Almost Too Bright Bike Light (blue or What Ever Color You Want)




A friend of a friend of mine asked me to build a rear bike light that would be better than anything he could buy (for a budget of $45). So I set out to build this light and I thought I might as well try to help anyone else out there that want to do a similar project. He rides road but there is no reason you cant light up the trail with this light too. He also wanted to go a little different from the traditional red rear light so I used cree's xre blue leds. Ill try my best to walk you threw what I did and what you can do with a few basic tools.

Also it had been brought to my attention that blue might not be legal in some areas (still checking if they are in my area). If they are not you can always use crees red xre led(make sure you check in your area before buying your leds so you dont waste money). It cost the same amount and puts out roughly the same amount of light.

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Step 1: Tools and Materials

The tools needed here are very basic:

Solderign iron

screw driver drill press (although a hand held drill and a steady hand will do just fine)

wire cutters/stripers

heat gun (a hair dryer will work too, If you don't have one just borrow you girlfriends/ boyfriends, if you don't have one of those then a heat gun can be bought online pretty cheap and comes in handy more than you think)

Just a little plactic adhesive (or hot glue if you want, I just normally don't like to use it for permanet things)


2x CREE XRE led (I got blue, $6 each on ebay)

2x CREE 3 watt led driver ($10 for two on ebay)

2X lens for cree leds ($2 ebay)

2x Lithium ion batteries 18650, I pick 1500mah but you can use whatever (you can get some online fairly cheap but I just happened to hove some from another project but will probably cost you $15)

A alumimum case for the leds and batteries (I got one on ebay that was just the right size for $7)

A dc-dc buck for the charger ($5 ebay)

A 12 volt 500ma transformer (I also have one lying around, really anything from 6.5 volts to 30 volts will do)

2x copper pipe plugs (2 bucks each at home depot)

Thermal compound

Some type of battery connectors, the ones I got on ebay for 2 dollars

One on off switch (also had laying around but one 2 dollars on ebay)

One lipo protectiong circiut (very important so you don't ever overcharge or discharge your batteries) $3 ebay again (you would think they sponsored me the way I keep talking about them but there just had the best prices)

also a plastic case for the charging circuit (any old thing will do, remember we are on a budget) free!

Step 2: Builting the Guts of the Light

The circuit is very simple and I have a picture of the actual lights cuts and the wire diagram. You must have a lipo protections circuit though if you want your batteries to last and not catch fire. I used some 22 gauge wire I have laying around (these leds only draw at max 1 amp each).

Step 3: Buildign the Housing

The case I got off ebay just need some holes drilled into it and it was pretty much ready to go. I borrowed my dads drill press to make it easier but its not necessary.

You need to drill two holes in the back fro the clamp mount (stole it from a crappy 5 dollar light). For each copper plug with an led inside it you also need to drill 2 mounting holes for the leds to be screwed into the aluminum housing. You also need two small holes for the wires. You need to drill one hole on the top plate for your switch and two holes on the bottom plate for your charging wires.

Once you screw the leds to the copper pipe plug and the housing (with thermal compound under both the led and the copper plug (where it has contact with the Aluminum housing). This is a important step to insure there is good heat sinking. once attached you will use the plastic adhesive to secure the lens to the led.

Step 4: Building the Charger

This is a really simple quick summary to building a lithium battery charger. There are really good instructables that give better detail but pretty much you just need to solder your dc transformer wires to the input side of the dc-dc buck converter and the output side to the battery connector you bought. Using a multimeter set the voltage to 4.2 and the constant current to 1-1.5 amps(this will insure long lasting batteries and will charge in 2-3 hours).

Step 5: YOUr Done... Almost

Now just shove everything(being sure to insulate the top of the battery to not short out on the case, I used some rubber pieces I had) in tot he case and solder the final wires and test it out. This particular set up will last on full power for about 2 hours on full power and 20 hours on low power.
well, if you have any questions be sure to let me know and ill do what i can to help explain my processes or help with an any other project you are working on.

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    10 Discussions


    6 years ago on Introduction

    I replaced the cree xre blue leds with the xpe for teh legal red color... still decently bright


    6 years ago on Introduction

    Calif. laws prohibit the blue lights, as those are on the Calif. Highway Patrol bikes out here. Blue lights under the car or on the back of a vehicle are not allowed. Don't know if you'd get a ticket on a bicycle, but you sure would on a motorized vehicle.

    1 reply

    Reply 6 years ago on Introduction

    I found that out after I made the light.... That's what I told the guy that I built the light for so I order some cree Zoe red less... They will be slightly brighter and not illegal


    6 years ago on Introduction

    That's great! I think it will be nicer with our LED flexible strips, then, hehehe!!!!


    6 years ago on Introduction

    Nice! But you might let your friend know that blue lights on non-emergency vehicles on the road are illegal (excerpt from Wikipedia): "... The colour of light emitted by vehicle lights is largely standardised by longstanding convention, first codified in the 1949 Vienna Convention on Road Traffic and later specified in the 1968 United Nations Convention on Road Traffic. Generally, but with some regional exceptions, lamps facing rearward must emit red light, lamps facing sideward and all turn signals must emit amber light, lamps facing frontward must emit white or selective yellow light, and no other colours are permitted except on emergency vehicles..."

    1 reply

    Reply 6 years ago on Introduction

    This is very true and i will have to check the ca dmv to be sure and if they are not legal then i will have to switch them out with the red cree xre leds... no big deal i guess but i did think blue was cool looking.


    6 years ago on Introduction

    It looks great. But I must agree with d_duck and Polyhistor. Local laws must be followed in terms of light color to be used.


    6 years ago on Step 5

    You've done a good job of explaining your project. It's clear and very useful. There is one word or caution I'd like to throw in. If this bike is going to be used on public streets you should check the laws about displaying a color other than red from the rear of a vehicle. Certain colors are also restricted. Blue is sometimes limited to police or other emergency vehicles.