Via  SALt – Sustainable Alternative Lighting – is a portable LED lantern that uses a simple galvanic reaction with salt water to power an LED; it is targeted at developing nations.  According to their site:

Just add water and salt!
Add 1 glass of water and 2 tablespoons of salt, use the lamp for 8 hours.
Cost Effective
There are over 7,000 islands in the Philippines and most of these islands do not have access to electricity. We want to eliminate the sustaining cost in areas that rely on kerosene/battery powered lamps and candles as their main source of lighting. And to provide a more efficient light source for people who use lamps and candles as an alternative source of lighting. Replace consumable every 6 months! Using SALt lamp 8 hours a day every day will give you an anode lifespan of 6 months. Use this as an alternative light source will prolong the life of your anode for more than a year.

I hope they can use a commonly available anode material, to ensure local populations can maintain this long into the future.