Introduction: Kilo-Lumen Bike Headlight

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.

Step 2: Bill of Materials

6 Cree XR-E (Q5-WC bin) LEDs mounted on carrier PCBs
<<<< Update - Technology marches on. I built this light back in August and since then Cree has come out with a new higher bin XR-E, the "R2" These put out up to 275 lumens versus 240 for the ones I'm using. Alternatively you can use the new MC-E which i 4 dies in a single optics package. Each one of these puts out ~700 lumens. A wide selection of optics exist now for that as well, and it is easier to drive than the SSC-P7 (another 4-die part). >>>>

1 BlueShark current driver
1 10 kohm potentiometer with built-in switch
1 barrel type connetor pair
1 hookup wire (I used 20 guage, 22 should suffice)

1 package of Artic Silver Epoxy (not the grease, but the two part silver loaded epoxy
1 3 inch long section of 2" by 3" by 1/8" thick rectangular aluminum tubing
1 3" by 2" by 1" block of aluminum
1 3" by 2" by 1/4" plate of aluminum
1 3" by 2" by 50 mil sheet of aluminum
12 4-40 flat head 1/4" screws
1 bike mount
6 Lenses of your choice

For the Battery
1 Ryobi 18 volt battery
1 Ryboi 18 volt flashlight
1 Amphenol Power PowerPole connector pair
Silicone sealant
JB weld

For the taillight:
18 Lumileds Pirhana LEDs
1 Taskled CC1W current driver
1 scrap housing
1 piece of lexan or other suitable clear plastic
1 Silicone adhesive/sealent
a bunch of screws to hold it together


LEDs and lenses:

BlueShark Driver:

Taillight Driver:

Handlebar mount:

I bought the alumnium from a local metal supply place. I take a trip every month or so looking for interesting remnants and have a decent stockpile of pieces now. I designed the light to fit the materials I have. There's nothing special about the dimensions except that they lenses fit well.

Step 3: Basic Diagram of Headlight

Picture of Basic Diagram of Headlight

Before getting started, here's a basic diagram of the headlight, mecahnically and electrically. I'll add more detail in subsequent sections, but for now this gives you an idea of what things do and where they go.

Step 4: Machining the Heat Spreader

Picture of Machining the Heat Spreader

The heat spreader is a crucial component of this project. The heat spreader must conduct 10-15 watts of heat to the outer housing which acts as a heat sink. This means that the dimensions of the spreader are critical. Gaps between the spreader and the housing will result in poor heat conduction resulting in a potential overtemperature condition within the LEDs.

I used a Harbor Freight table-top milling machine to shape the heat spreader. It didn't come out perfectly but it came out close enough and with the use of screws on the side of the housing, it works fine.

The front face of the spreader is just as flat as possible and has holes for power supply wires. Additionally there are holes tapped for 2-56 scrwes used to hold the LEDs in place while the epoxy cures.

I overdid it with the silver epoxy, evidenced by the look of a flooded surface. The compression of the screws ought to maintain a reasonably thin interface between the LED PCB and the spreader. I reccomend using an ink roller and rubber ink pad to spread a 1-2 mil layer of silver epoxy.

The back of the heat spreader is machined out to make room for the driver circuit. The first driver I used required a small pillar for heat sinking. I blew this driver up, and changed to another type (the BlueShark) which comes with a copper heat spreader. I reccomend this driver over the Taskled maxFlex (which I burned out) simply because the Blueshark uses a potentiometer for brightness control. The maxFlex is a really great board but I like the variable control.

Alignment of the LEDs is critical. The square lenses I used are almost 1 inch square. This means there is little room for error in the alignment of the LEDs. Careful layout with a set of calipers should provide adequate alignment. This is another useful feature of the scrwes, as they keep the LEDs in alignment while the epoxy cures.

This heat spreader goes into the blue housing and is secured on the sides by screws. The sides provide the majority of the heat conduction and as such, the wider the cross section the better (hence the 1 inch thickness of the spreader).

Step 5: Machining the Housing

Picture of Machining the Housing

This is yet another step where I assume some knowledge of milling machine techniques.

I used a 1/8 inch end mill to machine 70 mil deep channels across the length of the housing. This provides heat sinking and more than doubles the thermally emissive surface area of the housing. The channels were cut front to back with respect to direction of travel of the bike. This allows the airflow from riding to dissipate the heat better. Cross cutting in the other direction resulting in a checker board pattern would increase turbulence and potentially increase cooling effectiveness. I have found though that after my 15 minute commute on cool evenings that the housing is just barely warm to the touch.

There are some excellent comments below regarding the coating of the housing. It turn out that for an application where convective airflow is the dominant cooling mechanism (as is the case here) that coating the surface of the aluminum will not measureably improve its heatsinking performance. In any case I decided to powder coat mine for durability and aesthetics. As stated above, the cooling performance of the housing is sufficient, so overall it seems to be working fine.

Step 6: Machining the Slide Mount

Picture of Machining the Slide Mount

The slide mount that I use is from PlanetBike. They sell it as a replacement for a few dollers. The great thing about their site is that they encourage the fixing of old or broken headlights rather than replacement. Thus they offer complete replacement parts for their products. If only more copmanies would take that approach!

Anyway, lest you think I am getting paid... I had bought a really crappy Planet Bike headlight a few years ago and decided to use the same old mount which is actually very well made.

I just needed a matching base for my headlight. I took measurements from the headlight that I had and replicated it in aluminum.

Here's where I will update this with a diagrammed drawing at some point, but to summarize, the slide is about 100 mils thick, and just under 0.75 inches wide. Make sure to machine a small gap for the locking hook.

I made this slide from two pieces. 1 piece is that 1/4 inch aluminum plate called out in the BOM. The other is the 62.5 mil sheet called out. Screws hold the two together as seen in the picture. Again, the milling machine came in handy here, this time with smaller end mills (1/8 inch I believe).

Step 7: Control Panel, Wiring, Etc.

The control panel is made from another piece of that 62.5 mil sheet, and has holes in it for a power LED, a brightness control pot, and a cheapo barrel type DC input connector. This is held onto the heat spreader with standoffs and the whole thing slides into the housing and is held in place on the sides by the 8 4-40 screws.

Wiring of this is simple. If you've gotten to this step you will have the regulator board which comes with hookup instructions. To use an external pot, there are also links to threads on CandlePower Forums about that...

As a word of caution, even to the most experienced builders, CHECK YOUR POLARITY and then double check it. This is how I blew out my first driver board. Don't be a dummy like me!

Step 8: Lenses

Picture of Lenses

So the lenses I'm using here are really cool because they come with their own mounting solution. I discovered these lenses (and derived inspiration for this project) from the excellent web site . In fact, I should have mentionted the site before because the design and construction techniques featured there are much simpler and require no milling machine.

The lenses are made by Ledil and available through Order a variety of lenses and figure out what works for you. I chose a combination of spot sizes (narrow, diffused medium spot, and wide oval).

To mount the lenses, peel off the white backing to reveal an excellent adhesive strip. Some work is required to make room for the solder connections to the LEDs, but once thats done, stick in place and hold for a moment.

Step 9: Fire It Up!

Picture of Fire It Up!

After finishing my headlight I wanted to see just how bright it was. The following pictures show the headlight (center) and the high beams of an Audi TT (with HID headlights). Essentially the Kilo-Lumen headlight is as bright as the car's highbeam, maybe a little brighter, and certainly with a higher color temperature (the high beams on the car are halogens).

Step 10: Battery

Picture of Battery

Powering a headlight like this requires a substantial amount of power, enough that if you were to add it as resistance to pedalling by means of a generator, it would be very noticable. I chose to use what I had, namely power tool batteries. They are cheap, available everywhere, and in my case you can get LiPo replacements for much higher capacity.

The challenge with using power tool batteries is the connections. The freebie that comes with many of these power tool kits is a flashlight and I found that I never used it. So with one quick slice with a hacksaw (well many actually) I transformed the flashlight into a battery adaptor. I added a powerpole connector to the adaptor and epoxied it in place. I also sewed a pouch to carry the battery on the frame of the bike. A small aluminum cap glued to the top provided debris protetion until it fell off. I haev yet to bother to replace it.

Remember to fuse your conenctions. I didn't but then I'm just lazy. Or maybe I'm hoping that someday I can increase my visibilty riding to work in one bright flash of flame.

Step 11: Taillight

Picture of Taillight

Possibly the most important light on a bike, most taillights are woefully inadequate. 18 Superflux/Pirhana LEDs work well, and if you have a rack on the back of your bike, its a convenient place to mount it.

This build is really easy. Find a surplus metal housing, gut it, cut out a plastic cover, and glue in the strips of LEDs. Of course first you have to find strips of LEDs, or make a PCB etc. In any case, its a box with LEDs, a Taskled CC1W current driver and thats it. People haev told me I look like I'm on fire. Its as bright as the LED brake light of many cars, and its wide dimension distinguishes itself from the majority of bike taillights. I also have this running off the 18 volt Ryobi battery.


kc6qhp (author)2008-11-23

I will be uploading the diagram as soon as I get it done, sorry for any inconvenience :(

mhenriksen1 (author)kc6qhp2012-07-19

4 years later ... :)

kc6qhp (author)mhenriksen12012-07-19


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.

TheMaker888 (author)2012-04-22

"I swear Officer, i Didn't See him"
wouldn't be an acceptable excuse in this case XD

Reble_45 (author)2011-03-22

Looks like the store you got the LED's from might be out of business.

hogey74 (author)2010-08-29

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.

crunchie1000 (author)2010-08-06

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)crunchie10002010-08-07


KT Gadget (author)2009-07-04

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 Gadget2009-07-06

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)

KT Gadget (author)kc6qhp2009-07-08

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 Gadget2009-07-08

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.

KT Gadget (author)kc6qhp2009-07-08

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.

KT Gadget (author)KT Gadget2009-07-09

Oh, these are the 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.

sensoryhouse (author)2009-05-14

Nice, I used my Ryobi batteries all the time for projects - like this

sangchinok (author)2009-03-18

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)sangchinok2009-03-19

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!

sangchinok (author)kc6qhp2009-03-20

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)sangchinok2009-03-20

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.

sangchinok (author)kc6qhp2009-03-23

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

mortso (author)2009-03-11

Why didn't you use a "T" cutter end mill to cut your mounting slot?

kc6qhp (author)mortso2009-03-11

Didn' have one :)

aburton (author)2008-11-26

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)aburton2008-11-27

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 (author)kc6qhp2008-11-27

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 (author)roosta2009-03-11

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 (author)mortso2009-03-11

Right, but in this case it is not a strong mode of heat transfer. You're better off leaving the aluminum uncoated.

therian (author)2008-11-30

how many car driver was blinded and killed ?

Evil Bike (author)therian2008-12-27

the world may never know...

BeanGolem (author)Evil Bike2009-02-18

And even if we did know... who says less car drivers is bad! haha. I jest...... maybe.

Evil Bike (author)BeanGolem2009-02-18

that inspires deep thought on my part...

BeanGolem (author)Evil Bike2009-02-18

On a related note, I was thinking of making a bike-mounted harpoon launcher.

Whatnot (author)2009-01-31

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)Whatnot2009-02-01

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.

hg341 (author)2009-01-29

overkill but well done(if only i had 150 dollers and a bike)

Evil Bike (author)2008-12-27

Why do you need this. the point is for people to SEE you, not be blinded by you...

PyroMonger (author)Evil Bike2009-01-27

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

goodgnus (author)2008-12-02

Congrats on the win!

drakedm (author)2008-11-24

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 (author)drakedm2008-11-28

Where would I get info about what constitutes "illegally bright"? I love this concept.

kc6qhp (author)Myself2008-11-28

I tried looking through the California DMV's web site and could not find anything about the specifics of bicycle headlights. Maybe the US DOT has regulations governing them. I know there are regulations pertaining to headlights, turn signals, etc., for cars, but I have not found anything about bicycle headlights. The first night I was using this headlight though I was coming up the final hill and since there were no cars I turned it up to full brightness. It was just at that moment that a police car crested the hill and was coming towards me. He didn't stop me so I guess it isn't THAT illegal. Or maybe he didn't know what section of the VC to apply :)

uberchoob (author)kc6qhp2008-11-29

Any restrictions on the brightness of car headlights will be applicable to any vehicle that is road legal, including a bicycle. You might have gotten lucky with that cop, or he may have not considered it to be to bright, or maybe he was just to awed by the insane ingenuity of this instructable that he couldn't possibly ticket you!

Myself (author)uberchoob2008-11-30

awed by the insane ingenuity of this instructable that he couldn't possibly ticket you

That's my feeling. Unless you're actually endangering people with how it's aimed, the cops are probably just gonna smile and shake their heads. And I doubt they carry photometric equipment in their cars! It'd be a hassle to issue.

If anyone DOES get such a ticket for this, please scan it, redact the personal parts, and post it! I'd frame the thing for my wall.

Silence (author)Myself2008-12-01

if its aimed sleightly down and to the right it shouldnt cause a prob for oncoming drivers and your too slow on a bicycle to cause a problem in the rear view of drivers ahead of you even if its not aimed correctly.

drakedm (author)Myself2008-11-29

Well, I worked for a scooter importer for a while, and there were a whole series of regulations covering every aspect of any vehicle allowed on public roads, I suspect this is a state-by-state issues, but I know there is a maximum allowable luminosity for car headlamps, and this bike light is decidedly above high intensity car headlamps. I would probably look at the NHSA (National Highway Safety Admin). or possibly to the NYSB (National Transportation Safety Board) for these regulations- I know they exist and they probably have to do with luminosity, color and height from the ground.

Yerboogieman (author)Myself2008-11-28

Cops get mad at my Cold cathodes, its funny.

mweston (author)2008-11-28

Wow... umm this is pretty intense Great job!

aburton (author)2008-11-27

Thermal emissivity only applies to radiant heat. In this situation, radiant heat is going to be negligible compared to forced convection. The properties you want to be looking at are surface area and thermal *conductivity*, not thermal emissivity. You're right that it is preferable to increase the turbulence across the surface of the housing, but it is HIGHLY unlikely that you'll be able to coat the surface of the housing with something that can increase radiant heat and keep the convective heat constant. Anodizing won't help either. When you anodize, you're coating the surface of the aluminum with a (relatively) thick layer or aluminum oxide. This also doesn't conduct heat as well as pure aluminum (or 6061 aluminum, which is probably what you're using.) The result will be that you're actually insulating the aluminum from convective heat transfer. The important thing to keep in mind is that you're not radiating much heat. You're going to get several orders of magnitude more heat transfer from forced convection. If you want to increase the heat transfer, try to maximize your surface area.

kc6qhp (author)aburton2008-11-27

Yes, you are correct. Now here's a question (because I honestly don't know)... At a microscopic level what is the mechanism of heat exchange during convection? Molecules of the cool air (while in their convection cycle) get in close proximity to the heatsink, or even touch, but what imparts the thermal energy from the hot heat sink to the air? Is it direct contact (conduction)? Is it microscopic radiant heat exchange? In any case you do need excellent conduction of heat to that interface surface, but what goes on at that boundary in convective heat exchange? Also, as you said, increasing the surface area is important. From the perspective of a surface, a polished surface has the smallest possible surface area. Anodizing chemically etches the surface and results in a larger surface area. By how much I don't know. Finally there's the issue of material longevity. Bare aluminum will form an oxide on its own, and eventually that oxide can (depending on the alloy) get thick, thicker than an anodized surface which I believe will stop the oxide growth to some extent.

aburton (author)kc6qhp2008-11-27

It's actually a very complicated issue, and we're actually getting into some basic fluid mechanics. On a very, very small scale (think atoms), the interface between the air and aluminum is what's called a "no slip condition" ( In this small region, the air acts as a conductor, not as a convector. As you move away from the surface of the aluminum, the atoms begin to move more and more, and the collision of molecules transfers the kinetic energy of heat through convection. You need good conduction to have good convection.

There are three forms of heat transfer: convection, conduction, and radiation. Materials which are transparent to infrared, like air, do not absorb or emit radiation. Thus, you would not have microscopic radiant heat between molecules.

Aluminum is EXTREMELY reactive with oxygen. It's virtually impossible to expose a piece of aluminum to the atmosphere without it immediately forming a thin film of aluminum oxide. If you scratch the surface of that film, the surface of the scratch will immediately form an aluminum oxide film. Once the film has formed, it doesn't spread down any farther through the aluminum. The entire purpose of aluminum anodization (other than the obvious aesthetic one) is to increase the thickness of this layer to an unnatural thickness. I think what you're thinking of is a 3000 series aluminum, which has pretty poor oxidation properties, and tends to get some white scale on it when it's left outside. 95 times out of 100, you'll be a 6061 or 6063 aluminum to make your housing, and this won't be an issue.

You will find that chemically etching the metal, as in anodizing, will not give you a measurable increase in heat transfer. Try to put thermal fins (like a CPU heat sink) on the body, or better yet, try to improve the thermal interface between the heat source and heat sink. Thermal greases usually outperform epoxies, so you might want to use a mechanical fastener to physically attach the LEDs, and a thermal grease to actually transfer the heat.

Coating or anodizing an aluminum housing *will* decrease the amount of heat transfer from this application. Perhaps not a significant amount, but it should be made clear that coating the housing is not that important. Especially from a functional standpoint.

About This Instructable




Bio: I'm an electrical engineer. By day I design chips, by night I like making stuff that is unnecessarily complex.
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