The Lumen flashlight uses a thermoelectric generator to transform body heat into electricity to power an LED (Credit: Lumen)
Whether it be for everyday carry (EDC), outdoor adventure, or disaster preparation, flashlights tend to be found towards the top of must-have items. But one common aspect of these luminescent devices is that they’re only as good as the batteries inside. If you’ve ever switched on a flashlight only to experience a flood of frustrated disappointment, you might appreciate owning an “eternal flashlight.” Lumen is designed to be powered by body heat, never needing batteries.
The finger-sized Lumen flashlight uses a small thermoelectric generator (TEG) to power a single 5-mm ultrabright Cree LED. We’ve seen successful use of such technology in consumer products before, such as with Power Practical’s PowerPot. Researchers have been experimenting with wearable TEGs to extend the battery life of small devices, and, quite famously, a Canadian high school student created a working prototype of a body heat-powered flashlight as a science fair project. Lumen, however, could be the first of its type to be readily available to the general public.
Lumen works to transform heat into electricity through a difference of body and ambient air temperatures. So if it happens to be 82 º F (28 º C) where you’re at, Lumen is designed to produce about 15 mA at 3 V, enough to power the LED for 3000 mCd (millicandela of output. Any excess power is stored in an internal capacitor. The body of the Lumen flashlight is made of machined aluminum or titanium, weighing 1.2 oz (35 g) for the former and 1.5 oz (45 g) for the latter. These metals are not only durable, but they double as a heat-sink to help make the TEG work more efficiently.