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| Re: silly inverse square law question. || |
curious80 wrote: Shiny surfaces with specular reflections need a slightly different treatment to understand their behavior.
It is a statement like this that renders much disagreement ... maybe even if only pedantic to some, but it is suggestive that the laws of physics of the nature of light do not hold true for all circumstance. It is by definition of a law of physics, that it necessarily does hold true in all circumstance.
I just mean that the microscopic details of how the light rays bounce around would be different because the surface structure is different. The governing laws are of course the same.
The exact same laws of physics determine how light reflects off of a shiny surface, as it does for a diffuse one. This is AI=AR.
Light moves iaw trigonometric (vector force) functions. ISL is a specific explanation of a specific omnidirectional non-reflected scenario (iaw trig)
It would not matter whether it is reflected or non-reflected. Surely you would agree that in those cases where AI=AR results in divergent omni-directional beams, the intensity would still fall off with square of distance. You are right though that ISL only applies when the light flow is omni-directional. So if reflected light is for example completely coherent then there would be no drop in intensity with distance, just like ISL does not apply to coherent light sources like lasers.
(Well the light flow doesn't have to be omni directional. Even if the light flows out in a cone, ISL still applies. Real light sources like soft boxes etc are not really omni directional, but send out light in a cone, but I think we both know what we mean here)
AI=AR is how reflected light changes direction when acted upon by an outside force (iaw trig), i.e. the object it is reflecting off of. Reflected photons continue to follow the straight line path of their AI=AR iaw with Newton's First Law of Motion.
You seem to be intent on wanting to take it from diffuse and work backwards, making allowances to explain for special cases. I seem to be intent on taking it from singular photon, the nature of light, and work it forward holding fast to the tenets of the law @ AI=AR for all things.
No. I just take diffused case as an easy to discuss example. All cases including the diffused and non-diffused cases can be explained by detailed study of AI=AR as well as the motion of rays after the reflection.
As I mentioned to Helen & you earlier, I think that we'd eventually find the "missing link" that is garnering the distinction from which we are misunderstanding each other. I will hold fast to AI=AR, (opaque, translucent, transparent, index of refraction, etc.) for reflection/refraction (i.e. outside force acting upon), Conservation of Energy and Newton's First Law of Motion in regard to reflected light.
So do I, as I have mentioned on a number of occasions now I just think that you are refusing to accept some implication of AR=AI. I have shown those implications for the specific example of diffused surfaces, again because that is easier to analyze. I have explained how AR=AI predicts an inverse square drop off at least for that particular case, and you have not addressed that so far.
As to your question @ using reflectors, also consider the parabolic reflector/umbrella, or the beauty dish. These are all simply variations of intentionally designed applications of AI=AR. Whether, you are diffusing or concentrating or collimating light ... it is always a product of AI=AR. There are no "slightly different treatments" required, only a full cognizance of all the factors involved for a given scenario.
Again I agree. The behavior is determined by the AR=AI in all cases - to that end we have no disagreement. What I am pointing out is that in both the case of a white sheet reflector (diffused) or a say a silver reflector (not diffused) we will have the reflected light dropping off with inverse of the distance. I hope you don't disagree that this is true at least for these specific cases (under the AR=AI no doubt ). And yet when we photograph these, they will have constant exposure when we move the camera away, even though the light intensity is falling with distance. So I am interested in knowing why in your opinion the exposure does not change if you photograph say a white reflector from increasing distances, when we know that the light reflected from that reflector drops with intensity.
And yes I agree that there will be other scenarios where the reflected light intensity will not fall with square of the distance, depending on the specific AR=AI arrangement. However those cases are not going to follow the constant exposure either.