Sharp cutoff high-power LED lenses
 

I have installed a custom lighting solution with two high-power LEDs onto my bicycle, but after doing some final positioning adjustments, I ran into a small problem.

Namely, oncoming traffic gets totally blinded!

However, if I aim the lights down, they illuminate too close, too intensely. The lights are low-mounted (below front wheel axle), which definitely intensifies any angle issues, but is otherwise extremely beneficial since it shows the road profile much better. I do not want to change the light position - lighting from above is much less useful in my situation - I drive on paved roads and seeing potholes and other defects is the most important goal for me as far as lighting goes.

What I need seem to be sharp-cutoff lenses, like used in cars. Unfortunately, I have never seen any designed for small LEDs.

Here is what lens I am using right now: http://www.leds.de/en/High-Power-LED...ain-tight.html

Have you run into this problem before? Are sharp cutoff lenses available from anywhere?

Do I have some other options here? Can I manually modify the lens? I did some experiments but nothing usable came out of it - just randomly more diffused light - it seems infeasible to modify the lenses with any accuracy.

I really don't want to blind drivers...

Perhaps your situation is a result of selecting the wrong lighting system.

If indeed you "blind" traffic, then you have a responsibility to change the power of your lighting system or mount it in a manner that doesn't create unsafe situations.

Altering the lens of a light to restrict its power is analogous to using high-performances tires and letting the air out of them for a better ride.

1. Why do you say the oncoming traffic is getting totally blinded? Are they running off the road, or ??? Because I doubt it's as big a problem as you think. Motorists have several thousand lumens of their own to see by, and are not easy to blind. Driving towards the rising or setting sun, yes, that's blinding.

2. Cutoffs don't work all the time anyway. If you're coming over a rise, the strong part of the beam will still hit oncoming people anyway. This is a daily fact of life for those of us who live where it's not dead flat. The simple solution is to not stare into the oncoming headlights, as most of us learned in Driver's Education.

http://i240.photobucket.com/albums/f...gon/cutoff.jpg
~10,000 lumens of beam-cutoff FAIL. But life goes on ;)


That said, you could try to get an optic from a Supernova asymmetrical headlight, but I have no idea whether it would match up with the emission pattern for your particular emitter or not.

Then why is it that ALL automotive lights are actually required by law to have just the sort of optics that he's describing? Why not just tell them that they are just using lights that are too bright, and they need to reduce the brightness until it doesn't bother oncoming vehicles?

In Germany bicycle lights are required to have this sort of optics. Unfortunately in the US they're not, so we get whatever's cheap, which is plain flashlight round reflectors with no cutoff.

German lights, like the asymmetric B&M lights, do have a fairly sharp cut-off. I understand Cateye used to make lights with this asymmetry. To be honest, I don't think it's feasible to make your own lenses or reflectors, because of the rather precise shaping that would be involved.

Perhaps you might mount your lights up at the fork crown. It's a compromise between your desired ultra-low mounting position and bar mounts. That would allow you to angle the light down a bit, reducing glare to oncoming traffic, while still giving you some parallax between the light and your eyes, allowing you to see part of the shadows from potholes or road debris.

Just a thought, but what about an old school solution to your problem? Use some tape (say electrical) and start shaping your beam by covering the outside of the lens.

I've tried that. It does work but not as well as you'd think. I suggest using metal fwiw. Electrical tape on a high powered light will just fall off due to the heat pretty quickly. I cut a small semicircle of flashing that fit over the lens and behind the bezel.

It's kind of a long story, but trying to shape the beam at the lens doesn't work well at all. You might think of a camera lens where you can vary the aperture. Open and closing the diaphragm of lens only make the image brighter or darker, it doesn't vignette the edges. The only thing that will really work is to put a shade the extends some distance in front of the lens, which probably isn't practical or desirable.

It sounds like the lens has alter the shape of the focus of the LED beam. Instead of the original footprint size of the OEM die for that Cree LED, you probably made it larger with the lens. Imagine a SST-90 with no reflector and that's probably what driver is seeing. If that is the case, then I think a deeper reflector may help here. It may help reduce the glare and retain more of the light into a forward projection.

In your original post, you quoted a "Custom made lightening system". By that, did you use a standard reflector for the that led or a small reflector that fitted the requirment for your housing? Matching a right reflector with the led you are using will change the aspect of the beam immensly, and even more so if you have modify the led with a lens as you did. If you can provide a picture of the LED in the reflector may help here. Personally I never builded my own flashlight nor bicycle lights, but I have looked into it, and from what info I gather in the past, this might just be the problem you are having.

The full cutoff optics that I've seen that work very well have the LED facing downward and the reflector is swooped outward in nearly a quarter cylinder. This also can be shaped to make more light hit farther out, which has the effect of making a uniform light patch on the ground.

Someone else employed this trick when devising his anti-glare guard on his dynolight set-up. See post #79 in this thread from the Commuting forum.

I've tried aluminum foil over a lens as a cutoff. Walking a distance from the bike, and observing it in person, I literally couldn't tell the difference from having it right-side-up or upside-down. Nice concept, looks good when projected on a wall, doesn't help IRL.

That seems counterproductive. You don't want your headlight to be invisible to traffic in your front 180° arc. At least, *I* don't ;)

If you look at a good directional bike light (like, say, an IQ Cyo), you'll see the lens looks like a miniature car headlight. The "glass" incorporates Fresnel elements throughout its area that direct the light in designed directions, and you end up with well-defined edges, with enough bleed-out to help with visibility outside the main beam.

Thank you for your suggestions, everyone! I took a few hours to experiment last night and I believe I have achieved a satisfactory solution, which I will now describe.

First, here are some comparison images. The ambient lighting conditions were not the same for before/after but it's close enough for comparison.

Beam pattern comparison against a wall:
http://i.imgur.com/9BelK.png

The slight upwards misalignment of the right headlight on the before pic did not play a significant role.

Note how much light bleed-out there is outside the main beam on the before pic. This turned out to be the deciding factor in making the light traffic-friendly. As soon as I blocked off anything to the sides of the central beam, the blinding glare disappeared.

Comparison facing the bicycle, from roughly driver-height.
http://i.imgur.com/fgunD.png

Comparison with car high beams.
http://i.imgur.com/wxkQJ.png

Here you can see a modified light (picture left) together with an unmodified one.
http://i.imgur.com/yGKWM.jpg

My main inspiration was the Commuting forum post linked by no1mad, where someone had made a metal guard over his light. My metalworking skills and available tools are minimal, so I knew I had no chance of making anything presentable, so I went with the GhettoTech route of just throwing something together from things I had laying around.

Duct tape and beverage cans to the rescue!
http://i.imgur.com/6TPXJ.png

Originals.
http://i.imgur.com/Knpje.jpg

Modified.
http://i.imgur.com/NglbC.jpg

The cans and duct tape turned out to be surprisingly stiff. I was afraid they'd pop off when I went over the first bump but a 1-hour test ride on some bad roads resulted in no damage whatsoever.

I am very happy with the result. No more blinding light AND I get to keep my low-mounted lights that show me every little bump on the road. Perfect! Thank you for the help, everyone!

Some misc pics here, in case you're interested in my lighting setup.

http://i.imgur.com/rdcwv.jpg
Side view; with taillight also on; this is with pre-modification headlight.

http://i.imgur.com/kiSGx.jpg
Battery pack with 12V 9Ah lead-acid gel battery. No, it's not all full of battery :) The battery and mounting takes up less than half that box, the rest is cargo space and taillight electronics/switch/wiring.

http://i.imgur.com/E8EE0.jpg
Control box on the stem. It is annoyingly big but I couldn't find a better box. The bar on top of the stem is my cant-turn-the-bike-upside-down-if-it-rests-on-the-light-switch-you-dubmbass adapter (a block of wood). You may also have noticed the empty speedo holder... since the headlight electronics are not shielded, the EM emissions completely block the wireless sensor signal, so the speedo is just a clock when the lights are on. I just took it off for now...

New motorcycle LED headlights and passing lights
 

Sooner (in a do-it-yourself system) or later (in a commercial bike light) I expect to see the new LED motorcycle headlights or passing lights adapted for bicycles. These offer some very sharp cut-offs and real optics that put the lumens where you want them. In the first composite photo, note how sharp the cut-off is for the JW/HD passing light in the lower half of the photo. In the on road photo, first marker at 20 yards, then every 10 yards:
http://bikeforums.net/attachment.php...hmentid=198966http://bikeforums.net/attachment.php...hmentid=198967
They are a bit pricy now (although the passing lights are under $200). See this Feb 2011 review, LED Forward Lighting Comparison (the above photos are from this article) and browse over to what the manufacturers they mention have to offer.

Have you seen any that are self-levelling, a la automotive headlights, to avoid aiming the beam above the horizon when the vehicle's not level?

I sure am glad all those "auto lens" are working - i never have a problem - they are all just peachy-keen, never too bright - oh yeah they work great.....

If I am approaching pedestrians or other cyclists with little or no lighting, I hold my hand over my light or i turn it off or point it downward. But I'm just a """"tard what do I know.......

Automotive headlights do not do this. They're fixed to the body. In general that's what you want, because if the vehicle isn't level, it's because the road isn't either. It causes trouble on hills, when you're cresting a hill your low beams are shining right into the eyes of oncoming vehicles.

Obviously not all lights are legal (most if not all aftermarket "fog lights" are illegal) and there are people who don't have their lights adjusted correctly. Surprisingly, there's no such thing as a technology that forces people to use it correctly. That's not to say that the technology shouldn't be used.

Quite a lot of automobiles have headlights that adjust to the load of the vehicle, either automatically (by sensing excessive sag in the suspension front or rear) or by the driver turning a knob. Not common in the US, but normal many places.

Some do, particularly HID headlights. Do a Google search for auto-leveling headlights, they're stock on some cars.

And that's the point I keep mentioning when people get all goggle-eyed about how great cutoffs are, how inferior non-cutoff-equipped lights are, etc etc ad infinitum. If you ride a very flat MUP and are concerned about the oncoming MUP users who have no lights, or very weak ones, then maybe a cutoff-equipped Supernova, Cyo or Edelux is a good choice, sure. In city traffic, don't worry about your lights being too bright until the cops pull you over for it ;)

Some original research:

I saw this guy on the mtbr forums that makes special lenses for LED lights like the Magic Shine (and others)...

http://www.mtbl.robs-x.com/index.html

Site is a bit hard to figure out, but I'm sure if you just e-mail him, he'll let you know what can and can't be done.

---sam