The Real Reason for Throw - an in depth examination

[TorchBoy]

I'm trying to keep the surface brightness and size of the emitter out of this question. I just want to know exactly what effect greater reflector width and depth have.

Give up. You cannot simply ignore the type of LED to know the exact effect different reflector parameters have. Will you be happy with the generalisations and approximations you've already been given?

Correct me if I'm wrong. Increasing width is putting the same amount of light into a tighter spot thereby increasing brightness.

You're wrong. Increasing width only (leaving depth and focal length unchanged) will decrease the capture angle of the reflector, meaning less light is being directed forward, not the same amount of light. Whether the spot will actually get smaller or increase in brightness will depend on all sorts of things, including the kind of LED being used.

 

[gcbryan]

Give up. You cannot simply ignore the type of LED to know the exact effect different reflector parameters have. Will you be happy with the generalisations and approximations you've already been given?

What's your problem? Give up and be happy? Quit reponding.

No one is ignoring the type of emitter. I'm just not interesting in a long discussion of the various types of emitters as I already am aware of the specifics.

I specified that if one wants to speak in terms of an emitter that you can consider that we are talking about XR-E R2.

How exactly are you contributing anything with this particular post?

You're wrong. Increasing width only (leaving depth and focal length unchanged) will decrease the capture angle of the reflector, meaning less light is being directed forward, not the same amount of light. Whether the spot will actually get smaller or increase in brightness will depend on all sorts of things, including the kind of LED being used.

"
Originally Posted by TorchBoy

You can increase the intensity of the hotspot by focusing the same amount of light into a smaller spot. That can be done using a larger diameter reflector.

You an also increase the intensity of the hotspot by increasing the amount of light being focused into the same sized spot. That can be done using a deeper reflector, since it will capture more light from the source."

 

[TorchBoy]

If you're going to play off my comments made in the context of one thread - where you specifically asked for "some simple answers" - against comments made in the context of another thread - where you've specifically asked for exact effects and the thread itself is "an in depth examination" of throw - I'm going to get very unhappy very quickly.

You have repeatedly stated you want to ignore the type of LED used so you can have some simple generalisations. These have been provided by myself and others, with the caveat that ignoring the LED type is not always easy to do. In response you have also repeatedly stated you want to assume the use of an XR-E, which isn't actually the best-suited LED for a reflector, but that's your call. Do you feel you've made any progress in understanding reflector parameters? If someone now asked you, would you be able to explain how a parabola collimates light?

 

[gcbryan]

If you're going to play off my comments made in the context of one thread - where you specifically asked for "some simple answers" - against comments made in the context of another thread - where you've specifically asked for exact effects and the thread itself is "an in depth examination" of throw - I'm going to get very unhappy very quickly.

I'm not "playing off" anything nor am I overly concerned with how unhappy you are. An arrogant post will elicit such a response and with over 4000 posts I'm quite sure you are used to it.

You have repeatedly stated you want to ignore the type of LED used so you can have some simple generalisations. These have been provided by myself and others, with the caveat that ignoring the LED type is not always easy to do. In response you have also repeatedly stated you want to assume the use of an XR-E, which isn't actually the best-suited LED for a reflector, but that's your call. Do you feel you've made any progress in understanding reflector parameters? If someone now asked you, would you be able to explain how a parabola collimates light?

I'm glad that you have followed my posts but if they bother you perhaps you need to quit following my posts quite so closely.

I understand that a XR-E directs it's output in a 90 degree beam rather than 120 degrees as might a XP-E or XP-G. I understand that the surface brightness of the XP-E is greater than the XP-G. I understand that the XP-E R2 might be more suited to a reflectored thrower.

I have a "thrower" using a wide and deep reflector that is using a XR-E so it's more practical to use that as an example but I do understand that the emitter beam shape changes with different emitters.

Since I understand that, it doesn't add to my knowledge of reflectors if someone just says that it depends on the emitter. That is a way of not answering a question by, in effect, saying it's too hard to answer. In many cases it's because someone knows about emitter difference and doesn't really know the answers I'm after regarding reflectors and therefore just chooses to answer the questions that they do know.

That is why I've asked questions the way I have.

I'm not an expect regarding ray tracing and reflectors...that's why I've asked questions. Not that I need to be quizzed by you but in general I do understand that an emitter placed at the focal point of a parabolic reflector will have it's emitted rays become collimated as they hit the parabola I understand that more of the beam from an XR-E will go straight out and thereby missing the parabola.

I have learned from all of these posts including understanding where I need to change the way I'm looking at things. Saab's recent post was helpful in that regard. Learning is a process...

If you don't have the temperament to deal with someone asking questions then don't respond. Not everyone who understands a particular subject is necessarily a good teacher.

If you feel the need to pick a fight I would suggest that you simply not respond. This is a discussion board. Those who already completely understand a subject don't need to discuss this particular subject. I can assure you that there are many who don't completely understand this subject and they will be asking questions in their own way and perhaps not in a way that suits you. Perhaps you need to get used to it. Or don't respond if it upsets you.

 

[TorchBoy]

Since I understand that, it doesn't add to my knowledge of reflectors if someone just says that it depends on the emitter. That is a way of not answering a question by, in effect, saying it's too hard to answer.

Would you be prepared to accept that without knowing an exact combination of reflector and LED an exact answer might really be "too hard to answer"? That without detailed knowledge of LED beam pattern and reflector size and shape and, or trying the combination yourself, you might just have to settle for a generalisation or two? Asking questions is great, but not acknowledging answers (as others have given above) along the lines of "it depends on all these factors" isn't a path to enlightenment.

 

[gcbryan]

Would you be prepared to accept that without knowing an exact combination of reflector and LED an exact answer might really be "too hard to answer"? That without detailed knowledge of LED beam pattern and reflector size and shape and, or trying the combination yourself, you might just have to settle for a generalisation or two? Asking questions is great, but not acknowledging answers (as others have given above) along the lines of "it depends on all these factors" isn't a path to enlightenment.

That's not been an issue. I haven't been asking for an exact answer given that I'm not specifying an exact reflector/emitter combination. That's the whole point.

I haven't had an issue with anyone who answered the question and added "but the details really depend on the specifics". I understand that of couse.

The only reason I made that comment was because in some of the longer threads on this subject the practical application is never gotten around to.

People argue over the definitions for a hundred posts or don't come out and explain what they are attempting to explain and then use examples if people don't understand rather than before.

I'm not complaining about any threads on this subject. However if you read this thread and RA's thread of a few years ago you will see that they get derailed.

If someone is an expert in this subject (any subject) they should be able to explain that subject matter to a layman in layman terms in a couple of paragraphs...wouldn't you agree?

I can do that in any subject in which I'm very conversant and I've noticed that other can as well. Those most knowledgeable in a subject are usually the one's who can adapt the explanation to a novice. Those who attempt to make it look difficult generally don't have a through grasp on it themselves.

I'm not referring to RA, Saab, or you for that matter here. Nothing personal. But in general, wouldn't you agree?

 

[saabluster]

However if you read this thread and RA's thread of a very years ago you will see that they get derailed.

I tried hard to get people to understand why I requested that the majority of people refrain from posting in this thread. It was not out of a sense of elitism or the desire some people have to never be challenged. I simply wanted the layperson to understand and knew that hundreds of posts of dead-end lines of reasoning was going to make that goal difficult to achieve. Now you can see quite clearly the reasons for my request.

That said we have discussed some things in this thread that I was not thinking of covering but needed much consideration by the community.

If someone is an expert in this subject (any subject) they should be able to explain that subject matter to a layman in layman terms in a couple of paragraphs...wouldn't you agree?

I agree with you if it is a one on one setting but when you have a thousand critics that are waiting for you to leave out even the tiniest of details regardless of the relevancy it tends to make it very difficult to write a piece like this thread was intended to be.


TorchBoy and gcbryan please stop going back and forth with one another. Let's move on.:grouphug:

 

[Lord Bear]

:wow:::touche::ironic::sigh::grouphug:
Please...

 

[dymonite69]

Can someone definitely answer this question...

what does greater reflector width determine.

Does greater reflector depth determine the narrowness of the hotspot

Ok I'll have a go...

Let's take the ideal conditions to maximise throw.

1) A point source emitting light with equal intensity in all directions
2) An infinitely deep parabolic reflector
3) Light source at the focal point of reflector

The width of the beam will be infinitely wide but its intensity falls the further you move away from the beam axis.

The 'narrowness' of the reflector will dictate how quickly the intensity diminishes at the edges i.e. the hotspot However, in both cases all exiting light remains parallel.

In practice the light source is

1) not a point and does not radiate equally in all directions
2) the reflector is not infinitely long or perfectly shaped
3) parts of the light source light outside the focal point.

This results in light that does not exit the reflector exactly parallel to each other and will eventually diverge - decreasing the intensity of the hotspot and reducing the throw.

So it is neither the width of the reflector or its depth that determines hot spot size and throw but how much the conditions deviate from ideal.

 

[Midnight Oil]

I started drawing some lines and curves in CAD to get an approximate understanding of how different points on the reflector redirects the light from the LED.

I draw a vertical line representing the vertical axis of the LED, then two diagonal lines, mirrored across the vertical line, to represent the emission angle of the LED. For an example, for the XRE-R2, the diagonal lines each form a 45 degree angle with the vertical line.

I then draw in a curve, loosely resembling a parabola, symmetric about the vertical axis. Where you cap off this curve determines the depth of the reflector.

The 45 degree lines each represent one of the infinite number of "rays" of light emitted by the LED. You can draw in any ray between the diagonal lines, of course, as long as they hit your curve for this experiment. For simplicity, I consider only the 45 degree lines.

Where they intersect my curve, I draw in a tangent line to the curve, and then a line perpendicular to the tangent line. Using the concept of the angle of incidence, a draw a line that represents the ray of light as reflected by that point on the curve.

Based on my lines and curves, it seems that in general, in order to capture as much light as possible from the emitter and project it into the hotspot, the reflector needs to be deep; and in order to reflect the light rays so that as many of them are as near parallel to the vertical axis as possible, so as to minimize the divergance angle of the beam, the reflector needs to be wide and the tangent lines to the surface of the reflector should be as far as possible from being nearly parallel to the vertical line.

Do I make any sense? Please correct me if I'm wrong.

 

[easilyled]

I started drawing some lines and curves in CAD to get an approximate understanding of how different points on the reflector redirects the light from the LED.

I draw a vertical line representing the vertical axis of the LED, then two diagonal lines, mirrored across the vertical line, to represent the emission angle of the LED. For an example, for the XRE-R2, the diagonal lines each form a 45 degree angle with the vertical line.

I then draw in a curve, loosely resembling a parabola, symmetric about the vertical axis. Where you cap off this curve determines the depth of the reflector.

The 45 degree lines each represent one of the infinite number of "rays" of light emitted by the LED. You can draw in any ray between the diagonal lines, of course, as long as they hit your curve for this experiment. For simplicity, I consider only the 45 degree lines.

Where they intersect my curve, I draw in a tangent line to the curve, and then a line perpendicular to the tangent line. Using the concept of the angle of incidence, a draw a line that represents the ray of light as reflected by that point on the curve.

Based on my lines and curves, it seems that in general, in order to capture as much light as possible from the emitter and project it into the hotspot, the reflector needs to be deep; and in order to reflect the light rays so that as many of them are as near parallel to the vertical axis as possible, so as to minimize the divergance angle of the beam, the reflector needs to be wide and the tangent lines to the surface of the reflector should be as far as possible from being nearly parallel to the vertical line.

Do I make any sense? Please correct me if I'm wrong.

I think that this is exactly what we need.

However, we need to take into account the beam emission as well.

For instance the Cree-XREs have a narrow beam angle of emission. Therefore to catch them, the reflector also needs to be relatively narrow.

On the other hand, a Seoul SSC-P4 has a much wider Lambertian beam emission. The reflector needs to be relatively wider here.

The McR27 reflector is wide but not long and works with Lambertian emitters like luxeons and Seoul SSC-P4s, but not with Cree XREs.

The McR19XR reflector was designed specifically by McGizmo for the Cree XRE and is much longer in proportion to its diameter (ie relatively narrow)

I think that the beam emission pattern relevant to the emitter in question also needs to be included when drawing these diagrams in order to show exactly what is going on.

How easy this is to do or not, I don't know though.

 

[Midnight Oil]

I think that this is exactly what we need.

However, we need to take into account the beam emission as well.

For instance the Cree-XREs have a narrow beam angle of emission. Therefore to catch them, the reflector also needs to be relatively narrow....

You're absolutely right. The actual amount of light distributed over the emission angle is not uniform, and should be accounted for.

I experimented with the narrower reflector, but got to the point where the light was actually deflected onto the opposite side of the reflector! A kind of internal reflection if you will. I suppose that light eventually end up as spill.

 

[melmartinez01]

This is the kind of thread that made me join CPF!

[advertising links removed]

 

[Midnight Oil]

So, in general, for a parabolic reflector, collimation is proportional to the diameter, and the amount of light scooped up into the hotspot, as opposed to distributed to the spill, is proportional to the depth?

That's why wider and deeper reflectors throw more, because more light is gathered into the hotspot and the light rays in the hotspot are more collimated?

 

[Midnight Oil]

One thing I don't understand is the relative effects of surface brightness vs emission angle of a LED on throw.

The hotspot consists of light deflected by the reflector. Since light that comes out near the top of the LED misses the reflector, it seems logical that a LED that emits more light sideways than straight from the top is more condusive to throw. As such, shouldn't a LED with a wider emission angle project more light into the reflector than one with a narrower emission angle?

If so, why does the XRE-R2, lumen for lumen, offer more throw than the other emitters? Is it because its surface brightness is so much higher that it nullifies any advantage gained by the other emitters from having wider emission angles?

 

[easilyled]

One thing I don't understand is the relative effects of surface brightness vs emission angle of a LED on throw.

The hotspot consists of light deflected by the reflector. Since light that comes out near the top of the LED misses the reflector, it seems logical that a LED that emits more light sideways than straight from the top is more condusive to throw. As such, shouldn't a LED with a wider emission angle project more light into the reflector than one with a narrower emission angle?

If so, why does the XRE-R2, lumen for lumen, offer more throw than the other emitters? Is it because its surface brightness is so much higher that it nullifies any advantage gained by the other emitters from having wider emission angles?

I think that good reflectors are designed taking the led's beam emission into consideration.

So reflectors for XRE emitters need to be narrower in order to trap the narrower beam emission and to prevent most of the light dispersing straight out.

If you look at McGizmo reflectors, you will see that all the reflectors for XREs (containing the letters XR), are designed to achieve this.

This is why an XRE emitter is not used in an Aleph 2 with its wider and shallower McR20 reflector, but is used in an Aleph 19 with its narrower and longer McR19XR reflector.

What I don't know is if a narrower beam angle correctly harnessed with a well-matched reflector will throw further than a wider beam angle which is also in a well-matched reflector if the surface brightness is equal for both.

What say you, saabluster?

 

[saabluster]

What I don't know is if a narrower beam angle correctly harnessed with a well-matched reflector will throw further than a wider beam angle which is also in a well-matched reflector if the surface brightness is equal for both.

What say you, saabluster?

Well saying "well-matched reflector" sure leaves a lot open for interpretation doesn't it? The easiest answer is the non-answer. It depends. I suppose the ideal situation with a reflector is to have the wide angle. That said there are some nuances here that I need to spend some real hard time thinking about because I have seen some strange results in doing comparisons between R2 XR-Es and R3 XP-Es. Always remember nothing replaces actual testing.:thumbsup:

 

[easilyled]

Narrow beam angle emission could be considered as an advantage in the design of small/pocket throwers.

I think that most of us have observed for example that smaller lights tend to throw better when they have XRE emitters compared to SSC-P4 or XPG emitters, for example.

Although surface brightness may be regarded as the obvious reason for this, I don't believe its the only one.

I think its also due to their beam emission being narrower, hence requiring a narrower reflector for similar harnessing of the beam into a spot.

This results in a less wide head being required for an XRE-emitter compared to an SSC-P4 emitter in order to produce a similar hotspot. (which translates into less bulk in one's pocket)

 

[saabluster]

Narrow beam angle emission could be considered as an advantage in the design of small/pocket throwers.

I think that most of us have observed for example that smaller lights tend to throw better when they have XRE emitters compared to SSC-P4 or XPG emitters, for example.

Although surface brightness may be regarded as the obvious reason for this, I don't believe its the only one.

I think its also due to their beam emission being narrower, hence requiring a narrower reflector for similar harnessing of the beam into a spot.

This results in a less wide head being required for an XRE-emitter compared to an SSC-P4 emitter in order to produce a similar hotspot. (which translates into less bulk in one's pocket)

The SSC-P4's problem is the way the phosphor is applied in a huge blob instead of a conformal coating. The XP-G has twice the surface area so unless you have twice the light you will not be able to match the XR-E. What would be best is to compare the XR-E and XP-E. Then we can start making some conclusions.

 

[easilyled]

What would be best is to compare the XR-E and XP-E. Then we can start making some conclusions.

Assuming that the XP-E has exactly the same surface brightness as an XR-E but a wider beam angle.

If this is not the case, I/we can only theorize about this.