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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

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:

• NEW and IMPROVED LED flashlight Junior
• One LED Flashlight
• One white or one red LED
• Two white LEDs
• Four white LEDs
• One or four white LEDs
• LED Headlamp
• Improved One or Six White LED Headlamp
• Simple One or Two White LED Headlamp
• Other Experiments
• Black Light LED Flashlight