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Converting Flashlights to use LEDs

LED Flashlight

Be careful with soldering irons.
Wear safety glasses solder can splatter, LEDs can explode.

You have several options here. One is to simply replace the light bulb with an LED. First of all you have to know the total voltage generated by the batteries. Alkaline batteries generate about 1.5 volts each when connected in series. For the typical flashlights that have two AAA, AA, C, or D that is simply 1.5 + 1.5 or 3.0 volts. Recall that the bright white LEDs need 3.6 volts. Well, they will operate at 3.0 volts, but they won't be real bright, but it will be very durable and last a long time.

The other option is to substitute different size batteries. This works well with AA size batteries. There is an N size battery that is about the same diameter as a AA, but shorter. For a flashlight that takes 2 AA batteries, you can substitute 3 N size batteries (providing 4.5 volts). You will have to make a small spacer to fill in the extra gap and use a resistor to reduce the voltage, but that is easy.

Remember the equation

R = (B - V)/I = (4.5 - 3.6) / .02 = 45 ohm

47-ohm resistors are the closest standard size.

There is a great web site called OtherPower.com that has very helpful instructions for converting flashlights to use LEDs.

Ready for more fun with LEDs? Try these out:

Copyright © 2002 Vincent Hale