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  1. #1
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    Road friendly light design

    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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    p.s. As a teaser here's a kit of parts I used for some earlier trial beamshots!

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    Cateye 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

  4. #4
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    Here is an interesting site for road friendly lights
    http://www.xs4all.nl/~swhs/fiets/tes.../index_en.html

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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.

  6. #6
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    Quote Originally Posted by brad72
    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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    Quote Originally Posted by emu26

    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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    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.

    Quote Originally Posted by emu26
    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!

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    Quote Originally Posted by mattthemuppet
    gyroscopes/ accelerometers plus servo controlled mirror, a la BMW motorbikes?

    Or just flesh and bones. 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 itís not as cool as some servos

    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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    Quote Originally Posted by bravellir

    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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    Quote Originally Posted by bravellir
    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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    Quote Originally Posted by emu26
    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
    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 wonít be as bright as a single led, but on the other hand, less lumens would be thrown away where they arenít needed.

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    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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    Quote Originally Posted by mfj197
    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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    I am really interested in this thread.
    I was searching for reflectors such as those of the philips bike light has but I haven't found anything. Instead, I found these.
    http://blogsci.com/science/how-to-make-a-silver-mirror
    http://www.make-stuff.com/formulas/mirrors.html
    So.. If you can't buy it, make it.

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    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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    Quote Originally Posted by mfj197
    HakanC, is the reflector in the Philips aluminium or plastic?
    (Sorry for my late reply.)

    I think the reflector is plastic, but metalized or aluminized (is that english?)

    /HŚkan
    SWEDEN

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    Quote Originally Posted by mfj197
    Beamshots when I get my camera back and when new reflector arrives.
    So... Can we see any pictures? I am really curious to see your results.

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    Quote Originally Posted by jellochaos
    So... Can we see any pictures? I am really curious to see your results.
    The current status is I have a number of reflectors to cut in half and mount on the testbed. They are:
    • Litho123 reflector for Mag C/D - 52mm smooth aluminium
    • P60 incandescent dropin - 26mm orange peel aluminium
    • Underwater Kinetics 4*AA - 23mm smooth plastic

    It's a shame the P60 dropin isn't smooth but I haven't been able to find one that is, excepting ones for LEDs which as mentioned above are no good. I was hoping the Underwater Kinetics reflector would be aluminium but it isn't, and it might be a bit small.

    Unfortunately I don't have any pictures just yet, and won't for a couple of weeks (first child due to be born in 6 days so rather busy!). The initial tests with a plastic Mag reflector were extremely encouraging. Will post pictures when I can!

    Michael

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    Apologies for the delay to this - the baby and necessary DIY have rather taken over! Anyway, managed to get some indoor beamshots today and hopefully some outdoor ones soon when I've found a suitable location.

    Firstly the test kit:


    The beamshots here are from the two aluminium reflectors, the excellent Litho123 Mag reflector on the left and the P60 orange peel drop-in.

    Here's an animation of the Litho123 reflector, moving from having the LED behind the focal point to in front. The beam starts off below the cut-off when the LED is behind the focal point, as in the first method in the initial post (I'll call it method A).

    Both methods could work. With method A most of the light is directed under the cutoff, including the spill. Method B would have to be inverted of course, and the spill is then upwards so outside the semicircular cut-off close to the front wheel may be a problem.

    What's interesting is that the beam can be tightened up by moving the LED in the vertical plane as well. For method A, moving the LED further up and away from the reflector, and for method B moving the LED further up into the reflector has the effect of tightening up the beam as follows (method A first):


    And method B:


    Finally, here's a couple of shots with the P60 reflector. It is such a shame I can only find orange peel ones as I really need a smooth one! Method A:


    And Method B:


    Michael
    Last edited by mfj197; 05-26-2011 at 01:34 PM. Reason: rehosted animated gif

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    Latest (zany) thought - LED mounted in the traditional orientation but the reflector cut and the top half moved aft, so the bottom works using Method A and the top using Method B, as in the following picture. This might mean I can use the smaller smooth reflectors that you guys are using elsewhere, rather than the 50mm monsters I currently have!

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    only issue with that approach is that you'll still have the direct (non-reflected) light from the LED itself, which is the issue with normal reflectors. Could be solved with a hood, like others do, but I still think your original approach is neater.

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    Good stuff! Thanks for showing us the results of your experiments. I can see a very nice road beam coming at the end of this!

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    True, matthemauppet, but the only light above the horizon would (probably) be that direct light from the LED rather than any light from the reflector, whereas a standard reflector aimed horizontally has a fair amount of reflected light above the horizon. I'll get a Regina or two to cut up and see, but to be honest I think you're probably right - the original methods might be best.

    The reason I need a sizeable reflector is most of the light is being reflected from fairly close to the LED, and that's where the issue with the XM-L being far from a point source of light comes into play. It makes the beam more floody than otherwise, although I think I can get pretty decent throw with the 52mm Litho123 reflector.

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    Dragging up an old thread I know, but I am also interested in creating the ideal road beam. Your ideas have hit the nail on the head, have a look at the Roxim rs3. It uses a single emitter at the top shining onto a compound parabolic reflector to achieve an almost perfect spread of light and comply with the new German standards. I have one which I am going to see if I can get apart without destroying it. On full power it is rated at 30 lux and based on the poor battery life from the 2 AA's I reckon it pulls around 1 amp.

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    Magnum9, coincidentally I was looking at your thread and looked up the Roxim RS3 early this morning! Fitting a more powerful emitter in that could well work nicely, assuming it can dissipate the heat that something like an XM-L produces. I've seen another couple of lights which work in similar ways; the Philips LED Bike Light of course, and the Trelock LS 950. Of these the Philips is the most impressive; nominally 80 lux and I have been tempted to modify one - if only it wasn't so shockingly ugly, and expensive to buy just to take apart! Be interested to hear your experience of taking your Roxim apart if it proves possible.

    I'm very envious of your access to the CNCs! Seeing as I'm using what are effectively upgrades for a Maglite I think I'll probably need to go with half a Mag head attached underneath a heatsink for each light. Still open to ideas on that one, and I still need to assess the exact position of LED to the reflector. It seems to work best if backed out a little above the reflector, narrowing the spread of light on the road ahead.

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    In theory I could machine up a compound reflector from billet aluminum but I don't have the design skills or software to do it. Plus it would take some tedious hand polishing to make it work. Over the next few days I will check out the Roxim.

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    Quote Originally Posted by mfj197 View Post
    Of these the Philips is the most impressive; nominally 80 lux and I have been tempted to modify one - if only it wasn't so shockingly ugly, and expensive to buy just to take apart!
    I have modified my Philis LBL to use a MS900-battery
    More about that here: http://www.candlepowerforums.com/vb/...=1#post3620285

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    I had another thought on this. Rather than trying to 3d mill a compound reflector I could turn up a full parabolic reflector then just mill off one side like you have done. That way it would have no hole in the back either. Is there any modeling software that will show the expected light pattern for a given reflector?

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    I'm afraid I don't know of any modelling software, at least not free (and I can't really justify purchasing something). However turning a parabola yourself would certainly give you the advantage of being able to tune it exactly to what you want, and to have no hole in the back as you say. I'm not losing a great deal of light through that hole but it is still there - I think I'll machine some solid aluminium to fill it to make sure all the light goes out the front.

    Interesting mod to your LBL HakanC. Shame the electronics still cut out after 45 mins, but sounds like you have that covered when you use the TaskLED driver.

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    Have you looked at the technique of those aspheric-type car headlights? I have one lying around that I take apart and post some pics if you like?

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    Thanks Rekkie, I have indeed - and actually I have an HID headlamp from a Mini Cooper S sitting in the garage at home that I might dismantle. What's your headlight from?

    That method requires an ellipsoidal reflector rather than a parabolic one, and the smallest I found when researching was 2 inches (50mm) in diameter, with a distance between the focal points also of 2 inches. (There are 2 focal points with an ellipsoidal reflector as it takes the light from one point and refocusses it at another, after which it subsequently passes through an aspheric lens in front of this second focal point.) So any light based on this would be a tube, 2 inches in diameter on the inside, and probably 3 - 4 inches long, with quite a heavy aspheric lens. That's possibly getting slightly too large? Tough call as it would probably give a good beam.

    Riken's good pictures earlier in the thread show both this method (for the main headlights) and the LED-firing-down-into-half-a-parabolic-reflector method.

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    The one I have is for an Astra (Opel / Vauxhall), picked up after some guy wrecked his car up my road. Took a quick measurement, seems this one has a 70mm glass aspheric, and 130mm from the tip to tip in length and it's fairly heavy as well. But it is composed different to those that Riken posted.

    Although a HID bulb, it has a vertical profiled part blocking the bottom half of light reflected from the ellipsoidal reflector, giving that angled beam shape.

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    can't u just put a shield to cover half the opening of a fraen reflector?

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    Just tried it with a stock D-Maglite and it kind of does the same thing that the half-Mag reflector above does, only the light is substantially dimmer.

    Will take apart the car headlight and see what it does when I add the asperic...

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    Ok, so I split the too pieces of the car headlamp and shined the stock (Krypton bulb) mag through the aspheric...



    Looks promising!!

    The headlamp:




    Hope it helps...

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    Ok, so in the aim of a perfect road lamp I have cracked it as you can see from the beam shots below. I am using my triple xml with medium triple optic powered at 2800mA and an aspheric lens with cutoff. The only downsize at the moment is the size but there is definitely a perfectly clean cut off of light and no upwards glare.

    Triple xml by itself



    Triple xml with cut off and aspheric


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    Looks good brad72. The horse in your field would be slightly less startled if you shone that at him! How have you used the aspheric and cutoff with your triple? Any photos?

    Rekkie, thanks for the teardown of the light. It looks like it is an HID for low-beam only (separate light for high-beam), so has a fixed shield to effect the cutoff. The one I have looks a similar size although it's what they called a "bi-xenon" headlight, i.e. the cutoff shield moves out of the way with a solenoid to effect high beam. We of course could make do with only half the reflector and the LED firing up into this for low beam, so no lost light. Shame about the size and weight though. Are you tempted to try and make a light out of it?

    Riken, the biggest issue with using a shield over a reflector is that you are immediately losing half the light emitted by the LED. Brad72's beamshots show that quite well. It should be possible to be a bit cunning as our LEDs only emit through 180 degrees rather than the 360 degrees of a bulb. There's also the issue that a shield in front of a reflector will only cut the spill, but the circular nature of the hotspot will (normally) still exist as it is a not particularly clear image of the LED itself, and is being transmitted from the top and bottom of the reflector. That is unless you move the shield even further over the front of the lens whereupon even more light is prevented from coming out.

    Having said all that, there is probably a point where the increased weight and complexity of a mechanism to harness all that light outweighs the additional weight of just adding more LEDs and cells in the knowledge that half of the emitted light is being wasted. But from a principles point of view I'd like to put as much light on the road with my twin XM-L setup as a quad XM-L with standard optics can!

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    I'll post some shots tomorrow but all i can say is that it is the biggest and ugliest thing i have ever seen. It was more of a curisity thing that has been niggling away at me for some time having experimented with Cut up reflectors and the like for some time.

    I used an aspheric assembly from a range rover headlamp which my father donated to the cause after obliterating a bush turkey at 120km/h. By aiming the triple xml upwards towards the top of the back reflector i was abld to increase the light output quite dramatically. Not using any optics gave next to no light and a horrible beam but the triple medium optic made it look great.

    Next to make it about 20 times smaller

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    Originally Posted by mfj197
    We of course could make do with only half the reflector and the LED firing up into this for low beam, so no lost light.
    The setup would be similar to one of the images that Riken posted earlier, but isn't there smaller aspheric lenses that can be used? (Think I've seen some on DX.) and then combine it with half a reflector? Also, the finish of the reflector would probably make a difference...OP would smooth out the beam and give more uniform light I think.

    Originally Posted by mfj197
    Are you tempted to try and make a light out of it?
    Yes, but the original idea was to copy the principle and make it smaller (like mentioned above)...for my use I would only need one XM-L or similar LED. Been busy with other projects so have not had proper time to play with it yet.

    Originally Posted by mfj197
    Having said all that, there is probably a point where the increased weight and complexity of a mechanism to harness all that light outweighs the additional weight of just adding more LEDs and cells in the knowledge that half of the emitted light is being wasted.
    Good point, but if you could get it right with a simple setup it could be worth it. Are you aiming at just a low beam, or a "bi-xenon"-like setup?

    Oh I forgot to mention that when I was playing with the mag and front aspheric part, I picked up that the shield is placed at the aspheric's focal point.

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    Quote Originally Posted by Rekkie View Post
    The setup would be similar to one of the images that Riken posted earlier, but isn't there smaller aspheric lenses that can be used? (Think I've seen some on DX.) and then combine it with half a reflector? Also, the finish of the reflector would probably make a difference...OP would smooth out the beam and give more uniform light I think.
    Yes, there are many aspherics out there which could make the front of the light design smaller. The smaller the aspheric the wider the resultant beam. However there's still the issue of needing to house the reflector and have a tube long enough to hold the whole thing together.

    I'm looking at just a low beam setup, as really that's all that's needed to illuminate (the road ahead). I have been rather tempted to get a light from this website to modify, but I'd still be very concerned about the weight and size of even the smallest of these. The low beam would be effected by having an LED firing upwards into only half the rear reflector, rather than needing a cutoff shield.

    Mind you, sounds like brad72 might be leading the way on large (but effective) lights at the moment! Look forward to seeing the photos.

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    As a result of the projector headlight chat in the last few posts I've sourced a very small projector headlight, 38mm lens, 100mm length, 195g all in. I'll cut the bottom half of the reflector off and mount an LED on a heatsink, so weight will probably be slightly higher but not by much. I had been planning two identical lights but if this one is quite a size and weight I may just run one. The next question therefore is ... XM-L, SST-50 or even SST-90!?

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    38mm lens sound a lot better! and 195g wouldn't bother me. I for one would go for the XM-L...cheaper, not as power hungry so smaller battery pack needed = weight saved...also never used a SST due to its price tag.

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    I know, but with one XM-L I think I'd feel vastly inferior to you guys with your triples!

    I think you're probably right. The projector headlight is designed to use an H1 halogen bulb which is 1,550 emitter lumens, and the dipped beam version immediately loses half of that so 775-odd. I'd have 1,000 lumens of well-controlled dipped beam light with a single XM-L. I should be happy with that I guess!

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    Correct me if I'm wrong...but I think you will probable end up with around 900 lumen out the front due to lens efficiency...but still, that would be 900 well controlled lumens.

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    You'd be quite right - sorry, I was talking emitter lumens only in the comparison with the H1 halogen 55W bulb. There will be losses from both the reflector and the lens - I don't know if the losses from an aspheric are any different from a normal window lens on a flashlight? I guess it depends on quality / imperfections in the glass?

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    Looks a promising start ...







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