UV Beads

[backstroke37]

For my science project, I am finding out how well different SPFs of sunscreen really work, and I am using those UV Beads to test my question. However, I can not find a single website that will tell me what they are made of. I was just wondering if anyone could tell me what they are made of so I can do more research on it.
Thank you very much!

[michellebayefsky]

Hi and welcome to sciencebuddies.com! That sounds like an interesting project. Here's some information I found on how UV beads work:

THE CHEMISTRY OF UV -DETECTING BEADS
By Ron Perkins
UV-sensitive beads contain pigments that change color when exposed to ultra-violet light from the sun or certain other UV sources. The electromagnetic radiation needed to affect change is between 360 and 300 nm in wavelength. This includes the
high-energy part of UV Type A (400-320 nm) and the low energy part of UV Type B (320-280 nm). Long fluorescent type black
lights work well; incandescent black lights and UV-C lamps will not change the color of the beads.The dye molecules consist of two large, planar, conjugated systems that are orthogonal to one another. No resonance occurs between two orthogonal parts of a molecule. When high energy UV light excites the central carbon atom, the two smaller planar conjugated parts form one large conjugated planar molecule. Initially neither of the two planar conjugated parts of the molecule is large enough to absorb visible light and the dye remains colorless. When excited with UV radiation, the resulting larger planar conjugated molecule absorbs certain wavelengths of visible light resulting in a color. The longer the conjugated chain, the
longer the wavelength of light that is absorbed by the molecule. By changing the size of the two conjugated sections of the
molecule, different dye colors can be produced. Heat from the surroundings provides the activation energy needed to return the planar form of the molecule back to its lower energy orthogonal colorless structure. Although UV light is needed to excite the molecule to form the high-energy planar structure, heat from the surroundings provides the activation energy to change the molecule back to its colorless structure. If colored beads are placed in liquid nitrogen, they will not have enough activation energy to return to the colorless form. The UV detecting beads remain one of the least expensive qualitative UV detectors available today. They cycle back and forth thousands of times.

I hope this helps! Let us know if there's anything else you need.

Michelle