PolarAlign

An ongoing project has been to design and build the best astronomy light I can. 

This light is made from a 4" automotive LED tail light/brake light. 

The tail light mode (dim) offers reasonable red light illumination for most astronomy tasks.  The light is diffuse rather than a beam.

The brake light mode (bright) is very bright.  It will light up a road with red light and allow one to leave a star party without use of headlights. I do not suggest that one drive with this light, I have used one on foot to illuminate a road while a driver follows slowly out to a main road.

The white light is diffuse and usable but not very bright. It is useful where white light is necessary and after observing is over, such as in a tent or vehicle.

Because the bright red light and the white light are not intended for routine use, the switches that activate them are concealed.  They cannot be activated unintentionally.

The lantern is powered by 8 AA cell batteries which deliver 12 volts.  Rechargeable batteries can be used.  Battery life is surprisingly long.  I've used an earlier generation light for years  without depleting the batteries.

I have measured the current draw of the lantern.  Low red draws 14 mA.   Bright red draws 178 mA.  White draws 20 mA.  The capacity of an alkaline AA cell is 1700 to 3000 mAH.  The capacity of a NiMH rechargeable is about 2500 mAh so run times should be similar.

With fresh batteries, we'd expect to be able to run the lantern on low red for about 178 hours.  The white light alone would run for about 125 hours.  The bright red should run for about 14 hours. 

The box is made from 1/2" Baltic Birch plywood.  The box without the swingover handle measures 6"X6"X4".  As shown, it requires 3 switches, two are SPST and one is a DPDT center off.  The handle is a 1" dowel turned down on the ends to tightly fit the 7/8" holes in the swingover arms.  The plywood pieces measure as follows:  Front, back pieces 5"X5", top and bottom 4"X6", sides are 4"X5". The hole for the red light is 4.25" in diameter. All exposed edges are chamfered as is the visible edge of the hole.

It is difficult to glue a box like this because so many pieces have to be held in place at once.  Initially I glued small internal blocks to the pieces to help with alignment. Finally I used biscuits placed with a biscuit joiner.  Biscuits are the way to go.

The battery box is made from 1/2" plywood.  Switches and the red light were placed before the box was assembled.  The recessed switches require blocks of 1/2" plywood which will interfere with installation of the red light.

Exposed surfaces were prefinished before assembly. It's nearly impossible to get a good finish after assembly because it's difficult to sand in the corners.  The plywood was finished with 6 coats of gloss polyurethane sanded between each coat.

Wires are soldered and joints covered with heat shrink tubing prior to assembly.  The top is held on with two #6-32 screws, countersunk.  They thread into two brass inserts.

The white light is a light for marine use made by Sea Sense.

The red and white lights were purchased from WalMart, the ball end on/off switches came from a home improvement center.  The DPDT switch came from Radio Shack.  The battery holder is also available from Radio Shack.

The swingover arms are hinged on 1/4-20 stainless bolts 1.5 inches long.

The rubber on the bottom was cut from a rubber mat. It is affixed with E6000 adhesive, available cheaply in the hobby section of Wal-Mart.

The swingover stop block is simply a small block of plywood glued to one of the sides.  The stop block should be small and should be glued near the top of the box.  If placed lower, the bottom corner of the swingover arm will hit the block.

Here is a detail of the hinge support, it's the lower hole pictured below.  A 7/16" flat bottomed hole is drilled part way through the plywood then a 1/4" hole is drilled through.  Next a nut and washer are used to pull the head of the bolt into the hole.  The head of the bolt is pulled into the 7/16 part of the hole and the head of the bolt is held tightly which keeps it from turning later.  The exposed parts have their first coats of urethane. The uncoated part will be a glue surface.

You can also see the switch hole.  The inner aspect was pocketed with a router so the switch is the proper height on the outside.  The 1/2" wide pocket also holds the switch so it cannot rotate.  It's these additional inside pieces of plywood that necessitate installing the red light before final assembly.

Here are previous generations of this light.  The first isn't shown because it was given away.  The final version is in the middle.

The green ropes are "glow in the dark" ropes.  They make it easy to find the lantern in the dark.

The versions with the rope handles aren't so attractive but they're practical.  The rope can be untied then used to hang the light or a carabiner can be used.  The eye bolts secure the top to the box and are removed for battery replacement. I thought the swingover handle was more useful.

The version with the black front was made to see if it would reduce distraction to other astronomers.  It made no difference.

Here's another solution to finding the light in the dark:

This was done with "Glow-in-the-dark 3-D Paint" from a large hobby store, the t-shirt painting section.   The recessed areas were filled with the glow paint and allowed to dry.  There's a faint glow for several hours. It can be seen when dark adapted but it's not bright enough to affect night vision.  

Here's a close up in the light:

You can make out the glow around the red light.  

Finally here's a picture of the white light in its original packaging. 

 Overview

click lower right corner of any picture to enlarge.

Off

 On, low

On high

White light off

White light on

Swingover handle up

Swingover handle back

Bottom

Details

The ON/OFF switch is directly under the end of the handle.  When the lantern is held by the right hand, the thumb or finger can activate the switch.

Important switches are concealed under the swing handle ensuring the the light cannot be operated in an unintended mode.  Above is the white light switch.  On the other side of the lantern is the Dim/Off/Bright red light selector switch, pictured below. 

When this switch is in the middle position the light is off so the top on/off switch has no effect. This can ensure the light cannot be accidentally turned on when not in use.

The bottom of the lantern has a tripod socket.  The light can be mounted on a tripod and easily aimed where the light is needed.  The lantern also has a nonslip rubber bottom.

The white light contains 2 white LEDs. This was originally a boat fixture. This light is diffused and quite usable at night.

The swingover handle stays in position so it can be used to aim the light from a flat surface. Swingover tension is set with the two plastic insert nuts (below)

The inner sides of the swingover handle have high molecular weight plastic pads between the wood surfaces.  These act as bearings so swingover operation is smooth and wear is minimal.

The swingover handle allows the lantern to be carried easily aimed at the ground.  Since the light is recessed, the walking area is illuminated but the bright LEDs themselves are not visible to other astronomers.

Not shown... the swingover handle can be rotated 270 degrees around underneath so it winds up forward.  This allows the lantern to be placed on the hood of a car.  The rubber protects the finish.  The lantern stays in place even if the car is moved. The handle keeps the lantern from tumbling forward.