The Jolly t-shirts will glow when 'charged' with normal light. The length of glow time can depend on how bright the charging light is. Typically, walking from a lit room into a dark one the Jolly will glow for a good 10 minutes or so, with the first minute being quite bright. You can also switch on the flash light of your mobile phone and quickly shine it on the Jolly for 2 seconds and voila, instant glow! Great for clubbing and a night out. A rabbit torch is awesome!