I got a scope out to prove it, but the Xmas tree lights are blinking around 500Hz 50% duty and nobody else can see it!

@revk@toot.me.uk I modified one of those cheap pocket oscilloscope kits (bashed the centre pin of the BNC input socket, spray-painted the shell black, and fitted an appropriately-biased phototransistor in its place) to do this for @NatalyaD@disabled.social, so she can tell which room lights are likely to trigger her migraines.

I can see (but am not particularly bothered by) flicker up to about 1kHz, which includes most things with microcontroller-controlled PWM dimming. She's sensitive up to 6kHz or so!

Given how problematic flicker can be for people on the autism spectrum, those with some visual impairments and photosensitive migraine/epilepsy, we could really do with requiring that manufacturers of light sources and display devices specify how much they flicker, so you aren't relying on buying them and testing with an oscilloscope to work out which light bulbs etc are safe.

(If I had my way I'd ban light sources PWMing at less than 20kHz - if we need 10kHz or so to avoid perceptible flicker, might as well get high enough to avoid audible inductor whine. Which is another one of those things that's everywhere but too many people seem not to believe in.)