Instructables user, and TreeHugger favorite, ASCAS has created another great clean energy project that is simple to make and super useful too. Here's what he had to say about the water powered flashlight:
"The flashlight runs 30 minutes continuously with tap water and 2 hours with saltwater. Not bad for a single celled prototype. This thing also works well with calculators, clocks & radios. Remember, adding a second cell triples the glow and lighting time!
How Does It Work?
This is a type of battery called the "Galvanic Cell," having 2 different types of metals and is connected by a salt bridge. It works like your typical battery but uses water as its electrolyte. The output voltage is pretty faint and isn't enough to run a single LED. With the help of our trusty "Joule Thief Circuit," the LEDs would glow even at low voltages.
Is It Really Powered By Water?
Well not really, the water serves as an electrolyte, a replacement for toxic chemicals used in regular batteries, which usually ends up in dump sites. So why call it water powered? Of course no one would be interested in the title "Galvanic Flashlight," plus that's what easily pops up in people's minds.
1st.) If you got lost and stranded out in the woods, you can't rely on batteries, eventually they run out. A mini version would save stranded people in the woods, just go to the nearest river and follow the river's trail (the river leads people) you'll have a 24/7 supply of light!
2nd.) School science experiment
3rd.) For Fun!"