Everyone's been up in arms about these cloned "glowing" cats and how they're horribly eerie because they glow. Well, I have to tell you they're not eerie at all because they're not really glowing, they're fluorescing!
"Glowing" is when the object stores up light energy and releases it later in the dark. "Fluorescing" is when the object absorbs light of one form (usually UV) and immediately releases it in a different form (usually visible light). These cats would be no fun at all unless you have a UV light source. Most "blacklights" are both UV and some visible violet, but the professional ones used in that photo are only UV, and so that's why it looks like there's no light at all; if they turned off their UV light the cats would immediately go dark, just like normal cats. If you don't use a blacklight regularly, you wouldn't see anything weird about the cats at all.
There now, don't you feel better about dropping a fortune on one of these cats once they become commercially available?
ETA: Here's a video about them on CNN, that shows their faces fluorescing (it appears it's only the skin that does it, not the fur), and explains why it's medically usful.