High-power LED mountain bike light
In preparation for the 2006 Sydney 24 Hour, I wanted new mountain bike lights. Last year's light was a 20W halogen globe and two packs of ten AA cells. This was nice and bright, but the battery packs got rather hot and only lasted about 40 minutes each.
This year, I raced solo. Recharging two battery packs per lap wouldn't cut it. My plan was to spend about an hour per lap - each lap was 10km - and sleep for an hour or two when I charged the batteries. So I was aiming for 3-4 hours battery life at about the same brightness as a the 20W halogen.
The new system weighs 715 grams and lasts for about four hours at 9 watts of output. Charging the batteries takes under two hours.
There are a number of bike light projects on this website:
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The whole lighting system: The head unit is on the left, battery pack at the bottom, and bottle with the controller on the right. The bottle also holds the battery pack.
I designed this light around Cree XLamp 3 7090 LEDs because there was a local distributor that had them significantly cheaper than the Luxeon parts. A 3021 BuckPuck was used for regulation, and a new bottle-cage battery for power.
I was quite pleased with the outcome, and got a number of positive comments during the race. I had absolutely no problems with it during the race, and got better than expected battery life.
Unlike most LED lights, the regulator and control circuitry are located in the bottle with the battery. This makes the mechanical design easier. The regulator will compensate for any losses in the wiring.
The 'low power' switch disables two of the three LEDs. Again, the regulator compensates automatically. I thought this would be good only for the commuting use case until I realised that many off-road trails only need weak lighting too. Having the switch on the handlebar means that it's easy to switch between low and high power mid-trail, saving battery life.
The LEDs around the regulator were originally meant for debugging. One is on when the regulator has power; the other is on when the main light is on. I used high-intensity blue and green LEDs, which look rather eerie at night. They work well as an emergency light for situations like mid-trail repairs. They use a trivial amount of power compared with the main light.
The bottle at maximum eeriness
LED Drivers
High Power LED Lights like the Cree X-Lamp are actaully more efficient when compared to the K2. I read several articles on Lunar Accents that prove this, about LED efficiency. Look here: http://www.lunaraccents.com/technology-high-power-LED.html
Re: LED Drivers
Most high-power LEDs are more efficient than the K2. When I originally planned out those lights, I was drawn in by the high current rating. Turns out it's not good for much (light output at 1500mA isn't much more than 1000mA).
My current set of lights is based on Cree XR-E's. I'm very pleased with them. Note that the original Cree XLamps (used in this article) are not particularly efficient themselves.
Thanks for the details
I have been thinking about doing the same thing for my bike since getting a Fenix P2D-CE - which uses a single Cree XR-E emitter - and being impressed with it's output. This article has helped a lot, thanks!
Was your supplier c*****, by any chance? I was thinking of ordering the bits from them.
Sam
Distributor
Can I ask who your located distributor was in Sydney? I'm in Brisbane...
Distributor
I had a poor experience dealing with them, so I'd rather not name them. If you've got the time to spare, buying direct from the US tends to be a reasonable option, despite shipping costs.
You definitely didn't get
You definitely didn't get the correct optics, I have a feeling based on the timeframe you got them in that those are Luxeon optics, not Cree (and as such, would be unpredictably bad compared to Cree lens spec sheets).... here is my "Cree optics comparison" website...
http://christexan.com/biking/bikelights/LensComparisons/
or if the registration (updated just before this post) hasn't propogated yet (subject to change anytime after the day of this posting)...
http://76.183.249.123/biking/bikelights/LensComparisons/
It is clear that a Cree with a 6* Polymer Optic is a very tight beam, nothing close to what you describe. And I've used them "loose" and bumped them around, they lose a little focus, but mostly it's just the hotspot moves within a very slight halo if it's even close to seated properly, so those are the wrong lenses. Glad they work for you though!