# An Engineer in Wonderland – Gravia

Civil engineers that I know are inclined to get a bit grumpy about architects, on account of their artistic flair getting in the way of actually designing buildings that work. But it looks like one talented architectural student has learned his lesson in practicality early, and will probably check with the engineers before he releases any real designs. US Virginia Tech student Clay Moulton designed the stunning Gravia concept – a gravity-powered floor lamp. The 1.2m tall device runs somewhat like a grandfather clock, with just over 20kg of brass weights that descend slowly – in this case running a generator.

“The light output will be 600-800 lm, roughly equal to a 40W incandescent bulb over a period of four hours,” said Moulton originally. Doubters ran their calculators over its various parameters, and worked out that it wasn’t going to light for very long without adding tonnes of mass. I have been “told it was not possible given current LEDs, but given the rapid pace of innovation in low-powered lighting, it would be a conceptual challenge”, Moulton said response. “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.” Fair enough. Gravia won second prize in the US Greener Gadgets competition. I have no idea how this prize was judged, but I cannot help feeling sorry for those that were beaten by this beautiful but hopeless objet d’art. What is also a bit of a shame is that it is such a nice looking design and, taken on face value, something green that the public might easily have taken to. I had to have a go at the numbers: My estimate, based on 20kg, 1m fall, and acceleration due to gravity being about 10 is that there is 200J of potential energy in the weight. I vaguely remember that the maximum theoretical limit for white LEDs is 300 lm/W – although from where this came I cannot remember, but they are just over 100 lm/W now, so 300 lm/W does not sound unreasonable. Assuming it is 300, then 600 lm will need 2W – or 2J/s. 200J will last for 100s with the best LEDs I can imagine. Oh well. Further Information “The mechanism itself is the novelty,” said Moulton. The weight descends, forcing a ball screw down the centre to rotate. This, in turn, pushes round a 1:160 harmonic drive which spins 12 rare earth magnets in a generator. A patent is pending on this mechanism – www.vtip.org if you are interested. Moulton’s MSc thesis is at http://scholar.lib.vt.edu/theses/available/etd-08292007-103115/ And the other Greener Gadgets winners are at www.core77.com/competitions/greenergadgets/projects/4306