DIY Euro-style Beam Shaping

kg6gfq

Newly Enlightened
Joined
Nov 9, 2015
Messages
14
I'm about due to build a dynamo headlight. Ideally, I'd like to match the pattern from nicer B&M lights. Something with a fairly consistent brightness both near field and far field, and a cutoff at the top (except some spill to illuminate street signs). That means, if you point it at the wall, you get a gradient from dim at the bottom to bright at the top, and possibly with a bit of spill over the top cutoff.

As far as I can tell, the options are:

1) Stack several LEDs with different optics, aiming a narrow beam further out and a wide beam closer in, with a physical barrier on top for the cutoff.

2) Create some kind of curved (parabolic? hyperbolic?) reflector, and aim the LED back toward it, as B&M (and several others) do.

I'd prefer #2, but it's the more challenging one to design. Does anyone know of software (preferably free and linux-compatible) that models optical systems with custom reflectors? How would you fabricate the reflector? (I'm figuring 3D printed shape with a reflective tape on it, but would welcome suggestions.)

Thanks!

Darin
 

A10K

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Joined
Dec 20, 2011
Messages
85
This has absolutely been tried before, there was a thread with lots of photos by somebody who did the same thing you are wanting to do.... except I can't find it right now (THIS might be it, but the links no longer work). My inadequate verbal description will have to suffice.

The jist of it is to take a full-sized parabolic reflector (from a Maglite, or some other cheap dollar store light), cut it down the middle, and aim the LED up into it. This gets you the basics of the cut-off beam; dimmest at the bottom, brightest at the top (furthest from your bike), with a sharp-ish cutoff right above that. I've personally experimented with this, and the best way to go about it is to just buy lights, disassemble them, cut the reflectors in half with Dremel/rotary tools, and mount them to LED boards.

Hopefully somebody with more direct experience will chime in.
 

Steve K

Flashlight Enthusiast
Joined
Jun 10, 2002
Messages
2,786
Location
Peoria, IL
I've seen reports where a person has taken a nice incandescent bike light, cut it down the middle, and mount a LED where the bulb would have gone. This gets a little tricky because the light usually used the reflector and some front optics to achieve the desired beam. Keeping everything together is harder when the light is cut in half.

Doing the same with a reflector that was designed to produce a circular beam seems like it would still produce a circular beam when cut in half. Moving the LED away from the focal point would change the beam shape, but it's not likely to produce a good beam like a B&M light (or that's what B&M and every other bike light manufacturer would do).

3-D printing a reflector might be possible, but the hard part would be polishing it and doing the vapor-deposition of the aluminum onto the surface. Considering how few bike light companies produce light with good beams, I assume that it is not something that a hobbyist could do well.

My personal approach is to find a dead B&M light, remove the B&M electronics and install my own electronics. The hard part is finding a dead B&M, because most folks can return them to the dealer under warranty for replacement. The best option might be to find an older B&M that is not covered by warranty... or get a functional B&M that someone is replacing with a more modern version.
 
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