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.)
Video of the Day
Video of the Day
![iPhone 6 black light](https://img.techwallacdn.com/375/ppds/c796698d-5f06-4c14-9722-e3a6668870e2.jpg)
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](https://img.techwallacdn.com/375/ppds/a56b222d-3974-429c-ad6f-cba7d9bf5b7f.jpg)
Step 1: Apply the Tape
Cut off a small piece of tape and cover the flash.
![Apply the tape](https://img.techwallacdn.com/375/ppds/78d83ff2-4a6c-4b9b-8800-493e8fde3bdd.png)
Step 2: Go Blue
Color the first layer of tape -- just the part covering the flash --with blue Sharpie ink.
![Blue Sharpie](https://img.techwallacdn.com/375/ppds/344d2b20-72b4-4687-8dff-221b48dcb782.png)
Step 3: Create a Purple Haze
Apply a second layer of tape. Use the purple Sharpie to draw over the blue-inked area.
![Purple Sharpie](https://img.techwallacdn.com/375/ppds/3827c07a-d7f5-4e58-abcc-0744d1a38100.png)
Step 4: Shine the Light!
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.
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](https://img.techwallacdn.com/375/ppds/5101f1bd-189b-4e6c-9ff9-57dc01d29ea5.jpg)
White paper glows too, so I created a paper airplane for the occasion.
![Paper airplane under black light](https://img.techwallacdn.com/375/ppds/96a699ce-1a78-46ac-9017-29a7db8a377d.jpg)
Halloween supplies are often black-light friendly.
![Halloween supplies](https://img.techwallacdn.com/375/ppds/953609a9-3376-4d9b-a2a9-48506ae56564.jpg)
The Skull of Doom glowed as well.
![Toy skull under black light](https://img.techwallacdn.com/375/ppds/26c3fbfa-a113-405d-b2a5-b5f64b0662b8.jpg)
What else glowed? A mouthful of toothpaste, but that photo (of me) was so disturbing that I chose not to upload it here.
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.