Turn Your iPhone Into a Black Light

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.)

iPhone 6 black light
credit: Jeff Bertolucci

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.

Project supplies
credit: Jeff Bertolucci

Step

Cut off a small piece of tape and cover the flash.

Apply the tape
credit: Jeff Bertolucci

Step

Color the first layer of tape -- just the part covering the flash --with blue Sharpie ink.

Blue Sharpie
credit: Jeff Bertolucci

Step

Apply a second layer of tape. Use the purple Sharpie to draw over the blue-inked area.

Purple Sharpie
credit: Jeff Bertolucci

Step

Turn out the lights (if it's nighttime) or find a windowless room and shut the door. Turn on the phone's flashlight and enjoy the eerie, bluish-purple glow.

Step

Let the glowing begin! Here's an example of neon-colored highlighter ink -- a yellow Sharpie, in fact -- glowing under my iPhone 6's black light.

Neon-colored highlighter ink
credit: Jeff Bertolucci

Step

White paper glows too, so I created a paper airplane for the occasion.

Paper airplane under black light
credit: Jeff Bertolucci

Step

Halloween supplies are often black-light friendly.

Halloween supplies
credit: Jeff Bertolucci

Step

The Skull of Doom glowed as well.

Toy skull under black light
credit: Jeff Bertolucci

Step

What else glowed? A mouthful of toothpaste, but that photo (of me) was so disturbing that I chose not to upload it here.

Step

Again, don't expect the vibrant glow you'd get from a dedicated black light, but this simple hack is easy and fun, particularly with kids.