

Our fluorescent blacklights do not flash on and off.

Actually any fluorescent lights flash on and off.  They just do it at such a rapid rate that the we don't perceive it as a flash.  I'm not sure if this is the reason that some blacklights effect epileptics as Andrew mentioned, I was just speculating.  When a ballast goes out that is when the flash is noticeable.

The electronic dimming systems I mentioned work by sine wave cutting.  A chip in the dimmer does this.  As the wave oscillates (at 60Hz or 60 times per second) and the chip/circuit (SCR, triac etc) cuts the top and the bottom of the wave off so it actually goes off for a breif period of time twice each phase.  This is why you can't use dimmed lights for film, but actually have to put something that blocks the light.  Again, the flash rate is so rapid we don't perceive it unless the dimmer is out of calibration.

A little tech theatre.

Marty