These UV beads are extremely sensitive to natural light and change colour dramatically from white to various colours when exposed to sunlight or- even on an overcast day. Containing trace amounts of a photochromic pigment that are sensitive to the ultraviolet component of daylight, the beads have many different uses ranging from scientific testing of (UV) sun block materials to the creation of 'smart' jewellery. Available as pack 200 beads per bag of assorted colours.