Watch white beads change to coloured when taken outdoor the building! When returned they turn back to white. What causes the change? Humidity? Temperature? Fresh air? Birds flying overhead? The beads contain pigments which react with ultraviolet light from the sun, even on a cloudy day. In addition they change with most classroom UV light sources. Students can make their very own UV light detecting bracelet by stringing the beads on a pipe stem or on a strip of rawhide. Great for teaching UV awareness! Use the beads to check the UV blocking effectiveness of sunblock, shades, windows, and so forth. Lesson activities are included. To be had in five colors, all beads are pale, off-white within the absence of UV light. The ultraviolet beads will cycle backward and forward (to bright colors and back again) over 50,000 times! Approximately 250 beads per package.