Cree Q5 Quad hack job!
 

I saw this light setup a little while ago, just after my HID stopped working. I figured I could cobble something together that would be similarly shaped and sized. I ordered my Cree Q5 WG LEDs on stars, Ledil lenses and bFlex driver from Cutter in Australia. I was going to duplicate Allen's setup, but decided to go with 4 LEDs at the last second. This necessitated a change to the design, but it worked out okay [so far].

The light body is constructed of 1" square aluminum tubing with 1/16" wall thickness. It utilizes plenty of JB Weld, so I hope you'll excuse the crudeness. If I had access to a machine shop and a TIG welder, it would have been really purdy. I have a piece of clear plastic across the back, but I may substitute some aluminum plate.
http://farm3.static.flickr.com/2117/...274a94c017.jpg

You can also see the switch and mounting system in this photo:
http://farm3.static.flickr.com/2351/...1e06de426e.jpg
I used a momentary toggle with a rubber boot to give some grip and make it a bit more weatherproof. The mounting system is a handlebar mount from an old Planet Bike blinkie combined with a hacksawed chunk of said blinkie bolted to the light itself.

On the bike:
http://farm3.static.flickr.com/2043/...f266d639aa.jpg

The beam pattern is the result of two tight spot lenses plus two narrow floods. It's more of an even pattern than my old Trailtech HID, with less of a hotspot. [Yes, I'll clean up my basement.]
http://farm3.static.flickr.com/2038/...c73c003ee9.jpg
It's being driven at 750 mA. At that level, I should be producing almost 600 lumen. I left it turned on for 15 minutes and it got pretty warm - not too hot to handle, but probably warmer than I'd like. That said, this light is designed for commuting, and the air temp will probably be in the neighborhood of 5C or less.

I'll add some nighttime pics - after it gets dark. :D
Edit: It's dark now...

The street in front of my house without the light:
http://farm3.static.flickr.com/2097/...db884a25f0.jpg

Lights on [sorry for the blurriness - 1s exposure and no tripod]:
http://farm3.static.flickr.com/2091/...23f81db867.jpg

The back yard:
http://farm3.static.flickr.com/2381/...f81a592481.jpg

A garage? Who knew?
http://farm3.static.flickr.com/2281/...cfc415341e.jpg

It seems like 4 crees or seouls are the minimum for a good light. I would have done the same if it didn't cost so much, but i would add an amber led to compensate the flushness of leds. I hear it helps. Right now i'm drawing around 2amps at 13v with my halogen setup. But i should be close to 1000 lumens.

So, how do you rate your 4 x Cree Q5 light compared to the old Trailtech HID, under actual bicycling use?

I've only had 1 ride with the light, so the review is preliminary. I rode to work in the dark on Friday morning, when the light was driven at 350 mA. At that power, it obscured my wife's 15W halogen almost completely. Compared to my HID, the beam is not as focused, with more spill to the sides. There's also less of a hot spot. So far that's a good thing, since I pick up more things at the side of the road than I did before.

I'm glad I went with 4 LEDs. The housing worked out really well as far as weight. It's about 1/4 the weight of the Trailtech. If/when I make another, I'll use a bit more aluminum for heat sinking, but keep the design similar. In terms of the light temperature, it's not as blue as the Trailtech. I'd say it's really close to my car lights, which are 4300K HID. That's pretty much ideal for me.

If I run two of these things with two separate battery packs, I'll be at 1200 lumen for ~$400 and a total weight of about 1000 grams. In a year, I'll probably be able to build a system that would run at 2000 lumen for the same money and weight.

That looks like a great amount of light for a DIY!

I love these type of projects!

Thanks very much! Someday I hope to make it a "well-executed" DIY light. There are a few things I will do differently next time.

Good work!
Whats your battery setup and runtimes?
Definitely replace that back plastic with aluminium, it will help cool things further (though when moving its probably not an issue).

for cooling, might be better to get two cheap finned heatsinks, and jbweld them onto the sides of the light next to the emitters.

Review #2
I rode to work with the light at full power this morning. It's definitely different than my HID. The hot spot is notably absent. There's just all this light in front of me. The housing didn't get more than warm on the way in, and it was 6C out with a little wind. I might throw on some heatsinks if it gets much warmer. I noticed that oncoming cars stayed on their side of the street more than usual. :D The hacked up mounting device is working very well. If I need to adjust the angle of the light, I just give use a firm hand and it points where I want it to go. I haven't used a handlebar-mounted light for a while, so I'm not sure where to aim it.

I picked up a new seat bag at MEC, and it does a good job of holding the battery steady. The battery is a 4800 mAh 14.8V Li-ion from Batteryspace.com, left over from my HID setup. If I want to run the light at 1A, I should probably bump up the battery to a higher voltage. I have no idea what to expect for runtime. I'm assuming it uses less juice than my HID, but I could be wrong. Does anyone have a formula to figure that out?

Your system uses around 14.8v (3.5ish for each led and 1 for the driver).
So its simply mAh/mA = h
You should see 4.8/.7 = around 7hrs runtime at 700mA!
But....
Not sure how well LiIon holds its voltage so things might dim down somewhat as the battery runs out. You really should have a few more volts or 1 less led. Your LEDs might use as much as 3.7 each...bflex will underdrive them in this situation.

Hmmmm. 4 x 3.7V + 1 = 15.8V = I need more volts! Can I get away with 16V, or should I try for 18V?

I believe OP is driving 4 LEDs at 750ma EACH.

So he's burning 3 amps per hour from a 4.8 amp-hr battery, for 4.8/3.0= 1.6. So it'll burn about 90 minutes by nominal values. Actually, its probably closer to 80 minutes if you factor in the driver conversion loss.

Later he's at 0.35A, then today at "full power" or 1.0A.

I think he'll soon determine his battery's true storage capacity....

well no, because they are in series so its 700mA total. The current doesn't add because the same electron gets to visit each led.

Pinkrobe, if you don't want to get a bigger battery you could run the 4 leds in 2 parallel strings of 2 leds, so you are only driving about 7v and the current is split between the two strings. You'll have to measure the individual Vf to match the strings and it means you can only run 500mA. One of my lights runs like this and works great, you can add a small resistor and switch to dim one of the strings. That way you can switch between spot and flood.

That's not entirely true either. You can run two parallel strings, each driven by its own driver. More expensive (an extra driver) and less efficient, but it means you can run the whole system from a lower voltage battery.

All this talk of parallel vs. series is making me dizzy! ;) I'm lazy, so I think I'll just get an 18V battery and save my existing battery for another project, like a triple LED light. Thanks for the help!

18.5V 4800mAh battery on the way...

That'll work well. You should be able to use a single 700-1000mA driver to run all four LEDs in a single series configuration.

Sweet. I'm going to order some more LEDs and such to build a 3-LED system for my wife using my old 14V battery. Woot!

pinkrobe -
Thank you very much for an inspiring DIY light thread. I especially appreciate your photos of the light in action at night. Light off, pitch black. Light on, BLAMMO! Illumination, baby!