What You Need:
- Black light bulb
- Petroleum jelly
- Piece of paper
- A white shirt washed in Tide brand laundry detergent
- New $20 bill issued after October, 2003
- Latex gloves
What You Do:
- Have your child dip her finger into the jelly, then use that finger to write a message on the piece of paper. Use more jelly if needed.
- Wipe any remaining jelly off your child's finger.
- Plug in the black light, then turn off the room lights.
- Shine the light on the paper to reveal the written message. Turn the black light off and the room lights on and the message will not be seen!
- Now, turn off the room light and shine the black light on a freshly washed white shirt. It should glow brightly under black light.
- Next, repeat the same procedure but this time shine the light on a new $20 dollar bill and your child will be able to see the thin anti counterfeit “security thread” that glows under black light!
- You may wish to challenge your child to search for other things in the house that will glow under the black light.
- If you have Latex gloves, put them on your hands. Reach into the jar of petroleum jelly and scoop out enough jelly to cover both hands. Rub the jelly over both hands, and then ask your child to turn off the lights in the room, and to turn on the black light. Hold your hand under the black light and watch them glow this is a great trick when telling ghost stories at night!
What’s going on here? The reason black lights are called "black lights" is because they produce very little light that our eyes can see, but a lot of ultraviolet light (UV), which our eyes cannot see. Petroleum jelly and most laundry detergents that advertise as making the whites “whiter” have phosphors that absorb UV radiation and emits it as visible light. The black light emphasizes their presence in these items.