@evnewbie:
After about 1/2 hour to 45 minutes of running the heatsink is warm. How warm? If it was bath water I'd typically use warmer, so maybe 90-ish F when the ambient air temp is high 70's low 80's. The LED's are reflow soldered at the factory on to MCPCB stars, which are then thermally conductive epoxied onto the heat sink. The back side of the heat sink is structural epoxied onto the rest of the metal housing. Two of the brass edges are exposed to ambient air. Theoretically, there should be lots of ways for heat to escape. I'm not sure the brass makes a real difference. Only used it because I had a piece. Otherwise, a piece of aluminum could be used and probably not make a noticeable difference.
The driver is an nFlex.
The LED's are CREE XR-E's. I'm too lazy to look up the specs, but I think they were 113 or 123 lumens per watt. I could be tempted when the XR-G's come out, though. I don't really need another light, but it makes a fun project, and mo' power is always a good thing. I would call this one water resistant, but not water proof. That probably would be the next thing to tackle.
Prior to this I was running a pair of over-volted halogen MR11's for 30W total. I ride a lot on country roads at night and was constantly met by oncoming traffic running down the middle of the road or even further over, simply because they could tell by the light that I was beneath their respect.
That does not happen any more. In fact, now they are the ones hugging the edge of the road because they can't figure out what kind of UFO is coming at them. I had been dipping from 100% full current to 70% for oncoming traffic. Then one night my wife was stopped on a side road at an intersection when I rode past. She pulled in behind me and then eventually passed. Later, her somewhat colorful description of what it was like driving in front of a 70% beam convinced me to dip to 30% for traffic.
As a test, one night I held it out the car window and turned the headlights off. Could still drive the car at 40 mph. All from 12 watts of LED light. Pretty cool. It's more than adequate for my 20-25 mph biking speed. Just amazing what's going on in the world of LED's right now.
@ needwheels:
Pros use light meters that read actual beam intensity as a function of degrees from centerline and distance. Nothing theoretical about it. I'm not serious enough about building lights to have equipment like that. A lot also depends on the reflector and how much of the light emitted from the chip is able to be scraped up and sent downrange, so the downrange meter gives a good real-world reading.
In the photo below the squares on the door are ~ 2 foot centers horizontally, and the light is 16 feet from the door. The camera is handheld, and the lack of blurring indicates a reasonably fast shutter speed was used. I didn't want to shoot in the dark because it overemphasizes the brightness of the light. From the other things visible in the photo (no flash) you can tell that although the sun is going down, it's still quite a ways from being dark. In fact, if you look closely you can see the sky reflected in the left rearview mirror just in front of the bag. The headlight really is that bright.
I can tell you that last fall the local bike club took a night ride on a bike trail. At 9PM on a tree-covered trail it was seriously black. I was in the rear. In front of me were about 40 bikes running lights ranging from 'you gotta be kidding' to pretty decent. None matched the output of this 12W system. When the trail was straight, I could see the lead bikes 1/4 mile ahead. People within 100 to 150 feet in front of me pretty much didn't need their own lights except the shadows were tricky. I used 30% most of the time just because it kept the shadows from being so intense and confusing.
MT
