Low cost bike light – Finished.

Here is the finished ‘low cost’ helmet light for my bike. Estimated output on high is 270lumen.

The finished bike light.

The general overview.

The LED, driver, optics and rotary switch assembly are mounted inside a 20mm diameter square aluminium tube. The LED is a single Cree XP-G mounted on a 20mm star metal cored printed circuit board. The optics is a Ledil square RS (real sight) optics with adhesive backing. The switch is a 4 position rotary switch for off, high, medium and low in that order. The LED driver is an AX2002 bassed “kennan” driver that was modified for variable brightness. Lastly the power is 8 AA 1.2v NiMh rechargeable batteries  that go in a bag on the belt when riding. The light itself is attached to the helmet with a thick strip of Velcro for quick detaching.

Some more photos.

So the the cost. With out counting the batteries or bag to go on my belt it looks something like this.

*This price is with out shipping. I live local and picked it up. All prices in the list are in Australian dollars.

Total Cost: $25.93AUD or around $24 USD.

A little over my budget of $20USD but close enough for the end result!

On high the LED draws 1A which according to Cree’s data sheet is an output of around 330lumen. Compensating for losses in the optics it might be reasonable to estimate around 270lumen out the front. More than enough for the casual night ride.

For more information on how to mod the LED driver take a look here.

Runtime is around 5 hours on high, 7 hours on medium and 16 hours on low. This is more than enough for even the longest ride. Combined with the use of low self discharge batteries the same set could be used a half dozen short rides before needing to be stuck in the charger. Very handy!

Overall i’m very happy with the results.

About Richard

I am a Materials Engineering working in the field of Magnetic Materials in Melbourne, Australia. This blog covers my personal interest in all things CNC.
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4 Responses to Low cost bike light – Finished.

  1. Wes Horton says:

    Hey, I’m building some lights that have more leds, but i’m using the xp-g’s, and cutter seems to be the only place to get them, now on the ledil square optics, the ledil site shows that they have one thats optimized for xp-e and one that is made for the xp-g, i’ve been trying to figure out if they have any differences, or if they just claim different part numbers, do you know if there’s any differences? Bike Helmet Led is awesome, nice job


    • Richard says:

      Hi, thanks your interest.

      For a few ideas of where you can buy XP-G’s from take a look here.

      I use cutter because they are relatively cheap, reliable and will include and then mount most LED’s on a MCPCB for you at very little cost.

      As for the Ledil optics, as far as I can tell the CXP and the CXP-G are the same optics in every way. However, although the optics are the same the XP-E and XP-G LED’s have different die sizes.

      Because of the larger die size for the XP-G, its beam is not as narrow as the XP-E even though it is using the same optics. It is for this reason that I think Ledil brought out the ‘new’ CXP-G optics so that the data sheet would accurately reflect how it preforms when used with a XP-G LED.

      In short, using the CXP optics from cutter with an XP-G should give you the same spec’s as the Ledil CXP-G data sheet.

  2. Tom says:

    Awesome helmet light!! My question is about the Ledil optics as well. I’m making a bar light out of 3/4″ alum square tubing and am looking at the pics of your light. It looks like the Ledil optics are a great fit! Did you have to shave them down any and do the optics mount right on the led board?? My first light so no experience at all! Thanks.

    • Richard says:


      I didnt need to modify the optics or the tube in order for it to fit. The aluminium tube I used was about 2mm larger in diameter than the optics. This left a 1mm gap on each side to slide it in. If your not sure if it will fit measure the internal diameter of the aluminium tube your thinking of using and compare it to the Ledil data sheet.

      The optics come from cutter.com.au already fitted with an adhesive backing that is very strong. I found this more than enough to keep it in place once installed. To help water protect you could then use a silicon glue to fill the gap.

      I did have to have to etch out a little gap in the back of the optics (the adhesive pad side) for the wires to run from the LED’s PCB to the driver. This wasnt a big job at all, just use small gauge wire and make the connection to the pad as small as possible. Then use a sharp knife or scalpel to etch away some plastic if the wire is still touching.

      Best of luck with your first light and be sure to stop by here if your after more ideas on bike lights.

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