Watch white beads change to colored when taken outside 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. They also change with most classroom UV light sources. Students can make their 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 test the UV blocking effectiveness of sunblock, sunglasses, windows, etc. Lesson activities are included. Available in five colors, all beads are pale, off-white in the absence of UV light. The ultraviolet beads will cycle back and forth (to bright colors and back again) over 50,000 times! Approximately 250 beads per package.