jbuch said:jbuch said: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.
You may want to visit
http://www.enhydralutris.de/Fahrrad/LEDWerfer0402/ and punch it into
www.babelfish.com if you don't read German. (This site was mentioned
in a another recent thread.) Their approach, working with Luxeon
super-bright LEDs, is to modify a commercial generator headlight shell.
Really, to light the road effectively, it's best to have optics
designed for that purpose. I've tried something similar to what you're
trying, with similar lack of success, although I started with a
brighter light. I had lenses that spread the light far too much side
to side, and I had lenses that made almost no difference, or gave too
diffuse a beam. You need precision. I don't think you'll get it by
accident.
Quoted message said: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.
I think Cateye's LEDs have paid some attention to optics. I think
that's what their "Opticube" advertising term is supposed to mean.
Interestingly, older Cateye halogen lamps (the cheap ones powered by
flashlight batteries) had what seem to be parabolic reflectors and
faceted lenses, some with front reflectors to reflect what would be
"lost" light back toward the parabolic reflctor. The paraboloid throws
out a straight parallel beam; the lens shapes it to fit the road,
usually into a rectangle or trapezoid.
Newer Cateye halogen lamps (the Micro whatever) dispense with the
faceted lens. They seem to use a complex, computer-generated reflector
to shape the beam directly. The idea seems to be to reduce losses in
the front lens.
To my eye, the beam shape is more precise with the old system; but the
total light output may be more with the new system. Certainly, most
new cars have gone to something similar. I know our Pontiac Vibe has
no faceted lenses on the headlights, and the beam's upper cutoff and
uniformity of spread are both outstanding.
Cateye's LED lamps seem less precise to me, but not too bad. I rode
next to a guy who had the CE-EL500. It's beam was somewhat amorphous,
and not as useful to my eye as my halogen generator lamp, but it wasn't
bad.
- Frank Krygowski
