My DIY Rear Light
 

I recently completed a DIY rear light and thought I'd share. It uses two Luxeon I red-orange stars powered off 3 AA NiMH batteries. Resistors are used to limit current to the LEDs. Current is about 300 mA to each LED with fresh batteries then decreases from there. I put in a rainproof toggle switch and rainproof power connector. The housing is a waterproof enclosure with removable clear cover. I frosted the cover with spray-on Krylon frosting. It didn't come out as good as I'd like but it works.

Run time is about 5 hours. Just on/off, no flash mode. It puts my Mars 3.0 to shame, particularly in off-axis visibility. Things I'll probably modify down the road are to add a third LED and run them in series off a boost converter and possibly diffuse the light a bit more to get a larger apparent light source. I need to make a more robust mount for it too.

The lumens are about 10% higher than the attached graph shows because I increased the current after taking those measurements. I used 53 lumens/watt as calculated from the Lumileds datasheet to determine the lumens numbers. Total cost was probably $75 or so including charger. The total weight is about 300 grams.

Nice!
You might consider using this driver circuit.
http://www.dealextreme.com/details.dx/sku.4451

http://www.dealextreme.com/customerp...5643145bfe.jpg

You get 5 for $8.51 with free shipping. Operates using 1 or 2 1.5 volt batteries. I would use 2 AA Ni-MH rechargeable batteries. Has 5 modes including flashing modes. You can operate one of your LED's on steady and the second in flash mode. You'll have 3 extra so you can build another blinkie for the front!

I recommend optics from Kai Domain. That's a lot of light wasted into the sky. With 3 AA batterys, check out drivers from the light DIY section of DX.

It's a taillight. Optics would narrow the beam making it less visible except directly from behind. I think his taillight is fine just the way it is.

Oval optics so the light still points all around but not up and down. A 6x25 would be good putting much more light where it counts...probably triple brightness.

I thought about using optics but I kind of like knowing that I'm highly visible from any angle. It's basically like looking straight into a Mars 3.0, but from any angle. I may play around with an oval optic though, thanks for the tip.

Update: So there isn't room enough for an optic in the housing but I was able to file down some reflectors I had lying around and stuck those on. They're filed down to about 10 mm. They just happen to fit perfectly over the Luxeon bodies. They are from BestHongKong and are meant for the Prolight brand of LEDs. Because the reflectors have been shortened quite a bit they let light out at broader angles, so off-axis visibility is still quite good while visibility from behind is significantly increased. I think I'll stick with this version. Even on a bright sunny day the light is very visible.

Pics - The Mars 3.0 is on the seatpost for comparison. There are two rear shots: one auto exposed and one less exposed.

It looks like you actually have enough room for about 6 LED's. Stick a waterproof connector in there for charging, a lithium polymer battery pack, and you've got yourself a 1000 lumen rear light.

I got it from Mouser. It's made by Hammond and they have many other sizes as well. They also make metal ones and ones without a clear lid.