“Joule Thief” LED Night Light
“Joule Thief” circuit is an inductor based voltage booster circuit to light LEDs with low supply voltage. The circuit was published in 1999 and has been quite popular. You can see the principle of the circuit here: http://en.wikipedia.org/wiki/Joule_thief
My version is a variation that uses single coil inductor, to make the inductor easily obtainable. I design the circuit using readily available parts only, to make it an ideal DIY project.
Please see the full article on Instructables (http://www.instructables.com/id/Joule-Thief-LED-Night-Light/)