Plans for a Folding Observing Lamp for Astronomers

In May 1999, I attended a regular monthly dark-sky observing session at Fremont Peak, California with TAC (The Astronomy Connection). One of the members, Jim Bartolini, had built a little observing lamp for another member (Marsha Robinson)out of wood...it folded up, was adjustable, and used a small LED keylamp you can buy in camping stores for around $15. (Jim built one of these lamps for himself, then built another one for Marsha. (Photos of Jim's original design are below)
Having used my red LED flashlight for several months and grown tired of having to hold it all the time while looking at charts, I thought the idea was inspiring. The only problem I saw was that the little velcroed-on keylamp used little non-standard batteries, and used them fast (Jim and Marsha have been using their lamps for months on the original set of batteries...however, a test I did with a slightly different key lamp than the one they bought showed that it would last for about 16 hours of continuous use, while my AA-battery circuit ran for 10 days continuous and was still going -- your mileage may vary)! I got an idea for building my own observing lamp, using standard AA batteries, having a light that spread out over a wider area, and would last for many hours of observing. I finally built it, and here are the plans and photos. It's turned out to be a wonderful addition to my observing toolkit -- I hope someone else can find the idea useful as well.

Plans

The lamp is very simple. I cut an 8-inch long by 4-inch wide base from scrap 0.5-inch birch plywood I'm using to build my travelscope (see here) for a base, and used some scrap 1.5-inch by 0.75-inch oak I had around to build the lamp arms.
I bought a AA battery holder, a push-on/push-off switch, a 100 Ohm resistor, and a 3-volt Jumbo Red LED from Radio Shack. Total cost about $7.00. The top arm of the lamp has a hole drilled lengthwise to allow passing the wires for the LED through it, and a hole drilled vertically for the wires to meet the lengthwise hole -- you'll notice from the pictures below that this vertical hole goes all the way through the wood...I needed the hole to be on top so I could push the somewhat stiff wires through and get them to come out the bottom! The LED itself sits against the bottom of the top lamp arm, and is held in place with a small dab of silicone -- this keeps it in place, but will allow me to remove it if it ever burns out and needs to be replaced.
Cut the wood pieces, drill the holes, use some long machine screws and nuts to hold it together, and it's mostly done. Total assembly time was about 2 hours. I finished all the wood pieces with Spar Urethane (waterproof) so it would hold up on dewy nights. The electrical connections are also very simple, refer to the schematic above. After it was all assembled and soldered up, I used heat-shrink tubing over all of the solder joints to insulate them and seal them off from the weather. Finished!
Folded up, the lamp is 8 inches long, 4 inches wide, and 3 inches tall. It fits nicely into a small spot of my eyepiec/accessory case. Unfolded, the LED sits at about 6 inches high, and can extend about 8 inches past the end of the base. The battery case acts as a nice counterweight to keep it in place. The Jumbo Red LED I used has a nice wide, diffuse beam that lights up charts nicely. It's a real pleasure to have a hands-free lamp out in the field! The lamp is also light enough to pick up and use as an LED flashlight when you need to examine your scope, or find that pesky wing nut you just dropped in the grass...
Pictures of the finished lamp are below. I hope someone else finds them useful for coming up with your own ideas for a nice observing accessory!
Special thanks to Jim Bartolini and Marsha Robinson at TAC for the original idea :)

Here are some pictures of Jim Bartolini's original design. Jim's lamp is taller and takes up a bit more space, but lets the lamp arm swing out further for larger charts. Jim also used a commercial LED keychain lamp instead of wiring up his own circuit...if you'd rather not mess with circuits, his design simplifies things greatly. Jim's lamp also has a swiveling head assembly -- a nice touch. Feel free to use ideas from either of these for a lamp that suits you!

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Questions? Comments? E-mail me! lefevre@midway.com