# Optic theory



## AilSnail

Newbie's ~2.5"dia ~1.25"fl aspheric lens with AR coating measured 37k lux with a cree xre at 3.some watts, IIRC. Way back I remember some mag luxeonIII measuring 10-12k lux. Point is, we have a lot of data points on this.
What I am missing in these boards, is guidance towards a theoretical and numerical approach to this as well. So that's what I am fishing for here. I have the feeling that ballpark numbers could be found without expensive and complicated raytracing.

To start with a simple question, if I were to scale an aspheric to half the dimensions, would I get 1/4 as many lux? I'm thinking that degrees in=degrees out; If I am sitting on the flat surface of the lens, the LED is covering x degrees of my view; and that is the resulting beam angle as well. If I and the lens gets two times closer to the LED, then the beam angle is doubled - resulting in the light being spread over an area four times as large.

There are lots of factors which may or may not be relevant to a napkin-class calculation - I would very much welcome the discussion of these.


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## AilSnail

....


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## AilSnail

*edited out some wrong stuff.*


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## AilSnail

...


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## AilSnail

Let me try again. Here is a chart showing how many percent of the total 
emitted lumens of an xr-e which falls within any angle. 





It shows that newbie's lens catches about the same as the hd45 and other
1:1(L/Ø) reflectors, about 70%.

It is made with the following method: The beam is divided into rings, and 
each ring's area on a sphere is calculated, and multiplied by the intensity as shown in the xre datasheet:




For instance, between 20 and 40 degrees included (10-20 deg half angle),
is a ring that projects upon 0,0225576 parts of a sphere. The average
intensity for that part of the beam is then ogled from the datasheet graph -
I'd say about 90 percent. 0,0225576 is multiplied with 90, to 
find how much of the total output of the led falls within this ring. Then the rings' light amount are converted to percent of the total light amount and added from 0-180deg and tossed into the chart. apparently in an inexplicable way. Hope it works.

*keep in mind the difference between half angle and included angle: 1:2*


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## AilSnail

Here is an image that shows what I think happens with the cree and a true parabolic ~45x45mm reflector. The apparent die image moves around a bit.










*the angles on the side should have a "-" in front of them.*


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## Ra

Hi AilSnail,

If you use a f/1 aspheric optical lens with lets say 50mm diameter, the f/1 determines the angle of light that is collected from the led.. So the f/1 determines the amount of lumens you collect.

Now if you would use a f/1 lens with 25mm diameter, the amount of lumens you collect stays the same, because it grabbes the same angle of light.

BUT: (And this is a fact! If you measure the lux output at a distance of lets say 10 metres, with the 50mm lens, you'll get a value 4 times higher than with the 25mm lens! (If both are properly collimated..)

You are right: with the smaller lens closer to the led the emitting surface seems 4 times bigger to that lens: Conclusion is: with the laws of light the 25mm lens 'sees' a 4 times bigger surface, so it illuminates a 4 times bigger surface at 10 metres distance than the 50mm lens does!! 

So with the 25mm lens the surface brightness in the beam at 10 metres is 1/4 of the surface brightness of the beam comming from the 50mm lens..

That is why the lens- or reflector-diameter determines the throw of a torch. (together with the surface brightness of the source)

Fact is that the Cree and Luxeon emitters are front-emitters, so don't work very well with conventional reflectors, indeed if you use conventional reflectors you'll need them very deep !!

The acrylic optics, especially designed for these emitters do a much better job: They grab the light where it is most emitted: directly at the front. They are also much more efficient because they use the 100% internal reflection law of light ! A conventional reflector reflects about 84% of the light at the most!


Any questions,, please ask..


Regards,

Ra.


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## Gryloc

Hey, nice graphs! I haven’t seen people here use those graphs of ray tracing. I agree that it is very complex.

It is too bad that nobody has replied yet. I have a post in this "general lighting discussion" area and only people who happened to wander on would give any help. Sometimes you have to search around to some of the "old" and experienced members that know their stuff and invite them over. It sucks that you have to post important lighting questions here only because they are not directly flashlight related. I was thrown in here because I was trying to discuss my LED headlight project. Oh well.

Now you asked some questions, and I am probably not qualified to answer them, but I do have some understanding of optics.


AilSnail said:


> … if I were to scale an aspheric to half the dimensions, would I get 1/4 as many lux?


 Is this when the lens stays the same distance away from the light source? Wouldn’t you get the same lux if you move the aspheric lens (scaled to half the size) to half of that distance? That may be because it is at the correct focal point of the lens. If this is true, I see what you mean that the beam angle would appear to be bigger. That would happen because to scale (with this smaller and closer lens), the LED die size would appear to the lens as being “bigger”. Then you said:


AilSnail said:


> If I and the lens gets two times closer to the LED, then the beam angle is doubled…


 Is the lens the same size as the original you were talking about in this statement (not the half size)? If so, then the beam angle coming out should be bigger (I don’t really know if it would be a pretty and exact double size). This should be because the lens is moved closer past the focal point, right? If the lens was half of the size and half of the distance, then the beam angle coming out would be only slightly larger, right? 

I hope that you know what I mean when I talked about scaling down the lenses and distances, as well as the apparent “size” of the LED die compared to the lens at this scaled down size.

Now I see that you changed your focus from the aspheric lens to a parabolic reflector. Do you have a question about this, or are you just showing what you had found? It is interesting using ray tracing. I tried doing this by hand to find the intensity of my LED headlights at different angles, trying to pretend that I do not have a cluster of 18 lights, but instead, one continuous 9 degree optic and light source. I wanted to find the beam angle of the projected light, and then consider how bright the light would be projected on the ground with the light tilted down at 1.5 degrees. It is tough and I will just rely on testing the finished product.

Anyway, what do you need to know now? Are you still trying to achieve that awesome 37K lux? That will be tough. That is like a 230 cd/lm on-axis efficiency with the optic (with the XR-E at 160lm). I mean the standard Fraen FHS optic has a 21 cd/lm on-axis efficiency, as well as the typical 27mm IMS reflectors. The optic that Cree makes has a supposed 46cd/lm on-axis efficiency (according to the specs sheet). These are all tiny optics, so you might have to stick with a larger reflector or lens. I don’t know. Did you need to achieve this 37Klux with a smaller optic or something, or are you trying to enhance the lux with the same size 2.5” by 1.25” optic?

Also, with this claimed 37K lux, was this measured at 1 meter, or even closer? You can blow that number out of the water with using those concentrator optics made by Polymer Optics, but this measurement is at 14.5mm. You can get up to 5 million lux at this distance, all in a 6mm diameter circle! This is with the LED at 160lm. This would be useless as a flashlight because the 14.5mm is the focal point, and the beam spreads out further from that, BUT, what if you could incorporate a second lens to turn this intensely concentrated light to a parallel beam? This would take some experimentation with different optics, but it is doable. I thought about getting a concentrator optic from an online store (used in projectors) to take this spot and project it forward at a narrow angle, but never did so. It even had the perfect focal point (of light coming in). A aspheric lens would do the same (they are similarly shaped), all you would have to do is turn it so the convex end would be facing the concentrator optic. Then just focus it in. 

I remember another way to project the light forward at huge distances, but I don’t think that the lux rating is that extreme. I managed to clamp in my old V-binned LuxV flashlight with 27mm IMS reflector into our 6in diameter reflector telescope where the eyepiece would have went. The thing probably was not efficient, but I could project a beam that is 8-12 inches across at huge distances (+100yds). The beam isn’t smooth at all, but it was cool because it felt like you were holding a light cannon.

Oh, I just remembered that I seen somewhere in CPF where someone used these XR-E’s in their D-sized Maglites with stock reflectors. This person made a mistake (I think) and they took off the dome lens from the XR-E. There was some silicone inside, but the wires were intact. They turned their XR-E with the odd 70 degree half angle intensity into a Lambertian beam pattern LED. The light was better focused with the stock Maglite reflector and more lux was produced! The beam was far more usable. If you can do this, then it would be just as easy to focus the light of the XR-E as the standard Lambertian Luxeon LED. As long as the reflector or optic doesn’t press against the delicate die and die wires (like an optic or reflector with a holder or legs), then you would be good! I will try to find that thread where this guy modified his XR-E and post a link.

What do you think? Sorry if my posts are too long. I cant help it. I hope you get stuff figured out. I think that what you are doing is just as important to the LED and flashlight world as what some do with optimizing batteries and driver circuits. Please keep us updated with graphs and pictures of your findings…


-Tony


EDIT:
Ha! I just realized that this was posted 5 minutes after the last post by Ra. It took me like 15 minutes to type this thing, so I missed that. Ra was right on the dot. Nice. Some of the things that I said was similar to what Ra said, but he said it in a shorter and more clearer way. If it sounds like what I said was wrong, well, I meant the right thing, but I just didn't say it right. Does that make sense? Lol...


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## AilSnail

Thanks! Nice to have some theories confirmed and seen from slightly different angles.

It is not real raytrace, but a rather long rhino3d session. The apparent die placement in the drawing is only what it looks like in the real world, and the base of the package is placed at the fp of the parabola.

I think it was 3rd shift who beheaded his cree and put it in a light.
Newbie's lens was 37k at 1m. Ra, I like how you are always talking about lux at 10m and more! I suspect that those readings can give a different picture than the 1m readings - which I believe can be skewed a lot from both the effect of aperture diameter and from crossover points in the beam.

I do have a question: I should like to be able to have excel (or openoffice) return an y value from the first graph when i feed it an x value. So that if I put 70degrees into one cell, another cell will show 50%. I think it would be called a look-up table.

Tony, I like it here in the slow moving backwaters.


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## Gryloc

Thanks. Well, I found another. Two have done this and took pictures so far (that I have seen), but several others claimed that they have done it. I guess that this mod makes the tint shift to a warmer color, but in a good way (as some has said). I guess that the lens can be removed easily, but the metal ring is more difficult. You have to use a cutting disk (like a dremel) to cut a small notch in the ring for grip, then set a sharp flathead screwdriver into the notch and bend and twist to pry it off. According to others findings, the hemispherical lens is made of a solid "glass"-like material (it isnt hollow). Between the solid lens and the die (in the region surrounded by the metal ring), it is full of a soft silicone material. So you can safely remove the lens (responsible for the 70 degree angle), and get a more lambertian beam. Make sure you cut or score the silicone on the inside edge of the metal ring before you pry it of. They say that there is a chance that if you dont, all the silicone may go with it, messing up the bond wires possibly.

For my next project, I might take the lens off of four of these in my Quad 2D Maglite upgrade. This way, I can use the existing IMS20XA reflectors that sat atop the LuxeonIII's. I may have to modify them a little to focus them, but that wont be difficult. I thought about using some clear silicone glue to attach old lambertian domes from some dead K2's I had to protect the dies even further, as well as make the beam pattern nicer. If I scrape a little silicone out, the surface will then be very rough, throwing light in random ways. If I use a dome over top filled with silicone glue, then those rough spots would be smoothed out (as long as I dont trap any air bubbles). This will be weird for the XR-E because the original dome was slid and glass-like, while the K2 dome is softer and filled with a little silicone. 

Anyway, sorry. Here are those links:
This was the first one I seen by 3rd-shift:
https://www.candlepowerforums.com/threads/143195
If you look at the first post in this thread, he made a link to the previous thread where there are better explanations.

Then I stumbled upon this one by Download. He shows it a little ways down:
https://www.candlepowerforums.com/threads/144141

AilSnail, I wish I can help you with the Exel spreadsheet. I learned how to add in formulas, and I have used it to measure out beam angles of my project before, but it is really time consuming. I tried today for a simple task, but it just didnt like me and I had to enter data in manually. I have no clue how to set up "programs" where you enter a number and it gives you a response automatically (like a calculator). I have seen it done with an elaborite database program made in Exel, but I am clueless how it was made.

That first graph of yours is confusing me. I am having a hard time gripping what you are trying to achieve with that one. It seems tough to read it and put it to use. Maybe if it turn it upside-down. LOL... 

-Tony


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## Ra

Yep, you are right Tony...

But perhaps I can enlighten you a bit: In that graph you can see how much of the lotal lumens-output you grab with a sertain lens: If you take a F/1 lens: It has a focal-angle of about 53 degrees, you can see in the graph that it will collect a little over 30% of the total lumens generated..

If you take a F/0.5 lens you would grab a 90 degree angle: 70% of the lumens output according to the graph..

Hope this clears things up for you..

Regards,

Ra.


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## AilSnail

Tony - Yes! It is "right" for lenses only. For reflectors you have to look at it the other way! Does it make sense now?
In the second graph, you can see that the beam has 50% intensity at 80 degrees. I believe this is what is usually referred to as "beam angle"? Maybe not.
In the first graph, you can see that half of the light falls within a 70 degree cone.
edit: you beat me to it Ra. thanks.


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## AilSnail

Here is the same data presented differently; It shows how much of the light of the XR-E that will hit a lens of a given F/#. The F/# is the same as focal length divided by diameter.


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## AilSnail

*Some wrong stuff deleted *


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## AilSnail

I think this drawing from wikipedia would be nice in this thread:


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## Doug S

Keep up the good work guys! This is one of the best discussions I read here on CPF in awhile.


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## McGizmo

> ......They are also much more efficient because they use the 100% internal reflection law of light ! A conventional reflector reflects about 84% of the light at the most!



I am not familiar with the 100% internal reflection law of light? The acrylic lenses I have seen which for the most part are a combination of TIR and refractive lens element certainly are not 100% efficient in their TIR aspect as I see much light leaving from the optic when viewed from the side? I understand that SureFire uses a very expensive grade of optical plastic and I believe they do see transmision efficiencies greater than those of an external reflective surface.

In terms of total efficiency, in the case of a reflector, we get at best your 84% transmision of that light actually encountering the reflector but we get 100% of the light which leaves the optic unaltered in direction. In the acrylic optic, you have all of the light traveling through the acrylic and its absorption loss will be levied on 100% of the source's output. Additionally, you will loose some light out the side due to the T in TIR not being Total but some fraction there of. Yes?

I guess the only point I am trying to make here is that there will be losses regardless of the type of optic used. If the primary goal is minimal loss in flux but with a secondary optic required, then one can identify the type of optic which results in minimal loss. Typically one is more concerned with more specific photon management and say a tight collimation of light. In such a case, the delivery of light on target is of primary concern and the nature of loss of light is not as important as the loss itself. :shrug:


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## AilSnail




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## AilSnail

This is at approx 1m.


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## Ra

Hi McGizmo, welcome to this dicussion...

I said that the acrylic optics use the 100% internal reflection law of light. I didn't say that the acrylic optics have 100% efficiency !!

All optics have losses, or else you would not see any light comming from the side!

Earlier in this discussion we agreed on the fact that the Cree emitters put out most of their lumens within a 30 degees or so at the front! 

Conventional reflectors are designed to work best with light-sources that emit their lumens sideways (Halogen with axial fiament, automotive HID, short arc.) So not with light-sources that emit at the front !

The acrylic optics use a combination of internal refraction and internal reflection, that means that these optics grab almost the entire lumens output of the emitter: Even the center-hole is covered by a collimating lens !

If they are kept very clean and undamaged, they have much higher total efficiencies compared to conventional reflectors with the same diameter (ofcource only if they are used with emitters like Cree and Luxeon)

AND NOW FOR SOMETHING COMPLETELY DIFFERENT : THROW :

And this will be the hard part of this post...!

Let me try it this way: Lets assume you are an object 100 yards away, that wants to be illuminated by a torch. Which are the things that determine the amount of light you actually receive 100 yards away ?? Or, in other words, what determines the apparent brightness of a torch, seen from a distance??

Well, two major things: Surface brightness of the source, and the dimensions of the source ! NOTHING ELSE ! (well,, atmospheric conditions, ofcource,, but lets say they are perfect...)

A reflector not only reflects lumens, it also reflects the sources surface brightness. FACT: The apparent surface brightness of the reflector cannot ever be higher than the surface brightness of the source! It always is lower due to reflection losses in the reflector.

Now its time for a picture:






What does it show? Two operating torches, directly photographed in the hottest part of the beam (through a type 13 welding-filter)
A 35watt halogen torch at the left, a 10watt HID torch at the right.
You see the reflectors, lit by the emitting surfaces (filament and arc)

These two torches have the same throw !! The low surface brightness of the halogen is compensated by the bigger reflector!

FACT: A torch has max throw when the entire reflector is lit by the source, seen from a distance.

You are propably not going to beleve what I'm going to tell you now: THROW IS ABSOLUTELY NOT AFFECTED BY THE FOCAL LENGTH OF THE REFLECTOR OR LENS !! ONLY LUMENS OUTPUT IS !!

From a distance the object 'sees' only a two-dimensional surface, no matter how deep or how shallow the reflector.

If you have a deep reflector, you collect more lumens from the source, that results in a wider beam (more sidespill) But you'll have the same throw with a shallow reflector, but because you send less lumens towards the object, the beam will be tighter (more laserlike if visible)

So, bottom line: With a lens diameter of 50mm and a focal length of 1 metre you'll have exactly the same throw as with a 50mm lens with a focal length of 30mm !! Only the beam of the first will be useless because of the pathetic amount of lumens its made of..

I hope this isn't too long for you.. any questions, please ask..

Regards,

Ra.


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## AilSnail

Doug, I like it too - Ra's last post has me confused though.

The green filtered picture illustrates how lux at 1m gets skewed in favor of small reflectors.

Ra, I'm not sure I am following you. You seem to be opposing your earlier post. A short focal length will not compete with a long focal length lens when it comes to illuminate something far away, especially if f/# is kept constant.

I'm going to think a bit more on what you are saying.


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## AilSnail

This one illustrates a long and a short fl, with the same diameter.
It shows that the light is spread over a larger area with the shorter fl, like we concluded earlier. It also illustrates that in a perfect lens, the only light beams which are going straight ahead, are the ones coming from the direction of the infinately small focal point. 

Now, I happen to have a 21.5mm aperture x 6.9mm bfl aspheric, and another lens with a focal like 50mm or so, which I masked to to get the apertures the same.
The latter is much better at lighting up distant targets.

So if I understand correctly what you are saying, Ra, either your theory is flawed, or my equipment, method or eyes skews my observation in favor of the longer fl.


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## Ra

That is what I meant with "This will be the hard part of this post !"

On these forums there is a lot of confusion and mis understanding about what determines the throw of a light !

But there is hope: Take a good look at the last picture AilSnail posted:

Now concentrate only on the green beams: That beam, comming out of the lens, towards the object is exactly the same with both lenses !!

That means that the center of each beam has exactly the same amount of light (lux at 1m), This also means: THE THROW OF THE CENTER BEAM IS THE SAME WITH BOTH LENSES !! And that is that I've been trying to tell you..

For the entire beam, I hope the earlier posts were clear enough about that: If the lens "sees" a larger surface, it projects a larger surface, but if the lens diameter stayes the same, the surface brightness at the object stayes the same!

So, back to the pic AilSnail posted: The lens with the short focus projects a bigger spot at a sertain distance compared to the lens with the longer focal length. But in the middle of both spots the lux-reading will be the same, so they'll have the same throw.

Now what happens is: The lens with the short focal length grabes much more lumens from the emitter, thats why the beam is wider. Now if you illuminate an object with this wider beam objects in the neighborhood light up as well by the wider beam, That is the main reason the narrow beam seems to throw further: You have a clearer wiew to the object, not disturbed by illuminated objects nearby !!

AilSnail,, Try to do the same experiment, but now measuring the lux at a distance of about 10 metres, at the center of each beam. The brightness of a illuminated object is directly related to the amount of lux it receives, so the amount of lux you measure at a distance is directly related to throw !!

Hope this helps you to understand..


Regards,

Ra.


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## AilSnail

Thanks for explaining more. I don't have a lux meter, but maybe I can set up something with a photoresistor.

Meanwhile I need to think some more about whether your theory holds up, in theory. 

What a cliffhanger.

Imagine that you put a reflector behind a star, a reflector so immensely large that the star is almost not measurable in comparison - I'm talking about a sincerely huge construction, almost half the universe. The reflector is parabolic, and focused towards the earth. That was just for fun, I'll get back to the theory shortly.


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## Ra

AilSnail said:


> The green filtered picture illustrates how lux at 1m gets skewed in favor of small reflectors.



Sorry, but no.. It does not !! the size of the reflector isn't a issue here, only the difference in surface brightness is: If I would put a halogen bulb in the smaller reflector the image would look like this:






The other thing you can see is that the surface brightness reflected by the reflector is mostly of the same intensity, no matter the source-reflector surface distance: The outer rim of the reflector is further away from the filament than the central part, yes ?? But it has the same intensity !! So no matter how small or big or deep or shallow your reflector is,, if its parabolic (with the source in focus..) it would look the same when you look into it from a distance, evenly lit over its entire surface !

The HID-arc has a much higher surface brightness than halogen: Thats why the picture with the small HID-torch looks like this: Not because of the smaller reflector!!:







Regards,

Ra.


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## AilSnail

> The HID-arc has a much higher surface brightness than halogen: Thats why the picture with the small HID-torch looks like this: Not because of the smaller reflector!!:



But the smaller one with the short arc reads a higher lux at 1m than the large halogen doesn't it? I guess it would depend on which sort of measurement equipment you use?


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## Doug S

AilSnail said:


> Here is the same data presented differently; It shows how much of the light of the XR-E that will hit a lens of a given F/#. The F/# is the same as focal length divided by diameter.



A very useful graph! Optics is a bit far from my formal training but I can offer one practical comment on using this graph. It becomes very difficult to design lenses with very low f numbers because at some point the rays from the source will strike the lens material at less than the critical angle and thus never enter the lens.


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## AilSnail

Nice of you to point that out, we should delve into that a bit also.


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## Ra

Every time I try to quote someone the link to CPF crashes!!!

So I'll try it this way: 

QUOTE: (AilSnail But the smaller one with the short arc reads a higher lux at 1m than the large halogen doesn't it? I guess it would depend on which sort of measurement equipment you use? END QUOTE.


No, it doesn't !! That is, not if the entire reflector of the halogen torch is lit by the filament!

The amount of lux you measure comming from a torch is a combination of the surface brightness and the dimensions of that surface. So with a lower surface brightness (halogen) you need a bigger reflector to get the same lux-reading at a distance, than with higher surface brightness (HID).

Every lightsource has its typical surface brightness (within a sertain range)

You can overdrive a halogen bulb to get a higher surface brightness, but physics of nature determine the limits: Going too far will melt the filament!
With halogen you'll never reach the surface brightness of HID!!

As a result: With a halogen torch with a 4 inch reflector, you'll never reach the throw of a HID-torch with the same reflector diameter!

AND: You'll never see military searchlights with a CCFL-tube as a lightsource !!


Regards,

Ra.


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## Ra

And...

QUOTE (Doug_S): A very useful graph! Optics is a bit far from my formal training but I can offer one practical comment on using this graph. It becomes very difficult to design lenses with very low f numbers because at some point the rays from the source will strike the lens material at less than the critical angle and thus never enter the lens. END QUOTE.

You are absolutely right Doug..

With short focal lenghts the lens absolutely needs to be aspheric, and even then there indeed is a limit of angle of the incomming rays at the edge of the lens.

F/0.7 is about the shortest possible focal length of a single aspheric lens!

A lens is the best way to grab light from an emitter that emits at the front.
A conventional reflector is the best way to grab light from emitters that emit to the side and towards the back.

The acrylic optics for use with emitters like Cree and Luxeon are a combination of the workings of a conventional reflector with a lens: They grab almost 95% of the lumens output of the emitter: more than ever is possible with only a reflector or a single lens!


Regards,

ra.


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## AilSnail

I have a photoresistor provided by doug owen a few years ago, that thread is probably here somewhere. It decreases resistance when light hits. It is probably about 5mm dia.
I hung it ~2.5m from where I sat with the lenses. I also got a filter from Doug, which was supposed to stop 50% of the light, with some rather good accuracy IIRC. Was a bit scratched though. I used a white plastic tube of 22.5mm ID and 30mm long, to "shutter" the 27mm on the front side, and the 38mm on the back (flat) side - this was the way they could be easily held, in front of the luxeon3. So effectively three lenses of different fl, two with the same D. Here is a link to the 27mm. The focal lengths of the two larger lenses are not accurately measured. The 27mm is brightest a bit further away from the LED than the fl, which I also wrote about here. I suspect the lens is the same as Newbie has, which I mentioned in the first post, and can be seen with many nice pics here, here and here. Here are the resistor readings.

27mm - F/0.31 - 22.5D x 6.9bfl - 1.77K- filter 2.55K
65mm - F/0.49 - 65.0D x 35bfl - 0.32K - filter 0.5K
Occ38 - F/2.44 - 22.5D x 55bfl - 0.81K - filter 1.25K
Ambient: 1.3Meg min.


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## AilSnail

Without mapping the resistor, and making corrections to get a linear scale, the most I will draw from this is that there is a high probablility that the 22.5x55 is more than twice as bright as the 22.5x6.9, and that the 65x35 is more than twice as bright as the 22.5x55.

Ra, these results are not supporting the theory you presented. Perhaps you could help me understand why? 

What were the lux readings of the two lights in the first green picture, at one meter?


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## McGizmo

> If you have a deep reflector, you collect more lumens from the source, that results in a wider beam (more sidespill) But you'll have the same throw with a shallow reflector, but because you send less lumens towards the object, the beam will be tighter (more laserlike if visible)
> 
> So, bottom line: With a lens diameter of 50mm and a focal length of 1 metre you'll have exactly the same throw as with a 50mm lens with a focal length of 30mm !! Only the beam of the first will be useless because of the pathetic amount of lumens its made of..



Hi Ra,

By side spill, are you refering to the divergence of the beam and the fact that it is no truly colimated? Since our image or source is not infinitely small, most of our image surface is not in focus, right? I have come to think that the greater the focal length of the reflector (parabolic) the better the collimation or less divergence one gets.

I consider spill to be that portion of the beam that is beyond the spot and is composed of light exiting the flashlight with no contact with the reflector along with light that is hitting the reflector in such a manner that it does not assume a collimated path. This latter would be from bumps on the surface of the reflector not conforming to the parabolic surface as well as from light originating well away from the focal point.

If we take the same LED driven at the same current and put it behind two 2 25 mm OD reflectors, one being very deep and of a short focal length and one being very shallow and of a long focal length, it has been my experience that the two will NOT have the same lux measure or throw. If I follow you, you are saying they will? The short focal length gathers more lumens but has more divergence and will have a larger spot. The long focal length gathers less lumens but has tighter collimation and will have a smaller spot but measuring the same lux as the short focal length?

Are your comments independent of source (image) size and independent of deviation from specular surface (orange peel)?


----------



## AilSnail

deleted


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## AilSnail

Luxeon3 added to the same old graphs. Intensity graph stolen from lumiled datasheet. I should like to know how to change the colour of the curves in Oo calc, and how to lay the intensity graphs of lux3 and xr-e over each other.


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## AilSnail

The yellow lines converge at the reflector axis. The focal point of the parabolas are at the bottom of the filament.


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## greenlight

I read this thread with my inova X1 in mind. It makes a good beam with its 5mm led, and the aspherical lens design seems very well thought out.


----------



## Ra

AilSnail: Try to figure out if the short focal lens (F/0.31) is fully lit over the entire 22.5mm diameter surface: That is very difficult with focal lengths that short !!

The best way to do this: Take a heavy filter to protect your eyes, make a tiny hole of about 3mm diameter in piece of paper and place the hole exactly on the place of the photoresistor, look through the hole during operation of the lightsource: The entire 22.5mm diametre must be evenly lit by the source! If not, the lens needs more collimating, till it does!

It is best to do this for each lens before you take a measurement !!!

The best and most reliable way to diaphragm lenses is with a piece of paper with a circular hole at the center ! Take three papers together, fold them once and cut half a circle out of the fold: you'll have three identical holes, one for each lens (they don't need to be exactly round, as long as they are identical! Ofcource the other option is to use only one paper with hole for the three measurements !

Only following the instructions above will provide honest measurements !!

Regards,

Ra.


----------



## Ra

And McGizmo:

You are right: Certainly a deep reflector (short focal length) has a very tiny focal spot! The part of the emitter that is not in that focal point causes sidespill !

Take a look at the drawings of post #22.. They exacty show what is happening: with a shorter focal length the source is closer to the lens so the outcomming beam will be wider. But at the center of the beam the surface brightness of the source is the same, no matter how long the focal length !

So with the longer focal length the beam will be narrow, but the surface brightness at the center of that beam will be the same !

Example: Take a piece of white paper, put some light on it sideways so that it is evenly lit. Now take a magnifying-glass or lens and magnify the surface of the paper.. You''ll see the details on the paper magnified, yes.. BUT, do you see more light through the magnifying glass??? NO !! If you magnify the piece of paper, the surface brightness is not magnified !! And that is what this is all about.. But now you have a piece of paper 1 square mm small, put that on a black surface: looking at it with the magnifying-glass makes it bigger! AND.. It seems brighter, but thats only because the surface seems bigger. Now look through the magnifying glass from a distance of about 1 metre. 

Now try to move the lens till the little piece of paper seems to occupy the entire surface of te lens.. Thats what a torch-lens or -reflector is supposed to do: magnify the surface of a light-source. But like you (hopefully) have seen before: surface brightness is not magnified !!

Conclusion: A point at infinity "sees" a surface with sertain dimensions, and a sertain surface brightness, only that will determine the amount of lux (throw) it receives.

So if we have perfect optics: (aspheric lens or parabolic and mirror-finished!! reflector):

With the same source: Bigger reflector or lens means more throw.. Same diameter reflector or lens, no matter the deepness or focal length means the same throw.
Higher surface brightness with the same reflector or lens means more throw.


Regards,

Ra.


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## Doug S

Ra said:


> The best and most reliable way to diaphragm lenses is with a piece of paper with a circular hole at the center ! Take three papers together, fold them once and cut half a circle out of the fold: you'll have three identical holes, one for each lens (they don't need to be exactly round, as long as they are identical!
> Regards,
> 
> Ra.



Actually, splitting hairs here, only the outer layer sheet will have a round hole. The other two will have holes with the same major axis but the minor axes (for you non-native English speakers, axes is the plural of axis, one of the many goofy English plural constructions that must drive you folks crazy) will differ by 1X and 2X the paper thickness. I like your second option better: 
*Of cource the other option is to use only one paper with hole for the three measurements !*


Ra said:


> If you magnify the piece of paper, the surface brightness is not magnified !!Ra.



In fact, if I am thinking correctly, the *apparent* surface brightness is decreased by the factor of the *area* magnification, that is magnification squared.


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## AilSnail

> You are right: Certainly a deep reflector (short focal length) has a very tiny focal spot! The part of the emitter that is not in that focal point causes sidespill !



Could you clarify what you mean by focal spot? Do you mean the area of the die that is projected within a given angle, hitting a cd at 1m away for instance?


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## McGizmo

> You are propably not going to beleve what I'm going to tell you now: THROW IS ABSOLUTELY NOT AFFECTED BY THE FOCAL LENGTH OF THE REFLECTOR OR LENS !! ONLY LUMENS OUTPUT IS !!
> 
> From a distance the object 'sees' only a two-dimensional surface, no matter how deep or how shallow the reflector.



I think I am really dense here. :green:

From a distance, _what_ object sees only a two dimensional surface? Is this object the source of light or an eyeball viewing the two dimensional surface being illuminated by the source of light?

From a distance, if I look into a flashlight, I agree I see a two dimensional disk of illumination. Obviously this disk will not appear to be the same brightness as my viewing location deviates from the Z axis of this disk.

I suspect I am not following your explaination well at all. I also can't buy into the statement:

THROW IS ABSOLUTELY NOT AFFECTED BY THE FOCAL LENGTH OF THE REFLECTOR OR LENS !!

In the case of a reflector held to a specific diameter (not a refractive lens):

By throw, I consider a measure taken at a consistant distance for both examples and from a position coinsident with the Z axis of the optic. Now this measure does involve collection of light over a finite surface and not at an infinitely small point. I assume that this measure will be maximum when a condition of focal length of parabolic reflector is best combined with the image (light source) and will be a function of the image size as well as its distribution pattern of light. As the focal length increases, the light managed by the reflector is better collimated but less overall lumens are managed by the reflector. As the focal is shortened (reflector getting deeper) more light is managed by the reflector but it is collimated to a lesser extent.

Let me try to explain with a specific example. Lets set a light meter at 10 meters from a Cree XR-E LED. THe light meter's sensor is centered on the Z axis of the Cree. We now place various focal length parabolic reflectors of 25 mm OD in front of the Cree LED and in such a focal adjustment that each registers maximum lux measurement on the light meter. I assume that if you were to graph lux measured against focal length that you would see some type of a bell curve where you would have a low lux reading for very short focal length reflectors as well as very long focal length reflectors and some optimal focal length identified by the top of the bell curve.

Am I false in this assumption?


----------



## AilSnail

This one again: Lux meters measures how many photons that fall upon them, just like my resistor does, right? 
Aren't the photons coming from the arc light much denser (more photons per unit area) than those from the halogen?
Would this not mean that more photons are hitting the small measuring device (when it is smaller than the reflector) which is placed 1m away?

Look at the image in #36; If your eye is at the point where the yellow lines converge, you can't see the filament reflected near the rim of the deep reflector. Ergo the deep reflector is equivalent to a smaller reflector at this distance "downstream".


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## Doug S

McGizmo said:


> Let me try to explain with a specific example. Lets set a light meter at 10 meters from a Cree XR-E LED. THe light meter's sensor is centered on the Z axis of the Cree. We now place various focal length parabolic reflectors of 25 mm OD in front of the Cree LED and in such a focal adjustment that each registers maximum lux measurement on the light meter. I assume that if you were to graph lux measured against focal length that you would see some type of a bell curve where you would have a low lux reading for very short focal length reflectors as well as very long focal length reflectors and some optimal focal length identified by the top of the bell curve.
> 
> Am I false in this assumption?



Let me answer a question entirely different from the one you asked (sound like anyone else we know :laughing: ) 

I am pretty sure your assumption is false if both your emitter and detector are infinitely small and the *emitter is lambertian in its flux distribution*. Note that is last qualifier belongs in much of the discussion in earlier posts.

Now in the case of your actual example where the apparent size of a Cree XR-E emitter is fairly large, it hurts my brain to try and reason it out. I'll leave that to others. 

I think some of the general confusion you may be experiencing is that when Ra speaks of brightness he means *photometric brightness* (a.k.a., luminance) which in fact does not vary with the distance from source to viewer. It is measured in that wonderfully named SI unit, the nit.


----------



## Doug S

AilSnail said:


> Aren't the photons coming from the arc light much denser (more photons per unit area) than those from the halogen?



Does this make them nitwits?  

Sorry if this joke doesn't translate well for non-native English speakers.


----------



## Ra

McGizmo: You are getting there!! 

The two-dimensional disk of illumination you see if you look into a flashlight from a distance is exactly what I mean (So, for a moment, you are the object that is lit by the flashlight!) !!

That disk always appears two dimensional.. So if you do the same with two flashlights: One with a deep reflector and one with a shallow reflector with the same diameter, YOU WON'T NOTICE THE DIFFERENCE !!

And now it comes: Only deviating from the Z-axis tells you which flashlight has a deep reflector: The disk of the shallow reflector will dim much sooner than the disk of the deeper reflector !!

At the Z-axis, the apparent brightness of the disk depends on only two things: The size, and the surface brightness: So a change in one of those two things (or both!) makes you receive less or more light (lux)

And Doug is right: 

If you magnify a surface with a sertain surface brightness, the magnification of the brightness is exactly compensated by the.. (its always hard for me to find the right words in english..).. fact that you see a smaller part (or area) of the surface..

And AilSnail:

With focal-spot I mean the area at the focus of a lens or reflector that is nearly free of optical abberations. With a longer focal length that area is bigger than with a short focal length!
Thats why with a long focal length you are biggining to see the exact form of the emitter projected (square image of the Cree-junction on the wall..)

With a short focal length most of the led-junction around the focal-point is blurred by the abberations of the lens or reflector, so you'll only see a bright, fuzzy spot!!.

Next question please..

Regards,

Ra.


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## McGizmo

Doug S,

I don't doubt my assumption is false if the emitter and measuring source are infinitely small but the reality is that they are anything but! :nana: Furthermore, when the term throw is used in regards to real flashights of real size illuminating items at a distance of real size and much larger in surface area than the surface aria of the two dimensional disk of illumination, I maintain that the deep reflector VS the shallow reflector does make a visible as well as measurable difference. Ailsnails images depict a projection of image that is not infinitely small in size. This is what we have to work with. A viable theory, in application or as a means to guide us, needs to account for this.

Hell, when one looks at the best reflector made or the cleanest and sharpest lens available and considers the surface at the scale of the photon that encounters it (forget infinitely small), these optics are anything but smooth and in compliance with the geometry they are to represent! 

I realize this thread is about theory and it seems that Ailsnail is after a practical and realistic application of optic theory?!? I know I am but I am so limited in terms of realisim as well as practical that it's quite a challenge! 

I think Ra has partially answered my question when he agrees that the disk of the shallow reflector will dim sooner but how is this effected by the relative size of the non infinitely small source of light compared to the focal length of the reflector?

My question about an optimal focal length based on optic diameter and image size has not been addressed to my knowledge beyond your pass on the question! 

Instead of a light meter at 10 meters, I'll place a 36" diameter integrating sphere that has a 10" diameter open port alligned to the flashlight's Z axis. We will measure the lumens within the sphere. As I vary a 25 mm diameter reflector's focal length in front of the Cree LED, what happens to the reading of flux in the sphere? I consider a high reading within the sphere to equate with good throw.


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## Ra

Ok.. yet another computercrash after quoting...

To give an answer to post #43 (by AilSlail):

Seeing this from foton's point of view does even make this more complicated than it already is !!

And: You should never go too close to a torch with a aspherical lens or parabolic reflector: They are designed to send rays from a focal-point to a point at infinnity !! Comming closer than that will decrease their optimal performance!

With small reflectors in combination with Cree emitters, you can come as close as about 0.7 meter, if you come closer, the reflector-rim dims !

An extreme example: My super-creation Maxablaster:






And The reflector:







The reflector has a diameter of 230mm and the source is only 0.11 square mm !! 3300 lumens comming from a surface of 0.11 mm2 gives a huge, guge surface brightness: capable of illuminating things more than 4 miles away:







Ohhh Welll, Forgot my point: With this torch (big reflector, ultra small source) I need to walk about 200yards away to get the apparent reflector-disk fully lit over its entire surface by the source..



Regards,

Ra.


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## Ra

McGizmo, Please read post #5 and further.

There you can find the answers about grabbing more lumens from a Cree-emitter with a short focal length optic !!

You don't need a integrating sphere, we already concluded that you are collecting more lumens with a lens or reflector with shorter focal length..

BUT: THROW AND LUMENS-OUTPUT ARE TWO TOTALLY DIFFERENT THINGS !!

Take a 5mW laser-pointer: BAD LUMENS OUTPUT.. SUPER THROW !! 

Put a CCFL-tube in a parabolic reflector: SUPER LUMENS OUTPUT... BAD THROW !!!

WHY?? Surface brightnessss : The laser-pointer beam comes from a 3mm lens and throws a mile !! A laser has the highest possible surface brightness..

The highest possible surface brightness with lamps: Mercury- short arc (Maxablaster)

Regards,

Ra.


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## AilSnail

double post


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## AilSnail

I have done some more measurements, using up to three layers of the 50% film to make a somewhat fuzzy R/relative lux calibration curve for the photoresistor. There would be multiple error sources: transmission accuracy of the film, reflectivity of the film when in several layers, holding the lenses in front of the LED, battery level, heat, interpreting the splined graph with few data points, off hand. From that, it seems that the 38x55 is about 35% brightness of the 65x35.

I occluded the 38 and 65 to 14,5mm with a single piece of paper, the 27mm is too difficult to operate with this occlusion so I don't trust the readings I get with it. 
65occ(14.5x45) - 0,95K
38occ(14.5x55) - 1.21K
This means that the shorter FL of same dia is 25% brighter (with an unknown error margin, probably huge) which may be accounted for by its grabbing more lumen due to the lower F/#?


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## Doug S

Ra said:


> Ra.


Only the Dutch would illustrate their point with a windmill as a test target!


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## McGizmo

> BUT: THROW AND LUMENS-OUTPUT ARE TWO TOTALLY DIFFERENT THINGS !!
> 
> Take a 5mW laser-pointer: BAD LUMENS OUTPUT.. SUPER THROW !!
> 
> Put a CCFL-tube in a parabolic reflector: SUPER LUMENS OUTPUT... BAD THROW !!!



Ra, the fact you felt the need to communicate this to me makes it clear that we are not communicating very well. My bad. Sorry for the interuption to this thread. 

I would suggest though that lumens measured as collected by an integrating sphere at some distance from the source are somewhat akin to "throw" or at least my interpretation of the term. The integrating sphere can also measure lux based on port size and of interest would be the relative change in any of these measures as a result of alteration of focal length, ceteris paribus. In other words, in regards to throw, I am interested in the surface brightness of the target as it is illuminated by the distant source with optic applied. :shrug:


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## Doug S

McGizmo said:


> Doug S,
> My question about an optimal focal length based on optic diameter and image size has not been addressed to my knowledge beyond your pass on the question!
> 
> Instead of a light meter at 10 meters, I'll place a 36" diameter integrating sphere that has a 10" diameter open port alligned to the flashlight's Z axis. We will measure the lumens within the sphere. As I vary a 25 mm diameter reflector's focal length in front of the Cree LED, what happens to the reading of flux in the sphere? I consider a high reading within the sphere to equate with good throw.


If you define the problem as above, i.e., lumens falling within 10" (25.4cm for our SI friends) at a distance of 10m, then I believe that the problem is reasonably solvable with a flat emitting surface of defined area and lambertian distribution. I am also confident that others are better qualified than I to attempt it. See earlier comment about brain hurting. What throws a huge monkey wrench (or spanner for our Brit friends) into the analytical approach to this is that very non-lambertian distribution of the Cree XR-E. Pretend for a moment that the Cree's flux distribution is all within 35 degrees of central axis. In this case you can see that there is a large range of *reflector* focal lengths that will do absolutely nothing. You can also see that in this example that reflectors and lenses with the same diameter and focal length will give very different results. Perhaps for you, the very best approach is the empirical one which is also what you do the very best!


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## shiftd

I just tried comparing 47mm with 60 mm FL AGAINST 52mmX37mm FL 
lux reading (only for comparison purposes) @ ~3m
McR 27 reflector 50 lux
60mm FL ~1750 lux
37mm FL ~1930 lux

the 52mmX37mm has bigger hotspot and brighter too. So it is obvious which one will go to my light


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## AilSnail

> I realize this thread is about theory and it seems that Ailsnail is after a practical and realistic application of optic theory?!? I know I am but I am so limited in terms of realisim as well as practical that it's quite a challenge!



Yep, some understanding (or creating a mental model) of how it works, and how to apply the understanding with calculations.


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## AilSnail

thanks for posting shiftD


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## Ra

Sorry McGizmo,

It is absolutely not my intention to offend you in any way. And you are very welcome in this discussion !!

Going this deep into things is dificult. As an optical engineer I have light and torchlights as a hobbie sinds I was eight years old... Did many tests to learn what is important with flashlights: How to increase throw for example..

And don't get me wrong: For throw, lumens indeed is an important factor: Without lumens, NO THROW !!

I thought I could convince you guyzz with the "what you see is what you get" approach: If a torch looks brighter from a sertain distance, that means that you are receiving more lux from that torch.

I also tried to explain that if you look at a diffuse surface with a magnifying-glass, surface brightness is not affected: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)

But the step from that to a lightsource seems to be dificult, but in a sence, its all the same: The piece of paper you are magnifying is a lightsource !



And AilSnail: If you want to measure the lux-output with your photo-resistor, it has to have a surface as small as possible !! You don't need filters if you are using the same lightsource. If you think you have too much light on the resistor, increase the distance, that is always better: if it is possible, at least 2 or 3 meter. Remember, in theory,, this theory only works at infinnity, so the more distance the better !!

EDIT: Ohh, I have a calibrated lux-meter, so I'm going to put my own theory to the test !!


Regards,

Ra.


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## AilSnail

> Perhaps for you, the very best approach is the empirical one which is also what you do the very best!



Let us not give up on him yet!

pee break everyone!


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## AilSnail

> And you are very welcome in this discussion !!


true!


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## Ra

AilSnail said:


> pee break everyone!




Ohhhh,, uhhh TOO LATE... damn!!


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## AilSnail

Ra, the digits get so small to look at from infinty! 



> if it is possible, at least 2 or 3 meter.



Could you explain why longer distance is better?


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## Ra

Longer distance is better because the beam will be wider, and it will be easier to measure at the center of the beam.

And.. ask for some observation-time on the Hubble-telescope.. Maybe that helps to read your measurements !!


Ra.


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## Ra

AilSnail...

Is it possible for you to take and post some pictures of your testbench...


Ra.


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## Doug S

Ra said:


> Sorry McGizmo,
> 
> I also tried to explain that if you look at a diffuse surface with a magnifying-glass, surface brightness is not affected: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)
> 
> Regards,
> 
> Ra.



Ra, I know exactly what you mean here and I agree. This statement, however, might confuse some. Allow me to add the necessary qualifiers.

I also tried to explain that if you look at a diffuse surface with a magnifying-glass held at the focal length from the surface, apparent surface brightness is not affected by the focal length for a given lens diameter: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)


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## Ra

OK, Guyzz,

I found two lenses: One with D=24mm F=80mm ANd one with D=24mm and F= 230mm.

I punktured a little hole in the cap of my lux-meter to get a measuring surface smaller than the smallest spot (the spot with the F=230mm lens)

I took two measurements: The short-focus lens gave 4.6 lux.. And the long-focus lens gave 4.5 lux !! Thats about 2% difference... 

So I'll stick to my theory !! ...any objections??


EDIT: Thanks Doug !!

regards,

Ra,


----------



## McGizmo

Ra,
I am not offended and I don't want to get in the way here either. I believe I follow your theory but perhaps I disagree that realistically throw is about lux right at the center of the beam on the Z axis. We all likely agree that someone asking for a torch with max throw will not be happy if they are handed a laser beam. If you allowed your light meter full view of the two projected beams instead of a pin hole, would you still be within the 2%? I doubt your light meter senser represents a very large field of view or viewing angle does it?

Doug,
I think the fact the Cree is not of lambertian distribution is key here and assumed it is part of the reason Ailsnail started this thread. I know it is significant in my consideration of the optimal focal length of a reflector given a constraint of OD. For starters I assume that such a thing as an optimal reflector exists and I base optimal on maximizing lux reading at say 1 meter where you are measuring light that is not dead nuts on the Z axis but presumably in the cener portion of the spot beam. Because of the relatively narrow viewing angle of the XR-E, I want a deep reflector to harness the lumens but deep implies shorter focal length and more divergence of beam since the light object or source is large relative to the small focal spot of the shorter focal lengths.

I have a 6 inch integrating sphere and I can set it 1 meter away from the LED. I can measure the light that enters the integrating sphere. I am of the convention that the higher the reading of light that enters the integrating sphere, the greater the throw. I now put all kinds of lenses and reflectors in front of the LED with the only qualification being that they are of 25 mm max OD. Will I get the same measure of light regardless of 25 mm optic used? Oh yeah, the integrating sphere has a port of 30 mm diameter.


----------



## Doug S

McGizmo said:


> Doug,
> 
> I have a 6 inch integrating sphere and I can set it 1 meter away from the LED. I can measure the light that enters the integrating sphere. I am of the convention that the higher the reading of light that enters the integrating sphere, the greater the throw. I now put all kinds of lenses and reflectors in front of the LED with the only qualification being that they are of 25 mm max OD. Will I get the same measure of light regardless of 25 mm optic used? Oh yeah, the integrating sphere has a port of 30 mm diameter.



Don, finally what you are after: A strait answer with no qualifiers. Absolutely not! 

And for the other folks in this discussion: A practical side comment. I recently came into possession of an McR-17XR reflector which is a deep reflector that Don designed specifcally for the Cree XR-E. (Thanks Don!). From the minute I tested its performance I knew that it was ideally suited to a specific need that I had. I have since designed it into a headlamp for my personal use. Consider this testimony that Don's empirical approach often works very well with no help, thank you very much, from those of us that enjoy the theoretical discussions. Don't let it go to you head, Don, I *do* occasionally see you with you head up your butt


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## AilSnail

*This was wrong too! I'll let it stay since Doug_S has commented on it.*


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## McGizmo

Doug,
If it went to my head then my head might get stuck on one of those frequent visits of introspection of which you made comment on. Although anatomically difficult if not impossible literally, figuratively, it's a place I call home. :nana:

(Why do you think I like lights?!?! It gets dark where I go and open flames are a no no!  )


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## Doug S

Ail, can you elaborate a bit?


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## AilSnail

Yea. Its the same data from the angular intensity graph in the sheet. If you add all the percentage readings within the angle of the lens, and divide by the number of readings, you get the average brightness of the light that falls upon the lens - relative to the peak brightness. 
For the L3 I have typed the mean values from the sheet - The peak value is thus 97 - so the lux3 average brightness curve is now normalised to 100% by multiplying the typed values by 100 and dividing by 97.
I updated the link.

The flux should be the same curves as before.


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## AilSnail

deleted


----------



## AilSnail




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## Doug S

AilSnail said:


> Yea. Its the same data from the angular intensity graph in the sheet. If you add all the percentage readings within the angle of the lens, and divide by the number of readings, you get the average brightness of the light that falls upon the lens - relative to the peak brightness.
> 
> The flux should be the same curves as before.



I am not sure this average is meaningful. I don't think it represents the average flux falling on the lens due to geometry considerations. It's late and I'm going to bed. If you don't agree, I'll think about it further when I am rested.


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## AilSnail

Ooops, I think I have been mixing concepts. I'll look at it later.


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## Ra

QUOTE: (Doug_S) If you allowed your light meter full view of the two projected beams instead of a pin hole, would you still be within the 2%? I doubt your light meter senser represents a very large field of view or viewing angle does it? END QUOTE.

ABSOLYTELY !! If I allow the light meter to see the entire beam, I would get a measurement depending of the amount of lumens in that beam: The beam from the short-focus lens will absolutely win!! Because it grabbes more lumens from the source.

But that is the whole issue: that is not measuring throw!!

Measuring throw you need to measure a erea as small as possible in the hottest part of the beam: And if two flashlights give the same lux at the object, then the object is lit by the same amount of light in that small erea..No matter how big the spot is !

Ofcource the light-output in lumens is higher with the short focal lens, but at the center of the beam the lux-reading will be the same!!

Regards,

Ra.


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## AilSnail

*dang, wrong again*


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## AilSnail

Don, do you happen to have a smooth HD45 with a cree? In post #6 I posted a trace of a 45D x 47.58L x 2.66FL - should be pretty close to HD45? According to the trace the bottom of the reflector is not lit at all, when looking at it from straight ahead and at a certain distance?


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## Doug S

AilSnail said:


> *dang, wrong again*



Ail, if I understand correctly what you did, Your averages would be correct for the light falling on the inside surface of a dome if you were to enclose the emitter with a dome and the emitter was at the center of the dome. The averages as a function of angle will be different if the light is falling on a surface of different geometry such as the backside of a lens.


----------



## Doug S

AilSnail said:


> Don, do you happen to have a smooth HD45 with a cree? In post #6 I posted a trace of a 45D x 47.58L x 2.66FL - should be pretty close to HD45? According to the trace the bottom of the reflector is not lit at all, when looking at it from straight ahead and at a certain distance?



Ail, I don't know if you have an actual Cree XR-E available. If not, here is something you need to know. The way that Cree gets that very non-lambertian flux distribution from what is nearly a lambertian source is to incorporate a lens into the dome. I just now looked at a dimly lit XR-E under a stereo microscope and measured the lighted portion of the die with a steel ruler graduated down to 0.25mm. The *apparent* die size is 2mmx2mm even though it is known that the *actual* die size is 1mmX1mm. One consequence of this, and the major point that Ra has been making, is that for a given diameter reflector/optic the peak beam lux from an XR-E will be less than that of a Luxeon I or III if both are emitting the same lumens since the real and apparent die size of the Luxeons is a much smaller 1mmX1mm. 
Your ray tracing exercise is even more complicated by the fact that the Cree XR-E apparent die size of 2mmX2MM only applies within about 40 or 50 degrees of the z axis. At even larger angles you start to view the die by looking under the lens which is formed by the top portion of the dome. Hence, my comment yesterday about the possibility of Don's empirical approach being best was based largely on the reality of the real world problem and not on Don's possible mathematical incompetence.


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## AilSnail

each led's plot is scaled so its luminance at 0 deg is 100%.
it assumes that the die size does not change relatively in size depending on angle of view, due to the dome.

I took the old interpretation of the datasheet luminous intensity graph, and divided the percents by the projecting area, which would be the sine of (90 - the half angle) - *unless there is distortion from the dome*.


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## AilSnail

> apparent die size is 2mmx2mm


thanks. that would light the whole reflector then probably.



> only applies within about 40 or 50 degrees of the z axis.


 right. there goes the *luminance* polar out as well.



> The averages as a function of angle will be different if the light is falling on a surface of different geometry such as the backside of a lens.


yes, but no *luminance* data, no *luminance* average :candle:


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## AilSnail

> AilSnail...
> 
> Is it possible for you to take and post some pictures of your testbench...



maybe. here is the test lamp with a 42mm optic and a beamshot of the 27mm on top of a creed fenix p1. The green is the testlamp with 42mm.


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## AilSnail

Ra said:


> Sorry McGizmo,
> 
> I also tried to explain that if you look at a diffuse surface with a magnifying-glass, surface brightness is not affected: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)
> 
> Regards,
> 
> Ra.





Doug S said:


> Ra, I know exactly what you mean here and I agree. This statement, however, might confuse some. Allow me to add the necessary qualifiers.
> 
> I also tried to explain that if you look at a diffuse surface with a magnifying-glass held at the focal length from the surface, apparent surface brightness is not affected by the focal length for a given lens diameter: The image through the lens has the same brightness, no matter the focal-length of the lens (=magnification.)



If the led is not lambertian, like the X-re, then the surface brightness of the edge of the magnifier gets less when you come closer, changing fl, keeping dia, because you are looking at the led from its blind side.

_ah, diffuse means lambertian_


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## AilSnail

gah. so, plotted in different ways here is 
% of total *flux grabbed by a lens*,
*luminance of the leds *as seen from different angles, scaled so that luminance at 0 degrees is 100%
and finally, *average luminance of a lens* (covering a certain angle, or having a F/#).
it is just the led angular luminance % weighted against the flat area of the lens, not sure how to say it. 

Keep in mind all the unknowns regarding varying magnification of the die vs viewing angle, which will affect the luminance.

Let me know if it looks like bunk.


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## AilSnail

so, interpreting the graphs with regards to throw is not straight forward with the Xr-e, since the apparent die, at high angles from Z axis, could be outside the focal point, ie no part of it is emitting from the fp.


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## Doug S

AilSnail said:


> gah. so, plotted in different ways here is
> % of total *flux grabbed by a lens*,
> *luminance of the leds *as seen from different angles, scaled so that luminance at 0 degrees is 100%
> and finally, *average luminance of a lens* (covering a certain angle, or having a F/#).
> it is just the led angular luminance % weighted against the flat area of the lens, not sure how to say it.
> 
> Keep in mind all the unknowns regarding varying magnification of the die vs viewing angle, which will affect the luminance.
> 
> Let me know if it looks like bunk.



Wow Ail, That looks like a lot of time on your calculator. One question: for the purposes of calculation were you assuming that the rear surface of the lens is flat? Ra can tell us better but I suspect that most of what is below around an f# of 1 would not be applicable due to the constraints of lens design.

A question OT to your recent post directed at Ra. Ra, it is rare that I have access to a real optical engineer so I want to ask a question I have been wondering about. It is marginally on topic since TIR optics were discussed earlier in this thread. As I said much earlier, I have no formal training in optics. I am an electrical engineer so I did over thirty years ago know a bit about electromagnetic wave theory. Much should be applicable to optics, the only difference is that for radio engineers our ''photons'' are ''bigger'' than yours, sometimes of the scale of kilometers rather than your nanometers. Now on to my question. With radiowaves, surface features below a certain fraction of a wavelength are essentially invisible. A practical example is the perforated sheet metal on the front of a microwave oven allows you to look inside without cooking your face because the individual holes are smaller than the wavelength of the microwaves. Now the question: As you polish the rear surface of a TIR optic, is there some level of surface roughness below which there will be no further reduction in light leakage (assuming that on a macro scale the necessary critical angle conditions are met)? If so, what is this roughness in terms of wavelength? This relates to an issue raised by McGizmo in post #17.
Thanks


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## NewBie

This might be useful Ail


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## AilSnail

flat lens, yes-doesnt apply because the light doesnt enter because critical angle?


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## AilSnail

ty jar


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## McGizmo

> Measuring throw you need to measure a erea as small as possible in the hottest part of the beam: And if two flashlights give the same lux at the object, then the object is lit by the same amount of light in that small erea..No matter how big the spot is !



Herein lies perhaps part of the communication problem. I don't know if throw is an accepted term in the physics of light management field; I always thought it was a term used by laymen and flashaholics to describe the ability to illuminate a distant target and measurable, at least in measurable or relative value, with a Lux meter. In theory, with a perfect lens or reflector and an infinitely small light source, I can follow comments and ideas which to not hold true in reality when faced with light sources of measurable size and optics well short of perfection. 

To my pragmatic aproach to a torch where throw is a design objective, I consider the the goal to be one of minimizing the divergence of the light being redirected via an optic (reducing the spot angle) as well as maximizing the amount of overall output that is governed and controled by the optic. These considerations are also within realistic limitations placd on optic diameter and some minimum spot angle ( a laser is not considered viable).

A viewer may place themselves at one mile from the flashlight and at a viewing orientation dead nuts on the Z axis of the flashlights being considered. With binoculars, they may report that a bald headed luxeon III driven at 500 mA is as bright as when it has a 27 mm reflector placed in front of it. They will report that the throw of the LED is the same, in both cases. The user of this LED however will report that when the LED is bald headed, he can see out so many yards with certainty and when the reflector is placed in front of the LED, he can see much further where the spot of the beam lands. He will report that the reflector increases the throw of the LED considerably.

Ironically, Doug S has joined in here in a discussion that uses a term that I recall he cares very litle for!  That term is throw.

Ra, perhaps I can follow your thoughts and comments more clearly if I have a better understanding of how you define throw. If it is a measure of lux at an infinitely small point on the Z axis, all comes very clear. If it is based on the area about the the Z axis confined to the diameter of the optic in use, I still think I follow. If it is about illumination of a target area that is significantly larger than the diameter of an optic then I remain confused.

I proposed what I considered a reasonable and doable "test". I also asked if there was possibly an optimal focal length given a fixed optic diameter and based on a real light source of finite and significant size, relative to optic size. I didn't ask how one would compute such an optimal and by optimal, I mean one which would yield a maximum lux reading. I only ask if such an optimal focal length would exist. If I could easily turn various parabolic reflectors of a given OD and measure the lux when these were optimally placed in front of a LED source, I suspect I could graph lux on the y axis VS focal length on the x axis and see a curve that rises and then starts to fall. At its peak, I could identify what I would consider to be the focal length that maximizes the throw of this LED with the given OD of optic. The measurement of lux at the Z singularity may have theoretical significance but means nothing to this real world consideration. :shrug: Well I don't think my question was answered but still feel the question deserves consideration?!?

Incidentally, my rough and inaccurate bench work puts the apparent image of light from the XR-E below the die itself. That is to say I seem to find the greatest lux measurements as well as see the most phosphor in the reflector when the LED is placed in accordance to the focal point of the reflector in such a manner as the image being below the die. This is based on lux measures as well as viewing angles centered on the Z axis but not limited to the infinitely small point pierced by the Z axis.


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## AilSnail

i need a picture viewer with a ruler in it.


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## AilSnail

I would like to point out that an infinately small source in a perfect optic (reflector/lens) would read much less lux at 100m than a very very small light source of the same luminance.

Illustrated in #74


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## AilSnail

I edited the #74 to represent the cree.

*Doug, you are completely on topic, the topic is wide open.

here is the thread with newbie's pictures of the cree from different angles.*


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## Doug S

McGizmo said:


> Ironically, Doug S has joined in here in a discussion that uses a term that I recall he cares very litle for!  That term is throw.


Good memory, Don. It always makes me think of mass, aerodynamics, and baseball players!



McGizmo said:


> I proposed what I considered a reasonable and doable "test". I also asked if there was possibly an optimal focal length given a fixed optic diameter and based on a real light source of finite and significant size, relative to optic size. I didn't ask how one would compute such an optimal and by optimal, I mean one which would yield a maximum lux reading. I only ask if such an optimal focal length would exist. If I could easily turn various parabolic reflectors of a given OD and measure the lux when these were optimally placed in front of a LED source, I suspect I could graph lux on the y axis VS focal length on the x axis and see a curve that rises and then starts to fall. At its peak, I could identify what I would consider to be the focal length that maximizes the throw of this LED with the given OD of optic. The measurement of lux at the Z singularity may have theoretical significance but means nothing to this real world consideration. :shrug: Well I don't think my question was answered but still feel the question deserves consideration?!?



Don, my post #68 was intended to be an unambiguous YES answer to your question.



McGizmo said:


> Incidentally, my rough and inaccurate bench work puts the apparent image of light from the XR-E below the die itself.



I fully concur with a determination by an alternate method. I looked at an XR-E through my stereo microscope at highest magnification and thus with the least depth of field. By varying the focus it was apparent that the die image lay in the same plane as the surface that the emitter was sitting on, i.e., the die image was in the plane of the backside of the ceramic base.


----------



## Doug S

AilSnail said:


> I would like to point out that an infinately small source in a perfect optic (reflector/lens) would read much less lux at 100m than a very very small light source of the same luminance.
> 
> Illustrated in #74



I'm not sure this says what you may have intended. 
The term luminance, properly used, becomes meaningless for an infinitely small source since the units of the term will involve a division by zero. Another way of looking at it would be that it would emit no light at all unless its luminance is infinite.


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## Doug S

AilSnail said:


> *Doug, you are completely on topic, the topic is wide open.
> *


I don't know. You took away the napkins while I was not looking


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## AilSnail

arr, you cought me.

What I mean to say, in #94, is that there is a minimum size of the source, if it is too small, the reflector or optic will not be all lit up - like Ra has pointed out earlier.

If the lambertian source is infinate small, all the light will be parallell coming out of the optic.
so the lux reading will be the same whether the optic is there or not, except with a reflector it will be double at any point along the Z axis - as long as that point is not at the axis or outside the reflector diameter - since you can see both the source and a reflection of the source (except that it will be hard to pick out an infinately small object at 100m distance).

What I am trying to emphasise perhaps (and it is probably obvious to most), is that not only parallell beams hit the target point. Probably pretty useless to convey this though since it is rather self evident. And in practical terms, the minimum size for the source is so small that you don't need to worry about it.

I don't think that infinate small means zero, but pretty close though. Perhaps the statement in #94 would be valid if you replaced "infinite small" by "very very very small", or "almost not tangible at all".
*edit: As far as I have learned, infinate small is actually impossible, since it seems that there is a minimum size for anything - we live in a world composed of things that are not infinately graduated - they have a resolution.*


_edit:
The illustration in #74 shows conceptually why and how the angular luminance distribution (surface brightness as viewed from an angle) matters._


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## AilSnail

> Wow Ail, That looks like a lot of time on your calculator. One question: for the purposes of calculation were you assuming that the rear surface of the lens is flat? Ra can tell us better but I suspect that most of what is below around an f# of 1 would not be applicable due to the constraints of lens design.


It is, as far as the numbers are correct, applicable to the extent of showing the average luminance of the source, as seen from the flat side of the lens - For it to be indicative of the throw, one would have to look at the refraction critical angle that you mentioned earlier. Is this what you mean?


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## Doug S

AilSnail said:


> If the lambertian source is infinate small, all the light will be parallell coming out of the optic.
> so the lux reading will be the same whether the optic is there or not



I do not agree.


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## AilSnail

> I do not agree.



Can you be a bit more elaborate? Meanwhile I will think about it some more and find out whether and why you are right.


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## McGizmo

It the light's image size is small enough to behave as a single point source and the optic is one of collimation, then I think the lux would be the same as measured solely on the Z-axis regardless of optic used or size of optic. The point is rather useless if even correct. It seems to me than in applied theories size and relative size matters or did she say that?

In economic theory back in college, we were instructed to assume that the consumer had perfect knowledge. I found the theories based on this asumption just a bit lacking in real world applications.  My point is subtle and well of the Z axis.


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## Doug S

AilSnail said:


> Can you be a bit more elaborate? Meanwhile I will think about it some more and find out whether and why you are right.



My apologies for the brief response. I was just going out to run 5 km. It is unusually warm today, warm enough to comfortably run with no clothes at all. I wanted to run before it turned cooler. Afterwards, while still nice out I took time to enjoy a beer outside on the porch. So, you think I cannot go off topic? I am guessing simply from your posting locations that both you and Ra are not native English speakers. I can say that a native English speaker would never know that from reading what both of you write because your command of written English is very excellent. Now my warning to you: watch out for that McGizmo guy. He is probably envious of your skills. Just to confuse you, his might try to slip some non-English words into his posts from a language spoken only on a few small islands in the Pacific Ocean. If fact, just today I saw him slip the word for ''porch'' (or Veranda, a word the English stole from Hindi) from this other language into a post in another thread. Be warned!

Now to your question: In the your example with lens and perfectly parallel rays, the lux falling on an area within the beam will be the same regardless of distance and the inverse of lens area as explained by Ra in several earlier posts. Without lens, the lux decreases by the square of the distance.


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## Ra

I've been away for a while..

This is quite a growing thread !!..

McGismo: Yes, in my book, throw is the measuring of the lux-output of a flashlight with a sensor as small as possible (close to infinite point) exactly on the Z-axis (brightest part of the beam..)

However,, you suggested that a graph with the lux-reading at the y-axis and the f/* focal length on the x-axis would give a curve-rise to optimum which after tha optimum falls...But I tried to tell everyone here that that is not going to happen: If the optical aperture stayes the same, the lux-reading at a sertain fixed distance stayes the same !! No matter how long or how short the focal length is !!

With a short focal length more lumens are directed towards the object, resulting in a wider beam, not in a higher lux-reading at the center of the beam..

AND: A very important note for those who want to test this in real life:

You need to exclude any factors that can distort the measurements: Dirty optics, optics that have possible abbertions that can influence the output..

You cannot compare TIR-optics with normal lenses, and normal lenses with metal reflectors!!

So if you are going to do an experiment to see if the lux-output depends on focal-length, then there are some important things:

In all cases the distance of the lux-meter must be exactly the same and measured TO THE FIRST SURFACE OF THE LENS YOU ENCOUNTER, MOVING TOWARDS THE LIGHTSOURCE !!

The optics with the various focal lengts must all have the same efficiency (=transmission) THIS IS VERY IMPORTANT !!

Use a diaphragm on your lux-sensor with a 1mm diameter hole !!

If you use lenses, use lenses of the same quality and form !

Use a minimum measuring-distance of 1 meter.

For my lux-test, many posts earlier, I used two lenses of exact the same brand, diameter and efficiency, only with different focal-lengths (80mm and 230mm) If throw is affected by focal-length, the difference between the two lenses would be much, much bigger than the 2% I came up with !!


Regards,

Ra.


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## AilSnail

doug, you are right, i was wrong. thanks for the compliment too. I am unfortunately going to a party now so cannot continue to recalc the luminance, with the area input from jarhead's pics.


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## AilSnail

> However,, you suggested that a graph with the lux-reading at the y-axis and the f/* focal length on the x-axis would give a curve-rise to optimum which after tha optimum falls...But I tried to tell everyone here that that is not going to happen: If the optical aperture stayes the same, the lux-reading at a sertain fixed distance stayes the same !! No matter how long or how short the focal length is !!



would you not agree then, that the lux is affected by the average luminance of the source, as seen by the lens? The focal length will affect this average for a non lambertian source.

For your test, the average luminance is almost the same.


----------



## Doug S

Ra said:


> I've been away for a while..
> 
> This is quite a growing thread !!..
> 
> McGismo: Yes, in my book, throw is the measuring of the lux-output of a flashlight with a sensor as small as possible (close to infinite point) exactly on the Z-axis (brightest part of the beam..)
> 
> Ra.



Ra, as I understand McGizmo the problem he cares about is as follows: 


McGizmo said:


> I have a 6 inch integrating sphere and I can set it 1 meter away from the LED. I can measure the light that enters the integrating sphere. I am of the convention that the higher the reading of light that enters the integrating sphere, the greater the throw. I now put all kinds of lenses and reflectors in front of the LED with the only qualification being that they are of 25 mm max OD. Will I get the same measure of light regardless of 25 mm optic used? Oh yeah, the integrating sphere has a port of 30 mm diameter.


I have been telling him, see post #68, that the focal length does matter even if you confine the problem to just one type of optic, i.e., reflectors. Do I have this wrong? Please note that the apparent image size of the die in a Cree XR-E is 2mmX2mm which is relatively large on the scale of a 25mm diameter optic and also its flux distribution is very non-lambertian. Post #54 best shows my reasoning.

BTW, there is a question to you from me buried in post #88. Could you have a look at it?


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## Doug S

AilSnail said:


> I am unfortunately going to a party now so cannot continue to recalc the luminance, with the area input from jarhead's pics.



Wow, you guys over in Norway sure party late! I'm usually in bed by that time of night. Enjoy!


----------



## McGizmo

Doug S,

If we are confining lux measure to the _very near_ vicinity of the Z axis and accepting the other conditions as I understand them from Ra's definition of throw and leval of measure, we could have a reflector of 1 mm focal length and 30 mm in diameter and a reflector of 3 light year focal length and 30 mm in diameter and the throw will be the same! Hell with your inverse square law! :nana: Lets take this definition to some obvious limits and consider its practical value.  Heck, a reflector with a focal length of 1 meter and 30 mm in diameter will not even see the light from any LED we might choose to orient in a forward, on Z axis, orientation! :green: 

I am not disputing Ra's claims about throw as he has defined them. If I define throw as the total amount of light delivered to a 1 meter disk at 10 meters with a further requirement that the complete disk must be visible to the viewpoint of an observer yielding the light source, in absence of any ambient illumination, I think I am giving a better picture of what I consider throw to be realistically about and the theory be danged!  Ra wants a pinhole on the light meter. I want to illuminate the lightmeter and the poor sod holding it at about 10 meters! I want to do this with an optic of a diameter that will fit in a pocket and I have to use LED's that are not lambertian in distribution by exact definition. I type this while sitting in shorts on my lanai which looks a lot like a porch!


----------



## Doug S

AilSnail said:


> It is, as far as the numbers are correct, applicable to the extent of showing the average luminance of the source, as seen from the flat side of the lens - For it to be indicative of the throw, one would have to look at the refraction critical angle that you mentioned earlier. Is this what you mean?


If I understand correctly, yes.


----------



## Doug S

McGizmo said:


> Doug S,
> 
> If I define throw as the total amount of light delivered to a 1 meter disk at 10 meters with a further requirement that the complete disk must be visible to the viewpoint of an observer yielding the light source, in absence of any ambient illumination, I think I am giving a better picture of what I consider throw to be realistically about and the theory be danged!


Well Don, that would be a hard statement to refute. 



McGizmo said:


> Doug S,
> 30 mm in diameter and a reflector of 3 light year focal length and 30 mm in diameter and the throw will be the same!



Actually this sounds a lot like something they shoved about 2 m of up my *** a few years ago. I am happy to report that they didn't find my head up there, or yours either for that matter.


----------



## McGizmo

[OT] LOL! Doug, I think I had the same experience but a hard right turn precluded a successful look see and we went with the barium instead. [/OT]

Ra,
I seriously do appreciate you taking the time here because optics are so important in these lights and you may be the only really qualified member who visits and posts here! Thanks! 

[OT] I have been hoping someone like SureFire would put together some lenses and groups if required in an adjustable package that would give us a true varible focus beam with the LED's. Is such an adjustable lens even practical or doable in a reasonable size? [/OT]


----------



## Ra

Thanks, McGizmo..

And as a remark to one of your earlier remarks: You are right on the spot !!.. Theoretically that is: 

A 30mm diameter lens or reflector with a focal length of 1 mm (hard to get I think..) Will give the same throw as a 30mm lens or reflector with one lightyear focal length!! (ofcource both reflectors with the same efficiency!)

But, like I said before: The lux-measuring distance needs to be the same, measured from the front-side (the side faced towards the lux-meter) of the lens or reflector !

You will encounter a few problems with your test tho..: A flashlight with a lens or reflector with one lightyear focal length will be quite long I think, and bad for its portabillity... And.. if you switch it on, you'll have to wait for a year before it actually begins to produce that 0.0000000000000000000000000000000000000000000000000000000000000001 (or 1*10 to the power -65..) lumens of light it will propably give !!! LOLOLOLOLOLOLOLOLOLOL

And your spot will be so ifinitely small that measuring it will be quite a challenge !!

But you understand the theoretics of this, and thats what counts..!


BUT one of your remarks does not add up: I don't exactly know what you meant with "THE HELL WITH YOUR INVERSE SQUARE LAW" ...

But in both cases (in fact in all cases where the surface-dimensions and surface brightness of the lightsource do not change...) The inverse square law still stands: If you double the measuring distance to the lens or reflector, you will measure 1/4 the lux !!!

The thing is: The inverse square law starts from the front of your torch (Not exactly: from the point where the entire reflector or lens is lit by the source..) So not at the lightsource itself..(=your little lamp or LED, a lightyear away..)

And if you are actually going to make this "lightyear" torch..: 

DON'T USE A TAIL-SWITCH !!!!!


EDIT..: Sorry, McGizmo,, I misread your post: You wrote about a 3 light-year focal length, not 1 light-year..:

NOW YOU SHOULD DEFINITELY NOT USE A TAIL-SWITCH !!!!!


Now I'm going to read some ealier posts and see if I can answer some questions...


Regards,

Ra.


----------



## Ra

Ok, guyzz..

Here are details of a test I did about one hour ago..:

Determining the throw of various lenses:

The particpants:







And:







The test: Project the spot 1 meter away from the lens at the door, exactly on the pinhole in the dustcap of the lux-sensor..:

The results:

Lens 22mm diam. F=195mm:






Lens 22mm diam. F=100mm:






And.. Lens 22mm diam. F=35mm:







The 0.2 lower lux reading of the last lens is propably the cause of draining batteries...

Conclusion: If at all cases the lux-reading is the same: The surface brightness at the object is the same: Throw is the same !!!

In all cases the lens-distance to the lux-sensor was 1 meter +- 3mm

Regards,

Ra.


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## Ra

And...

As long as I had this professional testbench working... I did a test involving a TIR-optic and conventional deep smooth metal reflector:

I said earlier that the acrylic internal reflection optics are much more efficient compared to conventional metal reflectors.. Well.. They are:






And..






This test required both of my hands, so I could not take pictures of the actual measurements.. Hope you'll beleve me on my words..

The results: At one meter distance of the optics: The metal reflector measured 2 lux.. and the TIR optic measured 3.4 lux !!

So.. conclusion: If you have a luxeon flashlight with a metal reflector that reads 2000 cp at 1meter, it will generate about 3400 cp's at 1meter with a TIR-optic of the same aperture !!

I knew there would be a difference, but I wouldn't expect a difference that big !!

This also proves you cannot use different type of optics to prove a theory about throw versus focal length...


Regards,

Ra.


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## Ra

Doug...

Here's the answer to your question in post #88:

You are absolutely right, If a surface roughness passes a sertain point, it will act as a reflective surface at a sertain wavelength..

With visible light (very short wavelengths compared to radio..) surface roughness must be below about 15-20 nanometres !! Otherwise, scattering will cause losses !

That is why even the tiniest scratches on optics will cause a loss in performance !! And the acrylic optics we use with LED-emitters like Cree and Luxeon can be damaged very easily because of the soft surface !!

Beleve me,, I handle my acrylic (TIR) optics wearing velvet gloves !!!


Regards,

Ra.


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## Doug S

Ra said:


> And...
> 
> As long as I had this professional testbench working... I did a test involving a TIR-optic and conventional deep smooth metal reflector:
> 
> I said earlier that the acrylic internal reflection optics are much more efficient compared to conventional metal reflectors.. Well.. They are:
> 
> 
> 
> 
> 
> 
> And..
> 
> 
> 
> 
> 
> 
> This test required both of my hands, so I could not take pictures of the actual measurements.. Hope you'll beleve me on my words..
> 
> The results: At one meter distance of the optics: The metal reflector measured 2 lux.. and the TIR optic measured 3.4 lux !!
> 
> So.. conclusion: If you have a luxeon flashlight with a metal reflector that reads 2000 cp at 1meter, it will generate about 3400 cp's at 1meter with a TIR-optic of the same aperture !!
> 
> I knew there would be a difference, but I wouldn't expect a difference that big !!
> 
> This also proves you cannot use different type of optics to prove a theory about throw versus focal length...
> 
> 
> Regards,
> 
> Ra.



Ra: Nice work! An excellent example of theory actually working in the real world. BTW, you had me convinced over 100 posts ago.  This discussion has been very valuable to me as it caused me to think about several optics related questions in a new light. 
Now possibly we can even make that difficult McGizmo guy happy. 
I am copying post #54 below: 


Doug S said:


> If you define the problem as above, i.e., lumens falling within 10" (25.4cm for our SI friends) at a distance of 10m, then I believe that the problem is reasonably solvable with a flat emitting surface of defined area and lambertian distribution. I am also confident that others are better qualified than I to attempt it. See earlier comment about brain hurting. What throws a huge monkey wrench (or spanner for our Brit friends) into the analytical approach to this is that very non-lambertian distribution of the Cree XR-E. Pretend for a moment that the Cree's flux distribution is all within 35 degrees of central axis. In this case you can see that there is a large range of *reflector* focal lengths that will do absolutely nothing. You can also see that in this example that reflectors and lenses with the same diameter and focal length will give very different results. Perhaps for you, the very best approach is the empirical one which is also what you do the very best!


Now at you, Ra:

If we confine the problem to reflectors and make the emitter lambertian of defined area, how difficult are the equations for the generalized problem: defined distance, target radius of interest, reflector diameter, and emitter area. I can see that the equations are best normalized on any one of the above (i.e., set one parameter=1 and express others as multiple of others). I can also see that the equations will be easier if we simplify the emitter area as circular. What I can best see is that even by 30 years ago I had forgotten too much calculus to do this problem and even back then would not have had the necessary optics knowledge to set it up.


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## Ra

Hi Doug,

These calculations you mention are quite complicated, and only doable with the help of optical design-software like Zemax or even better Zelum. Zelum is especlially designed for problems like these !!

For now I approach these problems with the brains and the 30 years of experimenting-experience I have now, and I must say: That works pretty well, for me that is.. Ofcource there always are some guys that are more difficult to convince !!


Regards,

Ra.


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## Doug S

Ra said:


> Hi Doug,
> 
> These calculations you mention are quite complicated, and only doable with the help of optical design-software like Zemax or even better Zelum. Zelum is especlially designed for problems like these !!
> 
> For now I approach these problems with the brains and the 30 years of experimenting-experience I have now, and I must say: That works pretty well, for me that is.. Ofcource there always are some guys that are more difficult to convince !!
> 
> 
> Regards,
> 
> Ra.



Ra, do you have access to either of these softwares, Zemax or Zelum, and the capability to use it?


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## NewBie

Okay, so I see what you are doing now.

On the optic/reflector end, you have it masked off.

On the measurement end, you have a sensor hole smaller than the lit up area.


However, I'm using an aspherical lens, and I am scratching my head, wondering why your lux reading is so low(6.5 lux). The range on the meter I am using here is set to x100, so we are looking at 38,000 lux @ 1 meter, which will leave you seeing spots for some time (I had a heck of a time trying to see the light meter after focusing things on the meter sensor). Here is an example of a XR-E and a 65mm dia asperic, flat rear face, AR coated, and very roughly 32mm BFL:








I've been fiddling around in TracePro (it is a 15,000.00 raytracing program) http://www.lambdares.com/products/tracepro/traceproed.phtml and I am seeing some interesting things regarding some of the statements folks have made. When I get a chance, I'll post the results from the program.


I did find some fairly low cost low F# aspheric condensers (high light gathering efficiency), designed for illumination and projecting, but have never tried them before:
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2454


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## McGizmo

Hi guys,

If you have a reflector that is 30 mm in diameter and has a focal length of 1 meter, you will have a very shallow dish that will sit behind the LED when adjusted for focus and not act on any of the light being produced by the LED if the LED is forward facing. For all practical purposes the LED will distribute its light in the same manner it would if there were no reflector involved. This is what brought rise to my comment about hell with the inverse square law. 

My understanding of the inverse square law is based on the assumption that you are measuring light over some finite surface area and not at an infinitely small point? At an infinitely small point coincident with the Z axis, and measuring the lux from an infinitely small point of lambertian distribution, you would measure the same lux regardless of focal length as Ra has stated and this includes the case of the focal length being infinite or large enough as to not have access to any light being produced by the point source of light. Wouldn't you be measuring only the photons that were fired straight out on the Z axis and these photons would not have their course altered by any collimating optic nor would any true collimating optic bring light fired off Z axis into contact with the Z axis at any distance to be measured as additional light or greater lux?!?! 

I submit that with any optic, regardless of size or focal length, that has no convergence of beam at the point where flux is measured, we will have the same lux measure from a constant rate photon emitter of lambertian distribution. I base my comment on particle theory and not wave theory and this may be my undoing. In other words if we consider the infinitely small Z axis and the stream of photons traveling down this line, this stream is unaltered by collimating optic intervention and the photon count should be the same regardless of distance from the source. The inverse law would have photons leave this path but they don't, do they? 

By the way, my simple mind considers a lux meter as a photon counter and I see it counting photons that hit its sensor surface area which is not infinitely small. Because of the collection area having dimension, I see the inverse law being observed. In realistic or pragmatic terms, I consider throw to be a function of maximizing the number of photons hitting a much much larger surface or collection area than that of a lux meter and because of this, I don't agree with Ra that focal length relative to source image (of real size) does not matter. I think it does matter. With a given target surface you want to hit with photons, a longer focal length diminishes the divergence angle (off Z parallel) for streams of photons origniating away from the focal point of the optic but the longer focal length manages fewer of the streams of photons emanating from the source. I believe Ail's graphics have been trying to identify this very issue and try to get a handle on it. :shrug:

The surface finish discussion and comments hold for wave theory of light and maybe I should be excused from this discussion because I can only picture the geometry and effect of optics from a particle theory approach; angle of incidence = angle of reflection. Well I guess I can think of this in terms of vectors where the vector can describe the path of a photon or the direction of wave travel?

OK, I'm simply in over my head! 

Ra,
I hope you can make some comment on the feasability of a "zoom lens" for a flashlight!


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## Ra

Hi Newbie, Welcome to this thread..

I hope you want to considder reading the entire thread, it may give you answers..

The problem was to figure out if the difference of focal-length of various lenses with the same diameter was of any influence on throw..

So we're not talking about lumens output here !! Ofcourse lumens output is pathetic with a 22mm F=195mm lens !!

If with your lens the spots center is big enough to overlap your entire sensor, then you can measure the way you did.

If it isn't, you'll have to increase your sensor distance: 38,000 lux at one meter equals 38,000 cp. But you can also measure the output at 10 meter:
The lux-measurement should give about 380 lux !! If it doesn't.. If its higher, you are to close to the lens at 1 meter !

Your sensor must be evenly lit by the brightest part of the beam, so there may not be any surface-erea's on your sensor tha receive less light !!

The 38,000 lux you measure only is a factor of the diameter of your lens and the surface brightness of your LED !!!

The lumens-output of your setup is a factor of the diameter and the focal length of your lens !!

If I take a lens with the same diameter as the one you have, and a led with the same surface-brightness, I will reach 38,000cp ! No matter the focal length !! However, with that setup (with long focal lengths) I will not, and cannot ever measure 38,000lux at 1 meter ! The spot is too small to cover the entire sensor !!
Thats why I made the pinhole...

That also means that ofcource the 6.7lux I measured is not 6.7lux at all !!
It was about comparing situations, not to measure the actual lux output: For that, you need the entire sensor !

So,, For you, and everyone who didn't know this: A learning moment:

THROW IS DETERMINED BY THE DIAMETER AND EFFICIECNY OF YOUR LENS OR REFLECTOR and THE SURFACE BRIGHTNESS OF YOUR LIGHTSOURCE.

LUMENS OUTPUT IS DETERMINED BY THE DIAMETER AND EFFICIENCY OF YOUR LENS OR REFLECTOR and THE FOCAL-RATIO OF YOUR LENS OR REFLECTOR

AND: These two rules only work when your reflector or lens is of high quality and used over its entire surface !

Hope this helps you to understand some of it..

Regards,

Ra.


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## Ra

Sorry McGizmo,

I can only say this:

I still get the impression that you're confusing throw with lumens-output

The way you define measuring throw indeed makes the focal-length of the reflector or lens important !! 

The only thing is: the way you define measuring throw is not measuring throw !! That is more like measuring the lumens-output !!

Ok,, If you want to talk photons,, we talk photons: If you want to measure the max surface brightness in a beam (THATS THROW !!), you'll only need to grab the photons in a small erea in the hottest part of the beam..(Z-axis)

And if that hottest part of the beam is very small, smaller than your sensor, then you need to increase the measuring distance till its big enough to cover your sensor,, or you need to decrease the size of your sensor !! And thats what I did..

Edit: Ofcource if I wanted to measure actual lux with my earlier experiments I should have recalculated the meter-readings with the factor I decreased its sensor-surface.. But I didn't need to do that because it was for comparishon only..

Remember,, Throw is difined in candlepowers, and can be measured at any distance, that is, with a transparent atmosphere..:

Throw= candlepower= lux at 1meter 

= lux X 100 at 10 meters 

= lux X 10,000 at 100meters 

= lux X 15,440.5476 at 124.26 meters

= lux X 1,000,000 at 1000meters !

Thats all there is to it


Regards,

Ra.


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## McGizmo

Hi Ra,

I am confusing them by your definition of throw and I think combining them with my definition of throw. See, I would say a Laser is not a good _throw_ device. By your definition it is and I concurr. Perhaps I will give up on the word throw and use some other term or convention. I think I will go with *20:1*. This ratio is distance to diameter. At 10 meters, the target is .5 meter in diameter. At 10 feet, the target is .5 feet in diameter. Further I will define a lights effective *20:1* as that distance at which the target has a minimum of 2 lux measured, anywhere on its surface. 

Now if I want to design a light of max diameter of 30 mm, I can chose to go with a TIR optic or reflector and for the sake of argument, I will not consider spill as an additional criteria for optic selection but limit my concern to the effective *20:1*. Depending on the LED being used, I believe there will be an optimal focal length for both a TIR optic as well as reflector. I assume that if I had access to ray trace software, the distribution data of the particular LED and the ability to use the software coherently, I could identify the optimal focal length for both a TIR as well as reflector solution. Would you agree, at least in theory, to any of this?

You will note that I believe I have defined the *20:1* as a beam angle and one with obvious divergence and not collimation of light. Your really cool windmill sourcher would not fair as well as some other lights that couldn't come close to it in terms of range. We could set the standard at 100:1 or 500:1 if we wanted to consider longer range devices.


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## NewBie

Ra,

You may want to consider the source size, since we do in fact have non-point sources.

If I have a non-point source, and the light doesn't come from the very center, the photons emitted at the edge of the die will not be culminated properly, and will cause a divergence in the beam.

Anyhow, here are some basic reflector concept pictures to consider:







If I were to hold the diameter the same, but then draw the reflector deeper, I would catch more photons to throw forward and the intensity of the hotspot (or lux) increases. But, as you draw it deeper, the criticality of alignment jumps quite considerably, and also, with a non-zero point source, you end up with more angular error near the edges (like on an LED die), and you get more divergence of the beam from that error.

Some old raytraces of parabolic, elipitical, lens setups:
http://www.molalla.net/~leeper/reflec2.jpg

Another picture for sake of discussion folks might refer to:






Reflector coatings:
http://www.molalla.net/~leeper/refcoat.pdf


Picture of the raytraces from a LuxV and various errors, I did back in January 2005 to illustrate some concepts:






The simulation results on a wall, and notice how at the last point, the reflector is focusing on such a small area, that it is actually focusing on the darkspot between the four die. Take a look at the intensities of each, and refer back to the reflectors in the previous picture:







For the simulation, I used enhanced protected silver reflector coating, so the losses are far less than with typical reflector coatings we find in flashlights.

Take note, how the more larger diameter reflector spreads the light out over a larger area, and how the narrow diameter reflector concentrates the light into a smaller area, while holding the reflector depth the same.


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## Ra

For those who want to know: Lesson 12.67.. Inverse square law:

What you need: A normal household bulb (60-100watts) A tripod; A lux-meter; A garden; 110 or 220 volts.


Place the bulb on the tripod, in the middle of the garden, away from any objects.. And switch it on..

The bulb emits its light omnidirectional, with sertain surface brightness and dimensions that do not change !!

Take your luxmeter and do a reading at 1 meter from the bulb..take note of that reading..

Do a measurement at 2 meters from the bulb: Theoretically, this should be close to 1/4 of the reading at 1 meter..

Do a measurement at 4 meters from the bulb: Theoretically, this should be close to 1/4 of the reading at 2 meters and 1/16 of the reading at 1 meter

If you double the distance to the bulb, the sensor 'sees' a 4 times smaller surface, and with the surface brightness not changing, this means a measurement 1/4 of the measurement at half the distance..

So, if you go from 1 meter to 3 meter you'll measure 1/ (3x3) = 1/9 of the reading at 1 meter..

That is the inverse square law.. !!

THIS WORK EXACTLY THE SAME WITH FLASHLIGHTS.. There is only one catch tho..:

The reflector or lens can cause difficulties.. Like I said, the inverse square law only works with both stable and fixed dimensions and surface-brightness !

The performance of a lens or reflector can vary during changing of the measuring-distance !

You must be shure that the apparent surface-brightness of the reflector or lens is at maximum and doesn't change !

Aspherical lenses and parabolic reflectors are designed to have maximum performance for an object at infinnity, not close by !!!

You can see this if you look into the reflector with a dark filter when the flashlight is operating: If you come too close the reflector or lens it is only partially lit !! THAT IS NOT THE PLACE TO TAKE YOUR LUX-MEASUREMENT..

You first must determine the distance at which the reflector or lens is totally lit by the source !! From that distance and further away, the lux-measurement should follow the inverse square law !!

Important: The measuring distance should always be measured from the lens or reflector, not from the bulb or LED !!

End of lesson..

Regards,

Ra.


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## McGizmo

Ra,
I consider lumens to be a measure of the total number of photon's emitted during a period of time. I consider lux to be a measure of the number of those emitted photons that hit the measurement area in a period of time. As I understand it, a perfectly alligned and perfectly formed parabolic reflector host to an infinitely small point source of light would have the two dimensional view from a distance that you describe. However this two dimensional surface would not have light leaving it in a lambertian pattern but strictly on parallel courses and parallel to the Z axis. The lux measures would not follow the inverse square law. Obviously I am confused at the core here. 

If you have a lambertian source and it follows the inverse square law and then you act upon this source with some type of light bending optic with some success at collimation, the inverse square law still applies? :shrug:



*EDIT: this is Ail's thread and I doubt I am assisting him in any form so I will leave it be and not cloud the thread any further. *


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## Doug S

Ra said:


> .





McGizmo said:


> .



So Don, Have you ever wondered why it is that I never liked the term ''throw''? :devil:


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## Ra

McGizmo,

The way you think about it, you should indeed better give up on the word throw.. 

Throw only is the abillity to illuminate distant objects, like a laser does !! But a laser indeed is absolutely not practical as a flashlight ! And you are absolutely right about the 20:1 ratio making a flashlight worth playing with.. 

Even my powerfull Maxablaster is not a practical light: If I want practical with lots of lumens and decent throw, I'll grab my HID-Thor !! And guess what: That one pretty much followes the 20:1 ratio !!

But here the discussion was not about practical or not ..

So, seems that we are on the same wavelength, with you more keeping practicallity in mind and calling that throw... Am I right??


And NewBie: The black/white picture shows the footprint of the beams too close to the reflectors.. try to generate the spots for each idividual reflector at say 100meters distance. That will give a totally different result !! That is if the program followes the laws of light..

PS. Nice quotes Doug....

Regards,


Ra.


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## Ra

QUOTE: (McGizmo) However this two dimensional surface would not have light leaving it in a lambertian pattern but strictly on parallel courses and parallel to the Z axis. The lux measures would not follow the inverse square law. Obviously I am confused at the core here. (END QUOTE)

Sorry, but IT WILL FOLLOW THE INVERSE SQUARE LAW !!: 

but only 'strictly on parallel courses and parallel to the Z axis'...!!!

But you're right: SORRY AilSnail,, are you still out here ????


Regards,

Ra.


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## McGizmo

Ra,
In my proposed example of the parallel light beam leaving the perfect parabola and infinitely small lambertian point source of light, won't the beam be the same in cross sectional intensity regardless of distance from source you cross section? (Yeah, also assuming a field of travle void on any particles to get inthe way of the photons)? If the cross section of this beam is consistent at all distances, won't any measureof lux using the same sensor positioned at the same location relative to radial position of the Z axis measure the same lux regardless of distance from source? Does a parallel flow of light dim over distance if there is no divergence from parallel??!?! For all intents and purposes, we consider the light from the sun and stars as parallel but it isn't really, is it? Is a laser parallel or pseudo parallel? In theory, does parallel light behave the same way whether you view it with particle theory or wave theory?

For me, the problem with pure theory is that we can't continue to jump half the distance to the end of the log. If we keep jumping we will leave the log. In practice, it's nice to know when one is about to leave the log! 

Ail, would you consider changing the title to "Practical Applications of Optic Theory"? :nana:

Doug S,
I was with you on throw but chose not to swim against that current.  If we are to accept Ra's definition of throw then it really is abused and misunderstood on this forum!?!? :green: (Dare I say rather useless in terms of flashlight comparisons as well?)


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## Doug S

McGizmo said:


> Ra,
> In my proposed example of the parallel light beam leaving the perfect parabola and infinitely small lambertian point source of light, won't the beam be the same in cross sectional intensity regardless of distance from source you cross section? (Yeah, also assuming a field of travle void on any particles to get inthe way of the photons)? If the cross section of this beam is consistent at all distances, won't any measureof lux using the same sensor positioned at the same location relative to radial position of the Z axis measure the same lux regardless of distance from source? Does a parallel flow of light dim over distance if there is no divergence from parallel??!?!



Don, I think much of the confusion in this thread is that we all are freely switching between the ''ideal'' models and the practical model. [ideal model mode ON]. In Ra's post #127 he includes a very important qualifier. The first time he mentioned it in a much earlier thread I had to think about it for awhile to fully appreciate it and then had one of those light bulb moments. 
His qualifier is this: 

*You can see this if you look into the reflector with a dark filter when the flashlight is operating: If you come too close the reflector or lens it is only partially lit !! THAT IS NOT THE PLACE TO TAKE YOUR LUX-MEASUREMENT..

You first must determine the distance at which the reflector or lens is totally lit by the source !! From that distance and further away, the lux-measurement should follow the inverse square law !!* 

In your example Ra's qualifier is never met if you believe the universe has finite scale. In fact, for the infinitely small source with less than infinite lumens, the reflector will always appear dark at any finite distance if you consider only the light that has been reflected (i.e., direct rays from the source are blocked). 
[ideal model mode OFF]


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## AilSnail

Hey since you guys obviously aren't capable of keeping a conversation going by yourselves, I'll throw in some chit-chat.



> As I understand it, a perfectly alligned and perfectly formed parabolic reflector host to an infinitely small point source of light would have the two dimensional view from a distance that you describe.



if you viewed it from a distance, any distance, the reflector would not be lit... 
for the rest, i agree, the light would be equally strong at any distance.
(like doug_s said too)



> And NewBie: The black/white picture shows the footprint of the beams too close to the reflectors.. try to generate the spots for each idividual reflector at say 100meters distance. That will give a totally different result !! That is if the program followes the laws of light..



very good catch, i was puzzled there...



> EDIT: this is Ail's thread and I doubt I am assisting him in any form so I will leave it be and not cloud the thread any further.



Every time you say you're gone, I just _know_ you'll be back...  so welcome back.



> But you're right: SORRY AilSnail,, are you still out here ????



no worries mate! I told you I was going to a party...



> Ail, would you consider changing the title to "Practical Applications of Optic Theory"?



So far, it seems many of us have spent a lot of energy for considering the basic conceptual stuff, like infinity and such. these ideas make understanding of reality much simpler, you can forget about dimensions and such. At least it helps for me. Finding out how and why these models differ from reality is ofcourse essential for applying the theories. so crossing over from what we see, to our concept of what makes us see what we see, to concept about "what if" infinity etc is good stuff.. I at least think I have a much sharper image of what is going on after a few pages of this thread.

As to whether we will find that we can apply all this stuff to our napkins and ballparks, we shall have to see. At the very least we may find out why we need a 10 000 dollar tracer or a cnc lathe.


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## AilSnail

Jarhead, did you happen to measure the angles the pics were taken from?


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## NewBie

Ra, 

You were correct about it being too close. I moved the "wall" to 1 meter and it cleaned up the rendering for the fourth reflector. I also switched the program over to lumens, and then lux at the wall.

I changed the spacing between the reflectors a bit, to make things a bit more obvious, I should have moved the top one further, but after an hour of rendering time, I need to do other work on the computer.

Maybe tomorrow I will re-run the simulation at 10 meters, spacing the reflectors more between them, and growing the wall accordingly.


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## McGizmo

Doug_S,

You want to block the light coming directly from the source! What kind of qualifier is that! :nana: Fine be my guest. I just jumped of the log anyway!  You can't hang ten if you only go half the distance and the surfs up so TTFN.

Ail,
Must have been some party! 

Ra,
You own the term throw. Use it well!


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## AilSnail

*there is something fishy about this graph as well.. see #164*





This were the sorts of measurements I took to calculate the viewing angle, and the apparent area of the die as seen by the camera, or an optic.
The results are quite different from the "geometric approach", which was sin(90-angle from Z) * 2.2mm^2 .

Luminance is intensity, as seen in the datasheet graph, divided by area.

These graphs assume an even distribution of brightness over the die - since the pictures seem oversaturated it is difficult to say whether this is a valid approximation. For the angles close to Z, I believe this is a very good approximation.
If this is not the case for higher angles, the peak luminance will be even higher at these angles than the below graph shows.

The luminance graph as calced from the pixel count is rather surprising to me!





the X is degrees. the Y is normalized to 100% at 0 deg, and also for the area it is mm^2 x 20.


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## Any Cal.

Hi all. I just wandered onto this thread and spent the last hour reading it, so I have to say a couple things I think I see. Ra's "throw" is one TINY, TINY pinprick of light. It is one photon striking a reflector at a certain intensity and then shooting off into the world. The reason this is at odds with CPF's idea of throw is that CPF's throw requires many photons to hit an area. The long focal length lets a reflector direct more photons. So, while none of those photons are hitting the subject with any more intensity, there are more of them, thus illuminating the subject more fully. So yes, focal length does not change intensity, but... yes, changing focal length does change the ability to illuminate a distant object more fully. Not trying to butt in, really appreciate all the effort and knowledge that went into these posts.


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## Doug S

AilSnail said:


> This were the sorts of measurements I took to calculate the viewing angle, and the apparent area of the die as seen by the camera, or an optic.
> The results are quite different from the "geometric approach", which was sin(90-angle from Z) * 2.2mm^2 .
> 
> Luminance is intensity, as seen in the datasheet graph, divided by area.
> 
> These graphs assume an even distribution of brightness over the die - since the pictures seem oversaturated it is difficult to say whether this is a valid approximation. For the angles close to Z, I believe this is a very good approximation.
> If this is not the case for higher angles, the peak luminance will be even higher at these angles than the below graph shows.
> 
> The luminance graph as calced from the pixel count is rather surprising to me!
> 
> 
> 
> 
> 
> the X is degrees. the Y is normalized to 100% at 0 deg, and also for the area it is mm^2 x 20.



Ail, this looks like a lot of good hard work here! 
One thing did not surprise me: 

*>The results are quite different from the "geometric approach", which was sin(90-angle from Z) * 2.2mm^2 .<* 

[real world mode ON] Even ignoring the lens effects of the XR-E dome, this is to be expected. An LED die has thickness and hence photons are coming out the sides. [ideal mode ON]A true lambertian emitter plane has no thickness. [real world mode ON] With an LED die even more photon come out the sides that you might expect based alone on the *area of the sides*. This is because some photons have been bouncing around inside the die due to total internal reflections. Some of the lucky ones finally leak out the sides of the die before getting uselessly absorbed. This is one of the big practical challenges of scaling up the area of a die. As it gets larger, photons created away from the edges have lower probability of getting out. Some of the more innovative things LED researchers are doing is to find ways around this problem. I believe that Newbie knows more about the details of this than me but let's not go there since it is a topic that could fill an entire thread of it's own..


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## Ra

QUOTE: (McGizmo) Ra,
In my proposed example of the parallel light beam leaving the perfect parabola and infinitely small lambertian point source of light, won't the beam be the same in cross sectional intensity regardless of distance from source you cross section? (Yeah, also assuming a field of travle void on any particles to get inthe way of the photons)? If the cross section of this beam is consistent at all distances, won't any measureof lux using the same sensor positioned at the same location relative to radial position of the Z axis measure the same lux regardless of distance from source? Does a parallel flow of light dim over distance if there is no divergence from parallel??!?! For all intents and purposes, we consider the light from the sun and stars as parallel but it isn't really, is it? Is a laser parallel or pseudo parallel? In theory, does parallel light behave the same way whether you view it with particle theory or wave theory? (END QUOTE)

McGizmo, 

you need to hold on to the link between theory and the practically possible: Theoretically the setup with an infinitely small lambertian source and a perfect reflector would indeed give the same lux-reading at any distance.. And I know for a fact that the lux-reading will cook your meter, and you, and earth, and the universe in a infinitely small fraction of time !!

Because that would give an infinitely high lux-value !!

Let me explain: An infinite point-source producing light, (and here it doesn't matter how much lumens) always has an infinitely high surface-brightness !! Because it has zero dimensions and still produces light..

So that is practically impossible.. However.. Theoretically:

You are absolutely right: A perfect parallel beam without any divergence will not dimm over distance !!

But practically, a lightsource always has sertain dimensions, so you'll always have divergence !! And weather you use a source with a lens or reflector, or look at the sun,, these all are apparent, two-dimensional disks with fixed dimensions and fixed surface-brightness (ofcource the reflector or lens fully lit by the source!) 

In a vacuum, with all these cases the light followes the inverse square law over distance, ofcource with the lens or reflector only at the Z-axis, with the sun omnidirectional..

Indeed, here on earth we have losses caused by pollution-particles and moisture...

So, the answer to your last two questions is obvious: No, the light from the sun and the stars is not parallel. With the sun its easy to see: With parallel light, the shadows will always be ultra sharp, no matter the object-wall-distance.. I hope you know that this is not the case in real life: Thats the proof that sunlight isn't parallel.

However the light of a single star would give a shadow that will be sharp over a very long distance !! propably millions of miles !! But.. try to make a shadow with the light of a single star...


Regards,

Ra.


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## Ra

And NewBie,

Hopefully I can save you the efforts by saying, that at 10 meters I still do not expect the outcome I expect at 100 meters.

So, if it is possible, try to simulate the beams at 100 meter wall-distance, or even better at 200 meters !!

regards,

Ra.


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## Doug S

Ra said:


> However the light of a single star would give a shadow that will be sharp over a very long distance !! propably millions of miles !! But.. try to make a shadow with the light of a single star...
> 
> 
> Regards,
> 
> Ra.



There have been instances in recorded history where it has been observed. With your interest in astronomy, like me, you would probably like to see it in your lifetime provided it is not too close.


----------



## AilSnail

This is from the EZ1000 sheet, the die they use in the xr-e far as I remember.

This shows intensity, like the ones from the L3 and Xr-e that I have shown earlier, right?



> I believe that Newbie knows more about the details of this than me but let's not go there since it is a topic that could fill an entire thread of it's own..



Let us hope for that thread to come then - I would like to learn more about how the dice work.


----------



## AilSnail

McGizmo: 
Here and here are two threads with focusable lens flashlights. If you look through the threads by Newbie that I linked to in #31, you will probably find a beamshot or two of a defocused aspheric.

The flood is very even, only a tad brighter in the center in my case. A bit like Surefire holographic filters. So, very viable IMO. There are chromic abherrations at the very sharp edges both of the spot and the flood - not really a problem. If you use a reflector behind the lens, you will be washing out the abherrations on the flood. You may prefer a more edgeless flood though.





The drawing is from The light measurement handbook by Alex Ryer.


----------



## McGizmo

Ailsnail,
I wish your links would work for me and the browser I use but at least I can get into CPF at all!  I have a couple Panasonic lights with adjustable beams but I think they are real lossy in light and merely a case of moving from focus to out of focus. I also have a Leonard flashlight with adjustable beam but it too seems to be a case of going from focus to out of focus. I was refering to an adjustable lens that will take the same image (focused or slightly our of focus) and increase and decrease its projection angle. Perhaps you have linked to such a device?

Thanks


----------



## AilSnail

Not really. Can you get these beamshots? (courtesy of newbie)
http://www.molalla.net/~leeper/asphhd45.jpg
http://www.molalla.net/~leeper/asphd452.jpg


----------



## AilSnail

It'd be lossy if there too low incident angle on the glass, when you pull the lens closer to defocus it (the pic with yellow fringes - I bet. The fringe on mine, which I think is the same lens, looks more like a rainbow, not particularly yellow).


----------



## McGizmo

I can see Newbie's images no problem. I just can't seem to get links to CPF threads to work but there is something not quite right about links within CPF and my browser and has been off for some time.

I made a simple head some time ago with a half ball lens and you can slide the lens up and back from the LED. It works rather nicely with the XR-E but the loss of lumens is a bummer. I like the idea of a real zoom lens that initially harnesses the brunt of the lumens and then sets them off in a slightly blurred projection (round the corners and fuzz the grill works of the die). This projection is then further altered from a tight beam angle to a wide beam angle.


----------



## AilSnail

Search terms for McGizmo:
zelda riflescope
amonra focussable
newbie consider pounding
newbie CREE XR-E die and comparisions
newbie Microfire poking


----------



## AilSnail

What is the distance from the base of the xr-e ceramic to the top of the ring?


----------



## Doug S

AilSnail said:


> What is the distance from the base of the xr-e ceramic to the top of the ring?



I checked two at 2.4mm from backside of base to top of ring.


----------



## AilSnail

thanks a lot.


----------



## PEU

*(Raytrace part of this post is incorrect, read my next post)*
Regarding LED modelling, here is an interesting PDF from the creators of Tracepro: Application Note for LED modeling



> Since manufacturer specifications are often incomplete
> (lacking material data and emission measurements for confidentiality reasons) and manufacturing tolerances of the
> LED die mass-production process creates characteristic variations, the resulting model may perform differently from
> the datasheet. Contacting the manufacturer could provide more information to help design a more accurate model, but
> one can use TracePro to bring the optics model into agreement with lab measurements.
> 
> ...For this example, we will consider the die’s side surface light emissions to be negligible.



Regarding the dome, it makes a difference if you consider it or not for raytrace purposes. I'm evaluating Tracepro and I'm waiting for some models I requested, so in the meantime I did my own models using my "virtual parts kit" I used a luxeon and a McR27L models (only external dimensions accurate) 

Here is what I found about the dome, keep in mind that my model may not be accurate:










Dome being used detail:






Pablo


----------



## NewBie

A trick I have used before is to put a narrow slit right over the die, which helps a person see the raytrace in a 2D world, the 3D world can get a bit confusing at first if you are not used to it, as the angles start looking wrong, until you rotate the results and get it on the right plane.

You can also go back and produce isopolar and a variety of other plots, and compare against the datasheet to verify your LED model, which is a good idea.

The software allows import actual Radiant Imaging files, and a wide variety of other things, such as pull in ACIS (*.sat), ACCOS (*.len), CodeV (*.seq), OSLO (*.len *.osl), SIGMA 2000 (*.len), Zemax (*.zmx), IGES (*.igs, *.iges), Step (*.stp, *.step), and STL (*.stl) files. It will even bring in SolidWorks models, if you buy the right options, and there is also a photorealistic option. Complex items are often easier to create in SolidWorks or Inventor.


----------



## Doug S

PEU said:


> Regarding LED modelling, here is an interesting PDF from the creators of Tracepro: Application Note for LED modeling
> 
> 
> 
> Regarding the dome, it makes a difference if you consider it or not for raytrace purposes. I'm evaluating Tracepro and I'm waiting for some models I requested, so in the meantime I did my own models using my "virtual parts kit" I used a luxeon and a McR27L models (only external dimensions accurate)
> 
> Here is what I found about the dome, keep in mind that my model may not be accurate:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Dome being used detail:
> 
> 
> 
> 
> 
> 
> Pablo



Pablo, welcome to this thread! It is rare that you see a thread in this seldom visited backwater of the CPF go well over 100 posts with descending into chaos. I think that this is testimony to the importance of the topic originally raised by Ailsnail as well as the small number of active participants. The later factor at least gives us a chance of keeping straight who said and meant what [though we do struggle a bit with the later].

Now a question about your very nice contribution. It addresses your statement: 

*Regarding the dome, it makes a difference if you consider it or not for raytrace purposes. * 

I have always assumed (maybe wrongly!) that the inside of the dome was a hemisphere with the die at the center of the full sphere were it to exist [I hope that makes sense]. If true, it seems that if the die were [ideal model mode ON] infinitely small it would have no effect on *outbound* rays since they are normal to the inside surface. The only effect of the dome then would be reflection or transmission of photons trying to reenter the dome from the outside having already been reflected at least once elsewhere. Is this the only difference that your Tracepro modeling is looking at or is it [real world model ON] accounting for the fact that the die has real size and/or some other consideration? I hope my question makes sense.


----------



## PEU

Well, I must eat my previous post with a little salt, because *its incorrect*  

Minutes ago I received a K2 model from Lambda Research and ran the simulations again with and without the dome and the results are almost similar:










Detail





I will leave the previous post intact to reflect how bad an improper modelled dome can affect the raytrace process. Put special attention to the inner dome reflections, the proper dome has almost none of them.

Im still not familiar with tracepro, but if you pay close attention, you will see that when using the dome some rays change the color. My interpretation of this is that the dome produces some color shift, not big but its there, again I can be wrong about this 


Pablo


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## AilSnail

*Doug_S said:
It is rare that you see a thread in this seldom visited backwater of the CPF go well over 100 posts with descending into chaos.*

Indeed, with peu's pictures, it seems we are headed for entropy. Thanks peu!


----------



## chimo

Great thread! 

Would it be reasonable to assume that due to the placement of the die on the Cree LEDs much lower than the dome (compared to the Luxeons) that it would have a greater effect on the ray tracing?


----------



## Doug S

chimo said:


> Great thread!
> 
> Would it be reasonable to assume that due to the placement of the die on the Cree LEDs much lower than the dome (compared to the Luxeons) that it would have a greater effect on the ray tracing?



I don't see how you possibly could have overlooked my comment in post #54!?!?  
:laughing:


----------



## chimo

Doug S said:


> I don't see how you possibly could have overlooked my comment in post #54!?!?
> :laughing:



Inconceivable! Humm, my excuse... I just got back from a run and my brain was still deprived of oxygen, ya... that's it.  

Paul


----------



## AilSnail

really nice pictures, PEU.


----------



## AilSnail

It looks like the blue lines are TIRed in the outer dome. It looks like some TIRs are not followed through.
edit: perhaps not even TIRed, some look like they are split-offs from red lines which also leave the outer dome.
The green one could be a red one re-entering through the inner dome from the reflector and leaving again.

What are the domes made of? What refractive index?


----------



## AilSnail

Dang, I had not scaled newbie's pictures properly - they appear to be taken at varying distance or zoom, I had not taken this into account for the apparent die area measurements.

I am having some difficulties scaling. The most accurate thing to measure for reference is the OD of the white ring between the dome and the metalized ring. 
The datasheet says the metal ring is 6.8mm OD.
If that is true, then the white ring is 5.34mm OD - found out by measuring the difference in the pics.
The dome without the slope at the bottom would be "about" 4.86mm.
Looking at the picture taken from the top, the die then becomes only 1.49x1.49mm...
trouble. I'm tired. night.


----------



## Doug S

AilSnail said:


> The dome without the slope at the bottom would be "about" 4.86mm.



I measure 4.78mm with consistancy among three samples about 0.02mm.


----------



## Doug S

AilSnail said:


> What are the domes made of? What refractive index?


Glass. I don't know the specific index.


----------



## AilSnail

I ment the k2 material, the double dome construction in peu's traces - wasn't very clear on the question.. you too? what is the inner one then?


----------



## AilSnail

have a look at this.. if the dome is 4.78, the die is ~1.5x~1.5.... Could it be due to camera/microscope lenses? (Doug_s measured it to 2.2x2.2mm earlier)


----------



## Doug S

AilSnail said:


> have a look at this.. if the dome is 4.78, the die is ~1.5x~1.5.... Could it be due to camera/microscope lenses? (Doug_s measured it to 2.2x2.2mm earlier)



Ail, I think you are thinking of this post were I measured one at 2mmX2mm 

https://www.candlepowerforums.com/posts/1736808&postcount=81 

Since the Cree XR-E dome acts as a very short focal length lens, small variations in die position in Z axis direction or variations in fabrication of the dome itself can result in changes in apparent die size. Oh No! Another parameter to bin with: apparent die size


----------



## AilSnail

yeah, incorrect memory..

2.25mm^2 vs 4mm^2 - would mean not too far from double the luminance.. Are anyone seeing the effects of these huge variations?


----------



## Doug S

AilSnail said:


> yeah, incorrect memory..
> 
> 2.25mm^2 vs 4mm^2 - would mean not too far from double the luminance.. Are anyone seeing the effects of these huge variations?


Possibly. See comment in the following post on measured beam angle: 
https://www.candlepowerforums.com/posts/1716762&postcount=63 



AilSnail said:


> 2.25mm^2 vs 4mm^2 - would mean not too far from double the luminance.. ?


I don't think you meant this part? No reports of 4mmX4mm apparent size.


----------



## AilSnail

Umm, what I ment, is 2x2mm = 4square mm area, and
1.5x1.5mm = 2.25 square mm area. Hmm.. sounds correct? 
You can not type 'square mm' like 'mm^2'?


----------



## PEU

I still didn't received the XR-E models, but maybe I can model one, Doug already posted that the die is 1x1mm, now for the parts I don't know, does someone has a defunct XR-E to strip and a digital caliper?







Pablo


----------



## Doug S

AilSnail said:


> Umm, what I ment, is 2x2mm = 4square mm area, and
> 1.5x1.5mm = 2.25 square mm area. Hmm.. sounds correct?
> You can not type 'square mm' like 'mm^2'?


Yes, makes sense. Sloppy reading on my part.


----------



## Doug S

Pablo, be sure that you have read posts 81 and 96.


----------



## PEU

Ok Doug, now I see that the die sits on the substrate like the old xlamp 7090, now for the last question, the dome is the same as the old 7090 or is different?

I will assume is the same, because it looks similar, Im drawing a model as I write this.


Pablo


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## Doug S

PEU said:


> Ok Doug, now I see that the die sits on the substrate like the old xlamp 7090, now for the last question, the dome is the same as the old 7090 or is different?
> 
> I will assume is the same, because it looks similar, Im drawing a model as I write this.
> 
> 
> Pablo



Pablo, I screwed up my last post. It should have read posts 81 and 96. I will edit that post. Also worth a look is post 54. 
I've never had an older 7090 in my hands but I'm certain that the domes *are different * . Also the phorphor is applied differently. See datasheets for the polar intensity graphs.


----------



## chimo

Here's a visual:


----------



## Doug S

chimo said:


> Here's a visual:



Nice photo! There was one more type not shown, it is the XR that has the round ring as the third from left but the dome and phorsphor application of the fourth from left.


----------



## PEU

Well, the model looks similar, but I'm not sure if its accurate, there is a lot of internal reflections inside it. You are my judges 























Pablo


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## Doug S

PEU said:


> Well, the model looks similar, but I'm not sure if its accurate, there is a lot of internal reflections inside it. You are my judges
> 
> [
> Pablo



I think the ring has a bevel on the inside. Newbie might have a better photo but this post has a picture of one sectioned: 

https://www.candlepowerforums.com/posts/1705945&postcount=111


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## PEU

Added a bevel, tried two sizes, and it made the inner dome reflections worse, so probably there is another mistake in the model.

Could the lens be aspheric?


Pablo


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## chimo

You are right on the bevel. Here is a not quite to scale dwg.





The bevel likely reduces the internal reflections a fair bit.

Paul


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## AilSnail

this is the first pic in newbie's Creeang1.jpg, with some effects.


----------



## Doug S

Pablo, Ail, or whoever might benefit from having a dome as an aid for developing your model: There have been a few threads or posts by folks that have pulled the dome off of an XR-E to have their way with the naked LED. Perhaps you could track down one of those posts/threads and solicit a spare dome. Nothing to lose by asking.


----------



## Doug S

chimo said:


> You are right on the bevel. Here is a not quite to scale dwg.
> 
> 
> 
> 
> 
> The bevel likely reduces the internal reflections a fair bit.
> 
> Paul



That is a nice drawing. From the dimensions that I can check externally it is very much to scale. Do you know where that drawing came from?


----------



## chimo

Doug S said:


> That is a nice drawing. From the dimensions that I can check externally it is very much to scale. Do you know where that drawing came from?



Me, thanks.  It's an AutoCAD dwg I started based on what I could extrapolate from the data sheet, my own measurements and from others' pics. I have a Luxeon on the same dwg (plan and elevation views) - if anyone would like the file, just PM me your email address. 

Paul


----------



## NewBie

PEU,

Look up in your help file, you will find an entry for iso-candela and many other types of plots of output. When your model is correct, you should get a plot that looks the same as the datasheet.

I have torn the XR-E apart, and have some pieces that I should be able to measure when I get a chance.

PEU, do you have the cavity area under the glass lens of the CREE filled with silicone gel? (refractive index mismatches and such...) GESilicones, NuSil, and Dow Corning all have specialty silicone gels made specifically for LED purposes, so you should be able to get the typical RI ranges from those.


----------



## AilSnail




----------



## AilSnail

PEU said:


> Well, the model looks similar, but I'm not sure if its accurate, there is a lot of internal reflections inside it. You are my judges
> 
> 
> 
> 
> 
> 
> Pablo


looks like there is too little coming from low down on the dome surface.

Where is your focal point?


----------



## AilSnail

palette modified Newbie creeang4


----------



## AilSnail

I have noticed some very large tolerances on this product - this one had a vf of 64 KV:


----------



## PEU

Here is a post with nice pictures of an un-domed cree. I just sent Download a PM asking if he can take detailed photos of the dome/ring


Pablo


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## Doug S

Ail: :laughing: #192 and 189 (the fish)


----------



## download

Here your call.


----------



## Doug S

download said:


> Here your call.



Thanks download!! Great pics. Question: assuming that you have the means, how thick is that donut wafer in the middle of pic above? Thanks.

*Never mind. I see now that it is the bottom of the ring.* Your pictures got me so excited that I could not see straight!


----------



## PEU

Cool pictures Download Thanks!!!

One more question regarding the ring:





Newbie, I was using air in there, I will fill that space with silicone or something similar. good idea on the iso candela plots.

Back to drawing 


Pablo


----------



## chimo

A new pic with a slightly modified reflector cup:





Paul


----------



## download

Pablo, please update

top bevel: 3.5mm
bottom bevel: 3mm
distance from top to dome seat: 0.7mm

Doom/ring Thickness: 1.5mm
Total Thickness: 1.68mm


----------



## NewBie

For your 3.57 measurement, I am getting 3.14 to 3.16 mm
Base of lens holder to lip of lens seat, 0.83 mm
Outside ring to inside ring "thickness" 1.83 mm
Top/front face thickness inside to outside 0.79 mm

Here are some photos to clear a few things up:


----------



## Gryloc

Oh my! This is awesome! When I first rang in, AilSnail and Ra was discussing getting the most out of the XR-E by using different aspheric lenses. Now you guys are reverse engineering the XR-E!!! Sweet! This is where I hoped this thread was heading.  

I was wondering... I see you have pictures now of a naked XR-E, so you got a better measurement, but I hope you make sure things are right with the Luxeon K2. Working on my headlight project, I have accidentally killed a few K2's and that gave me a chance to remove the domes. Even though these are lambertian domed LED's (which when looking at the die should have the effect no dome at all), but the die sizes are even smaller than you guys may think. The dome makes a HUGE difference of how the light is bent (as AilSnail was figuring working with those graphs of luminance vs. angle). Well, I cant find them (I may have left them in my dorm). I remember that the die size seemed quite a bit smaller when the silicone domes are removed. I have a dead K2 in front of me but I don't know if I want to mutilate it or not (I was thinking of making something out of them - crafty!).  

I think that when my XR-E comes in the mail, I will use it for a while in different tests, but when it comes time, I am going to carefully remove the dome (or maybe not) and replace the old Luxeon I in my Streamlight 4AA ProPoly. That thing has a deep reflector and it should work out nicely. Maybe find a way to boost the current (if possible). That is the only good factory built LED flashlight I have to play with. I try to mod my own lights but I simply lack the funds. Oh well. I wish I was as far along with testing as some of you are with the XR-E. I got caught up in school work so much the last few months that I just discovered the XR-E for myself in the end of November (I am a XR-E noob).

Newbie, I am just amazed by some of the tests you have done lately for the XR-E and I had some questions for you. First, where do you work and where do you get the test equipment to find the brightness in lumens and the temperatures of the dies in operation and the color rendition of the LEDs? I have seen posts elsewhere of your findings (amazing) and I have been using those numbers when coming up with plans for these Cree's. Also, what software are you using for simulating the beam patterns of different reflectors (not the ray-tracing one)? Was it very expensive? Is there free programs out there that can simulate light patterns and stuff, even if it is primitive and not very powerful? I always wished to test flux measurements of my headlight project at different distances, because it is tough to use a roughly drawn Solidworks drawing and Exel to figure formulas and stuff and get close measurements. Maybe you can help me out with that if it is at all possible. Thanks!

Finally, what is the goal NOW of this forum? Is it still finding the ideal reflector for the XR-E? I see that is where you are heading, but it is hard to tell when you guys use the seemingly jumbled ray-traces. Wouldn't it be easier if you experimented strictly with the naked XR-E and without that oddly positioned lens? Keep up the great work! This thread is moving fast! I still need to read some of the pages in between. Good luck...

-Tony


----------



## chimo

Newbie, they look like different rings. :thinking:

Has Cree changed parts?

Paul


----------



## NewBie

Gryloc said:


> Newbie, I am just amazed by some of the tests you have done lately for the XR-E and I had some questions for you. First, where do you work and where do you get the test equipment to find the brightness in lumens and the temperatures of the dies in operation and the color rendition of the LEDs? I have seen posts elsewhere of your findings (amazing) and I have been using those numbers when coming up with plans for these Cree's. Also, what software are you using for simulating the beam patterns of different reflectors (not the ray-tracing one)? Was it very expensive? Is there free programs out there that can simulate light patterns and stuff, even if it is primitive and not very powerful? I always wished to test flux measurements of my headlight project at different distances, because it is tough to use a roughly drawn Solidworks drawing and Exel to figure formulas and stuff and get close measurements. Maybe you can help me out with that if it is at all possible. Thanks!
> 
> -Tony



I do a lot of stuff at home.

I work for the Avionics division of a company as a Senior Design Engineer. Previously I was a Product Development Engineer, but I mainly did applied R&D)
Before that, I worked for FLIR Systems, Inc.
Before that, I worked on secret Electronic Countermeasures and Jamming, RADAR (weapons targeting, terrain following, and weather types), Flight Control Systems, Forward Looking Infrared Detecting and Ranging systems, Weapons control and release computers, Automatic Carrier Landing systems, Inertial Navigation systems, Doppler Navigation Communication Systems, and quite a number of other things.

I use TracePro from Lambda Research, and they are *extremely* helpful with their program too. Yes, quite spendy, but you may not need all the options, it does WAY more than what flashlight/headlight folks need. I don't have it, but their photorealistic rendering looks extremely cool. They do offer trial licenses.

Chimo-
Let me try and check to make sure I didn't pick up the old XL7090 ring on accident, which is possible.


----------



## Doug S

Gryloc said:


> Finally, what is the goal NOW of this forum? Is it still finding the ideal reflector for the XR-E? I see that is where you are heading, but it is hard to tell when you guys use the seemingly jumbled ray-traces. Wouldn't it be easier if you experimented strictly with the naked XR-E and without that oddly positioned lens? Keep up the great work! This thread is moving fast! I still need to read some of the pages in between. Good luck...
> 
> -Tony



Regarding the jumbled ray-traces, Newbie makes an excellent suggestion in post 155 to limit the model to 2D if possible for clarity of viewing. For those with the computer models to work with, you are going to leave me it the dust as I am of the school that if I cannot solve it with a slide rule and arithmetic, I won't tackle the problem. I **am**, however, very much enjoying the contributions of those with the computer models and the means to run them. We haven't heard from Ra in awhile, I hope he is one of those too. 
A question for you modelers: Is the capability of your softwares only to give resulting performance after you give it the source and optic parameters or can they *additionally calculate the optic parameters* given the source parameters and desired performance as well as some bound on optic parameters such as diameter or length? This question relates to my answer to the question raised by Tony: 
*> Finally, what is the goal NOW of this forum? Is it still finding the ideal reflector for the XR-E? <* 
I would like to see the answer to the real world problem raised by McGizmo. 
I think it is safe to talk about it now that we have successfully run him off with all of our ideal model mumbo-jumbo  
Here is my take on the real world problem: Given a defined source to optic size ratio and intensity plot, how do we maximize total % flux in a given radius for a set of ratios of R/D [radius/distance], say for 1/10, 1/20, 1/50, etc? Modelling to apply to distances beyond which the inverse square law applies, i.e., ignore the ''near field'' effects as we say in EM theory. 
Further, I think the Cree XR-E is a poor choice as the source for this exercise for the reasons I gave in post #54. Since this is going to take some considerable effort if anyone here has the means, ability, and time to tackle this problem, I suggest making it as useful as possible to the most possible situations. For this, a flat circular lambertian emitter, makes the most sense. I suggest circular only because it will be computationally easier than a square source and if for real emitters if we plug in the area equivalent circle into the model for any square die we may have, the result should be pretty close. This circular equivalent approach also avoids any confusion that could arise in the 2D model representations since you don't have the question of whether the plane slices the die across the flats of the sides, diagonal corner to corner, or anywhere in between.
Go for it guys


----------



## AilSnail

I disagree Doug. A model using an approximation of an oldscool LED as the source? That would be useful a year ago, and possibly in a few months again, but right now the state of the art LED has got weird radiation characteristics that are weird enough that any model not taking it into account is going to be quite inaccurate, it is my feeling. Especially the huge optical displacement, and the weird angular luminance pattern: you can see that the maximum flux within a solid angle is going to be achieved by something else than a parabola....


----------



## AilSnail

For instance you may imagine a reflector that is focusing always on the apparent hotspot - if you made that reflector, then you can see that the higher luminance average wil hit a very long fl reflector, see the last fishy graph, the luminance curve is rising towards higher angles.. utilising the angles between 40 andb 65 is going to be counterproductive to achieving highest lux.

It looks like for a high lux one could use a F/1 lens, combined with a 0.25 Dia/length reflector.. not a parabolic though. The bucket in the luminance curve would exit untouched, and the front peak would be collimated by the lens, and the side peak would be collimated by the reflector.

Finally, here is one for you Doug:






Tracing a ray to the surface of a parabola with a known focal length (f), sent from 0,d (x,y).
For d values vs angle values, refer to the optical displacement graph a few posts earlier. 
y on the napkin would be Z in the 3d world, as defined earlier in the thread.


----------



## AilSnail

> Further, I think the Cree XR-E is a poor choice as the source for this exercise for the reasons I gave in post #54.



Reminds me of this joke: Fellow looking for his keys under a streetlamp, asked by other fellow: "Where'd you loose them?" "over there" (points). "why you look over here then?" "Cause it's too dark to se anything over there".


----------



## Doug S

AilSnail said:


> I disagree Doug. A model using an approximation of an oldscool LED as the source? That would be useful a year ago, and possibly in a few months again, but right now the state of the art LED has got weird radiation characteristics that are weird enough that any model not taking it into account is going to be quite inaccurate, it is my feeling. Especially the huge optical displacement, and the weird angular luminance pattern: you can see that the maximum flux within a solid angle is going to be achieved by something else than a parabola....



Your disagreement is noted. We *do* agree that solutions for the XR-E are of interest now because it offers such high performance relative to it's competiton. I believe, however, that emitters that have approximately lambertian distributions will continue to be the majority. Other manufacturers are already packaging and releasing the high efficiency Cree die in emitters with approximately lambertian distributions. Further, for reflector applications it would appear that the lambertian distribution would be preferred over that of the Cree in most applications. Ultimately, the choice of what to model will belong to whoever is willing to do the hard work!

The Napkins are back! I was worried about them.


----------



## AilSnail

So, can you solve it or did you already smear popcorn butter over it? 
for a lambertian distribution without optical displacement you have already solved for the lux: it will be proportonal to reflector diameter squared times the luminance - which is equal at all angles if I understand the term lambertian correctly. 

correct me if I'm wrong.


----------



## Doug S

AilSnail said:


> So, can you solve it or did you already smear popcorn butter over it?
> for a lambertian distribution without optical displacement you have already solved for the lux: it will be proportonal to reflector diameter squared times the luminance - which is equal at all angles if I understand the term lambertian correctly.
> 
> correct me if I'm wrong.



I believe you are correct for the point source LED's. When I went to order some, however, they were not in stock  
The real world problem is still begging for solution.


----------



## AilSnail

Exactly, so what features does the real world have that will affect the mentioned relationship between lux, luminance and reflector diameter? * edit: Or are you saying the leds don't have a equal luminance in all directions, even when they are lambertian? (ie big enough deviation to make a difference)

I made a polar earlier in the thread, showing the luminance of the L3, assuming it had no optical effects, and no side (vertical) area. It shows a decrease to 90% at 80 deg.*


----------



## Doug S

AilSnail said:


> Exactly, so what features does the real world have that will affect the mentioned relationship between lux, luminance and reflector diameter?


*Area*. All of it but one point lies away from the reflector focal point.


----------



## AilSnail

so you are assuming that if you keep luminance and reflector diameter constant, area makes a difference in lux? (I edited previous post)


----------



## AilSnail

Or maybe you are talking about lux as the lux at a given beam angle, as would be consistent with your translation of McGizmo's problem....


----------



## Doug S

AilSnail said:


> so you are assuming that if you keep luminance and reflector diameter constant, area makes a difference in lux? (I edited previous post)



Yes, I have always *assumed* this. Perhaps only because I have not been shown that my assumption to be wrong. It certainly intuitively seems to be so, to me anyway.


----------



## Doug S

AilSnail said:


> Or maybe you are talking about lux as the lux at a given beam angle, as would be consistent with your translation of McGizmo's problem....


Actually stepping back a bit, I am interested in the McGizmo question of optimizing % lumens delivered within a defined radius at a defined distance or aspect ratio, e.g.. 1:20, where the die has area.


----------



## AilSnail

But Ra already told you that you are wrong, if you are measuring the center of the beam, only a *very* small area around the fp is projected onto your lux meter. Wheatever is outside that very small area will be projected to outside the luxmeter.
otherwise, show me how a parabola can redirect something that is outside the fp by 0.5mm to a point (or to the area of a luxmeter) on the z axis 100m away.

the area matters though, for the question in your post in #216. As for in what way it matters, along with the other parameters, uhh.. let's see in a few pages, maybe?


----------



## Doug S

AilSnail said:


> But Ra already told you that you are wrong, if you are measuring the center of the beam, only a *very* small area around the fp is projected onto your lux meter. Wheatever is outside that very small area will be projected to outside the luxmeter.
> otherwise, show me how a parabola can redirect something that is outside the fp by 0.5mm to a point (or to the area of a luxmeter) on the z axis 100m away.
> 
> the area matters though, for the question in your post in #216. As for in what way it matters, along with the other parameters, uhh.. let's see in a few pages, maybe?



My night to be off to a party. I will have to think about your comments another day.


----------



## NewBie

chimo said:


> Newbie, they look like different rings. :thinking:
> 
> Has Cree changed parts?
> 
> Paul




As I mentioned, I might have, and actually did.

Sacrificed another one to be certain:


----------



## chimo

NewBie said:


> As I mentioned, I might have, and actually did.
> Sacrificed another one to be certain:



Thanks Newbie! Looks like Cree may have optimized the curve on the reflector ring for the XR-Es.

Paul


----------



## Doug S

AilSnail said:


> But Ra already told you that you are wrong, if you are measuring the center of the beam, only a *very* small area around the fp is projected onto your lux meter. Wheatever is outside that very small area will be projected to outside the luxmeter.
> otherwise, show me how a parabola can redirect something that is outside the fp by 0.5mm to a point (or to the area of a luxmeter) on the z axis 100m away.
> 
> the area matters though, for the question in your post in #216. As for in what way it matters, along with the other parameters, uhh.. let's see in a few pages, maybe?



I think you are right that I had that wrong. I probably was thinking of the post #216 as I typed. As to: *>show me how a parabola can redirect something that is outside the fp by 0.5mm to a point (or to the area of a luxmeter) on the z axis 100m away.<* I don't think I can if you limit it just to parabolas. In any case, if it can be done, I am certain that we cannot carry it in our pockets!


----------



## Doug S

Newbie: nice photos!


----------



## PEU

Nice photos newbie, Im away from home (Im in the north of Argentina right now) but I will try to incorporate these modifications in the model im making as soon I return to my office. 


Pablo


----------



## AilSnail

Looking fwd to more raytrace goodies.

Some voluntary homework: http://en.wikipedia.org/wiki/Directrix


----------



## AilSnail

here is a curve to draw; a locus of points where angle (die fringe, p, focal point) = viewing angle from z.


----------



## AilSnail

so you would choose your va and distance between fp and df.
it will intersect the parabola at the edge of the lit part of the reflector.


----------



## AilSnail

Incidentally, this curve looks like a circle.


----------



## AilSnail

*almost:*Its radius appears to be radiusDie/4tan(va/2)
and its center at x=die radius/2 , y = its radius - *when fp is at (0,0) and die fringe is on the x*.
Not sure if it is extremely useful, but I think it is rather neat.


----------



## AilSnail

to reiterate, if you stand d degrees from the z, the closest point where the reflector is lit up is where the circle intercepts it.

edit: not quite, it appears, but almost 
edit: to put it more accurately, the center of the circle is where lines perpendicular from the middle of lines (p-f) and (p-die fringe) cross.


----------



## AilSnail

but ofcourse, the fp and df is on the circle, then it is accurate.


----------



## AilSnail

old napkin


----------



## Gryloc

Ha ha haa... Nice napkin notes! I try to make notes on napkins, but they tear too easily. I tried resorting to toilet paper, but that is even worse! I guess old scrap computer paper will have to do. I like the choice of pictures you used. It looked like you were pretty bored, unless cats, breasts, and that formula will solve the huge problems of today's optics... WAIT! I GOT IT! It is soo simple and it was under your nose the whole time! Oh, wait a minute... Actually, I was wrong. False alarm... Oh well. Sorry.  

I was wondering about the XR-E. Download and NewBie had experience with *naked*  XR-Es. What type of optical characteristics (radiation pattern) does it have without the aspherical lens and the holder ring? Would it have a true Lambertian radiation pattern or would it be different?

I was wondering because I was thinking about stripping the thing after I get some testing done and using it in a light that once used the classic high dome LuxI. Would the radiation pattern better match the typical Luxeon I or III if I would attach a different dome onto the the naked XR-E emitter? I have some old soft K2 domes that I can attach to the top of the die (using some silicone). I dont know if those dome promote a true lambertian beam pattern of of it would change it to what us Lumileds users are just used to. I hope that I am making sense here. Actually, what is the true Lambertian beam pattern? Is there a proper definition and is there a picture of the radiation pattern?

I was looking at the data sheets from Lumileds and the K2 has a wider lambertian pattern than the Luxeon I and III (funny since the LuxV was the "same" as the LuxI&III in the specs sheet). Does this wider pattern (while still smooth) make it more "Lambertian"? This doesnt tie into me using the K2 dome above over the others, it is all I have available.

Download and NewBie, when the XR-E is naked, do the bond wires look very fragile and vulnerable, or will it be safe in a secure place in a flashlight and safe from possible accidental touching? From pictures, it looks like the bond wires are really low and hidden under some silicon or something. Is there a hard coating over the die and phosphor coating? I know that most Lumileds emitters seem to be destroyed when you remove the dome, but is it easy to destroy the bond wires when modding the XR-E? I see so many people here at CPF doing this mod for their flashlights, so I am assuming the Crees were built a bit better. I sure do not want to put my new Cree in danger or anything. I also thought that the K2 dome glued on top might protect the die and bond wires a little. I seen how to properly remove the dome and ring on CPF, and I am confident I wont totally mutilate it.

I was thinking lately that maybe trying to create a dramatically new reflector and optic for the new and different XR-E might be pointless. I say this because both Seoul Semiconductor (with the P4) and Edison Opto are both coming up with the LED with the new Cree die while still using the Lumileds-style package design. Do you guys think that Cree will conform and use the Lumileds style in the future (even if it may be a patented design), or will they come up with their own idea that is even better? I think the current package is a nuisance because it still doesn't seem practical. It seems like they got the die right, but they didn't put the same thought into the package (I do like the true electric isolation and good heat transfer with the ceramic base). They just re-used their old designs it seems. I am not saying that what you guys are doing is pointless, because it is not at all. Designing an all-around better optic for LEDs in general is great! What do you guys think so far?

Keep up the good work. I just discovered an envelope in the pile of mail that was from Cutter Electronics, so I got my P3 bin XR-E and optics in the mail (hurray!). Time to start my experimentation! Muah ha ha haaa! Have a nice New years! 


-Tony


----------



## Doug S

*Quote Gryloc: I was looking at the data sheets from Lumileds and the K2 has a wider lambertian pattern than the Luxeon I and III (funny since the LuxV was the "same" as the LuxI&III in the specs sheet). Does this wider pattern (while still smooth) make it more "Lambertian"? This doesnt tie into me using the K2 dome above over the others, it is all I have available.*

Lambertian distribution has a specific mathematical definition. Leds with ''lambertian'' distributions are only rough approximations. A true lambertian distribution has an intensity that is proportional to the cosine of the angle off-axis. Intensity thus is zero at 90 degrees off-axis. Real Leds usually have non-zero intensity at 90 degrees off-axis due to photons coming out of the edge of the die.


----------



## AilSnail

gryloc, it was much better the first time but it got destroyed as napkins do.
the formulas aren't even solving the simple lambertian situation entirely, and the conic section isn't even a parabola. 
but so far i have learned lots about geometry and math, which was fun. 

a lambertian polar graph looks like a ring where the die is at the edge of the ring. see a bit earlier in the thread, the bare cree ez1000 intensity graph. the fun thing about a lambertian intensity is that apparent area has the same graph, and since luminance is intensity/area it is equal at every angle.
Here is another of the neat parabola formulas: if x^2/4fl=y, then distance from focus point f to any point p on the parabola is y+fl. You see, there is a secret line behind any parabolic curve, at 2fl from the f. It is called directrix, no kidding. 

One of the ways to calculate the beamshape would be to mask all of the reflector but a tiny spot p and use the p-f distance and angle to find out how large and what shape the reflected source is. Then remove the masking tape and move the spot a bit down, repeat and add. 
Another would be to calculate the projected lit area of the reflector, as seen by someone standing somewhat off axis down range. Can't help but think though, that with a circular lambertian die there might be an "integrating" formula that made lots of operations and summing unnecessary.

For the cree'd bola I tried to mod the fl in the std formula depending on angle from source. y=x^2/4(fl+d) where d is the vertical optical displacent of the cree for the angle in question - as it would be if the hotspot was assumed to stay on the z. It gets a rounder bottom as if you'd filled a condom with water. It'd have to be smoothed, and I haven't ray traced it to see if there is any improvement in the parallellness of the beam. It should also be possible to construct a formula from the standpoint that every section of the reflector curve have half the angle to Z as the light that hits it. It might amount to about the same end result, not sure.

Don't know why they chose all that magnification, probably had something in mind? IIRC newbie said it was optimized to get the light out of the thing, so maybe the lamb. versions will not be as efficient?
*edit: the lux readings from lights are better than the luxeons, aren't they? so the luminance can't be that horrible?*


----------



## zzonbi

"to find out how large and what shape the reflected source is"

Rays from focus of a parabola emerge parallel once reflected. The angle of the spot projected at distance is equal to the one the emmiter itself is seen from a point on the reflecting surface. If you remember the concept of 'arc capable of a given angle' you can find the point where the emitter is seen with maximum apparent size.

Picture a small circle with the emitter radius its diameter. Now grow this circle, keeping the emitter radius its chord, until it meets the parabola. That's the point.

Numerically, an approximation for the spot angle is atan(l/8f) (l=led diameter, f=parabola focal length). This works best when l<<f.

If we consider rays reflected from below the focal plane too, the angle can be much larger, but less than atan(l/f). In reality emitters are encapsulated in silicone which boosts their apparent size, so you need to account for that too (eg multiply with silicone refractive index). As for shape, I guess it roughly follows the emitter. 

So this is what it takes to have all reflected light in a spot size 1/20th of the distance (which has nothing to do with the correct throw definition, the one Ra gave, btw).


----------



## Isthereanybodyoutthere

Hi ,,i am pretty new here ,sorry to hijack this thread ,,but it seams like the one`s who know is here :thumbsup:
I have posted a thread earlier ( how do i make a god infrared flashlight )
Didnt get much response

So i did find this thread about a IR flashlight with a colminator lens looks perfect 
https://www.candlepowerforums.com/threads/125540
And this with a blue with a spherical lens 
https://www.candlepowerforums.com/threads/182716 

i have been thinking of using these IR led`s
does any one know of better ones ??
http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3247

So to the Q `s 

Correct me where i am wrong please 

If i use a spherical lens

If the led has a 120 degre angle 
The lens has to have a diameter that is 1,732xfl x2
If the lens is like in the blue mag 
The spot that the led would make at 35mm would be 
Tang to 60 degre (half the emitter angle1,732) x the focus lengthx2 (we only did use half the angle )=121,24mm 

To me it would seam that a lot of light would get lost ( am i right or wrong??)

But the beam shoot of the blue one is looking god and the relector gives some spill ,,but the spill is ""out there "

So the carclo lens would be the winner ( am i right or wrong??)

no meaning in trying to find a reflector if i want to stay at about 50mm ( am i right or wrong??)

I want as little spill as possible because the light close up would reflect back and might blind me 
And sins i will use a NV with 2,3 x magnification ,,its out there i need the light ,not close up


----------



## zzonbi

"To me it would seam that a lot of light would get lost ( am i right or wrong??)"

The calculus looks right, but in reality the led may leak light beyond 120 degrees too. It is hard finding a lens with such a short focal vs its diameter.

"So the carclo lens would be the winner ( am i right or wrong??)

no meaning in trying to find a reflector if i want to stay at about 50mm ( am i right or wrong??)"

Yes, TIR optics seems the best bet. A reflector only cannot control all light.

Before using an IR led I would check spill with visible light. Beware if using refraction, indexes are different at IR wavelengths, though perhaps not by a a whole lot. To stay safe you can also limit spill by adding a conical matte tube after the optics. That's how the blue flashlight doesn't spill much light, it actually absorbs it before the optics.


----------



## Nos

ive been reading this thread for 2 hours now.....and i think i got the most of it

this thread is just great....so many of my questions got answered

hands down to all of you ...

now feeling truly "enlightened" thank you guys


----------



## zzonbi

Sadly d/8f (d die diagonal, f parabola focal) is not valid for skew rays not in plane with the main axis. For those the angle gets as worse as atan(d/2f) as seen from where the focal plane cuts the parabola. The spot becomes 4:1 oblong, but rounds again for the whole paraboloid, because of the rotation symmetry.
Anyway these 3 values picture a reasonable estimate for what to expect for a paraboloid reflector.


----------



## koti

This is by far, the best thread I've red on CPF untill now.
I've spent at least 2 hours reading it, I dont understand everything but most (at least I think so)
It was pure pleasure to see that discussion about "throw" between Ra, McGizmo, Ailsnail, DougS and others. 
Physics & Optics knowledge combined with human perception differences - candy to my brain


----------



## Ra

Hi koti,

Thanks for your remark..

It shure was fun to do. And if you have questions about this subject, don't hessitate to ask!
That is what these forums are about! To shine light on what others want to know..

all the best,

Ra.


----------



## koti

Actualy I do have a question about the "optics" subject...
Can You get me an EF 70-200 f/2.8 L *IS* in that lab of yours for free for being a good sport ? 
I'll take a used one too...

cheers






Edit:
Just kidding Ra...thank you again for all your input in this thread, I learnt a lot.
As for surface brightness (I actualy got realy atracted to the term after reading your posts) which you mention a lot in your posts, I have a toy that should be able to beat Your Maxablaster 
Here it is...a 372mw (measured) green laser...full angle divergence = <0.9mrad
Runs on a single 18650 (2500mah lasts for 3 to 4 minutes max)





As for "throw" and surface brightness I should own all the participants of this thread
Unless that is...someone here has a true 400mw+ TEM00 green laser 







Ra said:


> Hi koti,
> 
> Thanks for your remark..
> 
> It shure was fun to do. And if you have questions about this subject, don't hessitate to ask!
> That is what these forums are about! To shine light on what others want to know..
> 
> all the best,
> 
> Ra.


----------



## koti

Ra,

As for real questions, I have one.
I dont want to make an idiot out of myself but here it goes :

If I have 2 flashlights with identical emiters and identicaly polished reflectors of same material (with the same circumference at the widest point) where one reflector has a larger "shine" area than the other, then the flashlight with the larger area reflector will give more throw ?
More simplified...if one of the reflectors is more "cone shaped" then "disc shaped" (has a larger area) then it will give more "throw"
If not, Im going to read the whole thread again and try to understand...


----------



## zzonbi

The deeper reflector gives a larger spot (smaller f), but both have the same throw (same lux at the spot center) because they are the same diameter. It's not the mirror area, but beam exit area.
Now go reread the whole thread with the remaining good eye ;-)


----------



## Bullzeyebill

If both have the same lux, or throw, then the one with the larger hotspot will illuminate more at distance, and appear to have more throw.

Bill


----------



## zzonbi

More but not farther.
Will appear to have more spot (perhaps less spottable, less edge contrast), but won't throw farther. A distant observer couldn't tell them apart.

If you want, more at distance (spot), but not at more distance (throw). Flux vs lux. Quantity and quality.


----------



## koti

Not further - agreed.
But deeper reflector will be brighter then a shalow reflector, right ?
Whats the reason behid putting deep reflectors into flashlights anyway ?
Oh and...its not the eye...its the green thing attached to it in the back I guess.


----------



## zzonbi

"Whats the reason behid putting deep reflectors into flashlights anyway ?"
To control the spot/spill ratio. More spot, less spill.

You seem to be confused by the fact that the mirror has more area. Try this: do you see a bulb vary brightness as you look at it in a tilting hand mirror? I guess not, same image. But as you tilt it more you're using more area of the mirror, no? I think yes.


----------



## koti

zzonbi said:


> "Whats the reason behid putting deep reflectors into flashlights anyway ?"
> To control the spot/spill ratio. More spot, less spill.
> 
> You seem to be confused by the fact that the mirror has more area. Try this: do you see a bulb vary brightness as you look at it in a tilting hand mirror? I guess not, same image. But as you tilt it more you're using more area of the mirror, no? I think yes.




So the deeper the reflector the more focused the beam - which is logical to me. But this has to mean more throw which I think is totaly oppposite to what RA was saying all along this thread ?! 

A tilting hand mirror doesnt focus light therefore I would leave it out because I moght get too confused and my head could


----------



## saabluster

koti said:


> So the deeper the reflector the more focused the beam - which is logical to me. But this has to mean more throw which I think is totaly oppposite to what RA was saying all along this thread ?!
> 
> A tilting hand mirror doesnt focus light therefore I would leave it out because I moght get too confused and my head could


The deeper reflector does two things when compared to a reflector of the same diameter. It captures and collimates more of the light output from the LED. And what it does capture on the "extra" portion of reflector is more collimated thus leading to more throw. The farther away from the source the reflecting surface is the better collimated the resulting beam will be because at that farther spot the source will "look" smaller and more point source. This makes for more throw and is why you see the thrower lights getting deeper and deeper reflectors in an attempt to one-up the other. Ra's posts don't make sense and I stopped listening to him a while back. Not trying to start a fight Ra, just saying.


----------



## koti

Now Im realy confused.
This is a lot of contradiction - I will have to read thru the whole thing again when I have time and rethink all this.
Im sure of one thing though...What Ra's is saying and what saabluster (and others) are saying contradicts totaly so this is not exhausted.

Im thinking...why do throwers have deep reflectors?
If what Ra's saying is coprrect then we should have tiny monster throwers available, why dont we have them ?

Also...if something is brtighter then doesnt it mean that it will throw further ? I mean...if You have 2 identical flashlights with identical reflectors only with different emiters (one stronger then the other) then surely one of the flashlights will be both brighter and have more (a little more) throw ?

This is all weird...


----------



## zzonbi

"So the deeper the reflector the more focused the beam"
I just said the larger the spot. Despite more reflected light maximal brightness is the same, except for minor differences caused by the smaller non emitting focal plane (the flat disc in plane with the die).

"If what Ra's saying is coprrect then we should have tiny monster throwers"
And we don't have them because it is correct: you need large diameters (easy) or high led brightness (not so easy, therefore Ra uses an arc lamp). Or 'cheat' with the laser effect.

Now you have all the cards. You need to decide yourself what is correct. Good luck.

PS I must remind that this theory applies to uniform or lambertian sources. Sources packaged in altering optics may skew the results one way or the other.
eg leds with beam tightening packages could hardly give a spot from a shallow reflector, a batwing profile may send less light to the edge of a deep one.


----------



## Nos

:bump:


----------



## saabluster

Nos said:


> :bump:


Do you have something to add here? If not why the bump? This isn't a sale thread.


----------



## Bullzeyebill

saabluster said:


> Do you have something to add here? If not why the bump? This isn't a sale thread.



Yes, bunping is usually used in sales threads. I think that Nos really wants to know if there is any new info available since the last post in January?

Bill


----------



## koti

Yeah, I got something to add...
Im too dumb and lazy too analize this whole thread from scratch plus there seems to be lack of a clear goal in all the talking, but...
If "Ra" is talking crap then how come he built the longest throwing flashlight existing on this forum ? He built it 2 years ago and still noone beat his achievement. Thats gotta count for something...


----------



## saabluster

koti said:


> Yeah, I got something to add...
> Im too dumb and lazy too analize this whole thread from scratch plus there seems to be lack of a clear goal in all the talking, but...
> If "Ra" is talking crap then how come he built the longest throwing flashlight existing on this forum ? He built it 2 years ago and still noone beat his achievement. Thats gotta count for something...


So what. I made the longest throwing LED flashlight by far but it doesn't mean I know anything.


----------



## koti

It has been a long time, finaly found some free time to read thru the Ra portion of this thread again...
 
I think that Ra's statements are all correct, couldnt find any contradictions. Maybe they are incomplete though ?

I just want to know why a Deerelight DBS thrower has this reflector:






instead of this reflector :







Ra please excuse my ignorance and lack of knowledge but could You please answer this simple question for me ?


----------



## gcbryan

koti said:


> It has been a long time, finaly found some free time to read thru the Ra portion of this thread again...
> 
> I think that Ra's statements are all correct, couldnt find any contradictions. Maybe they are incomplete though ?
> 
> I just want to know why a Deerelight DBS thrower has this reflector:
> 
> 
> 
> 
> 
> 
> instead of this reflector :
> 
> 
> 
> 
> 
> 
> 
> Ra please excuse my ignorance and lack of knowledge but could You please answer this simple question for me ?



I think the answer is so that the spot is big enough to see at a great distance (throw). The depth is so it doesn't look like a laser (pinpoint) and the reflector diameter along with the emitter provides the brightness (throw).


----------



## koti

I think the answer is so that the spot is big enough to see at a great distance (throw). 
This doesnt make sense to me...the spot in throwers is narrow in order to throw further. If it was big like You say, a thrower would not throw far. Besides the deepness of the reflector does not effect the size of the spot, the deepness of the reflector affects the amount of collected lumens from the source.
The depth is so it doesn't look like a laser (pinpoint)
So are You saying that if the DBS reflector was very shallow the light would look similar to a laser? I dont think so...
and the reflector diameter along with the emitter provides the brightness (throw).
According to Ra, the diameter of the reflector along with the surface brightness of the source will affect throw. Brightess and throw are 2 totaly different things. But Your last sentence seems correct 

Here are some quotes by Ra :

#7
That is why the lens- or reflector-diameter determines the throw of a torch. (together with the surface brightness of the source)

#20
You are propably not going to beleve what I'm going to tell you now: THROW IS ABSOLUTELY NOT AFFECTED BY THE FOCAL LENGTH OF THE REFLECTOR OR LENS !! ONLY LUMENS OUTPUT IS !!
FACT: The apparent surface brightness of the reflector cannot ever be higher than the surface brightness of the source! It always is lower due to reflection losses in the reflector.

#123
So, For you, and everyone who didn't know this: A learning moment:
THROW IS DETERMINED BY THE DIAMETER AND EFFICIECNY OF YOUR LENS OR REFLECTOR and THE SURFACE BRIGHTNESS OF YOUR LIGHTSOURCE.
LUMENS OUTPUT IS DETERMINED BY THE DIAMETER AND EFFICIENCY OF YOUR LENS OR REFLECTOR and THE FOCAL-RATIO OF YOUR LENS OR REFLECTOR
 
I dont understand why literaly all throwers have deep reflectors...why is that if according to Ra, throw has nothing to do with the deepness of the reflector?


----------



## IMSabbel

koti said:


> I dont understand why literaly all throwers have deep reflectors...why is that if according to Ra, throw has nothing to do with the deepness of the reflector?



Well...
If you look at it practiaclly: Your LED has an emittance pattern. The reflector diameter and the source size determine the hotspot diameter.
The deepness determines how much of the lumens of the light actually hit the reflector.
(leds are anisotrophic emitters)


----------



## koti

IMSabbel said:


> Well...
> If you look at it practiaclly: Your LED has an emittance pattern. The reflector diameter and the source size determine the hotspot diameter.
> The deepness determines how much of the lumens of the light actually hit the reflector.
> (leds are anisotrophic emitters)


 
What pattern are You reffering to, placement of photons along the viewing angle? Photon density pattern?
The reflector diameter does NOT determine the the hotspot diameter...at least thats what Ra is saying...
The deepnes of the reflector determines the amount of lumens that hit the reflector? Thats weird...
If LED's are "anistropic" then filanment sources are "isotropic" ?
That may be true since LED's are more directionaly dependent than bulbs but I dont see how that corelates to my question.


----------



## gcbryan

I'd like to see RA return to this thread!

I (now) think that the diameter (along with the emitter) determines how tightly focused the hotspot is and therefore how intense. I think that depth (to a degree) does the same thing by redirecting more lumens from spill to the hotspot.

I'm still not clear as to how RA would address this issue. I'm still not clear as to whether depth in addition to redirecting more lumens to the hotspot is also resulting in more collimated rays due to the increasing distance (more point source like). I'd like to hear RA's take on this.


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## Ra

Ok then, Here I am !!

Some of you exactly know what this is all about, but are still quite easily forced into doubt by others..
For example zzonby is exactly right:

With the same lightsource, throw is absolutely not affected by the deepnees of the reflector!! If it is affected, it's caused by other things like difference in surface quality of the reflector, or reflectivity of the reflection layer.

Yes: Deeper reflectors produce a wider beam, why?: Because they simply grab more emmitted lumens from the source, because they are more 'folded' around the source..

No: Deeper reflectors do not produce more throw because the apparent surface-brightness of the reflector remains the same. Note that this only involves reflectors with the same diameter !!

Important: These are theoretics, based on using the same source in both situations and using perfectly formed parabolic reflectors!

Why do few people actually measure otherwise: Shallow reflectors need to be more precisely formed than deep reflectors, in order to be totally lit by the source for an object far away.. You first need to be certain of the quality of the stuff you tend to use, before putting the theory to the test.. Beleve me: I've done it, and things behaved exactly as theory predicts..

Fact: Look in the reflector from a distance more than 50 meters, with the torch operating (use heavy sunglasses or a welding filter) Now if the reflector does not seem to be fully lit, you are not effectively using it. The shape can be wrong or you simply need to focus the reflector till it is fully lit.

Now take two situations: Deep reflector, and shallow reflector.. Both clearly fully lit by the source when you look at them from a distance of 50 meters or more..
Now try to tell wether you are looking at the shallow reflector, or the deeper one..

Let me tell you the result: YOU CAN'T !!.. Both reflectors seem equally bright. This also means that for the exact spot where you're standing that moment, the lux reading will be (more or less..) the same for both reflectors.

Only if you begin to move sideway's, the shallow reflector will be first in loosing effectivity, it will no longer be fully lit

The gain in wideness of the spot with the deeper reflector only comes from the fact that you grab more lumens from the source, which is evenly spread, further away from the center of the spot..


Sorry, I cannot be more clear than this at the moment.. 

If you have questions, post them here, I'll answer them (if I know the answers ofcource..)


Regards,

Ra.


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## Ra

saabluster said:


> So what. I made the longest throwing LED flashlight by far but it doesn't mean I know anything.




Wait till I really am going to design a LED-thrower... Could be in a few day's, or weeks, even month's.. But my (second..) time of glory will come.. :naughty:


Regards,

Ra.


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## gcbryan

Thanks RA.

So, just to clarify (I know it's obvious at this point but bear with me please)...

The reasons that lights that are considered to be "throwers" frequently are deep as well as wide are...

1. They have to keep the shape of a parabola so since they will have larger diameters (as opposed to a non-thrower) the depth will increase as well if for no other reason than for that reason.

2. Since the spot becomes more narrow and intense (tightly focused) with increasing diameter reflector depth is frequently increased to make the hotspot a little more useful at less than max throw.

Are those two statements more or less accurate?

Also, I have a reflectored thrower (Uniquefire HS-802) that has a reflector diameter of approximately 45 mm and a depth of approximately 56 mm. It uses a XR-E R2 driven at 1A. The hotspot seems (to me) very small even though the depth is relatively large.

The explanation for this (I know you don't have this light in front of you) would be that without the depth the spot would be even smaller?

Would that be correct?

Thanks again for coming back to clear up a few aspects of this subject. This thread was clear to a point with what throw is but didn't address as clearly the question of why do many throwers have deep reflectors if it's not related to throw.

Thanks for clearing this up.


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## Ra

koti said:


> Not further - agreed.
> But deeper reflector will be brighter then a shalow reflector, right ?
> Whats the reason behid putting deep reflectors into flashlights anyway ?
> Oh and...its not the eye...its the green thing attached to it in the back I guess.



Yep, a deeper reflector will be brighter, but only in lumens output, and more lumens does not nesseseraly mean more throw.. Definitely not when the reflector diameter does not change..

So the reason for putting deep reflectors into flashlights is obvious: By putting more lumens from the source into the main beam, you get a better compromise between throw and sidespill. Simply improving the efficiancy of the torch..

This is most true for LED's: Led's are front emitting.. The standard conventional reflectors are initially designed for side emmiting sources (Xenon-, normal or halogen light bulbs)
So when you use a led with a conventional reflector, you need a very deep one: The led emits most of the light strait forward, so even with the deepest reflector, most of the light still is not collimated within the main beam.

That's why led's work better with aspheric lenses: With an aspheric lens, you grab most of the light emitted directly in front of the led..

But no aspheric lens, or reflector can match the collimating power of a TIR optic !!

With a TIR, you can grab up to 95% of all the lumens a led emits, and put those lumens into a nicely collimated, but ofcource more sidespilled beam.


Regards,

Ra.


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## Ra

gcbryan said:


> Thanks RA.
> 
> So, just to clarify (I know it's obvious at this point but bear with me please)...
> 
> The reasons that lights that are considered to be "throwers" frequently are deep as well as wide are...
> 
> 1. They have to keep the shape of a parabola so since they will have larger diameters (as opposed to a non-thrower) the depth will increase as well if for no other reason than for that reason.
> 
> 2. Since the spot becomes more narrow and intense (tightly focused) with increasing diameter reflector depth is frequently increased to make the hotspot a little more useful at less than max throw.
> 
> Are those two statements more or less accurate?
> 
> Also, I have a reflectored thrower (Uniquefire HS-802) that has a reflector diameter of approximately 45 mm and a depth of approximately 56 mm. It uses a XR-E R2 driven at 1A. The hotspot seems (to me) very small even though the depth is relatively large.
> 
> The explanation for this (I know you don't have this light in front of you) would be that without the depth the spot would be even smaller?
> 
> Would that be correct?
> 
> Thanks again for coming back to clear up a few aspects of this subject. This thread was clear to a point with what throw is but didn't address as clearly the question of why do many throwers have deep reflectors if it's not related to throw.
> 
> Thanks for clearing this up.



Sorry gcbryan,

I noticed you posted just before me..

You are exactly right.. 

One remark about your point nr 2 tho: Increasing the reflector diameter increases the brightness at the center of the spot, so in fact, the spotsize doesn't change. It only seems smaller because the sidespill is pushed to the background by the brighter center of the spot. The sidespill doesn't change in brightness, so is more overpowered by the hotter center of the beam.

If something faint commes close to something bright, it seems to become fainter..



EDIT: That means if you use a deeper reflector with the same diameter, the brightness of the center of the spot does not change, but the extra amount of lumens you grab from the source will create more sidespill around the center of the spot..

EDIT nr2: Especially with a CREE, a conventional reflector is very inefficient, like I said in my earlier post. The Cree already has a kind of collimating lens (glass dome) which narrowes the emittance angle to a mere 145 degrees.. More suitable for use with an aspheric lens, not with a conventional reflector..





Regards,

Ra.


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## gcbryan

When you use the term "sidespill" you mean that in a way that is different than our use of the term "spill" correct?

I consider "spill" as that light that doesn't hit the reflector but rather just comes straight out (uncollimated) from the emitter.

1). You are using "sidespill" to mean that light in the hotspot that isn't the most highly collimated light in the very center...correct?

2). Also, although TIR is more efficient it's not going to provide the most throw and isn't practical in the larger sizes...correct?

I like TIR as well and wish it was used in most flashlights (all but the dedicated throwers).

3). You mentioned that increasing the diameter of a reflector increases the intensity but doesn't actually change the hotspot size. What does? It's a matter of the emitter size and what else? I assume it's just reflector shape? Some reflectors have a larger flat spot next to the emitter. Is that it?

4). What is the relationship with an aspheric between intensity and increasing the diameter. If you go from a diameter of 30 mm to 60 mm if lux at 1 meter for the 30 mm was 15,000 lux what would the expected lux be for the 60 mm diameter optic?


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## saabluster

Ra said:


> Wait till I really am going to design a LED-thrower... Could be in a few day's, or weeks, even month's.. But my (second..) time of glory will come.. :naughty:
> 
> 
> Regards,
> 
> Ra.



I look forward to it. With your skills making TIR optics I suppose you are going to go down that route? Should be interesting. Working on a little something-something myself. Who knows when I will be able to complete it though. One thing that has not really been done yet is a large format LED spotlight. You thinking about something like that or do you want to keep it as a true flashlight?


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## McGizmo

With all of the discussion of optics, lenses or reflectors, there seems to be no mention of focal length or how it plays a role with an image source that is not infinitely small. Yet it has been my impression that focal length is a significant consideration and behind the scenes, that which dictates the significant differences between various optics being compared.

TIR, to my limited understanding refers to total internal reflection. Most TIR optics I have seen are actually a combination of both reflector and lens. The reflector redirects the photons by virtue of bouncing them off in a new direction whereas the lens redirects the photons by virtue of refraction at the plane(s) where light enters and then exits a medium other than air and one having a different refractive index than air. In a TIR optic I believe light is both bent and bounced. In a simple reflector, the light is just bounced.



> The deeper reflector does two things when compared to a reflector of the same diameter. It captures and collimates more of the light output from the LED.


I would suggest that the deeper reflector with shorter focal length that the shallower reflector of same exit diameter does bounce more of the light from the source but in terms of collimation, the shallower reflector is doing a better job of getting the reflected light out in less of a divergent beam. 

With a given light source (say LED) and a specified exit diameter of a reflector, I believe there is an optimal focal length for a reflector that will maximize the lux measured at some reasonable distance. A shorter focal length than this optimal one will provide for more of the light getting bounced but in a more divergent pattern. A longer focal length will do a better job of actual collimation but it will be redirecting less of the total light output, in its beam.


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## Ra

gcbryan said:


> When you use the term "sidespill" you mean that in a way that is different than our use of the term "spill" correct?
> 
> I consider "spill" as that light that doesn't hit the reflector but rather just comes straight out (uncollimated) from the emitter.
> 
> 1). You are using "sidespill" to mean that light in the hotspot that isn't the most highly collimated light in the very center...correct?
> 
> 2). Also, although TIR is more efficient it's not going to provide the most throw and isn't practical in the larger sizes...correct?
> 
> I like TIR as well and wish it was used in most flashlights (all but the dedicated throwers).
> 
> 3). You mentioned that increasing the diameter of a reflector increases the intensity but doesn't actually change the hotspot size. What does? It's a matter of the emitter size and what else? I assume it's just reflector shape? Some reflectors have a larger flat spot next to the emitter. Is that it?
> 
> 4). What is the relationship with an aspheric between intensity and increasing the diameter. If you go from a diameter of 30 mm to 60 mm if lux at 1 meter for the 30 mm was 15,000 lux what would the expected lux be for the 60 mm diameter optic?




Ok here are some answers:

1: Yep, correct

2: Correct: TIR is a solid acrillic or in my case, glass based optic, so larger diameters become very heavy, in most cases heavier than aspherical lenses.
TIR gives aprox the same throw as an aspherical lens setup with the same diameter.

3: Spotsize indeed is highly affected by the source size.. With high quality collimators, the smaller the source (filament, arc or led-die) the narrower the beam, and so, spotsize.

4: That is an easy one (in theory..) When the F ratio is the same, the 60mm optic would give 4 times the lux at the same distance. So the answer is 60,000 lux.
The 60mm has twice the diameter, so four times the surface. The surface brightness doesn't change, so seen from the enlightened object, you see four times the surface with the same surface brightness, so you measure four times higher lux.

Again, when in this case the focal ratios of the two lenses are not the same, you will notice differences in total torchlumens (which should be the same with the same focal ratio's)
And like I said earlier, altering the focal ratio of a lens (same diameter) does not affect throw.. It only affects the sidespill in the way you mentioned in point 1


Regards,

Ra.


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## Ra

saabluster said:


> I look forward to it. With your skills making TIR optics I suppose you are going to go down that route? Should be interesting. Working on a little something-something myself. Who knows when I will be able to complete it though. One thing that has not really been done yet is a large format LED spotlight. You thinking about something like that or do you want to keep it as a true flashlight?



Hi saabluster,

Yep, it definitely will be a TIR based design. And I indeed want to keep it more practical than a large spotlight.
It will have a revolutionary 7 times more effective led-cooling heatsink setup (compared to a copper heatsink..) Unfortunately, this last fact makes it impossible to setup a production line..
So it will (again..) be a unique torch. At the moment, I only have the ingredients to build two of them.. Beleve me, one of the ingredients is very rare, so very hard to come by..

But like I said, completing this still can take month's, maybe up to a year or so, as the telescopes I'm building have (much..) higher priority right now..

Regards,

Ra.


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## saabluster

Ra said:


> Hi saabluster,
> 
> Yep, it definitely will be a TIR based design. And I indeed want to keep it more practical than a large spotlight.
> It will have a revolutionary 7 times more effective led-cooling heatsink setup (compared to a copper heatsink..) Unfortunately, this last fact makes it impossible to setup a production line..
> So it will (again..) be a unique torch. At the moment, I only have the ingredients to build two of them.. Beleve me, one of the ingredients is very rare, so very hard to come by..
> 
> But like I said, completing this still can take month's, mayby up to a year or so, as the telescopes I'm building have (much..) higher priority right now..
> 
> Regards,
> 
> Ra.



Wonderflonium?


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## Ra

saabluster said:


> Wonderflonium?



uhhhh... what the blieb is 'Wonderflonium' ??? Something that doesn't exist (yet..) I beleve?


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## jabe1

Unobtainium!


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## gcbryan

Thanks RA. Your posts are always so clear and understandable. It's nice to have an optical expert around CPF.

It sounds like maybe the "world's greatest throwing TIR" is in the works!


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## saabluster

Ra said:


> uhhhh... what the blieb is 'Wonderflonium' ??? Something that doesn't exist (yet..) I beleve?


*Wonderflonium* is an exotic material required for Dr. Horrible's freeze ray. Bad things can happen if it is bounced. It is also a part of Dr. Horrible's death ray, due to the fact that if wonderflonium is bounced, bad things can happen.


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## headophile

Ra said:


> Hi saabluster,
> 
> Yep, it definitely will be a TIR based design. And I indeed want to keep it more practical than a large spotlight.
> It will have a revolutionary 7 times more effective led-cooling heatsink setup (compared to a copper heatsink..) Unfortunately, this last fact makes it impossible to setup a production line..
> So it will (again..) be a unique torch. At the moment, I only have the ingredients to build two of them.. Beleve me, one of the ingredients is very rare, so very hard to come by..
> 
> But like I said, completing this still can take month's, maybe up to a year or so, as the telescopes I'm building have (much..) higher priority right now..
> 
> Regards,
> 
> Ra.



you got me excited here, chief. very much looking forward to this one


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## Ra

saabluster said:


> *Wonderflonium* is an exotic material required for Dr. Horrible's freeze ray. Bad things can happen if it is bounced. It is also a part of Dr. Horrible's death ray, due to the fact that if wonderflonium is bounced, bad things can happen.



That explaines a lot... I think I'm going to use Wonderflonium !!

Regards,

Ra.


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## gcbryan

RA, if you are still around ... I'm going to switch gears just a bit and ask about the practicality of throw.

I think we would all agree now that throw is a measurement of max intensity of the most collimated portion of the hotspot.

In practical terms max throw is used in a limiting way rather than as an exact distance since weather, eyesight, the target's reflectivity all play a role in whether we can actually see that beam at the max calculated distance. One could determine whether you need a minimum of 1 lux on target or 2 lux or whatever. That's not the issue here.

It's the practical side I'd like your viewpoint on.

We would all also agree that in designing a practical flashlight focal length is important since lumens off center from the Z axis plays a large role in the practicality of that flashlight.

So, I'm not asking about those areas in which everyone is probably already in agreement.

My question (practically speaking) is max throw as has been defined actually what contributes to throw as we visually experience it? I'm really asking I guess how large is that Z axis beam that you are measuring with a pinhole in your lux meter by the time it only produces 1 lux at it's maximum throw?

Is this something that our eye can actually distinguish? If so then max throw is a useful thing. If not then shouldn't we use some form of average throw (meaning average lux in the hotspot)?

I'm trying to figure out if practically speaking we need to consider the throw that comes from the sidespill (your term) if at a certain distance sidespill is the only reason we can see the hotspot? Part of what I'm asking it how intense is the beam just to the side of the Z-axis (one beam over so to speak)? If it's almost as bright then that would be affected by focal length and it may be the only reason we can see the subject at a certain distance.

Again, when I look at the hotspot on the wall in front of me using an aspheric I see the image of the emitter. I'm not aware that it's brighter in the very center.

When I shine that light outside and try to find maximum throw the spot I see (that illuminates the subject) is also of the entire emitter shape.

Focal length would change how much lumens were in this area correct? If so, in a practical sense, isn't the focal length effecting throw?

I'm not disputing the point you've been making. I'm just coming up with the term "practical throw" or "average throw" to try to describe how flashlights are actually used.

I'm not suggesting that term be considered however if you can tell me that max throw (as we've been talking about it) is enough for the human eye to make use of it at some "max" distance.

In other words, we all already know that more lumens in the beam of a flashlight is more practical but that's not what I'm getting at. I just want to know if max throw actually works with our perceptions outside of theory.

I'm asking because I don't know how large the max intensity spot is at max distance. If it's usable then that's the answer and everything else is just lumens for a bigger spot.

If it's not large enough to be usable then those lumens are necessary in a practical sense for throw. Which is it?

Thanks.


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## Dr.Jones

Hello... I just learned about this thread (and actually joined CPF for it and similar ones , though the most important things are already said (praise RA 



> Focal length would change how much lumens were in this area correct?



A shorter focal length would increase that area (in m^2) and the total luminous flux (in lumen) in that bigger spot while keeping the same illuminance ('brightness', flux per area in lux=lumen/m^2).

About practicability...
I think 'throw' is best defined as the distance at which the illuminance on the target drops below a certain value (e.g. 1 lux).
That does give a laser pointer a huge throw, so other criteria might be helpful to get an idea what a good thrower flashlight should have, in that case the 'spot size' or better the beam divergence angle, I suggest mrad (milli-rad) as unit.
(It's similar with binoculars: important specs are magnification and field-of-view...)

While a laser pointer has extreme throw, it's beam divergence is very small, usually around 1 mrad, which renders it useless for typical thrower applications.

So what spot site should it have?
This picture might give an idea:






That's a spot size of ~8m at 260m distance, beam divergence ~8m/260m=0.030rad=30mrad. It's for you to decide if that's useful.
Someone else in this thread wanted [email protected], that's about 100mrad; again everyone must decide for themselves if less would suffice, too.


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