While screwing around at my dad's house, we shone a black light (ultraviolet light) on some US money. Not sure why we decided to do this, but we found an interesting result: the strip of plastic that is in currency glows different colors depending on the value. The pictures here really don't do the glowing justice. Next time you're out clubbing, take out some money and see for yourself...the strips really glow in a brilliant set of colors.
Ten American dollars has a red glow to it.
Twenty is green.
Five is blue.