Or gels... This was after probably about 3-4 pops at full power. It was sitting behind my bike: I posted these just showing off the pics in another thread, but here's what happened; I was taking pictures with my 580EX II sitting behind the bike with a dark red gel over it to see what kind of effect I could get off the back lighting. So I was coming out with some good effect: And about my fourth or fifth shot I noticed that the 580EX II wasn't firing. I remembered some one saying it would do that because of some built in thing to keep it from over heating and melting down and figure that was the cause. I waiting a minute then snapped three more shots, and though that something looked a bit funny on my lcd...my red back light changed to purple?: I went to check after the third shot and sure enough, I melted a hole in the gel. I really like the color you get from it, so I'm going to keep it and try not to melt it anymore. Fortunately the flash is fine. I was playing with it last night at my friend's place.