Reflector design - thoughts and input.

I've come to the conclusion from trying lots of lights and a lot of reading that good reflector design is very task specific and ofter overlooked. This thread was started because some reflector design issues were taking other threads off topic.

For my first musing I'll be talking about using a flashlight to walk at night, I would assume this is a common task for flashlight use.

When you walk with a light what do you do. You shine the light down the path in front of you. Lets say 50 ft or so because you want to know what is coming up. When you are walking you do want a wide spill so you can see your feet as well. If you have a narrow spill you have to angle the light so the spot is only a few feet in front of you, this is undesirable. Now as you double the distance an object is away from you you have to increase the Lux by a factor of four for it to appear the same brightness. This is why you want a beam that has a well designed transition from spot to spill (preferable logarithmic **EDIT Sorry its the inverse square law **EDIT**).

Lets take the case of a light that has a tight spot at a very high lux level then has a sharp transition to a spill beam at a much lower lux level (McR18, Fenix). When you shine this light down the path, it is pretty bright at your feet, then your eyes perceive that the ground gets dimmer and dimmer the farther away it gets until you reach the edge of the spot beam where it gets very bright again.
The goal for path walking is a light that lights up the path an equal amount as it progresses away from you. This is more important the faster you are moving, aka cycling, driving. Car lights are designed this way.

The HDS light does a good job at this, the FF3 as well. I think the U2 isn't the greatest for walking because its narrow spill angle.

So reflector design is task specific and always a bit of a compromise. The McR18 reflector in my Spy is good and an excellent overall performer, but maybe not the best for walking. This is not a knock against Don's design, he understands this. When the Joker LED's came out, Don actually liked the wider beam, but he came out with a joker specific reflector because CPFers demands tight bright spots that perform well on white walls.

Say could we define some terms while we are at it? Please corect me or add inputs.

Beam Angle: Overall angle of total beam. Not including coronas.

Corona: I think this would refer to the rings of light sometime seen in the outer perhiphery of the beam. Some people seem to use this and spill interchangably, but I really don't think its the right term. (2) Beer commonly drunk with lime while testing flashlights.

Faceting: A non-random (disco ball like) reflector surface treatment used to smooth out the beam. Often seen in household halogen lamps.

Optic: Could be any system for photon managment but it usualy refers to a piece of plastic or other transparent material molded to use refraction instead of reflection for beam management.

Spill: The area of light surrounding the spot to the edge of the beam. Not including coronas. Sometimes there is no clear transition from spot to spill.

Spot: The central bright portion of the beam.

Stochastic: Also refered to as "Stipling" or "Orange peel" surface. A random irregularity applied to the surface of a reflector to smooth out the beam.

Dave,
In terms of symantics, I have always felt that spot (significant portion of light redirected by reflector) and spill (light directly exiting with no influence from reflector) comprised the overall beam distribution from a reflector light. I too took a corona to be a ring or corona which could be an artifact from window or bezel lip reflection or what have you. Once I came to realize that many CPFe's were using the term corona to describe what I felt was the spill, I relaxed my terminology in attempt for better commnication if not clairity.

An ideal beam such as you describe for a path illuminator may not be physically posible given the constraints of lamp size relative to optic size. The McR-20 is based on the shortest focal length reasonable as defined by the physical size of the Luxeon emitter dome and image location below the dome. I have a bunch of reflectors all based on this same focal length; McR-11 (in process), McR-16, McR-18, McR-20 and the McR-27L.

Since no image or object source is infinitely small, you will have divergence with any parabolic reflector regardless of focal length but the longer the focal length, the lesser this divergence occurs. I believe this is due to relative size or volume of image VS focal length; the greater the focal length, the closer the image comes to behaving as a single point source.

If you compare the McR-27L to the McR-16, it is initially hard to believe that these two share the same focal length or parabolic curve. The spot seems larger and more defined (relative to the spill) with the McR16 VS the McR-27L. IMHO, the McR-27L is the most ideal path beam of all of my reflectors with the McR-38 in third place and the McR-45 in second place but certainly open to disagreement. I think a light for path illumination should be held parallel to the path and ideally it would provide the same level of return ilumination from the ground 5' away as it would from a distant target. I believe the McR-27L accomplishes this best because it is a relatively deep reflector and due to the orange peel as well as divergence of light from true collimation, it takes much of what is spill with the McR-16 and distributes this light with emphasis in the center but additionally on out and into the spill as well. The narrower the spill angle (deeper the reflector), the greater the amount of overall light output you are managing with the reflector. Because the reflector is not 100% efficient in transmission, you will see reductions in flux as you go to a deeper reflector but this may well be acceptable given more on target light as well as a possibly preferred blend in distribution from spot to spill. :shrug:

For a reflector like the McR-18 in the SPY005 to perform in the same manner as the McR-27L, the LED package would have to be much smaller and the image smaller in size as well. I am waiting for the Cree 7090 LED's to grow into their reported flux potential as I feel this LED coupled with the McR-19 (much shorter focal length than the McR-20 series) may provide a good viable path beam in a smaller diameter package still.

Well that's my two cents worth and then some! :nana:

And to the real experts,



So what! :duck:

Well you are what passes for an expert here

Thanks for your input. For some reason I was under the impression that a "perfect" tightly focused hotspot was harder to create than an "imperfect" beam where the hotspot was wider and less defined. Since I prefer the imperfect beam, I thought it could be easier to obtain. You seem to be describing the exact oppostie effect, but I'll have to read it a couple more times and think about it a bit before I understand.

I'm actually really amazed at how tight the hotspot is on the McR18. I always thought a stochastic reflector would blend the light more from spot to spill. Yet from a purely visual observation it appears very similar to the beam produced by the smooth Fenix, although a bit less lumpy.

Have you thought about a using a non-perfect parabola? Perhaps a slight flare or over-curve at the front end.

Little off topic but saw your username and got me to wondering. Are you a member of the NSS? If so what is your last name, my family might know you. We know a few cavers from around VA.

Dave,
If I had CNC abilities and could cut my own reflectors, there are a number of ideas I would try just for the sake of curiousity. As it is, I sweat bullets on the McR-20 while waiting for the first article to arrive. I had no certainty that any light would even come out the front end! While a reflective point on a bump in the peel may be way off alignment from the focal point of the reflector, it may be ideally suited for a photon coming from outide of the focal point as its origin. If you consider the size of a photon and then look at the surface of a smooth reflector under a microscope you may find that at the scale where it counts, the smooth reflector is anything but smooth!! At 10,000' a dry lake bed may look viable to a pilot as a landing spot but with a low fly by, the truth could be all together different. The IMS reflectors were generated with the aid of computer modeling by guys who knew what they were doing. The McR line wasn't and by someone who doesn't. :lolsign:

I may pass gas but I won't try to pass as an expert. When science is inexact, an inexact approach may have better yield. I think the physics of optics is exact but modeling to a light source that is not exact or predictable in location requires some fudge in the program. A form fit device is usless if the form it fits is not the form it is to be mated to. It seems to me that the level of precision in design should be on par with the level of precision in reality. The more forgiving and less demanding of compliance a design is, the more tolerance it will allow in actual function. I am not sure any of these comments are relevant but it feels right making them. If all else fails I do have a tried and true fallback:

an optic may not be conical in shape.

the solution to your request is horsepower.. I have reflectors in lights that do exactly like you wish... illuminate everything from your feet to 50-100' away with nearly equal brightness to your perception.. they do so by having a very 'soft' beam.. heavy stippled reflector.. so that the transition from spot to flood takes quite an angular distance.. the problem is.. that this kills the throw.. so if you want to have a lot of spot throw and a lot of flood you need a LOT OF POWER.

I have lights with 3W that have nearly 1/2 the lux output of my 3500L IRC lamp.. but it's not hard to guess which one will light up a path the way you describe.

If you have any high-power incans.. try to take an 1185 lamp in a medium or heavy stipple reflector and i think you'll see what you are looking for... your entire path illuminated as far as you care to see at the moment.. from your shoes to the tree tops and up to say 50' away.. not much of an appreciable spot.. it's a sight to see!

I have monkeyed with some options to get what you are aiming for with far lower power lights (than 35 or 125W) like described above..

If you have a tri-lux mag mod.. and put in several different reflectors.. you will achieve what you are looking for.. it is quite simply stunning to see what 3x 17IMS coupled with 1x 27IMS will do to a path!


This is my 12W light with the above reflector combination.. but a much more reasonable solution can be had with just a pair of reflectors.. say an IMS20 for throw and an IMS17 for flood side by side.. try it out with two separate lights just for testing sake..

There are also ways to diffuse the beam like frosted lens.. hit it with sand blast etc.. (vveeeeryy liggghtly). that will take a 'too well focused' light and get you more flood (but be warned frosted lenses ssuuucck for anybody observing YOU.. because now they don't have to be on-axis to get blinded by your light.

Go check out my small reflector post in HMM or in the LK14 thread (in incan).. i have some very interesting diagrams of reflectors in those two threads.

-awr

The issue with many of the optics and reflectors used in flashlights is they are based on imaging optics - think of the TIR image on a wall - it's square because the LED die is square.

Designing a more efficient reflector or optic requires consideration for the light source not being a point. The first time I saw this in application was on the first LED tail light applications.

IMO, Reflector texture is a bandaid which masks the underlying inefficiency.
I'm convinced that better optics for Lux V's could completely eliminate the donut without killing throw the way orange peel does.

Perhaps a modified truncated hyperboloid?

"Nonimaging Optics"
W.T. Welford and R. Winston
1989 Academic Press

I have a xerox of this text which I am happy to mail to anyone who is serious about designing some kick*** optics.

I think of the spot as the stream of photons managed by the curve of the focused parabolic reflector, and the spill as light that (largely) that comes directly off the LED without reflector intervention. The lux within the spot would be fairly even if the surface brightness of the emitter were fairly even.

Corona would be those photons that would be in the spot with a smooth parabolic reflector, but have moved somewhat outside that area due to reflector irregularities like orange peel, etc. Lux values in the corona slope off rapidly as you move from the spot until the spill area is reached, which is again an area of fairly even illumination.

I know that is an imperfect model and many practical matters influence beam shape as Don has pointed out, but it seems to me to be a useful way to think about it.

i agree about the bandaid but it's not about inefficency. it has more to do with imprecision of the curve or more importantly the odd and large size of the image we are trying to reflect. if you have a non-point light source a parabola quickly falls apart as an ideal imaging medium. Like Don pointed out.. often it's seat of the pants stuff that will get you where you want.

I agree on the LuxV situation and have designed a reflector to deal with that, but havn't had the time or the need to build a prototype. The solution i came up with is a brute force simple concept based on real life experiments..

Take 4 1/4 parabolas and set them apart by the distance between the lux dies in the emitter.. so that in effect you have four separate reflectors that have each of the four emitters in focus.. rather than one big reflector that has NONE of the emitters in focus. The donut hole in a LuxV is because the primary focus is on a dark spot.. GIGO..

\
here is a picture of my computer model of said reflector.


And the top-view of just the top edge.. to show how subtle it is.

My theory goes like this.. the nearest emitter die will get the most light to the near 1/4 reflector.. when looking at a luxV in a reflector it's really clear there are 4 'lobes' of brightness and NOT the circle or torrid of light we see if we look at a lux3 etc.. and.. i'm hoping that bringing each of the 4 dies into actual focus will restore that 'ring of light' we expect to see.. pull that off and the donut will go away. keep a perfectly smooth reflector.

testing this theory requires an IMS 20 and a sharp saw and a lux V of course.

improving on the theory would need 2 or 4 reflectors to have them still touch in the joints.. to replace what is lost by the saw kerf.

a very interesting thought you just brought to my attention regarding the 'non point' situation.

a movie theater projector uses about a 16" reflector and a 3000-5000W xenon arc lamp.. the reflector is a perfect ellipse (or part of one of course).. the distance between the two foci of the elliptical section is about 5'.. which means.. that that pin=point of about 2mm x 1mm of light that is roughly 1300W of actual light energy or 90,000 lumens.. is focused to a point that happens to work out to be just beyond where the film is.. so that the entire 35mm width of the film is almost perfectly illuminated edge to edge.

reverse engineering this thought.. it would be possible to use an elliptical reflector focused to a point just behind the square lux die to get the light down to a pinpoint at the other focus of the ellipse.. of course.. what to do with that is the question.. there usually ends up being an obstruction.. usually the reflector.

So.. try this one out for size.. an elliptical reflector.. with the foci a long distance apart.. with the emitter pointing into the reflector.. but de-tuned as mentioned.. so the focus is a couple mm behind the lux die.. this will put a pin-point of light at the far focus.. and by fine-tuning the mis-match of focus you can probably get a very decent beam with extremely high efficiency.

andrewwynn said:

My theory goes like this.. the nearest emitter die will get the most light to the near 1/4 reflector..

Click to expand...

Assuming you can position the tiny die *exactly* where you want it, and keep it there...

It's an interesting idea, awr.

chesterqw said:

an optic may not be conical in shape.

Click to expand...

Right you are. Here is a Fresnel type optic from the Tikka XP:


Some of the coments seem to imply it is impossible to create a reflector with a nice transition from spot to spill. This is not so, I have lights that do it already. HDS, FF3, UK eLED come to mind.

I reject andrewwynn's version of more power is better reality and substite my own that the 10 lumen primary HDS has a beam that has a nice transition from spot to spill and is good for walking. The main point of my post was to suggest that better beam is more important than more power. Granted I give up throw because I have to give up something with a fixed amount of lumens. But I am OK with that.

I think Henry says it best in his flashlight white paper:
http://www.hdssystems.com/Articles.html

"A general purpose light should provide enough light outside the main beam so your eyes can comfortable move between the beam center and the outer areas and take in a large viewing area. Better still is to provide a smooth transition zone between the two areas. The broader the transition zone, the lower the contrast and the safer you will be when using the light to navigate rough terrain. You will find that you can use less total light with a smooth broad beam. In fact you might want to carry two lights - one with a braod beam for walking and general use and another with a narrow beam for spotting distant objects."

The bold and spelling mistakes are my own
-Cave "buy both" Dave

I agree that for our purposes optic is fine to describe clear, solid collimators. Traditionally that's what we've used though it's not accurate. However, by definition, a TIR optic uses reflection. This reflection has two points where refraction comes into play. 1. as the ray leaves the plastic medium and 2. as the ray re-enters the plastic medium. The primary refraction takes place as the rays are initially bent by the lens.

From Fraen:

[font=Verdana, Arial, Helvetica, sans-serif]"1. Are Fraen's standard FHS and FLP optics "lenses" or "reflectors"?

Our optics are hybrids (reflector + lens). They are primarily total internal reflection (TIR) optics, but the center section (the hole) contains refraction optics (lens)."

I agree with corona. I have only a few lights with coronas. One is the SF A2. Side spill is not corona but corona resides in the side spill.

Stochastic? Stipple and orange peel are two different things.

Spot, I think can be broken down. A perfectly focused WA1666 has batwings, a spot, a hot spot and a super spot (think opposite of sub umbra). Those are terms I use and are unofficial.

For walking outside in the real world, especially in the woods, using the dynamics of a beam is important. I line my incan filaments up with the switch. If the trek has a wide path I let the batwings or oval portions help horizontally. If the path is narrow with flora growth on both sides, I rotate the light 45 degrees to be more useful longitudinally. If I want to see something in the distance I use the hottest part of the spot.

cavedave -

Have you seen FiveMega's two inch deep reflector? I think you would like it. The transitions are so smooth it's hard to identify a main spot. The super spot is very clear and is stronger than a mag style reflector. [/font]

Im toying with the idea of a custom reflector, already passed the CAD stage or at least I think I have :green: and the simulation stage :green: :green:

Now Im learning CAM programming to machine it in my CNC Router, it may work, it may not, I will be able to tell in a few months I guess

Here are some teasers from the ray tracing app, BTW Im using many T fluxed lux3s for the simulation

40000 rays projected


Rays hitting one of the test walls


Wall at 1 meter


Wall at 10 meter


Wall at 50 meter


Wall at 100 meter


Please keep in mind this is just a simulation, real life shoots are way ahead in time


Pablo

Most of the models I have seen break down because they fall into a few traps
- Error 1 - For the single die emitters, they attempt to use the die location as the origin of light, when in fact Lumileds has a lens inside the dome which dramatically alters its output.
- Error 2 - For single die emitters, they then attempt to treat the light as though it is coming from an artificial surface which surrounds the dome. This works as long as the "artificial surface" to "reflector" distance is large enough. If that is the case, you don't need to model very much.
- Error 3 - For multi die applications, they attempt to use the same methods as 1 and 2.

A lot of the donut and focus problems of the Lux V in fact come from very - very slight differences in the distance between the die package to package. For a large reflector, this is a non issue, as are many tolerances. As you start to shrink the optical package, tolerances in the optics build increase VERY non - linearly.

The FRAEN guys are in general correct, TIR does in fact use a combination of reflective and refractive elements.

I have gone a step further and use reflective, refractive, and diffractive elements in my design. The main challenge it faces is cost, not technology. Like most things in life, they can be purchased.

As far as achieving the ideal "walking beam" perhaps the answer lies in a technique which increases the lumen output when you raise the angle of the flashlight to look at a more distant object.

cave dave said:

Corona: I think this would refer to the rings of light sometime seen in the outer perhiphery of the beam. Some people seem to use this and spill interchangably, but I really don't think its the right term. (2) Beer commonly drunk with lime while testing flashlights.

Click to expand...

And "spill" is what you try not to do with said beer...

cave dave said:

...Some of the coments seem to imply it is impossible to create a reflector with a nice transition from spot to spill. This is not so, I have lights that do it already. HDS, FF3, UK eLED come to mind...

Click to expand...

I agree and I would add to that list the Amilite Neo T3, though the HDS remains my first choice and comes closest to the ideal of combining broad near field coverage with a surprisingly long-throwing spot.

There was discussion about this in reference to the SPY005's Mc18 reflector whose excellent spot beam was felt by me and Cave Dave to be a bit narrow for comfortable walking or hiking. I also agree with him that a broader beam requires fewer lumens to adequately illuminate an area (i.e. walking on an unlighted rural road). I have recently proven this to my satisfaction comparing the HDS Ultimate60, FF3, Amilite, Peak Carribean, Fenix P1 and L1P and SPY005.

The FF3 proves that a tiny (smooth) reflector can produce a beautiful bright flood. Such a reflector with a bit less flood and more spot would IMO be a viable alternative to the SPY's Mc18 for those who do not need a narrow penetrating spot. I would love to have such a reflector in one of my Spy005's.This is no knock on the Mc18 which is a superb reflector for those who don't need broader illumination for walking.

Brightnorm

whoa what a busy thread today.

green LED.. it would not be hard to align the refl. to the die.. the DIE i'm positive has a precise relationship to the emitter leads.. you would just have to permanently fix the reflector (glue the feet etc) so it stays lined up.

I think the McR series of reflectors to a grand job of transitioning from flood to spot..

My comment of 'more power'.. was in reference to this comment:

cave_dave said:

The goal for path walking is a light that lights up the path an equal amount as it progresses away from you.

Click to expand...

I was saying.. that to pull of THAT particular feat.. you need a TON of power.. been there done that.. but not saying it's not impossible to achieve something very worthy with reasonable power.. Somebody earlier suggested using an imperfect curve and that is what is needed.. if you start with a parabola focused just below the lux (so that the whole of the lux die is filling the reflector. but is slightly out of focus).. but bend the outer rim of the reflector curve outward slightly (think water lily).. it would turn some of what would be spot into flood.. tweaking this curve should get you the mix you desire.

I am in agreement about beam is more important.. i was only pointing out the enigma of your quest.

I am 'mister flood'.. i love the flood beam.. heck the other day when we were trying to spot a dog at 500' in an open area with a woods on the other side.. the beamiest light in the world was absolutely useless (Maxabeam).. even a Mag100 was doing a better job of being helpful.. and of course the LarrkK14 just lit up the whole place like the sun just came up..

I'm a very big proponent of vision-filling light.. most of my high-power lights have textured reflectors so that i don't focus on the artifacts in the beam and i get that smoooth transition from flood to spot.

PEU.. nice stuff with the upcoming reflector.. can you let us in on the size of the reflector?

Harry gave me an interesting idea.. how a bout a shaped, non radially-symmetric reflector.. set up. such that the flood is more pronounced near-field..

In-fact that reminds me.. i wanted a reflector with max through but max of 12mm width.. the thing was.. i could have much more 'depth' that 12mm.. so what did i do.. i took an IMS 17 reflector and cut off about 1/6th on each side.. the flood that spilled out the side made for an absolutely fantastic 'walkin around' beam.. it was a bit funny to look at on the wall.. with three distinct lobes.. but out in actual use.. it filled the field of view and still had a very nice spot.. you should really try it.. it might be exactly what you are looking for.. if you cut off of just the bottom edge.. you will not see a change in the circular spot.. you will see a drastic increase in the flood brightness on the side where you cut off the outer edge of the reflector.

Have you tried to just de-focus your reflector a bit.. shim it out etc..

when trying to smooth out the beam on my lionheart.. i discovered.. that i could put some rubber bands below the feet of the reflector.. and actually tune the focus by twisting the bezel.. much to the shagrin of maglite who would rather not have me be doing that :-D

-awr

I haven't had a chance to look into this further but the McR-19 reflector coupled with a Lux III and placed up against the LED gives a flood beam that is pretty concentrated (Narrow spill angle) With the two components in contact, the image is way in front of the focal point of the reflector but there is no donut. I believe this is because the focal length is so short relative to the image size. I did build one light with the die and focal point alligned but this meant that the LED was backed significantly out of the reflector and there is loss of lumens to be sure. You do however get collimation to a much greater extent and can illuminate targets at greater distances. There may be some middle ground which might provide a more even gradient of intensity drop as you move from center to perimiter of the overall beam. :shrug: If the reflector were mounted in such a way to allow for variation of image to focal point dimensions (adjustable beam :duck: ) .....

Another viable means of fine tuning the beam is with the POC LSD film. The SF beam shapers are wonderful devices but too powerful in their divergence of beam for some applications. They are 20 degree as I recall. POS has other films that go down in diffussion angle to .5 degree I believe. Perhaps a 5 degree film would be enough fuzziness for some of these applications. :shrug: