LED Astronomer's Flashlight for under $5

by Don Peckham
Home:  dbpeckham.com

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.

LED Flashlight



Circuit Diagram


  1. Open up the battery holder (must remove a screw).

  2. 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.

Open the battery holder

  1. See the position of the resistor and LED.

Photo of circuit layout

  1. 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.


Some of my astronomy projects:

12.5" F4.5 String Telescope     
Two Cylinder Equatorial Platform with Floating South Mount      
Flex Ring (Flexible upper ring used with four strut string telescope)   
String Telescope Concepts   
Truss Tube to String Telescope Conversion   
Greg's Right Angle Telrad