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3 edits
reply to SparkChaser

Re: GravityLight: lighting for developing countries.

I definitely watched the video. This is really nothing more than an awesome night light. That's how effective a single lower power LED is. It's hard to do anything by such little light, especially one that will be hung across the room.

said by aurgathor:

When you have a choice between this and a lamp that runs on petrol (roughly the same light output), or no light at all, I think the choice is pretty clear. Anything solar powered will normally require batteries -- they are expensive and wear out, especially in less than ideal operating conditions.

Maybe, maybe not. This light won't be bright enough to light up a room. It won't be bright enough to read by unless you stand up next to it. Don't be deceived by the video and pictures. This is not a bright light. Kerosene lamps are brighter and more portable. Kerosene can also be used for cooking. Really, the gravity light is an attempt to solve a problem without taking into consideration what is actually required to solve the problem. Simply making a light that costs nothing to run won't solve the problem. It has already been done.

The battery problems of solar lights were solved some time ago through the use of super capacitors. Although the company making the lights appears to have gone bankrupt. There wasn't enough demand for their lights, in part due to the price. NiMH batteries can be purchased for under $1 and last years.

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I get the feeling you will never be convinced but I throw this out anyway. A 10 YO study, so the LED technology has had 10 years to improve. The kerosene technology, not so much.

Summary and Conclusions

The energy use and light output of kerosene lamps vary widely depending on the type of
lantern used, maintenance of the wick, and the cleanliness of the “globe”. Moreover, our
measurements indicate that light distribution is very uneven in both the horizontal and
vertical planes, i.e. depending on the angle of view. Kerosene-based light is poor for
reading and many other tasks, particularly on horizontal surfaces.

Our estimates of useful illuminance on typical tasks show that the kerosene lamps deliver
between 1 and 6 lux (lumens per square meter), compared to typical western standards of
300 lux for reading. Light output deteriorates considerably from these already inadequate
levels within a few hours of operation (by up to 83% in our tests) as the globe becomes
soiled, requiring frequent cleaning. In contrast, “lumen depreciation” in electric lighting
systems is typically in the single-digit range after years of operation.

A competitive analysis of kerosene lanterns versus conventional electric alternatives
(both grid-based and grid-independent) and emerging white-LED alternatives shows
considerable potential for economic and environmental benefits. When evaluated in
terms of total cost of ownership (fixed and variable), the LED systems emerge as the
most cost-effective solution, with payback times from several months to two years.

»evanmills.lbl.gov/pubs/pdf/offgr ··· ting.pdf
"Facts do not cease to exist because they are ignored." - Aldous Huxley

That's an interesting read.

I have no doubt that LED light is superior to kerosene. What I doubt is the power source of this light. I can't see this light putting out enough light to be useful. Even with the most efficient LEDs on the market.