I do tend to see rainbows & I have always had a bit of a lazy eye, you know wanders out of sync with the other. When I get tired it tends to do this, and some forum members have said they become more susceptible to rainbows when they're tired. So, if the eyes are out of sync then they may pick up what the colour wheel is doing - whatever that is, someone with more knowledge might be able to expand on this. This would explain why some people suffered & some didn't. Additionally, this might put undue strain on the eyes, with perhaps the strobe effect (not sure if it has a strobe effect, just a theory) of the colour wheel interacting on each eye differently - rather than in sync with a person who's eyes are properly 'locked' together - thus creating a strain on the eye muscles with the brain trying to marry these two slightly different signals. There you go. A load of old twoddle , or is there something in it? Answers on a post card, or failing that, reply to this thread.