Amazon Kindle

Umm, que?

I think you must be referring to a non epaper device, so not a kindle. Kindle's get easier to read the brighter it is, since they work by reflecting, not emitting light. These "towel heads" of which you speak were probably trying to read an iPad which is a very fragile device.

Or they weren't wearing sunglasses and have extremely sensitive eyes.

Sounds weird though.