[Ivojo]

The closest I've ever come across to an explanation is our differing flicker fusion threshold (worth Googling). It's the frequency at which our eyes stop seeing pulsing light and start to see solid light and varies from person to person.

I've been a bit unlucky with this as I've started suffering from the rainbow effect later in life. I don't consciously see it very often but I do find even 4 and 5 speed 7 segment DLP projectors a strain to watch for more than about an hour without a break.