WASHINGTON (TIP): A 15-year-old girl in Canada has invented a flashlight that produces light just by using the warmth of your hand. Ann Makosinski, from British Columbia , invented the thermoelectric ‘Hollow Flashlight’ that works via the thermoelectric effect. The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa . “I’m sure we’ve all had that annoying experience when we desperately need a flashlight, we find one, and the batteries are out,” she told NBC News. “Imagine how much money we would save and the amount of toxins leached into the soil etc reduced if we didn’t use any batteries in flashlights!” she said.

To create the flashlight, Makosinski measured how much electricity could be generated from the heat of a palm — about 57 milliwatts — and how much she needed to light the LED — about half a milliwatt. Next, she got several Peltier tiles which when warm on one side and cool on the other could generate electricity, and a few other bits necessary to make the current usable by a normal LED. Finally, she mounted the tiles and circuitry onto a hollow aluminum tube; air inside the tube would cool the Peltier tiles, while the warmth of a hand would heat the other side. With a little tweaking of voltages and other components, the invention worked. The light generated is modest, but enough to find your keys or light the page of a book. It worked for around half an hour in her tests at an ambient temperature of about 10°C.