Design of appropriate low-tech devices for third-world people is an area of special interest to me. I recently noticed a solar lantern (by SolarSister), but it seems quite pricey at $48 US. Now comes a really wonderful design which has all the markings of sustainability – as gravity is with us everywhere, and its free!
Kerosene is used by over 700,000,000 people to light homes; fumes are equivalent to smoking two packs of cigarettes per day. CO2 from this is projected at 190 million tons annually. All of this can be made unnecessary with a device costly less than $10. After three months recovery of investment, it saves families walking to buy fuel/petrol. More info: http://deciwatt.org/#gravitylight
This then is the message we have heard of him, and declare unto you, that God is light, and in him is no darkness at all. ~1John 1:5