In this video Julian Ilett demonstrates his DIY 100W LED flashlight:
I discovered that due to a lucky co-incidence of voltage and internal resistance, a 100W LED can be connected directly across the terminals of two 18V Nickel Cadmium power tool batteries. And that means you can build a 100 Watt (7,500 Lumens) flashlight for less than $10 (not including batteries).
Note: Don’t try this with other battery types – you’ll almost certainly fry the LED!
Via Hacked Gadgets.