Turn on a black light in a dark room, and you’ll see a dim, purplish glow. But, the bulb also produces ultraviolet light, which you can’t see.
As you know, certain things glow under black light — white T-shirts, fluorescent posters, toothpaste, and petroleum jelly, just to name a few. Why? Phosphors in these objects emit visible light in response to UV radiation from the black light. (Interestingly, the phosphors in white T-shirts come from the detergents we use to wash them.)
Here’s an oldie-but-goodie phone hack that’s fun for Halloween, takes only a few minutes, and probably won’t cost you a dime. We’re going to turn a smartphone’s camera flash into a black light!
OK, so maybe it’s not the world’s greatest black light — call it Black Light Lite — but it does work. Here’s how to do it.
Things You’ll Need : Transparent or “invisible” tape (e.g., Scotch tape), Blue Sharpie marker, Purple Sharpie marker, Smartphone with an LED flash (I used my iPhone 6)