Pixie dust is unsuitable for household lighting:
It’s a funky looking thing, which was widely reported around the gadget blogs, and was alleged by its designer, Clay Moulton, to give the equivalent light output of a 40-watt incandescent bulb for four hours from the energy of a weight dropping about four feet, or 122cm. When the weight gets to the bottom, you just lift it back to the top and away you go again.Now, it stands to reason that a mere 1.2-metre drop isn’t going to give you forty actual watts for four hours unless the weight is incredibly heavy. Ignoring losses, it would by definition take forty watts of power over another four hours to lift the weight back up again, which is 160 watt-hours, which is quite a lot. A normal adult human in reasonable shape can manage about 75 watts of output when pedalling away on a bike connected to a generator; it’d take more than two hours of such pedalling to raise that weight back to the top of the Gravia light’s tube, if the weight were heavy enough to make a constant 40 watts on the way back down.
So I just assumed the lamp’s brightness was greatly overstated, and wasn’t even four-watts-of-LEDs-that-are-sort-of-equivalent-to-forty-watts-of-incandescent. But since they’d clearly actually made the thing and it’d won an award, I presumed it did work, if only as a night-light. Fair enough.
But neither Clay Moulton nor anybody else has, actually, built a Gravia.
The damn thing doesn’t exist.
And Mr Moulton, who apparently designed the thing as part of his Virginia Tech master’s thesis, didn’t even bother to check whether his design could possibly bloody work at all, even if you built it with LEDs from ten years in the future.