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.
6 thoughts on “Emergency LED light”
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Nice project. If you do a version 2, you might want to consider a Luxeon III LED (http://www.lumileds.com/products/family.cfm?familyId=8). It’s a single $4-10 LED that will give more than twice as much light as your entire array.
Lose the resistors- they are eating power without producing any light. Wire the LEDs in series/parallel. The LEDs will run at less than 20 mA, reducing light output only slightly and increasing operating lifetime beyond your own. Bring the light output up by adding more LEDs- they are almost as cheap as resistors anyway.
Many sources on ebay sell 5mm white LEDs at outputs up to 150,000 mcd (probably marketing BS). They produce a narrow beam. The high power LEDs from luxeon and prolight have wide radiation pattern (lambertian). It is great to light up a room, but not really useful if you want bright light in a small area like a flashlight beam. You can get collimators (made by Luxeon and Fraen) for the Luxeon parts that squeeze most of the light into a very bright, narrow beam.
Ignore rehorstmark. He has no idea what he’s talking about.
If you leave out the resistors, you are shorting the battery through the LEDs. The only limiting factor is the internal resistance of the battery. On size D batteries this is insignificant, so you’ll be forced to have a total voltage under the Vf of your LEDs, so they will only partially light on brand new batteries and not light at all once the batteries are 5% used.
Also the Luxeon I LEDs are available in a wide pattern and a focused pattern.