Re: "Lumen Flashlight Never Requires Any Batteries" Permanent firefly keychain light?
This thing has quite a few issues.
First, the amount of energy that you can harvest is very small, TEGs are very low efficiency, and the TEG is being run at a very small thermal gradient. This light will be quite dim. The animation of the "internal parts outside the case" showing it lighting up is deceptive, since the TEG in the animation is larger than the one used, and the heatsink is much larger than the final product. Further, even if this light achieves the predicted 3cd output, that's less than 0.5 lumens assuming a 25 degree LED.
Second, since the design uses the case as a heatsink for creating the thermal gradient, you can't hold it! If you wrap your hand around it, you'll be warming the cold side (the housing) and the hot side (the fingerprint bit) to the same temperature, so no current will flow.
Third, it isn't really green. TEGs can use fun stuff like lead telluride. The embodied energy is quite significant, compared to a plastic keychain light with coin cells. A common AAA flashlight using an eneloop would be superior since the battery can be recharged and recycled, and the flashlight can be as well (assuming an aluminum one), and there's no hard to recycle TEG involved. Plus, it'll be far brighter if you need it to be.
Finally, generic Kickstarter issues: The person running the kickstarter has no electronics experience according to his Kickstarter profile. He's a engineer working on molds and tooling, so while the housing should be as expected, the guts are suspect.
