The LightCap 200 is a smartly designed solar-powered light that converts standard-sized water bottles (such as those made by Nalgene®, Camelbak® and GSI®) into a useful and safe lamp.
The LightCap 200 is a great little green gadget, completely waterproof, uses no batteries, and weighs only 74 grams. The LightCap uses four small but bright white LEDs that switch on automatically when it gets dark. The LightCap is screwed onto a water bottle filled with water and will diffuse the light if the water is sufficiently cloudy. Adding a fruit squash or cordial to the water will turn the light different colours too.
If you need a supply of water or light in an emergency, you have both!
Source: LikeCool