Picture of Kilo-Lumen bike headlight
I started biking to work this summer and needed a good headlight and taillight. I didn't want to spend a lot, but I wanted extreme visibility. For about $150 I ended up with a headlight that puts out somewhere around 1200 lumens, and a really effective tail light. The power source is an 18 volt Ryobi power tool battery which is both easily replacable, and quickly charged.

Warning! This project is not a beginner's project. As such I'm not documenting it as such. This will be more of a guide and list of critical elements rather than a comprehensive How-To.

Step 1: Design Choices, thermal considerations

The first step is to determine what you want/need for your bike light. Total light output and beam shape will determine the type, number, and configuration of LEDs needed. Additionally mounting, portability, weather resistance, and access to machine tools will weigh in.

I started out with the intention to build the brightest lights around for the purpose of being noticed. This means for the headlight over 1000 lumens (although there are a few 1000+ lumen bike headlights commercially available, they cost close to that amount in dollars).

I settled on using 6 Cree XR-E LEDs, which from the appropriate bin will put out in the range of 180 - 230 lumens each at a 1 amp drive level. (UPDATE: The new R2 bin XR-E LEDs put out up to 275 lumens) This gives me a headlight which (ignoring losses from the lenses) will put out between 1080 and 1380 lumens. A number of considerations have to be made when using an array of LEDs of this magnitude.

- At 1 amp, these LEDs will requrie about 22 watts of DC power, carefully regulated to avoid over current and overvoltage conditions.

- With the LEDs running somewhere under 50% efficiency, the array will dissipate somewhere between 10 and 15 watts of heat. This must be disposed of properly to keep the LEDs within their rated junction temperature limits.

- Having 6 emitters will allow customization of the beam pattern. Each LED will have its own lens. The end result is a superposition of narrow spots, medium spots, and wide angle oval. This ensures side visibility, while providing good, even lighting towards the path ahead.

- A suitable power source needs to be provided. The array is a series connected string of 6 LEDs, each with a Vf in the 3.7v range, meaning that a power source in the range of 15 to 25 volts is required (This is to keep the regulator from working too hard to boost or buck the native supply voltage.)

- With the weight of the 6 LEDs, a suitable heat spreader, and heat sinks the headlight is going to have a pretty decent mass and needs a solid, adjustable mount that allows for quick dismount when parking the bike outdoors.

- Brightness control is handy so that when you are riding towards oncoming cars you don't piss off drivers by blinding them. This light is so bright that in darkness it can be blindingly bright. A measure of caution and restraint is needed when using a light this bright.
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kc6qhp (author) 6 years ago
I will be uploading the diagram as soon as I get it done, sorry for any inconvenience :(
4 years later ... :)
kc6qhp (author)  mhenriksen13 years ago

4 years later I'm still using the headlight almost every day. Do you need any specific information that isn't here? I don't recall what diagram I was referring to, but if you need any pointers I can try.
TheMaker8883 years ago
"I swear Officer, i Didn't See him"
wouldn't be an acceptable excuse in this case XD
Reble_454 years ago
Looks like the store you got the LED's from might be out of business.
hogey745 years ago
Great project. I'm a cyclist and I find the commercial BLTs etc are too bright when riding towards them. Much brighter than cars! I know they're great off-road but they're a bit antisocial on bike paths. I think dipping lights should be the next development, just as on cars. Maybe you have to go for reflectors and rear-pointing bulbs? I am going to give it a go.
i would like to make something like this for my motorbike, running it off the bikes battery. could it be done?? thanks crunchie
kc6qhp (author)  crunchie10005 years ago
KT Gadget6 years ago
I just ordered my Cree leds for an old overhead projector I'm converting to video. Instead of the thermal epoxy, will regular thermal grease work if I used screws to hold the leds down? because I might use the leds for a different project later and be able to swap them out.
kc6qhp (author)  KT Gadget6 years ago
That should work fine. You can probably get away without thermal compound, but it can't hurt to add it assuming it is a thin layer (1-3 mils)
Alright, cool. Just got my lens, drivers and holders in the mail, just waiting for the LEDs now. And as for a power supply, would a laptop charger at 15V 4 Amps work ok even though its built for (either lithium or polymer) ion batteries? Because I have a couple lying around the house and there not being used since the laptops have been recycled.
kc6qhp (author)  KT Gadget6 years ago
That sounds okay. I would think that the charging circuit is probably contained within the laptop or the battery itself. You could check by putting a voltmeter on the output of the power suppyl and just checking to see if 15 volts is present. 15V at 4 amps should be sufficient for a bunch of LEDs. Remember though that when using a boost (or buck) converter, the difference in the supply voltage to the converted voltage has a lot to do with determining the efficiency of the conversion, and that any inefficiency is turned into heat within the converter. So if you are boosting up to 21 volts (for 6 LEDs running at 1 amp) then you have a 6 volt difference which may be too large (check with the manufacturer of the converter) or it may be fine.
I am only going to put around 5 LEDs, give or take an LED, for each of the 3 series I am making. I am going to use copper caps that match the diameter, or a bigger cap, and use aluminum soda cans to dissipate the heat more, if needed since I do not have access to a milling machine. If i need to, I will probably get 3 5W resistors (gotta determine the value again) to drop the voltage down to 12V. Other than that, i should be able to make the projector work once more, if not better than before.
Oh, these are the http://ledsupply.com/buckpuck.php which run at 1000ma output, and I got the ones that were prewired, but do not have a dimmer since i do not need it in this case.
Nice, I used my Ryobi batteries all the time for projects - like this
sangchinok6 years ago
i'm just wondering... with a lot of 12V 1.0A 10W warm-white 600 lumens LED making it ways to international market from China, is it possible to imitate your rig and attach it to my motorcycle and replace its 12V 1.25A 25/35W halogen bulb? Or more importantly, are the figures advertised realistic? BTW, The stock headlight is not bright enough for cloudy dark night on dark street, and your creation seems marvelous...
kc6qhp (author)  sangchinok6 years ago
Yes, I think LED automotive headlights would be great. In fact I'm planning on replacing my car's headlights with LEDs. There's a trick though with automotive lights - legality... You are much more likely to get pulled over by the police for having improper headlights on a motorcycle or car than on a bicycle. So keep that in mind. In any case, be very careful about how you choose the lenses or optics you plan on using, and to make sure you have sufficient cooling. Do it and post your results here!
thanks for the vote of confidence but my main concern would be the ability of the battery and/or engine to keep up with the electrical requirements. Having no experience with electricity in practice (and i did flunk physics!), I'm afraid i might blow up the 12V 3Ah acid-lead battery! or stall the 110 c.c engine. About legality, over here in Malaysia, we don't have the luminence value of headlights written down, or what type of illumination we use for that matter, so that's not a big problem: unless it's HID/Xenon bulb in non-xenon/HID calibrated headlights which is illegal. So, I plan to fit the LED assembly into the stock headlight assembly, hoping it won't blind anybody... and make holes for some air. But the electrical supply issue bugs me. Big time.
kc6qhp (author)  sangchinok6 years ago
Ahh okay. So first of all, my light draws somewhere around 20 watts. If you are using a 25 watt halogen bulb, this should present no problem. You should also get more light, and in a more visible (to other drivers) spectrum of light. So yes, you have plenty of power from your alternator, and the only extra thing to consider is the quality of that power. A halogen bulb is very tolerant of momentary spikes in voltage, but a delicate switching current driver like the one I use may not be. So I would encourage a bit of work in making sure you have clean voltage source (EMI filtering, reverse protection diodes, etc.) I believe that here in the US the issue is more about the aiming of light rather than its total luminance. The HID/Xenon issue is the same here, because of the aiming. Some of the aftermarket HID/Xenon lights are driving lights or fog lights and others are just HID bulbs made to fit standard housings. In either case, they generally don't confine the beam as well as properly projector beam headlights do. If I can figure out a way to shape the beam well, I'm going to retrofit my car with LEDs.
so, it's not gonna blow but i need clean voltage source... hm... this gonna be harder than i thought. (rub hands, giddy with excitement etc., etc., etc...) ;P
mortso6 years ago
Why didn't you use a "T" cutter end mill to cut your mounting slot?
kc6qhp (author)  mortso6 years ago
Didn' have one :)
aburton6 years ago
I'm sorry, but I'm not quite sure what you mean when you say "Bare aluminum is not as good a conductor as one might think." Do you think you could explain this a little further? As it is currently worded, this is a deeply misguided statement.
kc6qhp (author)  aburton6 years ago
If you aren't quite sure, how sure are you that it's deeply misguided? :)

Anyway, a polished, or smooth aluminum heat sink will dissipate heat poorly compared to a heat sink where the surface is anodized, painted, or otherwise roughed up. Of course if you paint it with an inch thick of rubber that no longer holds true. The point is that aluminum when machined as I did, comes out pretty shiny and giving it certain coatings will help the aluminum dissipate heat better. So maybe the word "conduct" was inappropriate.

effect of anodizing

Here's a table I found for thermal emissivity:
Polished aluminium 0.05
Polished copper 0.07
Rolled sheet steel 0.66
Oxidised copper 0.70
Black anodised Al 0.70
Black enamel 0.85
Dark varnish 0.89
Black oil paint 0.92

I suppose I would hae been better off with a thin flat black coating.
roosta kc6qhp6 years ago
this is because dark surfaces radiate heat far more effectively than a shiny surface. its stated in one of the laws of thermodynamics, but i hate physics, so im not going loking for it :P i cannot understand why people dont paint their radiators matt black. far more efficiant than white.
mortso roosta6 years ago
So the inverse of Solar radiation is happening, where Black absorbs more solar heat than shiny or white surfaces. I never considered the reverse to be true, very cool thing to know. thanks!
aburton mortso6 years ago
Right, but in this case it is not a strong mode of heat transfer. You're better off leaving the aluminum uncoated.
therian6 years ago
how many car driver was blinded and killed ?
the world may never know...
And even if we did know... who says less car drivers is bad! haha. I jest...... maybe.
that inspires deep thought on my part...
On a related note, I was thinking of making a bike-mounted harpoon launcher.
Whatnot6 years ago
I don't think you need a stipulation in some local code to cover this, this just falls under the header 'reckless endangerment', and not just other people by the light but also yourself from the reaction people might show, there's a good change someone takes matter into their own hands without consulting brightness regulation websites and you should take that into consideration too.
kc6qhp (author)  Whatnot6 years ago
The headlight has a brightness control knob. I use it constantly. I try to be courteous to drivers. Where I ride, there is plenty of ambient light and while the light would be truly blinding in a very dark place, its not nearly so bad in the city on well lit roads.
hg3416 years ago
overkill but well done(if only i had 150 dollers and a bike)
Evil Bike6 years ago
Why do you need this. the point is for people to SEE you, not be blinded by you...
yes but its also for them to see the road themselves....if there are no cars around then brightness can be increased so there is less strain on the eyes while riding
goodgnus6 years ago
Congrats on the win!
drakedm6 years ago
This is without question the king of all bike light builds. I have seen people use MORE lights, and even car headlamps, but this offers the bst of everything. I suspect that this light is actually illegally bright, which is about the best thing you can say about a home brew project. Cheers for over-engineering. Also, I'd love a tail light demo photo, akin to the head light demo photo, just for reference.
Myself drakedm6 years ago
Where would I get info about what constitutes "illegally bright"? I love this concept.
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