silly inverse square law question.

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HelenB
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p.8 #1 · silly inverse square law question.

You need to find something that offsets the decrease in image area, because you have discounted the inverse square law (ie the law of conservation of energy) as a reason for the energy flux (energy flux entering the lens from an area element of the object) decreasing as the lens gets further from the object.

Dec 10, 2012 at 09:36 PM

RustyBug
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p.8 #2 · silly inverse square law question.

You go ahead and believe that ... I prefer something a little simpler to get my head around it.

I'll just keep believing that a ball thrown straight and bounced will keep going in the straight direction is was bounced ... (sans gravity, other outside force, etc.).

AI=AR
If I bounce 1 ball (at the appropriate angle) toward you, then you'll receive 1 ball.
If I bounce 3 balls (at the appropriate angle) toward you, then you'll receive 3 balls.
If I bounce 20 balls (at the appropriate angle) toward you, then you'll receive 20 balls.

If I throw 20 balls in 20 different directions (ISL) ... some of those balls may bounce toward you if they are the are the ones going in the same direction as those indicated above.

If I stand 100 feet away from my bounce target when I throw twenty balls in 20 different directions ... not very many are going to land on the target area I need to hit in order for them to bounce to you.

If I stand 1 foot away from my bounce target when I through twenty balls in 20 different directions, more of those balls will hit the target area necessary to bounce them to you.

So, when we move our source closer to our object that will be reflecting the photons ... THAT is when the the illuminance (volume per area) is determined. The reflected energy (sans absorption, refraction, etc.) continues iaw AI=AR in the amount and color accordingly.

ISL is like (akin to) shooting a shotgun, reflection is like some of those pellets ricocheting off the sign that'll put your eye out kid. Stand far from the sign and only a few get reflected back at you. Stand close to the sign, and you'll get a whole bunch coming back because more hit the sign (before they got spread too wide by ISL). The volume (small or large) that reflects off the sign will still travel iaw AI=AR.

Edited on Dec 10, 2012 at 11:00 PM · View previous versions

Dec 10, 2012 at 09:39 PM

HelenB
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p.8 #3 · silly inverse square law question.

Are you trolling?

Dec 10, 2012 at 10:03 PM

RustyBug
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p.8 #4 · silly inverse square law question.

Me .. trolling ... not a chance.

I just understand that while we are likely at an impasse, there are fellow FM members lurking who aren't versed in physics such as others might be. As such, I try to bounce (no pun intended) in & out of analogies (pretty loose sometimes, I know) that hopefully will strike a chord with those who might be watching, but not fully following ... knowing that they might then be able to go back and re-read something such that it does then "click" for them.

Me, troll on FM ... never. Rarely will you find seasoned FM'ers who troll ... Trolls typically either get flushed out early or become converted to seasoned FM'ers. Although, we do have a few who like to stir the pot now & again, and we can head off into some derivative tangents at times.

Fred has set forth a modicum of decorum for FM members to conduct themselves ... and to Fred's credit, FM has a great member base that support his goals for our members.

FM ROCKS !!!

Which BTW ... a way overdue ... WELCOME TO FM !!!

Edited on Dec 10, 2012 at 10:31 PM · View previous versions

Dec 10, 2012 at 10:09 PM

HelenB
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p.8 #5 · silly inverse square law question.

OK, I believe you. Please accept my apologies, and thanks for explaining your reasons. Thanks for the welcome. I know that I didn't exactly endear myself to you guys - I genuinely thought that consensus was closer to being reached than it now appears to be, so did not expect this kind of discussion - I am just a little bemused by what is going on here, especially given the qualifications of some of the players.

I don't think we have reached an impasse and I'll never say die to sound reason. This is not about belief, or it shouldn't be. I am genuinely interested in how you explain the paradox that you say the same energy flux (from an area element of the object) through the lens occurs independent of distance, yet that same energy is distributed over a smaller image area the further you get away without resulting in an increase in image brightness.

Similarly I find a problem with your theory when comparing lenses of different focal lengths and the same entrance pupil diameter when used at distances that result in the same image area. It just doesn't hold together as a unified photometric theory.

Dec 10, 2012 at 10:30 PM

RustyBug
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p.8 #6 · silly inverse square law question.

No worries ... you came across fine to me. I suspect that there is a "missing link" somewhere in the realm of luminance & flux between physics theory and photographic explanation therein that is keeping the camps divided from coming to a unified consensus ... thus the ardent passions for presenting that which we hold to be true.

As I mentioned earlier ... your reference to flux energy isn't "up my alley" so I may be having some trouble figuring out how to "speak your language". It can be tough sometimes in cyberworld ... but you've conducted and presented yourself VERY MUCH in harmony with the conduct that FM'ers ascribe to ... even if we are at temporary impasse and ardent in presenting our positions. We have still done so with respect for each other ... i.e. no rude, no trolling, etc.

No worries @ endearing ... you've presented yourself well, even in disagreement.

Again, welcome to FM.

Dec 10, 2012 at 10:37 PM

RustyBug
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p.8 #7 · silly inverse square law question.

HelenB wrote: yet that same energy is distributed over a smaller image area the further you get away without resulting in an increase in image brightness.

it would be much easier to show if I could draw worth a hoot ... can't so I use a camera.

Do you still have a copy of Light: Science and Magic? If so, I can reference some pages there to maybe bridge the gap that my words are failing at.

I've got the red cover (3rd edition, iirc).

I think the thing that messes with most people is that while the theory of AI=AR holds true, they are not recognizing that you do have some "swapping" of originating angles involved due to the area of the object, not being a single point. This is where the illustrations in Light: Science and Magic can be helpful in the angles of inclusion sections. Combining the array of trigonometry for vector forces alongside the illustrations and you knowledge of physics ... hopefully it'll help illustrate what I've failed to connect with you on to this point.

Dec 10, 2012 at 10:43 PM

curious80
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p.8 #8 · silly inverse square law question.

Guari wrote:

This thread should die it's course. Disseminating flawed knowledge is bad stuff.

I am sorry but I am in your supposed group of people who do not know what they are talking about.

Google my name, it's on my facebook web page. I am a research scientist,, who did a degree in geophysical engineering, then I did a master and now I'm nailing a PhD. Physics is the second name of my career.

I had stopped looking at this thread and had decided no to post to it anymore. However I stumbled upon it today and saw this comment and I think it needs a response.

You have your beliefs which is fine. However please note that just because you do not agree with someone else doesn't allow you to attack their words as flawed knowledge. Who is to decide that your knowledge is less flawed than the other party. Belief doesn't equate truth. The discussion has for most part been polite. However if you choose to resort to attacks rather than sound reasoning and demonstration then that violates the spirit.

As for your background, let me assure you that my engineering and science background is at least as well qualified as yours but thats not the point.

I'm sorry but this threadstill being alive is getting silly... I highly recommend reading the books instead of believing everything a person writes on the internet.

Sure please point me to a section in a book which explains this phenomenon in a manner that you are claiming and it would benefit us all

I have actually read Light, Science, and Magic and it doesn't have anything which is inconsistent with what I said.

What curious said is flawed on so many levels. But it sounds "alright". Plausible. Well, it is not.

It would be beyond my place to claim that I am a great physicist, because I am not. However instead of just dismissing my fairly detailed explanation from the very basic principles as flawed, if you could point out exactly where the flaws are then it would be great. As you are doing a PhD so you would know that clearly presenting your ideas in a convincing way is at least as important as the ideas themselves. If you really believe that your ideas are correct and my explanation is wrong then please draw for me the diagrams of the correct construction for the cases that I discussed above showing where I went wrong and how the science would actually work. It would be useless for me to re-iterate my views, or try to counter the arguments as I have already done that in as much detail as I could.

However if any of you is willing to go beyond words and put the ideas clearly in diagrams then I am still willing to work with you and discuss more. Drawing forces you to put the ideas from abstract to concrete and if you do that I am confident we will eventually reach a consensus

Dec 10, 2012 at 10:58 PM

RustyBug
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p.8 #9 · silly inverse square law question.

Curious80 ... when I mentioned "missing link" above to Helen, I had you in mind as well. (nothing snarky intended)

I know that what I've stated regarding AI=AR, energy, etc. to be true ... but I suspect that there is an issue of disconnect related to volume of energy (stemming from the amount of energy falling on our object iaw ISL) being mistakenly applied to further radiate iaw ISL.

At its core ... ISL is a spherically radial distribution concept. Reflectance is a planar concept. Reflectance doesn't radiate, it simply bounces iaw AI=AR, thus it doesn't follow ISL. My feeble drawing skills failed us before, but I don't understand why the provided link from the University didn't sufficiently illustrate it ... I'll see if I can find something else.

Dec 10, 2012 at 11:14 PM

Guari
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p.8 #10 · silly inverse square law question.

curious80 wrote:
Guari wrote:

This thread should die it's course. Disseminating flawed knowledge is bad stuff.

I am sorry but I am in your supposed group of people who do not know what they are talking about.

Google my name, it's on my facebook web page. I am a research scientist,, who did a degree in geophysical engineering, then I did a master and now I'm nailing a PhD. Physics is the second name of my career.

I had stopped looking at this thread and had decided no to post to it anymore. However I stumbled upon it today and saw this comment and I think it needs a response.

You have your beliefs which is fine. However please note that just because you do not agree with someone else doesn't allow you to attack their words as flawed knowledge. Who is to decide that your knowledge is less flawed than the other party. Belief doesn't equate truth. The discussion has for most part been polite. However if you choose to resort to attacks rather than sound reasoning and demonstration then that violates the spirit.

As for your background, let me assure you that my engineering and science background is at least as well qualified as yours but thats not the point.

I'm sorry but this threadstill being alive is getting silly... I highly recommend reading the books instead of believing everything a person writes on the internet.

Sure please point me to a section in a book which explains this phenomenon in a manner that you are claiming and it would benefit us all

Hi curious.

I gotta say sorry. It was never my intention to sound inflamatory.

It is frustrating. I know that a lot of the core concepts are flawed. However, I do not, recall from memory all involved equations and minutae. It would take me time to go to a library, grab a Feinman, study it and revisit a lot of the things involved to construct the case.

Though, point sources suffer from spherical divergence due to the ever-increasing radius for a set (constant) amount of energy emmited. Imagine a kid blowing soap bubbles. Now imagine that all the soap the kid has to blow into a bubble in 1 turn is equivalent to the total energy radiated from a point source. Now the kid blows. As the bubble grows, there is less and less soap available for the bubble to grow. Basically, the soap is redistributed into an ever increasing area as the bubble grows. Same thing with light. It's energy content will decrease due to an increase in surface for a constant amount of energy as the inverse to the square of the distance. But a photon will always have the energetic level of a photon, it's energy does not decay will the path traveled unless there is interaction with an object/substance in the pathway.

As I said, I have studied lot's of physics but I have migrated away from it into earth sciences and it has been quite a while since I've touched those kind of books.

If I do get the time, count me for sure that I can send you some references and construct the case. I just don't have the time to do that.

Thanks and have a nice day.

PS: Rusty for sure has a way of explaining in very simple terms what can be made to sound complicated. Look at his post just above mine, that's the essence of it.

Dec 10, 2012 at 11:17 PM

Chiefdog72
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p.8 #11 · silly inverse square law question.

I’ve been following the discussion and think it’s very interesting.

Welcome to FM Helen.

Rusty, I’ve found my third edition Light Science & Magic; I think I’ve found the pages you spoke of but would you give them to me to verify…..Thanks.

Also, here’s an inverse square law graphic I found; does it help anyone?

Edited on Dec 11, 2012 at 12:03 AM · View previous versions

Dec 10, 2012 at 11:51 PM

HelenB
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p.8 #12 · silly inverse square law question.

The energy of a photon being independent of distance traveled is a bit of a red herring, and it is causing lots of confusion here.

I wrote earlier (with extra unit information):

The object luminance (SI unit: cd/m^2) – ie the luminous energy flux (lm) from a given area element of an emitting or reflecting surface in a given direction over a given solid angle – is constant. That is a consequence of the conservation of energy. (1)

Do you have any problem with that Guari? It's a really simple statement.

I strongly suspect that when you refresh your memory about this subject the problems you are conjuring from poorly remembered principles will disappear.

PS, I've just spotted an obvious typo in my original. I wrote lx instead of lm as the symbol for lumen. I guess no-one read it.

Dec 10, 2012 at 11:53 PM

HelenB
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p.8 #13 · silly inverse square law question.

I only have an older edition of LS&M. Here is what it says on the subject:

"Did it alarm you to read that the camera that sees the direct reflection will record an image "as bright as the light source"? How do we know how bright the direct reflection will be if we do not even know how far away the light source is?

We do not need to know how far the source is. The brightness of the image of a direct reflection is the same regardless of the distance from the source. This principle seems to stand in flagrant defiance of the inverse square law, but an easy experiment will show why it does not.

You can prove this to yourself, if you like, by positioning a mirror so that you can see a lamp reflected in it. If you move the mirror closer to the lamp, it will be apparent to your eye that the brightness of the lamp remains constant.

Notice, however, that the size of the reflection of the lamp does change. This change in size keeps the inverse square law from being violated. If we move the lamp to half the distance, the mirror will reflect four times as much light, just as the inverse square law predicts. But the image of the reflection covers four times the film area. So that image still has the same density on the negative. In plainer words, if we spread four times the butter on a piece of bread of four times the area, the thickness of the butter stays the same." End of quote.

So there we have it, from a hopefully trusted source. Sorry for the pun. It does not matter whether the illuminated surface is a translucent lampshade or a lamp's reflector, or a white board, or a person's face, the principle remains the same.

Dec 11, 2012 at 12:09 AM

curious80
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p.8 #14 · silly inverse square law question.

Thanks Helen for bringing that up. Hopefully this will help convince.

Dec 11, 2012 at 12:46 AM

curious80
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p.8 #15 · silly inverse square law question.

RustyBug wrote:
Curious80 ... when I mentioned "missing link" above to Helen, I had you in mind as well. (nothing snarky intended)

I know that what I've stated regarding AI=AR, energy, etc. to be true ... but I suspect that there is an issue of disconnect related to volume of energy (stemming from the amount of energy falling on our object iaw ISL) being mistakenly applied to further radiate iaw ISL.

At its core ... ISL is a spherically radial distribution concept. Reflectance is a planar concept. Reflectance doesn't radiate, it simply bounces iaw AI=AR, thus it doesn't follow ISL. My feeble drawing skills failed us before, but I don't understand why the provided link from the University didn't sufficiently illustrate it ... I'll see if I can find something else.

In addition to what Helen quoted from the book, let me also address your comment. First I agree with AR=AI and I also agree that a point on an object is not a point light source. However what I explained earlier was that the way reflection from diffused surfaces works, the reflected light rays will get distributed in all directions and the result in principal will look similar to how the light rays spread out from a point source. Note that it does not matter if the light itself is diffused or directional. Even if you have highly directional light rays (such as those from the sun), they will spread out in different directions after reflection from the diffused surface due to the surface properties of the diffused objects (For an illustration see Light, Science and Magic Edition 4, page 35. It also contrasts it with the direct reflection a few pages later). And since the light rays spread out from every location on the subject so the net result is similar to what happens in case of point light sources and ISL.

Dec 11, 2012 at 01:06 AM

curious80
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p.8 #16 · silly inverse square law question.

Guari wrote:
Hi curious.

I gotta say sorry. It was never my intention to sound inflamatory.

No worries

Though, point sources suffer from spherical divergence due to the ever-increasing radius for a set (constant) amount of energy emmited. Imagine a kid blowing soap bubbles. Now imagine that all the soap the kid has to blow into a bubble in 1 turn is equivalent to the total energy radiated from a point source. Now the kid blows. As the bubble grows, there is less and less soap available for the bubble to grow. Basically, the soap is redistributed into an ever increasing area as the bubble grows. Same thing with light. It's energy content will decrease due to an increase in surface for a constant amount of energy as the inverse to the square of the distance. But a photon will always have the energetic level of a photon, it's energy does not decay will the path traveled unless there is interaction with an object/substance in the pathway.

Sure we don't have any disagreement here. In other words a point light source sends out photons in all directions in a sphere. These photons spread out more and more as they move farther from the source. The energy of each photon itself is constant, as you mentioned. However as you move the subject away from the light source the number of photons which fall on the subject decrease and thus the total energy falling on the subject decreases. I think we are in agreement on this, Right?

The picture that Chiefdog72 posted above illustrates this.

In fact a few posts ago Rusty also explained the same with the balls example.

Now lets move to the second half of the story. A diffused surfaces reflects photons in all directions and thus photons again spread out as they move away from the subject after reflection. Thus the number of photons which will fall on the camera lens from the subject will decrease as you move the lens away. There is nothing here which is inconsistent with what you are saying or what Rusty is saying.

Dec 11, 2012 at 01:18 AM

RustyBug
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p.8 #17 · silly inverse square law question.

curious80 wrote:

Sure we don't have any disagreement here. In other words a point light source sends out photons in all directions in a sphere. These photons spread out more and more as they move farther from the source. The energy of each photon itself is constant, as you mentioned. However as you move the subject away from the light source the number of photons which fall on the subject decrease and thus the total energy falling on the subject decreases. I think we are in agreement on this, Right?

The picture that Chiefdog72 posted above illustrates this.

In fact a few posts ago Rusty also explained the same with the balls example.

So far, so good ... (although "total energy" might cause some future issues, but okay for now).

Dec 11, 2012 at 02:22 AM

RustyBug
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p.8 #18 · silly inverse square law question.

curious80 wrote:A diffused surfaces reflects photons in all directions

My position is that light reflects iaw AI=AR, not necessarily in all directions.

My explanation would follow:

A diffuse subject reflects light in accordance with AI=AR, based on the angle of incidence and the multitude of varying angles of light being received and multitude of angles in the surface. Consider:

A single photon from a single direction, reflecting off a single surface angle will reflect that photon in a single direction iaw AI=AR.

Two photons coming from two varying directions, reflecting off a single (i.e. uniform) surface angle will reflect in two different directions iaw AI=AR.

Two photons coming from two varying directions, reflecting off of two different surface angles may reflect in two different directions ... but with four different possible permutations, iaw AI=AR. it is possible for them to both be reflecting in the same direction. This is of course the basis for intentionally varying angle design in a parabolic reflector.

Ten different photons coming from ten different directions, reflecting off a single (i.e. uniform) surface angle will reflect in ten different directions, iaw AI=AR.

Ten different photons coming from ten different directions, reflecting off of ten different surface angles may reflect in ten different directions ... but with 100 different possible permutations, iaw AI=AR. Again, some of those permutations may incur some reflecting in the same direction.

100 photons coming from ten different directions, reflecting off of ten different surface angles may reflect in 100 different directions, or less as some of the permutations may result in multiple reflections in the same direction.

100 photons coming from one direction, reflecting off of one (i.e. uniform) surface angle will reflect 100 photons in one direction, iaw AI=AR.

It is true that a diffuse surface with a multitude of varying surface angles will reflect light in a multitude of varying angles. Can we agree that this reflection into different directions is the product of AI=AR ... or are we still going to suggest it reflects iaw ISL?

The question (at this juncture) is:

Does light reflect iaw:

A) AI=AR
B) ISL

Dec 11, 2012 at 03:02 AM

curious80
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p.8 #19 · silly inverse square law question.

RustyBug wrote:
curious80 wrote:A diffused surfaces reflects photons in all directions

My position is that light reflects iaw AI=AR, not all directions (assumed to be meant as iaw ISL)

My explanation would follow:

A diffuse subject reflects light in accordance with AI=AR, based on the angle of incidence and the multitude of varying angles of light being received and multitude of angles in the surface. Consider:

A single photon from a single direction, reflecting off a single surface angle will reflect that photon in a single direction iaw AI=AR.

Two photons coming from two varying directions, reflecting off a single (i.e. uniform) surface angle will reflect in two different directions iaw AI=AR.

Two photons coming from two varying directions, reflecting off of two different surface angles may reflect in two different directions ... but with four different possible permutations, iaw AI=AR. it is possible for them to both be reflecting in the same direction. This is of course the basis for intentionally varying angle design in a parabolic reflector.

Ten different photons coming from ten different directions, reflecting off a single (i.e. uniform) surface angle will reflect in ten different directions, iaw AI=AR.

Ten different photons coming from ten different directions, reflecting off of ten different surface angles may reflect in ten different directions ... but with 100 different possible permutations, iaw AI=AR. Again, some of those permutations may incur some reflecting in the same direction.

100 photons coming from ten different directions, reflecting off of ten different surface angles may reflect in 100 different directions, or less as some of the permutations may result in multiple reflections in the same direction.

It is true that a diffuse surface with a multitude of varying angles will reflect light in a multitude of varying angles. Can we agree that this reflection into different directions is AI=AR ... or are we still going to suggest it is iaw ISL?

I have never said that the light is reflected in various directions due to ISL. I am also not arguing against AR=AI being the basis of diffused reflection. ISL deals with what happens AFTER light has been reflected from a diffused surface.

(Of course you would agree that even if all photons are coming from the same direction at the same angle then a diffused surface would still scatter them in different directions. This point is not critical to our discussion but it is still important to note that the discussion would not change whether the light is diffused as on a cloudy day or harsh and directional as on a sunny day)

Dec 11, 2012 at 03:18 AM

RustyBug
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p.8 #20 · silly inverse square law question.

curious80 wrote: ISL deals with what happens AFTER light has been reflected from a diffused surface.

Please apply Newton's First Law of Motion relative to your ISL assessment mentioned above.

If you can, please apply it in context of a finite number of photons so that we can more readily follow the application of your theory.

Edited on Dec 11, 2012 at 03:36 AM · View previous versions

Dec 11, 2012 at 03:30 AM

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