Heatsinks and wearable LEDs
My 7-year-old son and I are planning to create a "Lightning Man" superhero costume for him, using conductive thread and some superbright LEDs. Eventually I'll probably get a FLORA or other wearable Arduino to control the lights, but for now, I just want to sew a simple circuit with a 9V battery and a single 3W to 5W LED. (The "switch" will be him clapping his hands, since the palms of the gloves will be conductive...)
My question is an obvious one--what should I do for a wearable heatsink? Those bigger LEDs can get quite hot, and I don't exactly want to have to explain to my wife why our son has been branded with a little star...
If you're wondering, the LEDs do need to be VERY BRIGHT (according to my son). He wants to be able to surprise and blind people with his superpowers, and the little ones we've been playing with don't cut it. But don't worry, he promises to use his powers only for good. Chaotic Good or Neutral Good, maybe, but still Good.
Does anyone here have experience with heat issues on wearable LEDs?