I have found that purchased astronomer's red flashlights are too bright. With less than $5 in parts I built a small, dim LED flashlight.
I settled on a 680 ohm resistor for backyard viewing inside the city (neighborhood lights, etc.). A higher resistance resistor (dimmer LED lamp) is more appropriate for dark sky viewing.
Parts:
Battery Holder with built-in switch: Radio Shack #270-409
5mm Wide-Angle red LED, 1.7 volt, 20mA, 800 mcd: Radio Shack 276-309
Resistor: 680 ohms (higher resistance for dark sky use), 1/4 watt.
Circuit:
Instructions:
Open up the battery holder (must remove a screw).
Remove the screw from the little cover at the switch end of the battery holder. Note that the cover is heat-welded in place, so you need to use a knife to break the heat welds.
See the position of the resistor and LED.
Drill a hole for the LED in the location shown. Make sure the hole is a little small so that the LED will have a snug fit.
