Most of the condoms I have used have a pretty tight fit. I'm not sure what my physiology is compared to the average but a tighter fit would certainly not be desirable to me.

Wouldn't work. I tend to go into these types of operations in the dark anyway.

I'm pretty sure I've never heard of a polymer that contracts in the dark. Maybe in the cold, but that wouldn't work here. And like sand said, tighter isn't better.

Get it to vibrate in the dark and you may have something.