Why do blacklights change the colors of things?

Question

I was wearing BLUE pj pants with a blacklight in the room, and they looked WHITE. Why does in change the appearance of things?

And the pants weren't light blue either, here they are: http://www.kohls.com/kohlsStore/juniors/sleepwear/separatessets/PRD~c14188/Little+Miss+Sunshine+Pajama+Separates.jsp

It's creeping me out.

Answer 1

Black lights emit Ultraviolet (UV) radiation. UV rays are above the visible light spectrum but they interact with phosphors and change the way things look.

White T-shirts and socks normally glow under a black light because modern detergents contain phosphors that convert UV light into white light. This makes whites look "whiter than white".