A reader writes:
I’m sure many others are writing about this, but that light device is not being powered by gravity. The energy is being supplied by the person who lifts the weight. It is a semantic quibble, but an important one since people who just see the headline will think that we will have gravity-powered perpetual motion hovercraft in the near future. None of this diminishes the genius of the Gravity Light, or other innovations like it (I also liked the plastic bottle solar light fixture that I think you linked to a while ago).
Another clarification:
It’s no different than a cuckoo clock. Force needs to be applied externally to create the potential for gravity to do its work. You could use a battery or an engine or electricity to apply that force, but in this case they’re using human power in the same way you would wind-up a watch. Would you say a wind-up watch is powered entirely by spring force?
Another:
A wind-up spring has greater energy density, and can be placed anywhere and moved around while its working. Wind-up lights have been available for a while. I carry one with my camping gear.
Another delves further into the science:
While I hate to crimp your mirth, this is not a "breakthrough". Gravity is not powering these lights. Human beings lift a weight (injecting potential energy into the system), and gravity just "cashes it in". The humans can lift that weight because of chemical energy in their blood and muscles, which comes from food. This is no different than powering a light bulb by riding a bicycle with wheels attached to magnets, other than having the pulley system as a "buffer" to hold the energy.
The real innovation here comes from the low-power LED light bulbs. A big part of why they’re so low power is that all of their consumed energy is in the visible spectrum, whereas with a kerosene lamp, most of the energy is lost as heat rather than light. LED bulbs are getting cheaper, and they will soon start replacing incandescent bulbs worldwide. That will add up to a huge energy savings (eventually)
Anyway, the point is, while this is a great product for an African village (bravo to the inventors!), there’s no "breakthrough" here, and gravity is doing nothing special. Sorry to ruin your day.
One more:
Add me to the list of skeptics. "Light generated entirely by gravity" has been around at least since the first hydroelectric power plant was connected to a lightbulb (according to Wikipedia, this took place in 1878, and as it happened, that first power plant powered exactly one arc light). Hydroelectric power is clean alright, but whether its environmental impact is altogether positive once it's scaled up is a more complicated matter (for an example, google the Three Gorges Dam).
As to the GravityLight, its energy is ultimately supplied by the person who lifts that bag – and if human physical labor were a viable source of mass-market electric energy, we'd be on it. The problem is that humanity's energy consumption, according to a back-of-the-envelope calculation, is 30 times the output of the global population's capacity for sustained physical labor. If we limit ourselves to a 40-hours-on-the-treadmill week and exempt children and the elderly, we need 200 humanities to satisfy humanity's current energy needs.
The GravityLight may well solve issues of availability, economy, and safety (the video doesn't say so, but I imagine that's a major problem with kerosene lamps), but its environmental impact is a different issue; it's made of plastic, and its manufacture may well consume more energy than it will emit as light over a lifecycle. In any case, it's no more a "clean energy breakthrough" than the idea, no doubt viable, of making all trips on foot, moving all goods by porter, and powering all lighting, heat, and industry with people on stationary bicycles.
Update from a reader:
Quite aside from anything to do with the "gravity light," I love the expression your reader uses here – "crimp your mirth." It's probably the best thing I've heard today and I can't wait to start using it. Thanks.
The Dish 