Lumen creator Ross Zhuravskiy (call him "Rost") is my new favorite person. Watch his video, I think you'll see what I mean. Then check out his touch-operated flashlight powered entirely by its toucher's body heat, and I think you'll see even more.
Lumen shines at a brightness comparable to a smartphone's, but unlike the latter, using Lumen as a flashlight will not drain its battery. Ever. Lumen converts human body heat, transmitted through a finger, into light, so the device will work indefinitely. At least as long as you have 98 degrees to pony up for it. Rost created Lumen from a thermoelectric generator (TEG) fitted with a small ceramic bar that can produce an electric current at the onset of a temperature difference between the upper and lower parts of the TEG.
In testing Rost found that if the air temperature is 82 degrees F, the approximate 16-degree difference between it and your body heat is enough to generate power for a single Lumen LED. The Lumen's metal casing then serves as a radiator. At these numbers output is about 15mA at 3 volts. When the temperature difference is larger, the excess power gets stored in Lumen's capacitor for later use when needed. Lumen's TEG can typically harvest enough energy to power a 5mm Cree LED at 3000 mCd of light output. That's basically bright enough to find your keys...or underwear on that girl from the bar's floor...in the dark.
Rost keeps the good news coming when he notes, "Before you can use flashlight you need to find it! (Yep, I'm a fan of Captain Obvious)." To make Lumen location easier he is giving buyers the option of adding a small orange tritium tube to the top of their light. (You can read more about tritium here.)
Lumen seeks crowdfundig on Kickstarter through November 13, 2015. Backers have a choice of aluminum or titanium flashlight cases.