A home-made red LED flashlight


A red LED flashlight is a MUST on an observing session. It provides enough light to read charts and fiddle with your equipment and won't destroy your night vision (or anyone elses). I have a Starlight flashlight that is powered by a 9v battery but found that the small LEDs used in it just weren't bright enough some times. Also, it was long and slim and wouldn't hold a Velcro strip. I hang my flashlight from the mount with Velcro so its always handy and needed more space for the Velcro's adhesive to hang on to. The Starlight has a dimmer circuit (see below) to control brightness and I found that I didn't generally use anything but the highest setting so I built my new one with two intensities with the 'low' setting the same as the Starlight's highest.

Building an LED light is cheap and simple if you can handle a soldering iron and drill. You can even make a small board to clean things up as I did, use perf-board or just 'dead-bug' the thing.

Parts list
  • Suitable project box
  • Three high-intensity red LEDs (I'm using 4500mcd 20mA parts)
  • Three 360 ohm 1/4W resistors
  • Two 820 ohm 1/4W resistors
  • Five 1N4148 diodes
  • One SPDT on/off/on switch (toggle or rocker)
  • One 9v battery pigtail
  • Some wire
This version has two intensities, three LEDs pass 20mA each in 'high' and two LEDs pass 10mA each for 'low'. There are a lot of times when you just need a bit of light. If you want your 'low' setting even lower you can substitute a 1K ohm resistor for the 820 ohm resistor to deliver 7mA or use a 1.5K ohm resistor to supply 5mA. This project cost me about $15.

I used an SPDT toggle switch (on/off/on) to select high/low intensity. I couldn't find one with a short toggle on it, and the switch stuck out a long way. To get around this I cut the toggle short (about 1/4") with a Dremel tool. Then once the build was done I mixed some epoxy and put a good ball of it on the toggle. Then I just sat it on a shelf with the toggle hanging down and let the epoxy sag. Some dropped off but what was left formed a nice, small teardrop end. It feels good on the thumb.

We're using resistors to cut down the current to the LEDs. In 'high' mode there is a 390 ohm resistor and in 'low' mode there is an 820 ohm resistor. These are connected in parallel from the toggle switch to each LED. Each resistor has a diode (I used 1N4148s) paired with it in series to keep power flowing the right way around the circuit when the swich is thrown; see the circuit diagram below





If you want to make a small board you can clean up the build. Here is a PhotoShop document.

LED Dimmer circuit

If you want a dimmer you can do it with resistors and a pot, or you can do something just as simple with a couple of transistors. This circuit measures .56" x .78" (less than 1/2 square inch of footprint) and will fit in a very small space. Here's a diagram.



Here's how big the actual circuit is; that's a dime next to it.



Here's a PhotoShop document you can use to build a board.

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