Malcolm Stewart wrote:

Absolutely certain about it.
I spent some time looking at the 3 x 2 mode pattern and for two weeks afterwards
I could see this same pattern whenever I relaxed my eyes and looked at a plain
surface. The demo was in a slightly darkened room (always a bad thing) and if
you examine the back of your hand there's a little specular reflectivity there.
Fortunately, it didn't last longer than 2 weeks - and it was in 1963, when I was
supposed to be working on cutting edge stuff! I do remember that it was some
time before we were able to measure laser power levels with any real precision,
and the academic journals were full of articles on how best to do it.

Hmmm...

I suspect if you arranged a few medium brightness LEDs (not
hyperbright, maybe 50mCd or so) in a pattern, and spent some
time staring at them in a darkened room, you'd be seeing that
pattern for a while afterwards.

Doesn't mean there was any retinal damage, just that you've
saturated a bunch of cells which are taking a while to recover.
Very surprised by the two weeks though.

--
Grunff