ASK A GEEK: Scott Fullam

Q: Can I hack a standard flashlight to use LEDs, making it brighter and longer-lasting?

–Jacob Miller, San Diego, Calif.

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Absolutely. A flashlight with at least three AAA, AA, C or D cell batteries hacked to use three 2300-millicandela LEDs will be as bright as an incandescent and last 5 to 10 times longer. Of course you can add up to 20 LEDs (as long as they fit in the reflector) if you’re planning to, say, man a lighthouse with the thing. Use a flashlight with more batteries, get more life. You’ll also need a resistor for each LED: For a three-cell flashlight, use 30 ohm resistors, 75 ohm for four cells, 130 ohm for five and so on. (Try for the parts.)

Trim the LED leads to about a half inch (maintaining their relative lengths), and the resistor leads to one-eighth inch on one end, 1 inch on the other. Solder the short resistor leads to the long LED leads. Carefully break the old bulb. Use a soldering iron to heat the bottom of the bulb case until you can push a long resistor lead through it, and clip the excess. Solder the hanging LED lead to the flange of the bulb case. Solder the remaining LED/resistor pairs in parallel to the first and stuff them all into the
reflector. Now shine on, you crazy diamond.

Click here for detailed instructions.

Scott Fullam is H2.0’s Hackmaster, and author of the recent Hardware Hacking Projects for Geeks ($30, O’Reilly). Now a consultant to consumer electronics makers, Fullam has been a toy designer (he once made Barbie talk) and an Apple engineer, and holds two degrees from MIT.

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