What makes for good throw?

As usual, I'm sitting around try to finish my homework but have flashlights going through my head. I was thinking about throw and how some lights have a lot better throw than others. I realize that it's going to be a number of different factors, but if I were to take two lights that are exactly the same (in output and bulb type, etc.), what would need to be done to get one light to outthrow the other? I'm guessing this all lies in the reflector, but what factor or factors has the most effect? Is it the size, finish, or the Shape of the reflector? Does one of these affect throw more than the others?

By far, the light in my collection with the best throw is my Space Needle. Taking a look at the reflector, I see a large (compared to my other lights) parabolic, mirror-finished reflector. Is bigger better in this case? And does the mirrored reflector make for better throw? Just trying to get a better feel for things.

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ZENGHOST said:

What makes for good throw?


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Mass and aerodynamics
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Doug S,

LOL /ubbthreads/images/graemlins/icon15.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/grin.gif

What I am waiting for is for someone to rig up a glass lens like is found in the Docter Aspherilux Midi 125 light and put on an E1/E1e or E2/E2e with low lumen bulb! /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/smile.gif

Neat article on the Midi at the torch review site:

http://torchreviews.net

Zenghost,

Ceterus Paribus, the larger the reflector, the closer the light source becomes to a single point of light; relatively speaking. A perfect parabola and a single point of light will give you a parallel beam of the diameter of the parabola. At some point in diameter size I would expect that increasing the diameter more would not increase the effective beam. I have no idea if that would be a 2' diameter reflector or a 3' diameter. The key is getting the light to go out parallel with no divergence. Oh yeah, a laser kind of does that. /ubbthreads/images/graemlins/grin.gif

Doug S.,

Perhaps you can come up with a more meaningful word that expresses what we *all* understand throw to mean in this context. Would non-divergent be appropriate? A beam with good ND (non divergence)?

- Don

I will stick out my neck and say this: Objective throw is directly proportional to the aquare root of beam intensity (measured in Cd)in an atmosphere of 100% transmittence. That is the easy part. The difficult part is how to get high intensity. With a uniform source luminance, the higher the luminance the higher the beam intensity with the same reflector. With the same source luminance, the larger the area of the exit opening of the mirror, the higher the intensity of the beam. All these assuming the shape of the reflector is perfect (thus a smmth surface) and that the source is as near a point source as is possible AND that the material choosen reflects all of the light. None of which is true in real life in a flashlight. In general however, assuming a good quality reflector, the higher luminance the source and the larger the area of the exit opening of the reflector, the longer the "reach" or "range".
The is objective, so it is easy to measure, right? Wrong! Measurement must be made at a long enough distance so the area of the spot is much larger than the diameter of the reflector (ie, for the inverse square law to apply). That usually mean a distance of at least 20m (66 ft?). I am not sure, but I think the IESNA recomends 50m. This also assumes the focus has been adjusted properlyto produce a beam of minimal divergence. Note that it is possible to get a converging beam by focusing the light at a close distance. This gives high illuminance when measured at the smallest spot. If the value is used to compute beam intensity, it will give a falsely inflated value. And we have not even considered the subjective aspect of it all /ubbthreads/images/graemlins/eek.gif !!

Doug-->

NewsFlash--couldn't find that article, do you have a more direct link?

McGiz--That was almost english to me /ubbthreads/images/graemlins/tongue.gif. Nah, actually it did make some sense to me and kind of follows what I had been thinking. Will there be a point where increasing the size will have a negative effect on throw, or will it just cease to have a positive effect? And does that optimal size depend on output/power level, or is it constant?

phyhsuts--a little bit over my head with the explanation but I think that I got a little of that (had to read it a couple of times, though /ubbthreads/images/graemlins/tongue.gif).

So the exit opening has much to do with it, but how about the length of the reflector? Will a longer reflector minimize divergence? And does the shape of it matter? I notice that Otokoyama's Mag reflector's are more cone-shaped than parabolic shaped--does that affect anything? And will a mirror finish outthrow the same reflector with a stippled/orange peel finish?

Thanks for putting up with me, guys, I'm learning a lot more than I bargained for, but I think I'm also coming up with a lot more questions as well.

ZENGHOST,

http://torchreviews.net/docter.htm

The filament also has a big effect, if you look at the Mag chargers new bulb it has a shorter filament and puts out a much narrower beam. The Lumens and runtime of the new lamp are the same however there is an increase in CP. How and why this is I have no idea. /ubbthreads/images/graemlins/smile.gif

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Thanks for putting up with me, guys, I'm learning a lot more than I bargained for,

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Zenghost, thanks for asking the same questions I've had.

The answers are concise and very informative, thanks everybody.

BC

Zenghost,

As the reflector gets deeper (same parabola) more and more light is caught by the reflector and added to the collimated beam with less light going directly out as spill. The beam becomes more intense. A perfect parallel beam is a result of a perfectly smooth parabolic reflective surface coupled with all of the light emanating from a single point (the focal point). As the surface of the reflector deviates from the parabolic curve or the source of light moves away from the focal point, the beam becomes less collimated and more divergent.

Although a 5W LED may put out 4 times as much light as a 1W LED, because the light from the 1W is coming from a smaller source of origin, the 1W will typically out throw (still waiting on Doug S.'s term)the 5W in the same reflector. I have high hopes for the new 3W Luxeons since they have a die the size of the 1W. As the flux increases in the 1 and 3 W, we will see more intense ND (my term /ubbthreads/images/graemlins/grin.gif ) beams with greater effective range.

In other words, regardless of reflector or optic used, the more one can get the photons to travel on a parallel course, the more intense (higher lux)and greater the effective range of the beam.

For the most part, we modders have been working with reflectors that have been designed for incandescent light sources. A lambertian Luxeon is a different animal than an incandescent element. The LED has a beam angle of roughly 180 degrees wheras the incan is 360 degrees. Because of the incan's beam angle, reflectors optimized for incans have a focal point up within the reflector. The reflector is designed to re direct light which is angled backwards from the source. This whole "rearward section" of the reflector is not used by the LED. To date, the best examples of Luxeon HD specific reflector design I have seen are the SF KL4,5 and 6. When one considers the relative depth and exit diameter of say a KL6 reflector compared to a KT turbo, you can see the difference in requirements of an incan compared to a lambertian LED.

We are also starting to see some ND beams from optic elements specifically designed for the LED's as well as reflectors designed specifically for LED's which would be totally unsuited for incan; the new Pelican light is a case in point, in addition to the SF KL's.

- Don

I believe if you look at the cut away view of the Docter Aspherilux, you'll find that the light first is captured and directed by a parabolic reflector, then passes through a narrow aperture (which cuts off the outer edge of the beam from the reflector), then through a lens. So there are actually 3 different things that impact quality of the beam - reflector, aperture, and lens.

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McGizmo said:
Doug S.,

Perhaps you can come up with a more meaningful word that expresses what we *all* understand throw to mean in this context. Would non-divergent be appropriate? A beam with good ND (non divergence)?

- Don

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Nah, I really don't have any suggestions. I was just letting my inner smartass come out for a little fresh air. /ubbthreads/images/graemlins/tongue.gif

How about "beam coherence" /ubbthreads/images/graemlins/grin.gif

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McGizmo said:
...Although a 5W LED may put out 4 times as much light as a 1W LED, because the light from the 1W is coming from a smaller source of origin, the 1W will typically out throw (still waiting on Doug S.'s term)the 5W in the same reflector. I have high hopes for the new 3W Luxeons since they have a die the size of the 1W. As the flux increases in the 1 and 3 W, we will see more intense ND (my term /ubbthreads/images/graemlins/grin.gif ) beams with greater effective range.

In other words, regardless of reflector or optic used, the more one can get the photons to travel on a parallel course, the more intense (higher lux)and greater the effective range of the beam....

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Aha, I am beginning to understand some of this. Thanks for explaining it, Don.

"the more intense (higher lux)and greater the effective range of the beam".....now I was hesitant to use that term, "effective range" but it communicates precisely to me.

I can go with "ND", but I think I prefer "BC". /ubbthreads/images/graemlins/grin.gif

BC

BC does work but it does have other conotations. I do like what it stands for; beam coherence. How about a tight beam map or tight BM? /ubbthreads/images/graemlins/tongue.gif

I've been wonderingly lately about the relative benefits of going deeper or wider for a reflector (for a given photon source). I have two excellent examples in my arsenal - both with 5W emitters in them: One is a deep, narrow reflector, made for the emitter. The other is a wide and shallow reflector that is made for an incandescent bulb. They both throw REALLY well, but they have some almost intangeable beam differences that interest the heck out of me. The more noticeable difference is the cut-off of the side-spill. The deep reflector cuts it off sharply, while the wide reflector tapers it off gently before the cut... and the spill is much wider.

Interesting stuff.

In Doug's defence, I originally dropped by here to post the same wise-*** comment after reading the subject line. What makes for a good throw is a crappy light that you hate, and a strong arm. /ubbthreads/images/graemlins/smile.gif

One thing I'm pretty confident in saying: The sun is setting on the days of incandescent dominance in the "small throwing light" catagory. I have seen the light, and it is good.

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McGizmo said:
How about a tight beam map or tight BM? /ubbthreads/images/graemlins/tongue.gif

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/ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

You're bad, so bad.

Yes, we don't want to get it confused with Ballistic Coefficient, eh?

BC

you could have a tight beam map or a sloppy beam journey

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Darell said:
...I have two excellent examples in my arsenal - both with 5W emitters in them: One is a deep, narrow reflector, made for the emitter. The other is a wide and shallow reflector that is made for an incandescent bulb. They both throw REALLY well, but they have some almost intangeable beam differences that interest the heck out of me. The more noticeable difference is the cut-off of the side-spill. The deep reflector cuts it off sharply, while the wide reflector tapers it off gently before the cut... and the spill is much wider..

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I think the nature of the spill light has a lot to do with the depth of the reflector and the diameter due to the amount of direct light emission out the front. While Lambertian LEDs and incan filaments have vastly different radiation patterns, they both still emit out the front. A shallow but wide reflector allows a relatively large cone angle of direct, forward emission. This forms one component of the spill light. The other component of the spill light is the non-collimated light reflected off of the sides of the reflector. Understanding this, it's not difficult to imagine how this might result in the spill characteristics you're seeing. The much wider spill of the shallow reflector is also a consequence of the shallower dish angle at any given point, resulting in a broader angle/cone of non-collimated light.

As for the throw of a central hotspot, that has a lot to do, I imagine, with the collection efficiency of the reflector design irrespective of the general nature of the shape.

There is no way to get around the fact that light is "lost' to spill. The only way to direct ALL of the emitted light is to use a two reflector system. Mount the source inside the first smaller reflector (facing away from the illumination target) and then direct all the light, reflected and direct, to the second reflector. Even so, you'd likely need some collimating optics (like an achromat).

Wilkey

This thread is the most informative on this subject that I've seen. It answers a lot of my questions.

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Brightnorm