Upgrade Your Flashlight to LED

Give Your Light New Life

As much as we owe Edison, his lightbulb is a model of inefficiency. While this may not bother us when it lights our homes, it can be a drain on battery-operated devices. It's time to breathe new life into those aging incandescent flashlights you have: Installing LEDs can make your flashlight brighter and improve its battery life by a factor of up to 50 times.

The difficulty with transforming conventional flashlights, however, is their voltage. Typically 3V does not provide enough voltage to power the bright white LEDs that can outperform the bulbs in brightness. That's why most commercial LED products use three 1.5V batteries. However, you can still get a useful and efficient flashlight by using amber-colored LEDs. If you have a flashlight that puts out more than 3V, spring for the brighter white LEDs. I had extra flashlights of both kinds laying around my house.

Upgrade One Single LED Bulb

 was the first flashlight I set out to improve. This being my first attempt, I tried for the simplest possible strategy.

The first step is getting access to the cathode and anode leads. You could try removing the bulb and trying to solder some wires in place yourself, but the bulb's casing does it all for you in a very convenient way.

Since the bulb won't be useful to us anymore, don't hesitate to take a hammer to it. Be sure to place the bulb inside a rag so that glass shards don't go flying.

Now that I had access to the leads, it was a piece of cake to solder an LED directly into place. Make sure that you don't solder with the wrong polarity. The positive terminal will always be adjacent to the notch in the bulb's casing. I checked just in case.

The simplicity is breathtaking, yes, but it's not the best we can do. The flashlight, while it may run for a millennium now, isn't nearly as bright as the original bulb. And it isn't the ideal situation for LED health either - it would do much better with a current-limiting resistor.

Upgrade Two to Five LED Bulbs

Onto flashlight number two, another 3V bulb. I connected five amber LEDs in parallel on a small piece of perfboard. I chose a resistor that would stabilize the current without drastically diminishing the brightness of the LEDs. 10 ohms did the trick. Yes, they will be brighter if you overdrive them, but not much, and they will last much longer operating at their prescribed voltage and current. The five amber LEDs were about equivalent in brightness to the original bulb. The reflector housing was small to begin with, so the LEDs were really cramped.

Only with my 6V flashlight was it possible to reap the benefits of super bright white LEDs. Rated at 4.5V, they could provide the necessary illumination to overshadow the original bulb's brightness. Because of the 1.5V difference, however, some of the energy is wasted by the necessary current-limiting resistor. (If you own a 4.5V flashlight, these LEDs would be perfect.) I went for a parallel array of 8 LEDs with a 50-ohm resistor in series. The results were great. It definitely outperforms the original bulb in brightness.