Not to nitpick, bit it's not powered by gravity, it is powered by people going over every 30 minutes and lifting a weight back up to its top position.
EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.
People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food.
The machine converts gravitational potential energy to electromagnetic radiation. People generate the gravitational potential energy by lifting the weight using kinetic energy, which was likewise created by converting chemical energy.
It's easier just to say "Gravity" because, without gravity, it wouldn't work with its inanimate weight.
> People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food.
Actually, it does, and that's the perfect way to analyze this. Food is good for keeping humans alive, but it's a pretty foolish fuel to burn in a human engine to accomplish things. It's perishable, it's eaten by rodents, it's hard to transport, and more. I chuckle darkly when someone tells me that something is "green" because it's human powered. Growing food isn't free - it uses conventional energy sources to harvest, transport, etc., and it's a ton less efficient than just burning that fuel directly.
That is not entirely true. Nuclear fission is not powered by the sun, nor are nuclear fusion plants on Earth (when they arrive). However, fission is only possible because of the existence of heavy nuclei that were initially created during super novae explosions in massive stars billions of years ago so you could argue that is is also at least star powered.
The ingredients needed for fusion on the other hand are thought to have been created during the some of the early stages of the Big bang so fusion is truly independent of stars.
When I think "powered solely by gravity" I think of something like a hydro electric plant which can generate more energy than is required to operate it.
At any rate, the phrase was written by Enpundit, not GravityLight. Their indiegogo page is less dramatic and more scientific about what powers their lamp:
Gravity isn't the storage mechanism; the ballast bag is. Gravity is the mechanism used to unleash the stored energy, the same way that the electro-chemical voltage difference between the two components of the battery is the mechanism that unleashes the stored energy in the battery. If anything, it's a ballast-bag-powered light.
I'd say you have the most accurate description of when they say "Gravity Powered". While lifting this thing, the energy gets stored and gravity is just a means by which the stored energy is released.
I was a bit disappointed by the title. I was hoping for something akin to a sterling engine, which is powered solely by a heat differential. As long as the heat differential is present and barring any mechanical issues, the sterling engine will operate continuously without intervention.
If you bury a heatsink, and then have an air-flow heatsink, it's plausible that you could power a Stirling Engine with this kind of power output.
You wouldn't do it for $5 though. Efficient Stirling Engines with a reasonable amount of torque actually require significant engineering, and that comes at a cost. However, they wouldn't require significant maintenance, they would provide power all the time that could be stored (again, at a cost), and might be able to trickle power an entire village.
Technically, really technically, and very pedantically, I expect what you have is a hot air engine, because it's unlikely that it includes a proper regenerator, which is technically what differentiates a Stirling Engine.
However,
Yes, Stirling Engines can be wonderfully efficient, and they are a delight to watch in action. Lovely machines.
I'm pretty confident that most comments that start with "not to nitpick" would be better sent to /dev/null. Nitpicking is usually a sign that deeper, more interesting arguments aren't available, but negativity must reign supreme!
Shouldn't it be said that it is powered by vacuum energy, since that is what kicked of the Big Bang? (And, before anybody tells me I'm wrong, let me say, "I'm wrong!" Instead of telling me I'm wrong, educate me. I love learning about this stuff, and I know my knowledge is weak.)
EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.