Let's design a road front light beam

[Bandgap]

Inspired by discussions in kristiancyclist/Boris's 'How much is too much?' thread, I am wondering if there is a consensus as to what a good, useful, on-comer-friendly bike front light beam should be like.

My proposal is:
With LEDs getting brighter and brighter the default 'circular' beam is getting dazzling to on-coming drivers and all that light above the horizontal could be better used lighting the road and roadside hazards.

There is no reason why the proposed light could not be used alongside a powerful circular beam in the same way that cars have dip and main beams.

In kristiancyclist post, I suggested that maybe the above-horizontal anti-dazzle limits applied to cars in Europe or the USA, or the German bike light limits, could be used as a starting point.
I now have a copy of the German regs and have printed the figures below.

I would be interested if anyone could run a light meter over an example of the famed Bisy (however you spell it) light.
I will try to run my light meter over my favoured Axa HR.

Also, can anyone contribute the parameters of the circular beams you find satisfactory - and in what circumstances.

For example: I use 40 lm in a +/-10deg circular beam , plus 40 lm in a +/-3deg circular beam and find this combination great for straight-ish unlit roads, but not wide enough for the twisty country lanes I now live amongst.
It is also nowhere near enough light when the roads are wet and shiny.

The German rules - as far as I can understand as I don't speak German
I have no way to put a diagram up today - here they are in words

All measured at 10m distance
Further than 3.4 deg above the horizontal, at any lateral angle, less than 2 lux
Horizontal straight ahead intensity (called intensity 'HV') - at least 10 lux
all the way between 4 deg either side of horizontal straight ahead - at least half of HV.
from horizontal straight ahead to 1.5 deg below - at least half of HV
From HV all the way down to 5 deg below - greater then 1.5 lux
all the rest of the box including 4 deg left and right, and from horizontal down to 5 deg below - at least 1 lux

So
- any ideas?
- any data?
- is there a German speaker who I could forward the regulations to for translation?

Steve

 

[vkan]

I like the looks of what Busch & Muller have already done for reflector design for a road front light beam (and Schmidt liked it enough to license their work for their LED bike light, the Edelux).

Their latest light looks even better:

http://bumm.de/docu/175q-e.htm

For the homebrew I want to make, I'm using two or maybe three emitters with these:

http://www.dealextreme.com/details.dx/sku.1919

which aren't ideal, but worth trying. If the light patch were half as wide and twice as tall, it'd be great.

I have one of those in my Lowes Task Force light and it's a great flood for near lighting, but just doesn't have the throw. So I want to see what having two or three of them aimed at slightly different vertical angles does, with a higher output LED+driver combo.

I suppose just getting a narrower angle oval optic and stacking two or three of them would work out better, or maybe combined with a flooder with a round beam.

 

[trout]

Hows about something with a beam like this

This is just a test rig I am working on experimenting with different sizes of acrylic bar

Now if you used a larger diameter bar and put 2 rows of leds one row dead centre and the other row above and maybe even less leds then to dip switch the centre off and the top on this then drops the beam a good amoumt this i hav not got round to testing yet.

 

[bbgobie]

My ideal beam pattern is slightly rectangular, but longer in the vertical plane when shot on the wall. The light would also get dimmer from bottom to top when projected on wall.

Reason is, when you turn that beam down on an angle, the foreground is not flooded as the distance is closer. And the cut off means no light is wasted up.

 

[Alex Wetmore]

This is an interesting discussion. In my mind the optics are the biggest limitation of homebuilt headlights.

The IQ Fly/eDelux beam is shaped like a trapezoid. The wide part is at the top and the narrow part is at the bottom. The optics send more light to the top too.

When projected on the ground this looks like a long difuse rectangle with fairly even lighting. The amount of light going up towards drivers is enough for them to see you, but not enough to dazzle them.

B&M's optics appear to mount the LED at the top of the optic and use a reflector. I played with duplicating this (just using a Maglite 4D reflector), but it is hard to do with a star mounted LED because the star creates shadows on the final beam.

I bet the right beam could be done with colminating optics. There just isn't the market for DIY bicycle specific lighting.

The best results that I found were from decentering the LED inside a L2 OPTX-3-008 triple optic. I need to experiment more with this option. The decentered LED (LED shifted up I think) seemed to produce a beam which was brighter and more tightly defined at the top, and with more scattered and dimmer light at the bottom.

alex

 

[LukeA]

I'm getting what I think are pretty good results with a simple and inexpensive system.

Low beam:

High beam:

Light with proto paper cutoff device: (low beam is 3+3, high adds the middle 4)

Light w/o paper (less blurry and overexposed):

A slightly more complex design could achieve an ECE-type right side to the beam that would light the non-traffic side of the road better. But that's for version 2.

 

[Eamon]

Steve,
Could you post a link to those German regulations? Or .Zip it up and attach it? There are several possible interpretations depending on the punctuation, and they're kinda' different. Maybe a Flickr post?

They seem to want a tightly controlled illuminant rectangle with a well-defined horizontal cutoff just above horizontal. That jibes with the German lighting that I've seen. The E6/BiSys, BUMM, and INO offerings have all had a pattern pretty much like that. It's a great dipped beam, but not so good at picking up things just off the road, or things in the distance.

I use a +/-4deg spot with 200/400Lm high and low. The 200 is good for low speeds, climbing, and for oncoming. The 400 for higher speeds and narrower roads. Neither is quite enough for descending in the dark, and nowhere near enough for wet work.

A German-compatible low beam would be fine for semi-urban areas, trafficked roads, and climbing. For longer rides, faster rides, and descents, it's not even close.

The light(s) that I'm putting together now will have outputs of (roughly) 300, 450, and 600Lm. The reflector is going to be either a +/-5deg or a +/-6.5deg spot, depending which I like better. If that 300lm were in a controlled-pattern low beam, and the 450/600 were a spot, that would be about perfect.

One of the first things to decide is how much light you want. The current German LED lights throw ~200lm from a single emitter, and that reflector is not small. If you add a narrow spot emitter/optic beside it, plus circuitry and heat sink, your light unit is getting rather large. If you're like me, and a 600Lm light sounds good, then you need two additional light sources beyond your controlled-pattern lo beam. You could arrange the sources radially around a single thermal sink, and tuck the circuitry around the outside, but it's still big.

I start to see a marginal-utility limit approaching here, in the balance between throw-weight, mass, and volume. This is the reason that I think more in terms of multi-die emitters and single optics.

Alex has been tinkering with emitter position in the optic, and someone in Germany has cut a BiSys reflector in half. This is a start. Getting multiple beam patterns from a single reflector is only new tech in the bicycle world. If there is demand, someone will design it.
The "center" of the light source in an MC-E can be moved as much as 1.4mm by addressing single dies. The P7 more so. In terms of an optic that's 35x17mm, that's a lot. The linear distance between high and low elements in an H4 bulb is 1cm, in a reflector that is much larger.

I envision an optic that has a horizontal cutoff, German-style, and can throw different beam shapes using either multiple emitters or a multi-die emitter. Long, Long ago, in a galaxy far, far, away....

Alex commented that there is no market for a sophisticated bicycle optic, and that is true, for the moment. Given the factors working in the bicycle world, that is subject to change without notice.

Eamon

 

[syc]

I came across a DIY light in a square aluminum conduit/pipe that had the LEDs and optics recessed in the conduit, and a front of the conduit bias cut so that the top edge extended further than the bottom edge.

I remember that the builder said it provided a trapezoidal beam pattern, but I had not bookmarked it at the time, and can't seem to find it anymore.

It seems that you could try doing this and also have the LED and optics offset so that it points slightly upward within it's recess, causing the hotspot to be closer to the top edge of beam pattern, and spilling more light downward right in front of the light, lighting up the region right in front of your wheel better.

You could probably prototype this with just some conduit, a hacksaw and an existing flashlight. I just tried it with a sheet of aluminum and a flashlight to see how it effected the beam and after you adjust for the beam angle, it seems to do a reasonable job of causing a sharp cut off of a bright top edge, and reflecting the light down in front of the light. But it only works if the LED beamline and the top "hood" aren't parallel. The hood has angle into the beamline. In a way, you could claim that its an improvement on the B+M design, because you don't have a dark area right in front of the bike anymore.

 

[znomit]

I came across a DIY light in a square aluminum conduit/pipe that had the LEDs and optics recessed in the conduit, and a front of the conduit bias cut so that the top edge extended further than the bottom edge.

I've been thinking of that post too. Today I tried my MCE polymer optic in a square tube, edges not so sharp but I'll cut an angle into the tube and open up the bottom, see how it goes.
I've been thinking of this for a while as the extended front of the tube, if left open, makes for very good cooling.

 

[Bandgap]

At last, with help from syc, and discovering that I have to use the non-simple editor, here is the diagram.



The regulations look pretty sensible, based on a mixture of fractions of cenral beam intensity, plus min and max limits.

It is from a document titled: StVZO Prufkriterien

Nachfolgend die Prüfwerte einer Lichtquelle
mit einem Lichtstrom < 42 Lumen:
• HV mindestens 10 lx
In HV soll die max. Beleuchtungsstärke liegen. Befindet sich die max.
Beleuchtungsstärke seitlich von HV, so darf deren Wert das 1,2 fache
des Wertes in HV nicht übersteigen.
• Von HV aus 4° nach beiden Seiten bis einschliesslich zum Punkt L1 bzw. R1 sowie
1,5° unter HV bis einschliesslich zum Punkt 2 mindestens die Hälfte der
Beleuchtungsstärke in HV.
• Bis 5° unter HV, zwischen Punkt 2 und einschliesslich Punkt 3, mindestens 1,5 lx
und von dort nach links und rechts bis einschliesslich zu den Punkten
L4 bzw. R4 mindestens 1lx.
• In der Horizontalen 3,4° über HV und darüber hinaus (Zone 1) höchstens 2 lx zulässig

Anyone want to translate?

Steve

 

[steve6690]

How about using a Polymer Optics eliptical optic ? it projects a beam 6 degrees in the vertical but 25 degrees in the horizontal..

 

[syc]

I'm getting what I think are pretty good results with a simple and inexpensive system.

Low beam:

The low beam is similar to what I was seeing with a sheetmetal hood. The difference I think is that your paper hood bends down and blocks the light from the upper part of the beam. If you just kept it as a straight, flat hood and angled it down into the beam, it would reflect the light downwards at an angle, lighting up the area immediately in front of the light. I noticed that with the smooth sheet, there was an obvious hotspot in the reflected light - maybe sputtering the reflective surface would even out the reflected light.

Along the linesof what Alex said w.r.t. offsetting the optic mount on LED, I wonder if you could just use a reflector and modify the rear of if so that you can mount the LED at an angle. It seems that putting the LED onto the optic at an angle would result in losing a lot of light to reflections off the rear of the optic, while a reflector might still get all the light going out the front (albeit at different angles). The guys playing with the MCE boomerange reflectors seem to have to do this anyway just to get it to mount right:

That reflector/LED gives an interesting pattern with a bright center hotspot and lots of spill. Could be very useful for a road bike light if you could recover the light that goes shooting off into the trees and clouds and direct it onto the pavement in front of you.

 

[Alex Wetmore]

How about using a Polymer Optics eliptical optic ? it projects a beam 6 degrees in the vertical but 25 degrees in the horizontal..

I've played a bit with that type of optic, but it doesn't do what I want. 3 of them stacked and aimed progressively higher might help.

25 degrees in the horizontal is more width than I need.

6 degrees on the vertical still either means the beam is bright too close to me or I'm wasting a bunch of light on the trees. The good beams really are the ones that are brightest at the top of the beams. Spot-type beams (circular or elliptical) are brightest at their center.

alex

 

[vkan]

The short, but wide pattern 35mm optics that dealextreme sells do provide a beam with a flat cutoff that is brightest at the top of the beam, at least on my flashlight.

But unfortunately, it is way too wide (for a bike light anyway) and not tall enough.

I do plan to try what you suggested, stacking them with progressively higher aiming.

 

[syc]

I've played a bit with that type of optic, but it doesn't do what I want. 3 of them stacked and aimed progressively higher might help.

Would it be better to flip it, so that the bottommost points straight forward, and the ones above it point progressively lower? You want the light that goes beyond the intersection point of the beams to go onto the pavement, not into the air, right?

As some more brainstorming, maybe using McGizmo's double sideshooter light mount:

But with the $15 E6 replacement reflector from Peter White you can get something approaching the E6 beam pattern?

 

[Eamon]

Syc,
Thank you for reminding me that Peter White sells those reflectors. I didn't want to buy E6's just to cut up the lens. I'm going to do some sectioning of different optics, and cheaper is better.

The BUMM reflector that people rave about is essentially a section of a standard parabolic with an emitter turned 90deg off-axis. It throws a very controlled beam like the E6 without the emitter being visible. That reflector is being used by Schmidt, BUMM, and INO(I think). I had not seen the McGizmo mods, but there are definite similarities. Another starting point.

Edelux cross-section:
The axial cross-section looks like a straight parabolic reflector. The lateral section is more complex, given the beam shape.

A rando friend of mine sent me this after he got his Edelux:

The edelux is fabulous. Did a 100 miler with a bunch of novices yesterday in the rain...of 14 people only two had flaps! used the light at the tail end and it was great.

A couple of days later, I got this:

Only complaint with edelux, now that I've had it a few days is that it is a very small patch of bright light. With the Dinotte it works fine, but it would be marginal at speeds.

The Edelux throws exactly the same pattern as the E6/BiSy. This guy was coming from using an L&M halogen with a Dinotte helmet light. It sounds like he's going to have to keep the Dinotte. He does the sort of riding that I do, and I know the hill he's thinking of when he says "marginal at speeds".

I can't speak for other people, but one of the things I would really like to avoid is the need for a helmet-mounted light. I use one to read cue sheets in the dark, and for sign-hunting, but I never leave it on. Helmet lights are blinding to anything you look at. I suspect they're far more irritating to drivers than almost any bar-mounts.

I know a lot of people who use helmet-lights because their bar-mounts just don't throw enough light. I would like to see a lo-beam shape that is sufficient in a broader set of circumstances.
The StvZo-compliant beams seem more than a little biased towards the driver, at the cost of utility to the cyclist.

Eamon

 

[Alex Wetmore]

The eDelux doesn't have the same beam as the E6/Bisy. It is quite a bit wider with more scatter. I have the IQ Fly now and have been using E6 and Bisy headlights for years.

If you think that the IQ Fly or eDelux is too narrow then you really wouldn't like the E6.

I've also considered sectioning an E6 reflector, but it seems like this kills the possibility of using the star mounted LEDs (the easiest ones to work with).

alex

 

[Steve K]

I've also considered sectioning an E6 reflector, but it seems like this kills the possibility of using the star mounted LEDs (the easiest ones to work with).
alex

Alex, do you really mean the E6 reflector, or are you referring to the lens that PJW sells? I'd be interested in seeing what can be achieved simply by mounting the E6 lens in front of a LED. The lack of reflector would certainly waste a lot of the LED's output. A full reflector & lens would do much better, I suspect.

I've got a BiSy headlight that I intend to cut in half and try mounting a Cree MR-E where a bulb would sit. I'm hoping that something can be done to modify the beam pattern, so as to throw a bit more light to the sides. Maybe just roughen the surface of some of the lens, or move the LED out of the optimal position?

I'm already behind in another project, so don't expect me to get around to this anytime soon. <sigh>

Steve K.

 

[Alex Wetmore]

Alex, do you really mean the E6 reflector, or are you referring to the lens that PJW sells? I'd be interested in seeing what can be achieved simply by mounting the E6 lens in front of a LED. The lack of reflector would certainly waste a lot of the LED's output. A full reflector & lens would do much better, I suspect.

I meant the E6 lens and reflector unit that PJW sells. I have 2 of them (and just offered one to Eamon since we live in the same city) since my E6 headlight broke.

I'm just stealing ideas from this webpage:
http://www.enhydralutris.de/Fahrrad/LEDWerfer0402/index.html

I'm also behind in projects and decided that I should probably just build one headlight that works before playing too much with optics, so I'm concentrating on that right now. I'm using the L2 OPTX-3-008 triple CREE optic with 2 LEDs. One will stay on for a standlight. It is just a normal spot optic, but it isn't bad for a first headlight. The round 50mm lens is easy to build a housing around.

alex

 

[Eamon]

Alex wrote:
The eDelux doesn't have the same beam as the E6/Bisy. It is quite a bit wider with more scatter. I have the IQ Fly now and have been using E6 and Bisy headlights for years.

My mistake, I typed without thinking. They are both tightly controlled, StVzo-compliant patterns that don't really suit my needs. I've never run either myself, although I've spent quite the time riding with people who do. Neither would work for me as a sole light source.

If you think that the IQ Fly or eDelux is too narrow then you really wouldn't like the E6.


My initial reaction to the E6 hasn't changed since the first few I saw. Namely, deep surprise that people can tolerate that little light.
I do partake in the better-to-have-and-not-need school, though.


Eamon