Just show them a video. Many cameras pick it up no problem.

Just about everyone. Wave your hand with fingers spread in front of your eyes and you will see it.

Could you please stop posting unsubstantive and/or flamebait comments and otherwise breaking the site guidelines (e.g. https://news.ycombinator.com/item?id=34794878)? We ban accounts that do these things, and I don't want to ban you.

If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful. The idea is: if you have a substantive point, make it thoughtfully; if not, please don't comment until you do.

Websearch 'FMVSS 108' for the relevant US regulatory framework.

Thanks. I'm scanning it, but it's huge.

Does it specify minimum LED refresh rate somewhere? Or is it lacking that today?

I usually use my phone's slow motion video to settle the matter. Negotiating where to sit on a restaurant is a prime use case.