Pony beads that contain dye molecules that changes fro
m white to a specific color when exposed to ultraviolet light are called UV Bead or photochromic beads.
Ultraviolet radiation (also called UV light) is a type of light energy also called electromagnetic radiation. The only light energy that can be seen is called “visible light.” Thus, UV light is not visible.
While you cannot see UV light, this high-energy light excites the dye molecules in the beads resulting in a change in the shape of the dye molecules. The new shape affects the light colors the molecule absorbs and reflect. Beads that turn red when exposed to UV light contain a dye whose molecules absorbs all the visible light colors except red. Any red light striking the bead is scattered in all directions resulting in the beads’ red color.
DISCOVER FOR YOURSELF
UV beads can be used for the following experiment ideas:
1. What kinds of light contain UV?
Expose the beads to light from different sources, such as sunlight, incandescent light bulbs, fluorescent light bulbs, colored lights, and a black light.
2. UV light causes you to sunburn. Can you get sunburned on a cloudy day? Determine if clouds allow UV light to pass through. Do this by placing UV beads in an open area. Do they change colors? If so, how quickly do they change color in comparison to being placed in bright sunlight?
3. Can UV light pass through window glass? Try different types of glass, including tinted glass and car windows (check the front window as well as 
side and back windows).
On Your Own
Read each of the following question, state your hypothesis, and then design experiments to test your hypothesis.
1. Does your skin receive UV light even in the shade?
2. How effective are different sunscreens?
3. How much UV protection do different types of sunglasses provide?
4. How does the amount of UV from the sun compare to the UV in tanning booths?