When I did research as an undergraduate, one of the MS students in the lab I was working in moved a powerful UV light used to cure glues from the corner of the room to the center and used it without putting a box over it as was standard procedure. Of course, he didn't look at the light himself, but he also didn't announce its use either. I saw the UV light as I was walking through the lab. It was basically a bright purple/blue light. Several hours later I was effectively blind due to pain, which continued for a few days. I basically had the equivalent of a bad sunburn on my eyes.

This was one of several reasons I quit that lab. Since then I've avoided academic labs that have UV lights or lasers because I don't trust that the students follow safety procedures at all.