Wala na yung original article but I remember this from Google Science Fair.

IIRC basically peltier device, but instead of pumping in electricity to make the cold side cold, she uses body heat on the cold side element to generate electricity.

Problema ng device nya is doesn't really work well when it's warm, kasi the electricity produced depends on the temperature delta between body heat (36-37C) and the peltier element which will be at ambient. So dito sa Pilipinas next to useless yan.

A paper on her flashlight said significantly more light output at 5C compared to 10C, but at 10C acceptable pa naman daw. Don't forget though that it's going to be significantly cold, and the device will be draining your body heat.

Harnessing Alternative Energy: The Body-Heat Powered Flashlight
Makosinski tested the flashlights and found that both were brighter when the air temperature was 5 degrees Celsius than when it was 10 degrees, due to the bigger difference between body temperature and the air temperature. But even at 10 C, both flashlights maintained a steady beam of light for over 20 minutes. All in all. the materials for each flashlight cost about $26, she said, but she thinks that if it were mass produced, it could be manufactured and sold for a far lower price.