[scott_s]

"D'oh, we forgot to charge our solar light earlier today."

"No worries, we'll just use the gravity light for now."

That scenario seems reasonable to me. The point is not the amount of energy the technique provides. The point is the utility people get out of it. And I see a place for both; GravityLight and Solar Aid seem like great projects.

[aplummer]

I think they would be good in a mine safe room or something, no need to ever replace batteries right. There are a bunch of cases you might not have a charged light.