Since Lumileds introduced high-power LEDs, several years have passed, but this technology still has not been widely adopted in bicycle industry. Luxeon 1W lights have become common, but the amount of light they produce is less than standard 2.4W halogen, which makes them only "to be visible" lights. At the moment of this writing (October 2005), I know of only two commercial models with one 3W Luxeon LED:
There are other manufacturers producing lights with 2 and more 3W LEDs, including mainstream CatEye. But why so few single-LEDs?
I went up for my own, pursuing desire to make something material. Examples of what other people have done include:
I got different (smaller) collimator than the three above mentioned tinkerers have used, so my light would not copy any of theirs.
The core components, 3W rank T Luxeon LED, 700mA constant current driver, and collimator were bought from led-shop24.de. First breathtaking try of connecting the components showed that the LED looks really bright and that the heat sink is really needed. Try to hold a burning 3W LED in fingers, after some 10 seconds you'll have no doubt in that.
LED operates at 700mA and the meter reads 3.4V on it, thus the power dissipation is 2.4W (not actually 3W). From the battery, exactly 3W is drawn, so the efficiency of the converter is 80%. That is what it said in the datasheet. So, correct comparison should have been done against 3W (but not 2.4W) halogen. I'll get 3W lamp just for purpose of this testing soon.
Above are light beams of 2.4W halogen Sigma Ellipsoid (with fresh batteries) and of the Luxeon light. 5x20° collimator is fine in 5 vertical degrees, but wasteful in horizontal 20 degrees. And my impression was that all 20° are lit as bright as Sigma's about 5°. Probably this can't be true because Luxeon does not produce four times more light. I'll test 5° round collimator; good that my design allows easy changing of optics.
The real creativity starts at constructing own mechanical part. I used a spare holder from Sigma Ellipsoid (available for purchace at various shops). The diameter of the collimator was 22mm, just covered by 1 euro coin. The future light case was found in home hardware supermarket as 25mm steel tube. Aluminium would be better (lighter, easier to drill/saw and higher heat conductivity), but was not readily available.
LED was glued with thermal paste to a coin, which exactly fit the inside of the tube. Coin, in turn, was glued to the walls with large amount of thermal epoxy, in hope that it would make enough of heat sink. Looks like there is no way to test it without a proper temperature sensor hidden at the LED.
The constant current driver fit horizontally inside the tube, leaving just enough space for switch and input socket above it. Overal construction is very compact; well, that is without battery.
Constant current driver is a great thing: any battery giving voltage 6.2V or higher (up to 30V) can be used. Except that it will be ruined drained down to the end. Some electronics at the battery end, giving feedback on its state, is absolutely necessary -- unless the battery is non-rechargeable. A dead laptop is what you need in that case. Their battery chargers are separate from the main CPU and are software-free (because charger works even when the laptop is turned off). Batteries have undercharge protection circuits. It was not obvious how to attach cables to the battery contacts, and I am wondering how others do it. I glued pair of metal contacts to a plastic board, which kind of works so far.
The electronics inside the battery pack somehow even shows the battery "actual capacity", which was 30Wh for my mid-aged battery. That means 10 hours of light - quite OK, I do not so far plan to ride longer than this in the darkness.
The last thing to do was the battery holder. An old big mobile phone case, tied to the top tube with toe-clip straps, did the job perfectly, adding some splash-water protection and minimal padding.
For comparison, the same Sigma Ellipsoid is mounted next to the new light. The 20° beam is wide. It is probably excellent for off-road riding, but then such amount of light would not be sufficient. On the other hand, for my daily 17km one-way commute along mostly lit streets and bike paths, this light provides excellent side-visibility, maybe even too much of it -- I'm afraid I'd blind the upcoming pedestrians.
First two weeks of riding made me quite much happy with this new light. Classic 2.4W halogens are in the past!