That's the kicker; there are some 'common' rates that can trigger (15, 30, and 60 cycles her second being the most encountered ones; failing fluorescent lighting, anyone? Or bad neon signs), but 'epilepsy' is very much a blanket term, rather like 'cancer' or 'influenza'. There really are no hard, fast rulesm, and how and where it can manifest is as diverse as the structure of the brain. Well, save one. =Anyone= can have a seizure; the only thing is that most of the populace has a trigger threshhold high enough that they are never bothered with it. Stripped of everything, all you are really talking about is a cascade effect; too much neural activity along certain pathways in too short a time period producing a self sustaining feedback. For the optical, the higher the contrast between flash states, the more potential danger there is. The sun-strobing is such a problem simply because of that contrast. Animated GIF's haven't shown any particular trouble, simply due to the fact that there isn't a great deal of contrast there; things move, they do not tend to strobe. You can =make= them a hazard (like the ads that flash a text message just barely readable at a rapid rate. That can do it). Chuck; I have no trouble with TV. I -do- have to make sure that my monitor and video card are capable of supporting non-interlaced function, though. TV CRT phosphors have a long decay rate compared to monitors; this was done deliberately to prevent the flicker that plagued the first B&W sets (and no, I couldn't have watched one of those). Now, if the -show- has a lot of strobing effects, then I tend to keep a pillow handy to block the light...just in case a hand or closed eyes don't seem to help.