Complete instructions for this Weekend Projects can be found at
The Solar Joule Bracelet combines two separate projects, a solar battery and a "joule thief," to build a wearable circuit that powers an LED. Solar energy flows through the photodiodes, building up a supercapacitor, which essentially acts like a battery. This energy is then delivered to the joule thief, where oscillations eventually exceed the LED's forward voltage, making it light up. Once fully charged, these oscillations will occur so fast that the LED will appear continuously bright, visible even during daytime!
Best of all, this circuit's design allows you to install it where and how you wish!