The Real Reason for Throw - an in depth examination

[gcbryan]

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

Take 2 converging rays of light from either side of the die. Then trace them to a near part of the reflector.

Do the same to a distant part. The rays have to converge much more to a distant part, therefore the image that more distant part is "seeing" is smaller.

Likewise when you trace the 2 rays reflected out, the 2 reflected rays at the nearer point in the reflector are more widely apart than the 2 reflected rays at the more distant point in the reflector.

Therefore the nearer point in the reflector projects a more diffuse and less intense image.

Why must the two rays converge out at the more distant edge...is this just the nature of it being a parabola?

Is the net effect that the rays converge due to the nature of a reflector at the edges and therefore the light is more intense there because more rays are converging at each point out there?

 

[Bullzeyebill]

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

That is an EXCELLENT question and would make a good topic for a thread in the Cafe.

It highlights why I had some trouble deciding what to do earlier, concerning koti's interventions. I was very much in two minds about whether or not it was right to ask him to refrain from further participation in the thread, and I am not sure I was right to do so.

I am delighted you have said this. I hope members will now respond appropriately.

Phew!!!! Yes, it was a dilemma.

Bill

 

[easilyled]

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

Why must the two rays converge out at the more distant edge...is this just the nature of it being a parabola?

Is the net effect that the rays converge due to the nature of a reflector at the edges and therefore the light is more intense there because more rays are converging at each point out there?

Excuse the oversimplification. I think that the reality is that rays of light spread out in every direction from all parts of the die. The lens (glass/silicon dome) over the die refracts them into a diverging beam of rays of light. The maximum angle between the most divergent rays from both sides out of the lens of the die is determined by the nature of the lens over the die and the optical medium within it.

The central straight rays will pass straight out the front of the reflector without hitting it.

Other divergent rays will hit varying parts of the reflector.

They are then reflected on at the same angle to a line at right angles to the tangent of the reflector at the point of the incoming ray hitting it, as the angle that the incoming ray makes to this line.

Depending on where the rays hit the reflector, once reflected they may bounce out of the top of the reflector, or bounce onto another part of the reflector before bouncing out. A small proportion will be lost to total internal reflection (ie. they will never make there way out the top of the reflector).

The image of the die is projected all over the different sections of the reflector from different combinations of emerging rays originally coming from different parts of the die.

The image of the die projected further down the reflector will be smaller though because as the reflected rays converge they have longer to travel and therefore move closer to each other.

If this is complete and utter drivel, then please correct me. I have only a rudimentary understanding of optics and even the rudiments are no doubt incorrect.

 

[the_guy_with_no_name]

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

Distance as it relates to reflectors

IMHO the OP has explained this nicely.

Still there appears to be confusion regarding this concept which I think may be arising from the 2nd paragraph about "Distance as it relates to reflectors" (in Post #1), This is a little harder to visualize...

saabluster:
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.

I'm guessing the OP may have planned to explain this further but I think the following may be helpful to understand what OP is saying.

As usual, a simpleton like me, believes we are dealing with too many complex factors here: reflection, multiple angles/surfaces of reflection, focal points, emitter sizes, intensity, etc, etc.

Allow me to attempt to simplify things so just momentarily, lets forget these complex factors and come back to the one basic optic principle

The Law of Reflection
Angle of incidence equals angle of reflection

If you can grasp this very simple concept, the more complex mystery about why the outer part of a reflector is able to create the more intense area of a hotspot/beam, will very shortly reveal itself to you.

DIAGRAM 1 (below)

ok this is self explanatory, no mystery here right?


DIAGRAM 2 (below)

If we measure the size of the reflected images at 1 meter from the reflector,
you will see that the further away the source image (or emitter) is, the smaller the size of the reflected angle and reflected image.

Still with me?

Ok, now in Diagram 3, we see how this relates to flashlights.

DIAGRAM 3 (below)

Now in diagram 3, I have added a multi-angled reflector (simulating the shape of one in a flashlight). The multi-angled reflector helps to guide the reflected beams into a more useable pattern (or what we might call beam profile).

I am simulating 2 reflections/beam patterns from the emitter source.
A) a reflection at an area in the center of the reflector & very close to the emitter.
B) a reflection at an area towards the outside of the reflector & further away from the emitter.

Can you see which part of the reflector causes flood/spill and which part causes the hotspot in this example?

So now we can see the relationship between emitter distance to different parts of the reflector.




As a bonus, we have also just uncovered the mystery of surface brightness

Just as distance to reflector reduces the "reflection angle", a smaller image will also reduce reflection angle.

DIAGRAM 4 (below)

Notice how the smaller source image creates a smaller reflection (and reflection angle)?

This means that if both source images (emitters) were to have an equal TOTAL lumen output (eg. both 500 lumen emitters), the reflected beam from the larger (A) source image will be wider (floodier) and the reflected beam from the smaller (B) source image will be narrower (tighter aka more throwy)

Additional Note:
For further clarity still, imagine in the Diagram 4 example that:
the larger emitter has a surface area of 5mm square (100 lumen per square millimeter)
the smaller emitter has a surface area of 1mm square (500 lumen per square millimeter)

We now get 500 lumens of output from each beam, yet comparing both beams,
one appears floody and one appears much brighter and tighter.


END

I hope that wasn't too long ...

Saablaster > as always, feedback most welcomed (and of course goes for all CPF'ers). Happy to remove/edit anything that is not appropriate.

tgwnn

 

[saabluster]

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

DIAGRAM 1 (below)

ok this is self explanatory, no mystery here right?


DIAGRAM 2 (below)

Nice work! I was working on some images last night when the power went out. Lost them and have to start over. There are some adjustments that would be helpful. It would be good to show both the difference in angle created by the more distant vs the other and to show how the farther emitter creates a smaller image at the same beam distance as the other one. With some adjustment these would be excellent to add to the main post if you are so inclined. Thanks.

Edit I just saw where you tried to point out the difference in the size of beam at the same beam distance. Maybe if that could be made to stand out a little more?

 

[the_guy_with_no_name]

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

Wow, that was a quick response :twothumbs

Nice work! I was working on some images last night when the power went out. Lost them and have to start over. There are some adjustments that would be helpful. It would be good to show both the difference in angle created by the more distant vs the other and to show how the farther emitter creates a smaller image at the same beam distance as the other one. With some adjustment these would be excellent to add to the main post if you are so inclined. Thanks.

Edit I just saw where you tried to point out the difference in the size of beam at the same beam distance. Maybe if that could be made to stand out a little more?

Sure, I'd be happy to.

point out the difference in the size of beam at the same beam distance

I'm guessing Diagram3?
If you wouldn't mind giving me a little more guidance as to how I might best tweak this image I'd really appreciate it.
Or if you have another image in mind, please let me know.

Thanks,
tgwnn

 

[the_guy_with_no_name]

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

Not sure its supported on CPF but if I can embed a flash file or something like slideshare, I can probably add a bit of animation to make difference in beam size a little more obvious.

does anyone know?

thanks,
tgwnn

 

[McGizmo]

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

tgwnn,
Excellent post. I considered suggesting the rule of angle of incidence equals angle or reflection a ways back because it is the rule in a reflector and does allow one to get a handle on what is happening but without illustrations as you were kind enough to provide, it can be difficult to get a mental picture. I also suspected that at some point the OP will get into lenses where light is bent rather than reflected and it gets a bit more complicated considering the refractive index of a lens material coupled with the surface geometry of the light where it enters and then exits the lens.

Another consideration is that of the viewing angle and distribution of light from the source itself. Not only is a LED not a point source of light, it does not emanate light at various angles with the same intensity. The lions's share of light from a LED doesn't even hit the reflector in most of our flashlights but escapes out the front unreflected or redirected. A lens on the other hand, in front of the LED, does have its way with this light being produced.

To go for maximum throw using a LED and reflector, one should at least consider a design where the LED is aimed with its maximum output, at the reflector. A good real world example of this is a "Recoil" light from Pelican. I don't know if they still offer these nor have I seen any other manufacturer come out with similar offerings. I know that their down fall or weakness was due to lack of spill or off angle illumination beyond their reflected beam. SureFire's first lens based light, the X200 if memory serves, was also deemed to be too tight of a beam and further revisions with SF lens optics opened up and increased the divergence of the beam.

While I am off on this tangent, I feel inclined to point out that the very first high power LED optics some of us remember were the plastic TIR lens/ reflector optics Lumileds provided along with the luxeons. I think TIR (total internal reflection) is pretty misleading in itself because it refers, I believe, to the reflector portion of these combo optics (by virtue of the material's refractive index) yet many assume it refers to the refractive lens component of the optic.

Back to lumileds original LED's and on the topic of throw as it relates to surface brightness, some of us old timers can relate in considering the Luxeon 5 compared to the original Luxeon single die LED's. The Luxeon 5 had much greater flux (lumens) but anyone buying a light that boasted a high lumen 5W luxeon was greatly disappointed if they thought it would out throw a 1W luxeon.

 

[easilyled]

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

Thanks very much for the very helpful diagrams and explanation tgwnn.
They make it much easier to visualize. :thumbsup:

 

[saabluster]

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

I also suspected that at some point the OP will get into lenses where light is bent rather than reflected and it gets a bit more complicated considering the refractive index of a lens material coupled with the surface geometry of the light where it enters and then exits the lens.

Yes I will be going into lenses as well.

Another consideration is that of the viewing angle and distribution of light from the source itself. Not only is a LED not a point source of light, it does not emanate light at various angles with the same intensity. The lions's share of light from a LED doesn't even hit the reflector in most of our flashlights but escapes out the front unreflected or redirected. A lens on the other hand, in front of the LED, does have its way with this light being produced.

As far as I understand it the LED's intensity is not dependent on the angle. Even at an angle the die is just as bright although since it is a 2D surface you start to see less of the die. That is why you see output reduce as the angle increases. Now this point in itself depends on how pedantic one wanted to be. There is a reduction but it varies from LED to LED and is hard to quantify. The reduction would come from the thickness of the applied phosphor and the thicker layer that the photons have to travel through to escape. This is not the case with a non-phosphor LED however so it is hard to say that as a rule.

 

[LuxLuthor]

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

tgwnn - truly awsome and clear post/charts. :thumbsup:

Since there was no response/acknowledgement to my previous post, I just want to respectfully suggest one more time (then I'll drop it) that if you are going to define and/or give "The Real Reason for Throw," the discussion should not be mostly limited to LED's.

The Maxabeam, BarnBurner, & DEFT.
​

If you want to have this only related to LED throw, perhaps make that clear, because including LASERS, HIDS, Incans which all have throw may be more confusing than you intend?

Thanks for your consideration.

 

[saabluster]

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

tgwnn - truly awsome and clear post/charts. :thumbsup:

Since there was no response/acknowledgement to my previous post, I just want to respectfully suggest one more time (then I'll drop it) that if you are going to define and/or give "The Real Reason for Throw," the discussion should not be mostly limited to LED's.

The Maxabeam, BarnBurner, & DEFT.
​

If you want to have this only related to LED throw, perhaps make that clear, because including LASERS, HIDS, Incans which all have throw may be more confusing than you intend?

Thanks for your consideration.

Lux I wasn't ignoring you on purpose. This thread is about throw in the context of flashlights. Lasers are not flashlights so I do not and will not include them for what I would imagine to be obvious reasons. Beyond that I have not in any way that I can think of said this was only for LEDs as it most certainly is not. It's just that what has been said so far relates to all pretty much across the board. There will be specific mention made for the different variety of emitters and their pluses and minuses as relates to collimization and efficiency. Maybe you are being throw off because I refer to the light source as an emitter? I just prefer a one word description than two as it gets said so much in a thread like this. If there is something better I'm all ears.

Michael, I understand what you are trying to contribute with this thread, and....well....you sure picked a doozy to try and simplify!

Understatement of the year.

I think the aspect missing in your proposed definition is that Throw seems to be a description of how effectively an originating light is able to project itself through significant (? outside ?) distances to illuminate a target.

OK let's go over it then.
You say "how effectively". The definition says "with clarity". Anything that meets or exceeds that can be said to be throwing its beam to up until this qualification can no longer be met. For instance the DEFT's beam can be seen on a water tower at about 3/4s of a mile away. You can't really make anything out at that distance so it probably would not be right to say that my light "throws" 3/4s of a mile. If you say a light throws whatever distance the point at which I think most people would start calling you a liar is if you couldn't see anything at that distance. Remember that the entire point of a flashlight is to allow humans to see. The point at which this can no longer be accomplished you can no longer say that that light can throw that far. For instance someone says to you. "Hey Lux can your light throw to that water tower?" You say sure it can!-then take the light and shine it in the direction of the tower. He can't see the town's name on the side of the tower just a faint glow of something. Did your light throw that far? What is the flashlights job again? Did it accomplish it's job at that distance?

So how does one figure out what is a word or not and how to define it?


"The editors at the Oxford English Dictionary spend untold hours deciding which precious bon mots belong in their coveted edition, and this year, they've added hundreds of new words to the list of what's officially correct English.
The choices involve picking items that regularly appear in either print, on TV, over the Internet or have simply been around long enough to attain the status of common usage."

This is why I have stressed the definition being informed by its usage. You or I can define it however we like but if it doesn't match the common usage what weight does it have? We can squabble about the particulars such as "all lights throw the same distance because the rays travel the same distance" or "what about the fog, what then?" but that is being a bit pedantic no? How many words get into the dictionary every year that started off as completely and utterly wrong. But if enough people use that word to mean the same thing then it will eventually be accepted as correct even if on a technical level it is not. Let's not get bogged down in the details and forget how people use it.

I like the points McGizmo raised in his post #61, but if you add how well the user actually sees the target (which includes reflection back), you are into another can of worms where a 250W floody incan light may actually illuminate the target better, but its flood reflects off moisture & particulates--wiping out your night vision and target discrimination.

You cannot add qualifications for every single variable that could ever happen.

In my own mind, I think the most accurate measure of throw is only valid with up close evaluation of the illuminated target in the distance.

OK I agree with you here. I am coming to see the need not to change the definition as I wrote it but to add an additional definition that describes throw as it is in common usage as relates to technical aspects such as lux. I will add a second definition for that as that is a separate and distinct usage I think. I agree that the distant measurement would be the most accurate but I do not think inserting a mention of the "best" way to attain that figure is appropriate in a definition. That is something better in an application notes kind of thing.

 

[saabluster]

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

I'm guessing Diagram3?
If you wouldn't mind giving me a little more guidance as to how I might best tweak this image I'd really appreciate it.
Or if you have another image in mind, please let me know.

Thanks,
tgwnn

No I was talking about #2. If it was more to "scale" with the source closer to the reflector and the beam farther out. I think that will be a little more understandable as people will be able to relate to it better. Adding in something to show the actual angle numbers would help people quantify how the emitter distance is causing a specific change. Just a thought.

 

[saabluster]

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

Not sure its supported on CPF but if I can embed a flash file or something like slideshare, I can probably add a bit of animation to make difference in beam size a little more obvious.

does anyone know?

thanks,
tgwnn

Part of what I want to do is some "animation". PM me if you can do it and we can talk it over. Thanks for your contribution!

 

[kengps]

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

Every user will have a different application and definition of "Throw" For an example "dark" target ID, "light" colored target ID, Reading "town names on water towers" etc. So how about "Throw" simply be a relative term. Because a light with more "Throw" will outperform a light with less "Throw" regardless of the users needs, and what meets their definition of what is adequate throw. No need to reference Human vision, etc. More Throw is simply more lux on the target.

 

[dymonite69]

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

I'll wade in on this one.

A subjective definition of throw:

The maximum distance a torch can usefully illuminate something for the intended purpose.

An objective definition of throw (much harder). The following need to be defined.

1) The area which is being illuminated. As someone has mentioned in this thread, even a low power laser has a long throw but possesses impractical breadth of illumination. You can't define it by a linear measure of the hot spot because it will have to be corrected for distance. A one metre circle might be useful at 150m but useless at 1000m without the aid of binoculars. A definition according to the visual angle being subtended as seen by the observer would be independent of distance.


2) Lux level. Again it can't be a fixed measured and has to be corrected for distance. The further the object, the brighter that target has be illuminated to be visualised from the observer's position. The threshold level of illumination also depends on the purpose e.g. identifying the silhouette of a ship, facial recognition or reading the licence plate of a car. There are various figures quoted in the visual perception literature about the threshold for these lux levels.

3) Colour rendition. The spectral content of the light may have to be appropriate for the illuminated target e.g. Even a well projected strong green tinged light will have difficulty illuminating green objects properly.

In the final analysis it is hard to have a universal definition for throw without actually describing the actual purpose that the flashlight is trying to perform.

 

[the_guy_with_no_name]

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

Thanks to all for the kind feedback.

saabluster > understood about diagram/animation.

I agree adding the degree of angle would be better.
I will try post an updated version in the coming days.

Happy to help with the animation if I am able.

Now I'm working on another post, hopefully I can complete it and post shortly.

btw

Originally Posted by LuxLuthor
Michael, I understand what you are trying to contribute with this thread, and....well....you sure picked a doozy to try and simplify!

Originally Posted by saabluster
Understatement of the year.

I agree, I think maybe at least a full semester course for such a topic.

tgwnn

 

[jtr1962]

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

I think the whole concept of throw seems a lot more quantifiable than it is made out to be. To identify a target you need a certain amount of lux falling on the target. However, this amount of lux is not a fixed amount, but rather varies with the square of the distance. 1 lux on a target 10 meters away might be enough, but you'll need 100 lux if the target is 100 meters away, 400 lux if it's 200 meters away, etc.

It's a simple matter of settling on how many lux is adequate at any given distance. This being done, you can make a chart which is valid for any distance by adjusting for the inverse square law. To determine how far a given light source throws, you would measure the lux at different distances. The point at which the plot of lux versus distance falls under the universal "throw" curve represents the limits of that particular light's throw. Note that you need to measure the lux at various points with collimated light sources because the inverse square law does not apply. Indeed, a perfectly collimated light source would have the same amount of lux no matter the distance!

 

[Mr. Tone]

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

The theoretical perfectly collimated source would still lose lux over distance in the real world because of moisture, dust, pollen, and other matter in the air to absorb or diffuse the light. Unless you were talking about a theoretical environment as well.

 

[the_guy_with_no_name]

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

Defining Throw

One thing I feel I can say about "throw" with certainty is
there are almost as many different viewpoints and interpretations about what this exactly means as there are members on CPF.

It could be said that "throw", as used on CPF is a somewhat relative term.

In my observation,
"throw" is a term used (on CPF) to describe the relative ability of a flashlight to illuminate distant objects.

The magic word being relative

Allow me to expand on this a little if I may.


A little googling reveals the following stats for pages with the word throw on CPF:

Results Phrase
17,600 throw


Now some more googling to find the word throw used in a relative context (Subsets of the 17,600 results)

Results Phrase
6,040 +throw +flood
2,550 more throw
2,640 throw further
1,170 throw as far
953 better throw
887 out throw

Sure, there are many other uses but is it fair to say a significant amount of usage of the word "throw" is relative?

eg. further than, more than, better than

Now, I repeat my observation a 2nd time,
"throw" is a term used (on CPF) to describe the relative ability of a flashlight to illuminate distant objects.

relative to what you may ask?

for starters, relative to other flashlights.

example of some chatter you might read on CPF.... (just fictional examples)

Eg.1: The XXX can easily throw further than YYY
Eg.2: The XXX outhrows all other lights in its price range
Eg.3: typically, a light with a tighter beam pattern is thought of as having more throw than flood though this is not a rule set in stone


all the words in red infer a comparison of some sort is being made.


Now, I repeat my observation a 3rd time,
"throw" is a term used (on CPF) to describe the relative ability of a flashlight to illuminate distant objects.

I focus on the last 3 words "illuminate distant objects".

I'll be honest, I have no idea at all what "illuminate distant objects" means.
How many flashlight makers claim "can illuminate objects up to xxx meters"?
Having a consistent meaning would be a big plus, for sure but the beauty of relativity is that
you are free to define "illuminate" however you like and my observation will still hold true.

Some simple examples:

One manufacturer sells 3 different models of flashlights and claims that:
Flashlight A can clearly illuminate a car at up to 50 meters.
Flashlight B can clearly illuminate a car at up to 200 meters.
Flashlight c can clearly illuminate a car at up to 500 meters.

Another manufacturer sells 3 different models of flashlights and claims that:
Flashlight A can clearly illuminate a dog at up to 50 meters.
Flashlight B can clearly illuminate a dog at up to 200 meters.
Flashlight c can clearly illuminate a dog at up to 500 meters.

To those of you who wish to specify that it means "you must be able to see only the outline", this is fine.

To those of you who wish to specify that it means "you must be able to see color and details", this is fine.

To those of you who wish to specify that it means "there must be at least 100 lux at so & so", this is fine.

As long as your personal definition is consistent, you can determine if the flashlight can throw the given distance or not.

So where layeth the answer to yet another mysterious question?

What if I want to explicitly measure and rate how far my super-new-mega flashlight can throw in non-relative terms?

I believe the answer is simple (I'm sorry for being such a simple guy all the time).

I think it may require a new thread altogether but here is my suggestion.

In many ways, the questions being asked is similar to
"which flashlight is better quality" or "which flashlight is the toughest".

When many people have different perceptions about a concept or word, it is useful and common practice to develop a rating scale.

For example to measure earthquakes, it is common to use Richter Scale.
To measure toughness, it is common to use the IP Code (International Protection Rating eg. IP68)
To measure hardness, it is common to use the Mohs scale (you can google it)

If we created our own scale, the CTS (CPF Throw Scale), we could define the different parameters, add an entry to CPF & Wikipedia and then we could simply state:

"flashlight throw" is a term used to describe the ability of a flashlight to illuminate distant objects as measured by the CTS scale. (the word relative is now gone)

In terms of format it might look like this (an example only):

Flashlight xyz has a throw rating of CTS-5A@100m
Flashlight aaa has a throw rating of CTS-10A@100m
Flashlight 6P has a throw rating of CTS-20D@200m

The scale parameters?

Just examples to give you an idea. This needs everyone's input.

CTS - CPF Throw Scale (just the scale name)

Size (First Digit) - minimum size of a square that must be fully illuminated by the flashlight in units of 10cm (at this Level, at this Distance). 5=50cm square, 10=1m square, 20=2m square etc

Level (First Letter) -
A: an observer 1 meter away could easily see all details of the object with maximum clarity as if they were sitting directly under a 100W incan bulb
B: an observer 1 meter away could see most details of the object as if they were sitting directly under a 60W incan bulb
C: an observer 1 meter away could see main details of the object as if they were sitting directly under a 25W incan bulb
D: an observer 1 meter away could see outlines of the object as if the object was lit by a candle
E: moonlight
F: etc, etc, etc

Distance - the number following the @ symbol is the distance (from the object to the flashlight) at which the object of Size (First Digit) is visible at Level (First Letter)


So the samples would be interpreted as:

CTS-5A@100m : a square 50cm x 50cm, visible in full detail at distance of 100m
CTS-10A@100m : a square 100cm x 100cm, visible in full detail at distance of 100m
CTS-20D@200m : a square 200cm x 200cm, visible enough to see outlines only at distance of 100m

Could sure use plenty of refinement but wanted to post sooner rather than later

tgwnn