Often used for government or military emergencies after dark, the glow stick gained favor among children (and concertgoing adults) in the 1980s. First sold as novelty entertainment at dances and circuses, glow sticks were adopted by kids who were going camping or trick-or-treating. Their illuminating effect comes from the chemistry inside: after the separate casings are broken, phenyl oxalate and fluorescent dye solution mix with hydrogen peroxide, causing a glowing effect that lasts for about 24 hours.