Headlight optics

I just finished making my first dynamo powered light. I used two gutted Romisen RC-G2 flashlights and the simplest circuit from pilom.com ( http://www.pilom.com/BicycleElectronics/dynamo1.gif ). It works great, but I'm not super happy with the optics. The problem I have is dazzling of pedestrians and drivers. My first thought is to put a shield on the top of the light to add some cutoff; that seems like the simplest thing to do.

I have some wide-angle cylindrical fresnel type lenses that fit a MagicShine 808 ( http://www.action-led-lights.com/collections/accessories/products/wide-angle-lens ). I taped one over each flashlight lens and it makes the beams a nice wide angle. There is still plenty of spill going up, but much more of the light is in a useful spot. Does anyone make something like this lens in other sizes? My googling hasn't found anything yet. I think I could just cut/sand them down to 24mm and it will be fine.

I feel like the wide-angle plus a shield on top will get me pretty close to perfect, but I would appreciate any advice.

The best solution is to use a light designed to meet the German standards for bike lights. They are similar to auto headlights in that the beam pattern is a bit compicated and designed to allow very little light above the horizon.

If you want to use a symmetrical optic/reflector, you might do better by using one that creates a narrow beam. With a narrow beam, you can still get some light further down the road without much light going into the eyes of oncoming traffic. I've been happy with the Ledil Rocket SS, with a beam that is 8 degrees wide (at the half power points). A shield may help too, at the expense of wasting some light.

Wide angle beams may be good for mountain biking. My experience with wider beams for use on the road is that it puts too much light too close to you. This impairs your night vision, making the headlight less effective.

I actually bought a few lights with shaped reflectors ( http://dx.com/p/xc-997b-cree-3w-200lm-3-mode-white-led-bicycle-bike-light-4-x-aa-108640 ) from DX hoping the reflector was at least close to the German regs. After getting the lights, it is clear that everything but the reflector would need to be replaced to have a nicely working light. Very little heatsinking & a plastic housing. The reflectors seem decent, though.

Because I wanted to get some lights going right away and cheaply, I decided to put the DX reflectors on the back burner and that I would try the Romisen solution.

I'm still working on a design that will use those reflectors, but I would like to fix the current lights to avoid dazzling people. Is a shield above the light the best option?

I think I'll try sanding down some of my wide angle lenses - I want to give them a try at least. Maybe one wide and one spot will be good. If it doesn't work out, no big loss.

I keep hoping someone will give me their dead B&M LED headlight so I can upgrade it. No luck yet...

Some folks have used some scrap aluminum (soda or beer can) or plastic to make a quick and dirty shield. Seems like a reasonable technique when you are starting with a flashlight.

taqueso said:

The problem I have is dazzling of pedestrians and drivers.

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Nice to see someone worrying about dazzle.

I use a B&M Cyo. which has an excellent anti-dazzle cut-off, as a 'dip' beam when I approach cars and pedestrians, and switch to a home made 'main' when there is no one to dazzle.

Another Steve

Bandgap said:

...I use a B&M Cyo. which has an excellent anti-dazzle cut-off, as a 'dip' beam when I approach cars and pedestrians, and switch to a home made 'main' when there is no one to dazzle.

Another Steve

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hey Mr. Bandgap, a question.... what's the purpose for switching to the home made light when dazzle isn't a concern? More light output? I'm not familiar enough with the Cyo to know whether it is bright enough for all situations.

My dream is still to modify a Cyo or other LED light with a good reflector & optics with a high power LED and a switching power supply that can optimize the power drawn from the dynamo.

Steve in Peoria

I made some quick cutoff shields out of a beer can last night. Worked ok, but the aluminum can is definitely not robust enough to be a real solution. I should be able to get some sheet metal from work that I can use instead. Any advice on the size of the shield? Is there any advantage to a shallow, long shield over a shorter shield?

The longer the shield is, the better it will be at keeping light from shining upwards. There is a practical limit to how long the shield can be, of course. I assume that 4 to 6 inches (or significantly less?) is the practical limit for most folks.

You may want to experiment with some paper or cardboard while shining the light against a wall in order to get a feel for how effective different shield lengths are.

hey Mr. Bandgap, a question.... what's the purpose for switching to the home made light when dazzle isn't a concern? More light output? I'm not familiar enough with the Cyo to know whether it is bright enough for all situations.

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Same reason you switch to full beam in a car when you can. I have very similar set up with a modded Philips Saferide for a dip beam, and a home made 1700 lumen main beam with a remote switch.

The Saferide is very good at lighting up the road and nothing else. This is obviously what you want to avoid dazzling people, but does limit what you can see of your surroundings. Cycling with the dipped beam is perfectly comfortable in terms of being able to see what you need to see, but putting on the full beam is much more relaxing.

taqueso said:

I actually bought a few lights with shaped reflectors ( http://dx.com/p/xc-997b-cree-3w-200lm-3-mode-white-led-bicycle-bike-light-4-x-aa-108640 ) from DX hoping the reflector was at least close to the German regs. After getting the lights, it is clear that everything but the reflector would need to be replaced to have a nicely working light. Very little heatsinking & a plastic housing. The reflectors seem decent, though.

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Do this. Please.

taqueso said:

I made some quick cutoff shields out of a beer can last night. Worked ok, but the aluminum can is definitely not robust enough to be a real solution. I should be able to get some sheet metal from work that I can use instead. Any advice on the size of the shield? Is there any advantage to a shallow, long shield over a shorter shield?

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My margarine tub and yoghurt pot shields have given me sterling service for several years.