How to build a simple Luxeon LED bike headlight
This is a simple bike light which can be contructed with a minimum of tools. It is bright enough to be useful as a headlight, is fairly robust, and cheap to construct. It's perfect for commuting and does a surprisingly good job for mountain biking too.
The whole thing, including rechargeable batteries, weighs about 200g and will run for over two hours.
There are a number of bike light projects on this website:
It's based around a Luxeon III Star. This is a very high-power LED that supposedly produces about the same amount of light as a 5W halogen bulb while using far less power. To focus the output, I used a Fraen narrow lens. It's designed to mount directly over the LED and produces a nice tight beam without wasting a lot of light to the sides.
Everything else is just there to support the LED and its lens. I used four rechargeable AA cells to power it (why?), which should last for about two hours. One of the nice features of the LED is that when the batteries go flat, the LED will continue to glow dimly for a while, so you're not invisible in traffic. The AA cells are contained in a battery holder and attached to the stem of the bike using velcro. A 1.5 ohm resistor prevents the LED from overheating. Everything is attached to a sheet of folded aluminium, which acts as a heatsink for the LED and prevents the light from dazzling the rider.
I built this light mostly for commuting, and it does nicely for this task. It's bright enough to see where you're going on unlit streets. It does get drowned out in street lights, but in that situation you really only need something so that drivers can see you anyway.
I've used the light for the mountain bike legs of a few adventure races, and it's held up quite well. It's a bit marginal in technical terrain, but for 95% of what's out there it's good. When you're out in the middle of nowhere with no street lighting for miles, it's remarkable how far 3W of LED light will go.