Utah Nature has a how to on making a LED emergency light – “This LED array uses 15 LEDs housed in a 1 inch PVC connector. Each LED has its own 100 ohm resistor to limit the current and reduce the voltage. The LEDs have a 20 degree light dispersion resulting in a beam much like a regular flashlight. Using 4 D size batteries, this assembly produces usable light for over 24 hours. This array is ideal for lighting dark work areas such as work under the car.” [via] – Link.