Introduction: High Power 3-LED Bicycle Light

This instructable is created and provided by the Edmonton Bicycle Commuters' Society (EBC) ( , , ), a non-profit organization that supports all cyclists in Edmonton by providing advocacy, education, free services at events, affordable used and new parts, and bicycle recycling.

EBC also operates BikeWorks, a fully-equipped, volunteer-run community bike workshop, where volunteer mechanics teach & help members of the public to learn how to fix their bicycles. EBC also sells used bikes.


This is the introductory video to building a high-power three LED bicycle light. The design here has 3 modes: High, Medium, and Strobe (blinking), and runs on a voltage between 5-10V. The price of the light, including batteries, charger, and worldwide shipping, is about $50 US. Including batteries, it weighs about 200 grams, and should last about 1.5 hours on high mode (and significantly longer on medium or strobe modes).

This light is something that you can build with minimal investment in components and small hand tools. You don't need to know electronics: there are just 18 solder points, 6 drill holes, a bunch of hot glue, and a few screws. It doesn't require a microcontroller. You don't need to know what an Arduino is. It doesn't require you to fabricate metal, use PVC tubing, laser cut anything, or weld. With a bit of experience (e.g. if, for whatever reason, you make a half-dozen), you can put one of these lights together in less than an hour.

The Edmonton Bicycle Commuters' Society occasionally runs in-person courses on designing and building your own custom bike lights: this design or one customized to suit your needs.

This light is the same brightness, about 600 lumens, as the "Three P4" design here: , but the design in this video is cheaper and easier to build and use, and has a cleaner design.

This light works in thunderstorms, blizzards, and has been used in temperatures below -30C.

That power source can be two lithium-ion rechargeable batteries, or four to six alkaline 1.5V cells in series, or five to seven rechargeable NiMH or NiCad 1.2V cells in series (any of AAA, AA, C, or D shapes). A 6V generator would also work, provided it can provide about 9-12W of power (this is a bit high for the average bike generator).

The parts you will need are:

=== POWER SOURCE ($20.11 US) ===
  • [DX sku.01251] - UltraFire WF-139 3.6/3.7V battery charger
  • [DX sku.19624] - 18650 3.7V 2400mAh lithium-ion protected battery (pair)
  • [DX sku.18074] - 18650 battery holder
  • Neoprene/velcro cell phone case (for the battery box -- something from the dollar store)
=== LIGHT ($29.20 US) ===
  • [DX sku.15084] - GU10 3-LED spotlight housing
  • [DX sku.02026] x 3 - SSC Seoul P4 (U-bin) LED emitter (buy three!)
  • [DX sku.05602] - Clicky switch
  • [DX sku.05031] - Silicone tailcap (glow-in-the-dark)
  • [DX sku.25516] - 5V~12V 9W 3*Cree 3-Mode circuit board LED boost driver
  • [DX sku.15234] - JST connectors
  • [DX sku.08274] - Universal bicycle mount
  • Two wood/metal screws, 10x1/2 plated steel, pan, button or round head (any hardware store)
  • Two small springs (scavenge these: in a pinch, you can use the spring from a pen and cut it in half, but if you can find a stiffer spring with a slightly larger diameter, it would work better. Springs from existing battery holders [e.g. for AA battery operated devices] can work well.)

=== TOOLS (if you don't already have them or can't think of a way to fake it) ===
  • [DX sku.22264] ($4.63) - 30W soldering iron (110V AC)
  • [DX sku.04593] ($2.14) - Heatsink thermal compound (20g)
  • [DX sku.04643] ($9.99) - 0.6mm Solder Wire (200g)
  • [DX sku.19908] ($3.39) - Diagonal cutters
  • [DX sku.46862] ($8.40) - Jeweler's file
  • Hot-melt glue gun (available at any hardware, craft, and many dollar stores)
  • Glue sticks
  • Small Phillips Screwdriver
  • Drill
  • Tweezers (beauty section of a dollar store)
  • Wires (cheap speaker wire is nice)

=== OPTIONAL TOOLS (you don't really need them, but they're handy) ===
  • [DX sku.23451] ($4.16) - 3 metres Black Heat Shrink Tubing - Five Size Pack (0.8/1.5/2.5/3.5/4.5mm)
  • [DX sku.51713] ($16.20) - Third Hand Soldering Stand with Magnifying Glass
  • [DX sku.21392] ($6.21) - Wire strippers
  • [DX sku.10018] ($12.07) - Digital multimeter (if you already have a multimeter, but it doesn't have a connectivity testing mode, you can just measure resistance. A resistance of nearly 0 Ohms is the same thing as a connection, which is the same thing as a closed-circuit, which is the same thing as a short circuit.)
  • Foil duct tape (available at any hardware store)
  • Metal file
  • Small pliers
  • Hot air blower or lighter (for the heat shrink)
  • Permanent marker
All DX parts can be purchased from . Prices there include worldwide shipping. You may be able to source equivalent (or better) parts for less money, or make substitutions, but I've provided the DX numbers to make things easy for those that just want to follow a detailed shopping list and know that all the parts will work together. When ordering the part numbers listed above, you'll end up with extra components, since some of them come in multiples.

Be warned: I have waited up to 4 months for parts to arrive from DealExtreme. I've always received my items, or received my money back if they couldn't ship it or shipped a wrong/defective item. But some times it's a long, frustrating process. They don't make you jump through hoops, but they can be extremely slow to respond.

They're pretty much a lousy retailer and unacceptable by any normal standards, but if you want to save a few pennies and not  leave your house, and you can afford to wait potentially forever, they might barely satisfy your needs. If you work at it, you can often find the same (or better) items on eBay for less money.

Step 1: Build the Battery Box

(Apologies for the focus. Still learning how to use my camera.)

Step 1: Clip away the four plastic protrusions/tabs at each end of the box (where the battery terminals will sit).

Step 2: Drill a small hole above each point where you clipped away the plastic. Drill as high as possible so that your battery-holder terminals will be near the centre of the battery terminals.

Step 3: Ensure that your screws and springs are conductive using a connectivity tester. If your multimeter doesn't have an explicit connectivity tester, you can measure resistance instead. A resistance of 0 Ohms (or under ~4 Ohms) is the same thing as a connection, which is the same thing as a closed-circuit (which is the same thing as a short circuit). This is what you want between the head of your screw and its tip.

Step 4: Drive one screw into a hole from the inside of the battery box. Drive the second screw into the opposite corner.

Step 5: Use pliers to pull open one end of the spring and feed it into one of the remaining holes, from the inside of the battery box. Turn it through about a turn and a half. Do the same with the other spring.

Step 6: Check to see if your batteries fit your battery box. If not, make appropriate adjustments of the springs and screws. Make sure you didn’t skip Step 1.

Step 7: Remove the batteries. You must not try to solder with the batteries still in the case.

Step 8: File the tips of the screws down so that you don’t stab yourself. This is an optional but recommended step.

Step 9: Strip a short piece of wire: strip about 1 inch from one side, and 1 cm from the other. Wrap the long stripped section at least one full turn around one screw, so that it wraps back on itself. Twist the other end of the wire around the nearby spring. Solder both in place. Make sure that the solder connects your wire loop on the screw. Test that the screw is electrically connected to the spring, using your multimeter. Touch the probes to the screw and the spring (not to your solder or the wire--you don’t want to bypass your solder points).

Step 10: Cut two wires, about 6-10 inches in length (speaker wire works well here because it comes paired already). If your wires are differentiated, select which colour will be your positive wire and which will be your negative. Strip one end of the “positive” wire about one inch. Wrap it around the screw and solder it. Strip a short length of the “negative” wire and wrap it around the spring. Solder it too.

Step 11: Strip short lengths of the other ends of the wires. Test the connectivity of these to the screw, spring, and each other (they shouldn’t be shorted to each other).

Step 12: Write polarity signs on the inside of your battery box. Screws are +ve terminals, springs are -ve terminals.

Step 2: Electronics Background Knowledge

This video provides some simplified electronics background. You don’t need to watch it to build this light, but it might be a little illuminating if you don’t have existing electronics knowledge.

Step 3: Attach the Battery Box Connector

Step 1: Strip a short length from each of the wires from a female connector. (NB: in this video, I used the male connector. Only do this if you’re confident that the power-supply/battery connector isn’t going to be accidentally short-circuited.)

Step 2: Hot glue around the head of the connector, including both the connector head and the wires. This adds strain relief so the wires don’t pull out of the connector head, if yanked.

Step 3: Slide a length of heat shrink over the two connector wires. Don’t cover up the stripped leads at the end. Apply more hot glue near the connector head, over the heat shrink. Heat and shrink the heat shrink. This holds the two wires together (so they won’t get tangled/caught as easily), adds some strength, and makes it look better. If you want to make it even less noticeable, use a black permanent marker to colour the remaining visible section of the red wire, and to blacken the connector head.

Step 4: Cut two short sections of heat shrink, and place them on the wire coming from your battery pack.

Step 5: Twist the stripped section of the red wire of the connector to the positive wire of your battery box (this is the wire that leads to the screw). Twist the black wire to the negative wire of the battery box. Solder.

Step 6: Slide the heat shrink over your solder joins, and fill the heat shrink with hot glue.

Step 7: Plug in your matching connector and check connectivity. The black wire should be connected to the spring, and the red wire connected to the screw, and the black and red wires should not be electrically connected.

Step 8: Close the battery box and cover the external portions of the screws, springs, and wires with hot glue.

Step 9: When the glue has completely dried (don’t be impatient), open the battery box. If it is glued shut, carefully cut away the glue that’s adhering to the box lid.

Step 4: Attach the LEDs to the Light-housing Circuit Board

Note: At 1:13, I say “conduct the light away from the body”. I meant “conduct the heat away”.

Step 1: Determine the positive and negative terminals of the LED. Check the datasheet of the LED ( - part number W42180). In the LEDs I have, a negative sign is inscribed along the top lip of the black plastic edge of the LED, and the negative side also has a split-metal protrusion (this is the cathode, or negative terminal mark).

Step 2: Spread a very thin layer of thermal paste on the slug (metal base) of the LED. Don’t get paste on the legs of the LED or the clear dome.

Step 3: Place the LED onto the printed circuit board (PCB) of the light housing, matching the positive leg to the first positive-labelled terminal of the PCB (the + sign nearest the large cutout on the PCB).

Step 4: Repeat for the remaining two LEDs. The positive leg of successive LEDs should connect to the negative leg of the preceeding LED. This is how we connect them in series.

Step 5: Check to see that the lens fits over your LEDs.

Step 6: Solder the legs of the LEDs to the PCB, being careful not to overheat the LEDs. Make sure the LEDs are seated flat against the PCB and that the solder flows onto the PCB pads as well as the LED legs. Otherwise you’ll have a poor connection (potentially wasting power and causing flickering or failure).

Step 7: Make sure the lens still fits. If not, you’ll have to desolder the misaligned LEDs to adjust their positions.

Step 8: Apply a very thin layer of thermal paste to the back of the PCB. Place the PCB in the light housing, lining up the three small screw holes and the large wire hole.

Step 9: Screw the PCB down using the smallest of the screws that came with the light housing.

Step 5: Trim the Driver, Then Solder It to a Power Connector and the LEDs

Step 1: Drill two holes in the back of the white part of the housing.

Step 2: File the sides of the larger (bottom) PCB of the driver until it fits (snugly) inside your housing. File parallel to the 3-pin header, and square the diametric side as well. Be sure not to file away the solder contacts of the tiny resistor on the top of the larger PCB, and avoid filing away the outer copper ring of the PCB.

Step 3: Hot glue the connector head of your remaining connector, and slip on a short length of heat shrink over the wires. Leave enough wire uncovered to feed through the back of the light housing, reaching out the top.

Step 4: Solder the black connector wire to the outer ring of the bottom of the driver PCB, near one to the flat sides. Solder the red connector wire to the inner copper circle on the bottom of the PCB, near one of the flat sides as well. If you solder your wires into the middle of the PCB, you won’t be able to fit your driver into the housing anymore.

Step 5: Feed the small leads (that came pre-attached) of the driver up through the back of the aluminum LED base. Solder the red wire to the positive terminal of the first LED (the terminal that isn’t directly connected to any other LEDs), and solder the black wire to the negative terminal of the third LED (also isn’t connected to anything else). Be careful not to touch the dome of the LEDs with your soldering iron, and avoid overheating the LEDs.

Step 6: Assemble and Test the Light

Step 1: Screw the lens on using the countersunk (bevelled) screws.

Step 2: Push the driver into the white section of the housing. Be careful not to pull on any wires.

Step 3: Screw the white section of the housing to the aluminum fins using the long screws.

Step 4: Test your light by plugging it into your battery.

Step 7: Connect the On/off/mode Switch

Step 1: Cut the positive (red) wire coming out the back of light housing.

Step 2: Strip a very short length off both ends of the red wire.

Step 3: Solder one end of the red wire to one end of the switch.

Step 4: Solder the other end of the red wire to the other side of the switch. You may have to add an extra section of wire to reach.

Step 5: Use hot glue to glue the switch to the top of the light housing. Cover up the terminals of the switch (covering the wire and exposed metal) to add strength and protect from short circuiting and moisture.

Step 6: Apply a small amount of hot glue along the bottom edge of the silicone button cap. Place it over the switch, being careful not to get glue on the moving portion of the switch. Continue applying hot glue over the top lip of the button cap, sealing it to the switch.

Step 7: Glue the back of the white part of the light housing to seal off the holes and provide strain relief for the wires that emerge from the back.

Step 8: Place a small strip of foil duct tape over the top of the aluminum housing fins to prevent your light from back-shining.

Step 9: Test. Have fun! Half-press-and-release the switch to change modes.

Note that on high-mode, the protection circuitry of these batteries will trigger (and cut off power) if they aren’t completely charged, due to the high current draw (the protection circuit assumes this must be a short circuit). You can run a second pair of batteries in parallel to avoid this problem--the current draw from each battery will be halved. You can also just switch to medium mode as soon as you turn on the light; you’ll get much longer run-time, be just as visible, and, most likely, still be able to see just as much, because medium-mode is still really really bright.


bobcov made it!(author)2014-11-15

Any chance you could publish any details of your on-paper new design? That way I could get the components and figure out a housing on my own. Thanks!

munkytec made it!(author)2012-10-23

I have all of the parts that you've listed here (I ordered them a long time ago), but I'm missing one of the LEDs and it looks DX doesn't have it anymore (or at least I can't find it). Do you know of some other LEDs that would be compatible with everything you've listed here? I imagine I would need to buy a set of three again since it may cause some issues to use the two old ones and one new?

fryingwoks made it!(author)2012-10-24

Sorry, link rot! I've fixed the links now. You can still by the LED from DX; just use the (updated) link in the above bill of materials list.

A word of warning: this light is really outdated now. I'll put together a new Instructable soon for a brighter, cheaper, more efficient, easier-to-build light. Even has USB charging.

That said, I haven't put together the new instructable because, while I've designed the new light, I haven't actually built it, because this old one is still working really great for me. It was bright enough a couple years ago, and my eyes aren't any worse now, so it's still plenty bright enough now!

watembsho made it!(author)2013-12-15

Thanks for this nice instructable !
Did you have time to work on the update you were talking about ?
It'd be great, I'm also particularly interested in the USB charging...

dangmpls made it!(author)2012-10-06

So I'm new to the world of these high power LEDs. An your previous discussion about using one XM-L T6 LED got me intrigued but a little confused, too.

Will it work if I use one of the newer LEDs [XM-L T6 885LM LED Emitter 6000K White Light Bulb (3.0~3.5V)] with a circuit board [5-Mode 1000mA 7135 Circuit Board for Cree and SSC Emitters] that says it can be powered by a single 3.7 volt cell, and if I hook the two 3.7 volt cells up in parallel rather than series?

Thanks for all your work on this.

fryingwoks made it!(author)2012-10-07

Short answer: yes, it'll work, and you can have it work quite well.

Putting Li-ion cells in parallel isn't generally recommended, but it's certainly possible if you're careful about it. (Google a bit to find some details about that.)

The simplest possible thing to do would be to just run a single 3.7V battery, and change it when it dies (instead of running in parallel). But that's less convenient in some ways (while saving you the hassle of worrying about matching cells).

A buck converter (a switched mode driver) is what I suggested in my previous comment about the XM-L. The 7135 is a linear regulator, and that circuit you quoted is designed to be used specifically in a design with a single LED powered by a single Li-ion battery.

If you wanted to use it in a differing design, you need to be aware of several things:

1) Dropout voltage: your power source must be at least some number of volts higher than the voltage required for your load. I think on the 7135 it's about 0.2V. e.g. to run your LED at 3.5V, your power source must be at least 3.7V. This shouldn't be a problem for the XML and a 3.7V battery. (Buck drivers have dropout voltage requirements, too.)

2) Any voltage higher than the minimum will turn into wasted energy when using a linear regulator (and depending on the actual circuit that you get, there is an absolute maximum voltage before it melts anyway). If you wanted to use a different battery configuration that results in a higher voltage, you'll just be wasting power. Running at 3.7-3.8V though, you'll see quite good efficiency.

dangmpls made it!(author)2012-10-07

Great. I didn't know what a buck driver was, but now I do. Will probably go with the single cell set-up, but will look into the parallel cell set-up (I'm guessing the downside is that the cells catch on fire!).

Will let you know how it turns out. Thanks again for the detailed how-to!

Mar+HK made it!(author)2011-11-02

I've had all the peices for this for a while, but (finally) put it together for the fall morning commutes, hours before the sun comes up. The bright setting is wonderful for the pitch black river valley, the medium is perfect for pothole detection on residential streets.

Enjoying this much more than the duct taped flashlight I used last fall.

-max- made it!(author)2011-06-05

upgrade to a 1000 lumen xml t6 led. it is 100 lumens per watt @ 1000 lumens and 130 lumens @ 1W

fryingwoks made it!(author)2011-06-05

Yep! They weren't available when this was designed several years ago (nor really even until late last year), but you're right: it's better.

There's a GU10 housing that's the same as this one, only the lens is for a single LED. So if you use:

- Single-LED GU10 housing
- Cree XML LED
- And an appropriate buck driver (you wouldn't want a boost driver for a single LED)

You'd have a brighter, more efficient light, for the same price! And it'd be less work to build.

One lingering advantage to the 3-LED design is that you can use LEDs with three different colour temperatures in one light, to get a much better spectrum covered. So you could put in a 3W warm LED instead of one of the P4s.

-max- made it!(author)2011-06-05

how bright is that one you have? it almost looks brighter than my flashlight with the t6 led in it being driven by a 18650 battery

fryingwoks made it!(author)2011-06-05

How much current is your battery feeding the LED?

I can't measure lumens, but I can say:

At 1.5A, my XML-T6 is not as bright as this 3-LED design at 0.8A. (the 3-LED design is consuming more power, though, since it's running at over 10V)

At 3A, my XML is brighter.

I tend not to run either light at max power, though. They're both plenty bright enough for me (on street and in dark trails) on the lower settings.

-max- made it!(author)2011-06-06

whats the voltage to the t6 led? if it were driven at full power, 1000 lumens. what is the wattage on the 3 led light?

fryingwoks made it!(author)2011-06-07

I didn't already give you these numbers in the previous post because I only had a rough idea.

So now I've actually looked them up!

The XML is 2.7-3.3V over its current range. It's nominally 3.3V at 3A. Which is 10W.

The P4 is 2.9-3.8V over its range. At 0.8A, it's about 3.65V. So all three together, at high power, consume about 8.76W.

-max- made it!(author)2011-06-08

the t6 led has to be brighter... it uses more power and is more effectiant than p7s right? is the p7 a cree led?

fryingwoks made it!(author)2011-06-08

I'm not sure what you're referring to now.

Brighter than what? This instructable never mentions P7s. The full details of the components are all linked to in the first page.

LEDs don't "use" more power than each other. LEDs have specified operating conditions, and some LEDs have a higher maximum power rating than others. That doesn't mean that you have to run them at their maximum, nor does it imply that a higher power LED is brighter than a lower power LED.

If you feed two LEDs the same amount of power, the more efficient one, by definition, will be brighter.

If you feed a less efficient LED more power than a higher efficiency LED, you can balance it so that they emit the same amount of light (at their respective power levels).

If you want to know which LED is more efficient, you need to look at the datasheets for the specific LEDs and read the data. Manufacturers supply the datasheets online for their products so that you can compare them and see if they suit your application.

I believe that the XML is probably more efficient than a P7, though I don't know the specs for the P7. You can look that up. If that's the case, then at the same power, the XML will be brighter. I have no idea which has a higher maximum power.

-max- made it!(author)2011-06-08

i meant p4s is you mentioned on you last reply. i understand how leds work, i am talking about there max output. but i dont think 3V drives ether of the leds at full power, but the t6 is more efficient it the same current and thus, brighter. p7 led its Chinese and i have a hard time believing its 900 LM at the max. its 10 mm square. i think they saids it draws 15W.

fryingwoks made it!(author)2011-06-09

Please just look at the datasheets. They have the exact empirical numbers there. Arguing with me on the internet about it won't make them any brighter.

-max- made it!(author)2011-06-09

i found a few places to look at the brightnesses. they are also 100 lm per watt bat i dont know how bright they are.

nielvaish made it!(author)2011-05-10

quick question!! can i use a only camera part of cell phone in other devices like in pc , rc car , etc........................................

fgerdes made it!(author)2011-04-18

beautiful instructable!!! Quick question, i found an old dynamo w/ 6v 3w output. would the driver still work w/ such a lower wattage?

fryingwoks made it!(author)2011-04-18

Depends on a lot of things.

1) Lots of dynamos say 3W, but are able to put out more.

2) The driver will likely drop into low-mode, and may or may not be happy with your power source, but you'd really have to test.

3) For running off a dynamo, this design isn't optimal anyway, and you'd be better off running only one or two LEDs at a lower current, and doing it without a driver, but instead using a couple resistors, a supercapacitor (for a standlight), and some additional simple circuitry.

4) Alternatively, use your dynamo (with appropriate circuitry) to charge batteries, and use those batteries to power this light.

fgerdes made it!(author)2011-04-18

That makes sense...thanks for the advice and quick response! I'll try a couple different configurations and let you guys know how it turns out. Thanks again

hanelyp made it!(author)2011-03-19

What kind of solder did you use on the LED board?

fryingwoks made it!(author)2011-03-19

Regular leaded solder.

t-bird made it!(author)2011-02-25

Where did the circuit board come from that you put the LED's on? Was it part of the spotlight housing?

fryingwoks made it!(author)2011-02-25

Yes, the housing comes with a PCB with pads for 3 LEDs.

Jeffromg made it!(author)2011-01-13

Thanks for the inspiration and VERY nice instructable. I know a lot of time went into this and I appreciate your taking the time to put this together!

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