The Real Reason for Throw - an in depth examination

saabluster

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I have seen a need in recent times to create a thread that will help people to understand the physics behind throw. It can be a very difficult thing to understand as intuition would tell you that a 2000 lumen light would out-throw a 300 lumen light every time. This is not necessarily the case for a variety of reasons. The recently released Olight SR90 seems to have shown light on a lack of true understanding among the CPF populace as to what makes a light throw. The reason for this confusion seems to stem from its extraordinary performance in the throw category while at the same time being an ultra-large die LED. People assume that it out throws the smaller die lights like the DBS because it is just putting out so much more light. There is no such thing as just using brute force to overpower the weaker small die LED lights. So what is it?

Let's try and understand the fundamentals and the reasons that one light has more throw than another. We will examine HID, incandescent, and LED flashlights and the various collimation methods used to create throw.

I am starting this thread even though I don't have the time to have it be fully featured like I would like but we can get the conversation rolling and I would appreciate any suggestions from those of you out there that might have a good way to illustrate it in a way that is easily understandable. Please refrain from saying what you think is the truth. This thread is intended to be a resource for CPF and to clear up confusion not create it so please think and read before you post. Questions are good and can help to refine the information or layout of the first post if some have a hard time understanding with the given information or layout. I will work as best as I can as time permits to refine this thread's first post.

Reading notes
-The intent of this is to enlighten the CPF layperson and therefore strays away from uber technical terms such as luminance or the adherence to literal or arcane understandings of such words as throw. I use terms that are in common use here on CPF but the scientific principles that this "argument" is based on is intended to be sound. I do not wish to hear from those who are trying to be overly literal or picky in the minutia. If there is a fundamental flaw in the arguments presented here then please speak up.

A request has been made to include a comprehensive definition of what "throw", as it relates to our usage in the flashlight word, means.
As with most things I do there was a great deal of thought that went behind it so before making suggestions otherwise think it through and have a well reasoned "argument" for its change if you see the need.


Definitions

Emitter- A device from which photonic energy emanates(such as a bulb filament or LED die).


Surface brightness- A characteristic of a light-source by which emitted light at the emitter's surface can be ranked from light to dark in correlation with its intensity.

Throw-The ability of a flashlight to illuminate and enable identification of distant objects.

Surface Brightness


It all starts with this one basic thing. This is the foundation. The higher the surface brightness the more the throw potential. This does not guarantee the most throw however as there are a lot of other factors that can ruin all that potential.

So what do we mean by surface brightness?

It can be defined as a characteristic of a light-source by which emitted light at the emitter's surface can be ranked from light to dark in correlation with its intensity.


Surface brightness is not dependent on the area of the emitter but the saturation of light within the area. The use of area in respect to surface brightness is only to quantify what the actual relative surface brightness is.

The emitter in the second picture can be said to have higher surface brightness. The LED die in this instance is aprx. 1mmx1mm. If the first emitter is putting out 10 lumens and the second one 100lumens you can calculate that the second one has 10X the surface brightness of the first one.



The very same thing applies to incandescent lights. The filament is the same for both pictures but one has more power going to it and therefore it is putting out more lumens. Since the area that emits light has not increased, only the amount of lumens in that area, we know that it has higher surface brightness.


If you have two lights of exactly the same spec in every way except the LED in one has higher surface brightness, the one with higher surface brightness will throw farther every single time. There are no exceptions to this unless you are God and can change the laws of the universe.

How can I say this with such certainty? Grab one of your multi-mode lights. Which setting does the light throw farther on? High or low? The only variable you have changed in this equation is surface brightness. You have increased the amount of lumens created without making the size of the LED die any larger thereby increasing the intensity. That means that on high there is now more light in the same amount of space(at the die level) and therefore it(the die) must have a higher surface brightness.

How do we figure out the relative surface brightness of say an LED of 9 square mm(SST90) vs an LED with only one square mm of emitting space(XR-E)? You need two crucial bits of information to make a calculation. Total lumen output and surface area of the emitter.
The top bin XR-E@1A(max per spec) puts out 270lumens inside of its 1mmx1mm box. 270 divided by the area(1mm square) gives us a figure of 270. Now let's do that with the SST90.
The top bin SST90 at maximum current is putting out 2250lumens inside of its 3mmx3mm box(9 square mm). To get the surface brightness calculation we take the lumens(2250) and divide that by the area(9) which gives us a figure of 250.

So at maximum spec the XR-E's surface brightness is 270 vs the SST90's 250. That means the XR-E has more throw potential than the SST90.

This same formula can be done with any type of light emitter such as HID or incandescent sources but it is far more difficult to figure out what your surface area is with these types of lights due to their 3 dimensional nature. Since LEDs are very easy to find the surface area of I have used those as examples.

Distance to Reflective/Refractive surfaces
This area of concern is a huge determining factor in how concentrated the beam from a light is. First there are some things we need to know to set this up so it will take a bit before you realize how this all relates to the distance of the surfaces away from the emitter.

Collimated light is light that is parallel or close to parallel when leaving the light. This means the beam does not spread very fast. Collimation allows a concentration and transmission of light farther than it would otherwise be capable of. This collimated light forms what is known as the "hotspot" of the beam.

Collimation in the truest sense of the word is not possible in the real world as it would require a point of light infinitely small. Assuming you did have the impossible point source of light, and this point was at the reflector or len's focal point, the resultant beam would never grow any larger than when it left the light. If I shone a light with a diameter of 80mm towards the moon there would be an 80mm beam of light on the moon.

Here in the real world we make due with collimation that we might call "good enough".
Collimation in the real world is a relative term as there are degrees in the amount of collimization from light to light. All of our light sources in the universe regardless of what kind they are(xenon, LED, incandescence, stars) emit their light from an area not a point. Because the light is being emitted from an area and not a point we now have to contend with divergence.

What do we mean by divergence? At the root of that word it means it is diverging from something. From what? It is diverging from perfect collimation. The light emitted from the very center of the source, say an LED die, does come close to perfect collimation. The light from the edge of the LED however is not at the exact focal point(notice point not area) of the lens or reflector.
(Keep in mind that while we can never have a point source light emitter, all of our collimation methods "require" a point source. NO EXCEPTIONS!)
Only the center of the emitter can be there. Sure you "could" move the edge of the LED die to be in the perfect focal point of the lens but then the center of the LED is no longer at the focal point.


Distance as it relates to reflectors

The beam from a reflector consists of an infinite amount of images of the source laid one over the other. Imagine for a second we were only dealing with one teeny tiny spot on that reflector-say the middle. The beam that is projected will be an image of the emitter albeit very dim. Now move to a spot directly to the side(not closer or farther to the emitter). The same thing happens here. Light from points all across the emitter shine at that tiny spot on the reflector and the beam sent out will be another image. However since you have moved to the side, essentially circling the emitter it(LED's image) will be rotated slightly from the other one. You can repeat this infinitely going around the reflector so that you have image over image over image. This repeated overlapping eventually creates a circle instead of a single image as you would have with an optic.
Now while the basics of what I just described do not change when you move closer or farther to the emitter one thing does change. The size of image that teeny tiny spot projects. The closer that tiny spot is to the emitter the larger the emitter appears just as someone far away appears tiny to you even though your brain knows otherwise. So that tiny spot close in throws an image of the emitter but larger than when we were in the middle of the reflector. And the opposite is true when we move to the outer rim of the reflector. From this vantage point the emitter looks much smaller. Therefore the image thrown is much smaller. Now remember that this whole process is just laying image over image.


So you want to know what part of the projected beam consists of what images? Let's start in the center of the projected beam or the beam you would see on a white wall at 20 feet or so(beam has to have space to mature). The most intense round spot you see is mostly what has been reflected by the outer area of the reflector. It also consists of the less intense and larger images created by the lower portions of the reflector. So all of the reflector contributes to the center of the projected beam but the outer portions of the reflector do not add any intensity to the outer areas of the projected beam.


So to recap. The images from the outer portions of the reflector are the smallest. As we move closer the images get larger.

For more information see this video.

object%3E


Optical System Efficiency

This is subdivided into two categories.

1-Efficiency of Reflective/Refractive elements

2-Emitter's Spatial Distribution vs Type and Diameter of collimating element.


This page is still under construction. Sorry I am such a slow typist.

 
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Outdoors Fanatic

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Re: The Real Reason for Throw-an in depth examination

Way to go saabluster! This is the kind of thread that made me join CPF! Remember Ra??

Cheers!
 

saabluster

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Re: The Real Reason for Throw-an in depth examination

Saabluster...did You have a chance to go through that old "Ra" thread again? (Ra is the Dutch optic expert as You remember)
It would be interesting to revive that thread : https://www.candlepowerforums.com/threads/143017
I did not realize someone started that one back up. There is way too much wrong information presented in that thread. Time to start with a clean slate.
 

McGizmo

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Re: The Real Reason for Throw-an in depth examination

I am no expert on these matters or even necessarily competent so I will respect the OP's request and not muddy this evolving discussion.

However I will put out a question/ comment on the the term of throw used in the subject line. This term is one that has evolved on CPF and it is a term that many of us use. It is also a term that has been debated numerous times since I have been a member and I believe it, in itself needs better illumination. If one considers throw as the measure of distance a light source can send light "to" then all lights have equal throw. That is the light emanating from the source will travel the same distance from the source whether it is collimated or not.

I suspect the OP has every intention of addressing this issue but considering the suspicion that the term throw is not one that would be found in any scientific study or discussion of light collimation I hope the OP will provide a comprehensive definition of the term here in this thread and perhaps as a foundation for further threads where "throw" is mentioned.

I find it promising that the OP is focused on real world and clearly making comment on where and how real world does not comply or conform to theory based on assumptions of perfection, infinitely small points and other such stipulations.
 

saabluster

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Re: The Real Reason for Throw-an in depth examination

I am no expert on these matters or even necessarily competent so I will respect the OP's request and not muddy this evolving discussion.

However I will put out a question/ comment on the the term of throw used in the subject line. This term is one that has evolved on CPF and it is a term that many of us use. It is also a term that has been debated numerous times since I have been a member and I believe it, in itself needs better illumination. If one considers throw as the measure of distance a light source can send light "to" then all lights have equal throw. That is the light emanating from the source will travel the same distance from the source whether it is collimated or not.

I suspect the OP has every intention of addressing this issue but considering the suspicion that the term throw is not one that would be found in any scientific study or discussion of light collimation I hope the OP will provide a comprehensive definition of the term here in this thread and perhaps as a foundation for further threads where "throw" is mentioned.

I find it promising that the OP is focused on real world and clearly making comment on where and how real world does not comply or conform to theory based on assumptions of perfection, infinitely small points and other such stipulations.
Thanks for the guidance on the issues with the word throw. I was not aware of any of the controversies over this term. I can see why some might take issue with it but it would seem that any view of this would have to relate to the real world. If I shine my flashlight at Jupiter then yes indeed some of that light will bath Jupiter but I can hardly be accused of lighting up Jupiter. Since the point of flashlights is to allow the human eye to see objects it would seem the determining factor of whether something throws or not would be whether or not we could see it with our eyes and not based on theoretical measurements. I get the feeling we both agree on that front. Thanks
 

wyager

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Re: The Real Reason for Throw-an in depth examination

OMG, WTF, this post made me realize that instead of saying "collimated", I've been saying "collaminated" for the past couple years :eek:oo: That's not even a word! :crackup:
lol, thanks.
 

Justin Case

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Re: The Real Reason for Throw-an in depth examination

Throw distance probably depends on whether you are talking about things like target detection (is something present or not), orientation (is the object roughly symmetric, is it horizontal or vertical), classification (is it a weapon or non-weapon), recognition (handgun or long gun), discrimination (real gun vs fake gun), intent (hostile or non-hostile). Or really simple, maybe you are interested in just basic target illumination (contrast).
 

mudman cj

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Re: The Real Reason for Throw-an in depth examination

Very good points Justin Case.

I too have been questioning the CPF use of the term throw, specifically the way in which it is often calculated as the square root of peak light intensity at 1 meter.

I propose a new empirical formula derived from real world experiments in which a group of CPF members get together with a variety of types of typical illumination devices and illuminate various targets from ever-increasing distances while determining at which point they consider the target sufficiently illuminated. Before beginning, they should consider the points mentioned by Justin Case and come to a consensus on what they should be looking for. The results from the individual participants could then be treated statistically to create a distribution of throw vs measured lux at some distance (unlikely to be exactly 1 meter IMO).

Each illumination device will have to be measured using the same equipment and method in a controlled manner at distances that conform to the inverse square law.
 

koti

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Re: The Real Reason for Throw-an in depth examination

Saabluster...could You explain to me what this thread is about?
Is it about flashlight throw and flashlight emitter surface brightness or is it about You wanting to know why the Olight SR-90 throws so well ?
Also...I would like to know how did You come into these conclusions:

"There is no such thing as just using brute force to overpower the weaker small die LED lights"
In my opinin the SR-90 does exactly that...it compensates for poor surface brightness with extreme emitter output and a well designed, huge reflector. I will explain this further below...

"you will see LEDs able to outdo even the best HID lights"
So You assume that LED's will surpass HID's surface brightness and its innevitable ? I think its possible but certainly its not a guarantee. For example, we could have a different technology emmerge in the near future which will bury LED's all together. The goal of outhrowing the best HID throwers is still far away I think.

It is essential that we know what we are talking about and what is our goal in this thread. Otherwise this thread will grow into something similar to Alisnails thread from 2 years back in which Ra was a big contributor.
Please enlighten me on what is the goal of this thread.

Although I do not have an extensive knowledge in this field (this is interesting too...why should we all shut up and let only optical engineers contribute to this thread?) I will throw in my thoughts, please correct me if Im wrong :

Surface brightness...let me use a couple of analogies :

1. Lets take two very small and very distant stars of the exact same energy output (they burn the same ammount of fuel per any given moment in time) They are located in the exact same distance from a distant observer (for example Earth) The only difference between the stars is their diameter...lets say one star is 1000 times smaller then the other - will they both be equally visible to a person on Earth?
My answer is NO. The smaller star will have a higher surface brightness and although they emmit the exact same ammount of energy, the bigger star might not be visible at all while the smaller one will be bright as hell looking from Earth.

2. This one is more down to earth. Lets take 2 identical flashlights...say Surefire 6P's with fresh batteries. Lets put a small diffusor on 1 of them and a larger diffusor on the other. Which one will appear brighter to a distant observer from lets say 1 mile away on a great weather day in complete darkness?
I think the answer is obvious...the one with the smaller diffusor. Thats because the smaller diffusor has a smaller area therefore it has a higher surface brightness.

Coming from this I have to contradict Your conlusion Saabluster that "there is no such thing as just using brute force to overpower the weaker small die LED lights" Again...I think the SR-90 does exactly that.

Edit: Saabluster, You mentioned in the previous thread that switching thru modes on a 3 mode flashlight increases/decreases surface brightness. I think this is totaly wrong.
From what I have learnt from "Ra" in that old thread (I suggest You go through it again...it took me 2 hours and it was worth it) , I understand that "the smaller the emitter size, the higher the surface brightness"
It's realy simple and You can use Your "gut feeling" on understanding it...not like quantum mechanics for example, where everything is "unnatural"

Another "cosmic" analogy that shows that this way of thinking should be right :

Again...2 stars, this time with identical masses. One star is smaller then the other. Which one will have a higher gravity on its surface ? Obvioulsy the smaller one...if You shrink it more the gravity becomes extremely high and it will become a neutron star or if the mass is sufficient - a black hole. This is just an example that objects with the same mass can have totaly different behaviour do to their size - just like with the same ammount of brightness we can have more throw if the emitter is smaller - its all about size !
Ofcourse the relector design comes into account and our Olight SR-90's emitter "brute force" too...as well as many other aspects. But as "Ra" was trying to tell us all along in that wonderfull thread - surface brightenss is THE KEY. The Olight SR-90 is just "cheating" But..
If You build a LED dome with 6 or 8 overdriven SST-90's on it, stick it all into a Polarion reflector, connect it to 80 IMR 26500's in Your backpack - You will never beat a 400 watt HID.
Untill we get LED emitters which are extremerly small in size and incredibly bright - HID's will be the best throwers.
 
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saabluster

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Re: The Real Reason for Throw-an in depth examination

Saabluster...could You explain to me what this thread is about?

As I said "I have seen a need in recent times to create a thread that will help people to understand the mechanics behind throw." Once you understand what creates a beam to throw you will better understand the products you buy. People here do not understand these basic things so I am trying to provide a thread that can educate the CPF populace.



Also...I would like to know how did You come into these conclusions:
Study, and application. Way more than has been made public. ;)

"There is no such thing as just using brute force to overpower the weaker small die LED lights"
In my opinin the SR-90 does exactly that...it compensates for poor surface brightness with extreme emitter output
It doesn't or that would make the designers God-able to change the laws of the universe.

"you will see LEDs able to outdo even the best HID lights"
So You assume that LED's will surpass HID's surface brightness and its innevitable ? I think its possible but certainly its not a guarantee. For example, we could have a different technology emmerge in the near future which will bury LED's all together. The goal of outhrowing the best HID throwers is still far away I think.
Yes that is assumption on my part. Anyone with deep knowledge of where we are headed would say it is a reasonable assumption as well. This is not what this thread is about however so I would prefer there be no more reference made to this in this thread so we can stay on topic.

Although I do not have an extensive knowledge in this field (this is interesting too...why should we all shut up and let only optical engineers contribute to this thread?)
The reason is I want this thread to be as "clean" as possible. I don't want 15 pages of nonsense people have to wade through. I also don't have a ton of time to respond to all the misguided lines of reasoning. Hopefully that will change in the future but it is the cold reality I am dealing with at the moment.

Surface brightness...let me use a couple of analogies :

1. Lets take two very small and very distant stars of the exact same energy output (they burn the same ammount of fuel per any given moment in time) They are located in the exact same distance from a distant observer (for example Earth) The only difference between the stars is their diameter...lets say one star is 1000 times smaller then the other - will they both be equally visible to a person on Earth?
My answer is NO. The smaller star will have a higher surface brightness and although they emmit the exact same ammount of energy, the bigger star might not be visible at all while the smaller one will be bright as hell looking from Earth.
Correct as far as I understand it.


Coming from this I have to contradict Your conlusion Saabluster that "there is no such thing as just using brute force to overpower the weaker small die LED lights" Again...I think the SR-90 does exactly that.

Edit: Saabluster, You mentioned in the previous thread that switching thru modes on a 3 mode flashlight increases/decreases surface brightness. I think this is totaly wrong.
From what I have learnt from "Ra" in that old thread (I suggest You go through it again...it took me 2 hours and it was worth it) , I understand that "the smaller the emitter size, the higher the surface brightness"
It's realy simple and You can use Your "gut feeling" on understanding it...not like quantum mechanics for example, where everything is "unnatural"
I hope you don't mind my being frank but that is absolute nonsense. You don't even understand what surface brightness is. I am going to go into that further when I have the time so hopefully that will help you understand. I have spent a lot of time trying to put things into a very simple and easy to understand way such as the multi-mode flashlight illustration. I assure you it is correct and that your gut feeling is way way off. Give me time to flesh out the thread.

I really do not mean to sound elitist or anything by saying I only want people who know what they are talking about to provide guidance. Can you appreciate though that there must be some constraints to keep this thread from getting out of hand? You recognize the mess the other thread turned out to be so I hope you can see the need to not repeat that here. Please honor my request to "refrain from offering suggestions unless you have extensive knowledge in this field."
 

koti

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Re: The Real Reason for Throw-an in depth examination

Saabluster,

You agree with my definition of surface brightness (the star analogy where they have equal energy volume emmitence but different circumference) yest in the next sentence You state that I "dont even know what surface brightness is" I dont claim that I do, I just stated my thoughts and said "correct me if Im worng"
I hope you don't mind my being frank too Saabluster;
I think You dont have the full picture as well but You try to look like You do. If You do have the full picture though, please enlighten me on 2 things;
- What surface brightness is (You obviously disagree with Ra in the Ailsnail thread) and You disagree with me (but I dont know where exactly You disagree)
- What makes the SR-90 throw well in Your opinion. I tend to think its "brute force", You stated that its obviously not that.
 

Th232

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Re: The Real Reason for Throw-an in depth examination

Hope you don't mind me chiming in on this bit Saab:

Edit: Saabluster, You mentioned in the previous thread that switching thru modes on a 3 mode flashlight increases/decreases surface brightness. I think this is totaly wrong.
From what I have learnt from "Ra" in that old thread (I suggest You go through it again...it took me 2 hours and it was worth it) , I understand that "the smaller the emitter size, the higher the surface brightness"
It's realy simple and You can use Your "gut feeling" on understanding it...not like quantum mechanics for example, where everything is "unnatural"

As Saab said, incorrect. From my knowledge, surface brightness is the amount of light put out by a given area, in this case, the area is the die. Surface brightness is a function of the phosphors, other die properties and the current being sent through it. Units are generally in lumens/mm^2, from what I've seen.

As that stands, without any qualifying statements, your above statement can be refuted by comparing an unpowered XP-E with a powered XP-G, it's obvious that the unpowered XP-E with a smaller die size will have a lower surface brightness (well actually, no surface brightness) than the XP-G, which has a bigger die size.

However, if we were to qualify that statement by saying: "For a set number of lumens, then the smaller the emitter size, the higher the surface brightness", then I would wholeheartedly agree with that statement.

Saab's example of a multimode flashlight is correct as far as I can see. If you get an LED flashlight where you can comfortably look into the emitter on the lowest setting (personally, moonmode on a Quark works very well for this), you can see that even on the lowest power setting the whole LED die is lit up. As you increase power, you get more light (obviously), but the area stays constant, since the light obviously won't be emitted from the substrate or anywhere else.

Therefore, same emitting area for more lumens must indicate a higher surface brightness. If not, where do you propose the extra lumens are emitted from?
 
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koti

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Re: The Real Reason for Throw-an in depth examination

Therefore, same emitting area for more lumens must indicate a higher surface brightness. If not, where do you propose the extra lumens are emitted from?

I think You are totaly wrong.
I think that the "extra lumens" (which are not extra lumens obviously) come from the density of the emitter. The denser the emitter (the smaller the emitter) the more throw will be generated.
Saablusters analogy to a multi mode flashlight is wrong too.
Flashlight related surface brightness is all about the size of the emitter. The smaller the emitter - the higher the surface brightness while lumen output stays the same. Just do a simple experiment...take two ideantical flashlights and put diffusors on them, 1 smaller diffusor, 1 bigger. You get the same ammount of lumens from both yet You get higher surface brightness on the smaller diffusor...and it appears brighter.
If You dont believe me, put those 2 surefire 6P's with different size diffusors in equal distance a mile away from Youeself (1 diffusor standard size, the other one the sieze of a basket ball) and see which one will appear brighter. Then come back to me and I will explain why You saw only 1 light instead of 2.

So to put it all simple:

1. Flashlight throw deppends a LOT on surface brightness. Collimation, lumen output (what the SR-90 is doing) are also imporant but the real key is surface brightess (HID's have the smallest emitting area)
2. Surface brightness in relation to flashlights deppends soley on the emitter size. The smaller the emitter - the less lumen You need to throw / the larger the emitter - the more lumen you need to throw.
 
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saabluster

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Re: The Real Reason for Throw-an in depth examination

Please refrain from posting further in this thread until I have a chance to provide further clarification in the first post. If you still don't understand then ask questions. As at this moment you are all mixed up. The more I have to respond to you the less time I have to finish the main post. OK?


I think You are totaly wrong.
I think that the "extra lumens" (which are not extra lumens obviously) come from the density of the emitter. The denser the emitter (the smaller the emitter) the more throw will be generated.
Saablusters analogy to a multi mode flashlight is wrong too.
Flashlight related surface brightness is all about the size of the emitter. The smaller the emitter - the higher the surface brightness while lumen output stays the same. Just do a simple experiment...take two ideantical flashlights and put diffusors on them, 1 smaller diffusor, 1 bigger. You get the same ammount of lumens from both yet You get higher surface brightness on the smaller diffusor.

So to put it all simple:

1. Flashlight throw deppends a LOT on surface brightness. Collimation, lumen output (what the SR-90 is doing) are also imporant but the real key is surface brightess (HID's have the smallest emitting area)
2. Surface brightness in relation to flashlights deppends soley on the emitter size. The smaller the emitter - the less lumen You need to throw / the larger the emitter - the more lumen you need to throw.
 

koti

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Re: The Real Reason for Throw-an in depth examination

Saabluster...You havent responded at all so far, You only stated that Im wrong without any meritorical arguments. You have no time, thats ok, I will wait.
 

Bullzeyebill

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Re: The Real Reason for Throw-an in depth examination

Saabluster...You havent responded at all so far, You only stated that Im wrong without any meritorical arguments. You have no time, thats ok, I will wait.

Please honor the OP's request per post #17.

Bill
 
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