Re: Modify LED Headlight Beam ? ?
- From: Marty <mart@xxxxxxxxxx>
- Date: Thu, 29 Sep 2005 11:10:53 +0800
Phil, Squid-in-Training wrote:
I'm starting to experiment with ways to alter the beam light dispersion of the typical LED bike headlights.
Most of them put out a "pencil beam" and not enough dispersed or scattered light to be something you can really ride with.
I have had this experience with Cateye EL300 and EL500 and with the Nite Hawk LED Emitter (non-digital).
Initial experiments are with a flat Fresnel plastic lens, of the type commonly sold as a flat plastic pocket magnifying lens. (The one with the rings of grooves that trick the light into thinking it is hitting a single curved surface, more or less.)
The Fresnel lens did spread the light beam on all headlights.
EL-300 The result was five light "halos" rather than one beam. The light intensity was pretty low as a result of the spreading. It was more or less useless. If you spread out 400 claimed candlepower, it is pretty dim.
EL-500 The result was a large light "halo" rather than a pencil. The effort to cover just 1/2 of the beam with the Fresnel lens produced a mixture of a "beam" and a "Halo", but it wasn't a very useful pattern for riding. Again, this lamp produces a claimed 1200 candlepower, and when spread out very much, it isn't a lot.
Nite Hawk LED Emitter - The result was a larger diameter spot rather than the narrow pencil. There still wasn't much scattered light to see ahead of you while turning, or thinking about turning. The larger spot was a nicer medium speed ride than anything else, including any of the headlamps without the Fresnel lens.
I would suspect that _I_ would be happy wtih outputs of nearly five times higher than the EL-500 or the Nite Hawk - and in a beamwhich has riding functinality.
I saw a 1928 Ford Model A today on my exercise ride and stopped to take a look.
The headlamps had the classic bulb, reflector, and focusing front lens. The focus elements in the front lens were simple vertical cylinder sections, so as to spread the beam out laterally. No optical elements were in use to control the fine details of beam forming except in the lateral direction.
More modern headlamps that I looked at had complex optical segmentation of small lenses that appeared to provide beam manipulation in both directions which may be why modern auto headlamps perform pretty well. Bicycle LED lights currently have none of this secondary beam forming optical design.
I can't speak to the beam optics control of HID or tungsten-halide lamps. At anyy rate, LED headlights have a long way to go to be mature. Right now, they are immature in design and performance.
The lenses are designed from the factory to focus very sharply. They give off comparatively little light to the sides, making reflectors kinda useless. A specific prism might be able to split the light just the way you want it. Personally, I would just mount a light to the helmet and be done with it.
This is my twin Luxeon setup on my triathlon bike. http://www.hyperactive.oz.nf/Lights2/Luxeon2.htm
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