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Discussion Starter · #1 ·
I'm designing a lighting solution for my commute to work, and am seeking the ideal of a beam that provides a lot of light on the ground but doesn't blind other road users or waste light up into the air. To repost my words on the XM-L thread:
With the advent of more and more powerful emitters the issue of reducing glare to other road users is becoming more of an issue. Not only that, but also it is more efficient to put the emitted light down on the road where it is useful rather than shine it up into the sky. The lights are now powerful enough to usefully see by, rather than the weedy things of past which were only good for being seen. Even a single P7 emitter is pushing the boundary of what's acceptable on the road if it is not controlled properly. However <snip> in the wet you really do need a lot of light hitting the road surface, especially if there are commuter cars all around adding to the glare.
The beam provided by a powerful flashlight does a good job of lighting up the ground, with the gradual change from spill lighting up the road nearby to throw projecting light further down the road. However it does an equally good job of lighting up the air and trees around, so surely those lumens could be better utilised in providing yet more light on the road?

A car headlight has to blank off half of the light to achieve a road-friendly beam. This is because the emitters, be they halogen bulbs or HID, emit through 360 degrees. We are using LEDs which only emit through 180 degrees with quite a sharp cutoff, so surely we can be clever and use all that light where it is needed?

One idea is to in effect use just half a flashlight, with an emitter firing down into a parabolic reflector as below:

This could work well, with the beam changing from focussed (part of the LED is at the focal point) through to wider flood (part of the LED behind, like a defocused Maglite). However it is quite difficult sourcing an aluminium parabolic reflector that is designed for an incandescent bulb not an LED, and which has a very narrow opening behind the focal point as I don't want to waste light out the back. It has to be a reflector designed for an incandescent bulb as reflectors for LEDs are normally cut off at the focal point, like thus:

The next idea is to flip the design vertically and move the LED forward, which is very similar to the way a standard halogen headlight in a car works. There the dipped beam is effected by having the bulb element in front of the focal point, and a shield preventing light emission down into the bottom part of the reflector. The design would be like this:

Either method requires cutting a reflector in half of course, but will give very good heatsinking as the LED star can be attached directly to a flat heatsink on the case. I've tried some beamshots with a Maglite plastic reflector and small LED, but have just received an XM-L through the post so will try and post some beamshots using that.

Another possibility, which I haven't any diagrams for, is along the lines of a projector headlamp. In that, the LED would be placed at the focal point of an ellipsoidal reflector, firing up in the same way as just described. The ellipsoidal reflector would refocus the light which would then pass through an aspheric lens, tightening the beam. This is the way car projector headlights (halogen or xenon) work. The only problem is the smallest ellipsoidal reflector I've found is 2 inches across, so the light would need to be a 2 inch tube from back to front (although the lens can of course be smaller). A cylinder 50mm across, 100mm long is probably a bit large for a single emitter light!

The wikipedia article on headlamps has good background information.
 

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[URL="http://www.cateye.com/en/product_detail/462']Cateye[/URL] have an interesting take on this - 2 1W LEDs back to back at the front of the light aimed backwards to shine onto the reflector. Had a play with one in my LBS by don't really have any real world experience with one
 

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I've been playing around with reflectors and the like for some time but just can't seem to get a good cut off with a small optic and still achieve a high efficiency . I've looked at lenses designed for HID but their diameter is around 3 inches and the focal point too far away making the light about 5 inches long.

I have a 1200mm x 2400mm sheet of acrylic mirror that I have been bending into different shapes but the reflective coating becomes dull as soon as the slightest bend is introduced. Perhaps I need to try and cut small wedges and join them together.

So far the perfect road light seems to be the holy grail, just out of reach.
 

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brad72 said:
So far the perfect road light seems to be the holy grail, just out of reach.
Check out the dynamo powered lights on the link posted above, the good ones seem to have the cutoff and beam shape set up well for road use and the consideration of other road users :) The philips light is ~100 british pounds? so $160 US. Add a dynamo for $30-50 and you have a battery/charger-free solution (assuming you can build your own wheel).
 

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Nice work mfj, the pictures make it so much easier for me to understand what you have been talking about elsewhere.

I'm eager to see how the beamshots work out. Given that this is for a commute I'm guessing the light will be bar or bike mounted so a loss of intensity isn't such an issue as the extra weight of adding a second, or third LED and the battery to drive it isn't as noticeable as it would be on your head. Obviously the key here is getting the beam exactly the way you want it.

Now for a bit of a grey area, the focused beam will be great when the road is flat but what about as you crest hills, this will presumably put a very intense beam at eye level of oncoming traffic and when you hit the bottom of the hills and flatten out it will give you a very bright hotspot very close which might effect your night vision. any plans on how to combat these issues?
 

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emu26 said:
Now for a bit of a grey area, the focused beam will be great when the road is flat but what about as you crest hills, this will presumably put a very intense beam at eye level of oncoming traffic and when you hit the bottom of the hills and flatten out it will give you a very bright hotspot very close which might effect your night vision. any plans on how to combat these issues?
gyroscopes/ accelerometers plus servo controlled mirror, a la BMW motorbikes?
 

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Discussion Starter · #9 ·
HakanC, thanks for the link - some very good discussion and reading there. I have wondered about modifying an existing light before, and possibly the Philips LED Bike Light could work very well. It seems to fire a pair of LEDs down into part of a parabola, confirming there may be mileage in that approach if I can get hold of a suitable reflector. My one concern with these lights is they are almost too effective - they light a track ahead of the rider with hardly any spill to the side, which can lead to accusations of the feeling of riding along a tunnel.

emu26 said:
I'm eager to see how the beamshots work out. Given that this is for a commute I'm guessing the light will be bar or bike mounted so a loss of intensity isn't such an issue ...
Well, to be honest I'd expect no loss of intensity - in fact I'd be hopeful of a gain in intensity of light striking the road. As an example the Philips LED Bike Light referred to above, with only 270 lumens, puts much more light on the road than single P7s or triple XPGs and is apparently comparable in usefulness to the 2011 Lupine Betty with 7 XPGs and 1850 lumens.
Now for a bit of a grey area, the focused beam will be great when the road is flat but what about as you crest hills, this will presumably put a very intense beam at eye level of oncoming traffic and when you hit the bottom of the hills and flatten out it will give you a very bright hotspot very close which might effect your night vision. any plans on how to combat these issues?
I think having a beam optimised for a flat road will probably be acceptable. I tend to ride with a small helmet light anyway which can provide a bit of fill if necessary. Regarding dazzling oncoming traffic as I crest hills I can take a leaf from the automotive industry. HID headlamps here in the UK are recognised as being very bright and by law have to have both headlamp wash and self-levelling. However the self-levelling is purely to counteract differing loading of the car - it doesn't counteract hills, so I don't think I would bother with trying to develop an approach that could. Interestingly of course this is one reason I need a good bike light, as the constant stream of traffic cresting the undulating road does dazzle!
gyroscopes/ accelerometers plus servo controlled mirror, a la BMW motorbikes?
Methinks you doth expect too much from me! :D
 

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mattthemuppet said:
gyroscopes/ accelerometers plus servo controlled mirror, a la BMW motorbikes?
Or just flesh and bones. :D When I'm in the road I usually use only the helmet light and I just look slightly down/right when there is incoming traffic.
But it's not as cool as some servos :thumbsup:

What about if instead a single large LED with a modified beam, we used a few smaller less powerful led and individual lenses with narrow beans. Would it be possible to point these individual beams so that they hit the road in a long and narrow rectangle?
 

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bravellir said:
What about if instead a single large LED with a modified beam, we used a few smaller less powerful led and individual lenses with narrow beans. ?
I don't think the beans will be much good for throw unless we're talking about a rear light.

On a serious note, whilst you may get the same intensity of light with more leds at less power I don't believe you'll get the same throw. Those extra lumens from the additional LEDs don't magically start at the furthest edge of the original LEDs, if that makes sense
 

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Discussion Starter · #12 ·
bravellir said:
What about if instead a single large LED with a modified beam, we used a few smaller less powerful led and individual lenses with narrow beans. Would it be possible to point these individual beams so that they hit the road in a long and narrow rectangle?
I guess that's what I do at the moment with a couple of cheap flood-to-throw zoomable flashlights with aspheric lenses. I use one aimed down on flood (nice, no hotspot) and one zoomed further in pointed nearer the horizon. It is much more acceptable to others than the P7 flashlight I also sometimes use. But it's not perfect by a long shot - the intensity of the flood light quickly diminishes until it meets the spot of the zoomed light. The zoomed light itself is providing quite a narrow beam as well, not emitting out to the sides. Plus at the end of the day they're not that bright.
 

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emu26 said:
I don't think the beans will be much good for throw unless we're talking about a rear light.

On a serious note, whilst you may get the same intensity of light with more leds at less power I don't believe you'll get the same throw. Those extra lumens from the additional LEDs don't magically start at the furthest edge of the original LEDs, if that makes sense
:D damm spell checker

I was just adding to the discussion. What I was imagining was some sort of 2*3 array off +-200 lumens leds.
Imagine a 7Up.. and some kind of optic that produces a group of beams that instead of being parallel, each beam would focus on a determinate distance ahead. Like mfj197 did with his 2 lights but with more leds to avoid the gap between the spots.
I know that it won't be as bright as a single led, but on the other hand, less lumens would be thrown away where they aren't needed.
 

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Discussion Starter · #14 ·
Nearly finished the test rig yesterday now the XM-L has arrived - just need to source some thermal mounting tape and a switch. Out in the garden yesterday I briefly tried Option 2 above (LED firing upwards into half a parabola) with the dissected Maglite C/D reflector. Seemed to be very effective indeed, with a clear cutoff and putting much more light on the ground than my Spiderfire P7 flashlight. No beamshots yet I'm afraid.
 

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mfj197 said:
HakanC, thanks for the link - some very good discussion and reading there. I have wondered about modifying an existing light before, and possibly the Philips LED Bike Light could work very well. It seems to fire a pair of LEDs down into part of a parabola, confirming there may be mileage in that approach if I can get hold of a suitable reflector.
Yes it does, it looks like your 1st picture

but its got 2 Rebel LEDs, side by side.

My one concern with these lights is they are almost too effective - they light a track ahead of the rider with hardly any spill to the side, which can lead to accusations of the feeling of riding along a tunnel.
Because of alla the snow in Sweden I haven't tried the Philips LED Bike Light (LBL) much, but there is som spill for sure.
The drawback with the currebt version of the LBL is its bad electronics and lack of a contact for external power.
But I will try to modify mine anyway.
 

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Discussion Starter · #17 ·
Interesting reading / viewing jellochaos. How would you go about creating the parabolic reflector substrate to deposit the silver on?

Had a good session out with the test rig a few nights ago using the stock Mag C/D reflector above. Method A, firing down into the reflector from behind the focal point, was more effective than expected bearing in mind the large 15mm dia hole at the back of the reflector. It produced a beam with throw and good cut-off, with the beam lighting all the way to the front wheel (spill from the LED). However there was quite a bit of light lost out of the hole in the back.

Method B, firing up into the reflector from forward of the focal point, put more light out of the front and threw very well again with good cut-off. The downside was the beam ended some 6-8 feet or so in front of me, with no light closer. This is of course because the only light reaching the ground is coming from the reflector, as any spill is lost upwards. Moving the LED forward brought the beam closer but at the expense of throw and beam shape.

I was surprised at the effectiveness of Method A. I've ordered an aluminium smooth Mag reflector with an 8mm hole to carry out some more experiments, and I also have an orange-peel reflector from a xenon P61 drop-in to try out when I've cut it in two. I might not be able to get in behind the focal point on this P61 reflector as it's 1" in diameter, but might work well using Method B. Shame it's O/P though - I can't find a smooth one!

Beamshots when I get my camera back and when new reflector arrives.

HakanC, is the reflector in the Philips aluminium or plastic?
 

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I was thinking of making a parabolic shaped substrate from the plastic used in CDs, then silver it. But every time I have tried to bend a clear plastic with heat, it always turns opaque or loses its transparency in some other way. I could bend it and deposit the silver on the outer side but it will tarnish.
It sounds really difficult..
But you had good results with available reflectors so I will also order some to experiment.
 
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