Home made solar lights.?

I recently saw the tail end of a program on the discovery channel. A guy somewhere in Asia was installing solar powered lights for the poor and needy. The lights were 2Lt Coke or Pepsi bottles filled 2 thirds with water and a chemical or chemicals. They were then installed in the roof with about half the bottle exposed to the sun. These bottles produce about the same light as a 55 watt bulb and last 5 years. Anyone know the chemical/chemicals used?