It must have seemed like a great idea at the time, at least until science got involved. Rather than powering your floor lamps by nasty, carbon footprint increasing mains electricity why not use gravity?

That’s what Virginia Tech student Clay Moulton thought. So he designed the Gravia, a metre high lamp powered by a slowly falling weight that users would lift to the top. As the weight falls, the theory goes, it can be used to power LEDs – producing 600-800 lumens, about the same as a 40-watt bulb over a period of four hours (press release).

Although it hasn’t been built, Gravia even came second in a Greener Gadgets Design Competition. Websites praised it.

Then people started crunching the numbers…

One person noted on a Slashdot discussion:

The drop is 58" according to the plan [core77.com]. This gives about 0.022W at 100% efficiency.

For reference, the highest efficiency LEDs that I know of get 131 lumens per watt. If we’re generous and allow them 150 lumens/watt, they still need 4W of power. This would require a drop of 255 metres using the 50lbs of weights he claims. Since we can’t really go above 1.5m high, we’ll need almost 4 tonnes of weights.

Later some estimates of the number creep up to 24 tonnes (ZD Net). It doesn’t seem likely this light is going to be in your shops anytime soon. We’re expecting a statement from Virginia Tech soon…

Read the university response in full below the fold.

While many people want to know when the lamp will be available, many others point out that it won’t actually work.

The criticism is that a great deal of weight – about two tons — would be required and current LEDs are not sufficiently efficient.

Designer Clay Mouton acknowledges that the current state of the art isn’t sufficient to actually build the lamp. The news release should have said: “based on future developments in LED technology.”

Moulton said: “I was told it was not possible given current LED’s, but given the rapid pace of innovation in low powered lighting, it would be a conceptual challenge. The mechanism itself is the novelty. I hope everyone understands that this criticism and even failure is all part of a process, and that my job as a designer is to take this feedback and work on.”

The award was for a conceptual design project based on future technology, and the lamp was one of many futuristic designs recognized at the Greener Gadgets Conference.