Light which reflects off a diffuse reflector is scattered preferentially in certain directions, as can be seen in the following image:    Why isn't light scattered uniformly in every direction by a diffuse reflector?
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Lambert's Cosine Law for Lambertian Reflectors states that the radiant intensity $I$ (watts per square meter per steradian) of reflected light as a function of the angle $\theta$ from the normal to the surface of the reflector is $I(\theta)=I\cos\theta$. Because of this law, uniformly-lit diffusely-reflecting planar surfaces (which approximate perfect Lambertian Reflectors) also appear uniformly-lit to an observer, which is to say that the radiant intensity of light reaching the observer from such a planar surface is constant no matter where on the surface the observer looks.  So far so good. There is, however, a deep mystery lurking beneath this simple principle, because it would seem that it would be far more parsimonious for the radiant intensity of light reflected by a Lambertian Reflector to be constant for all $\theta$ (i.e. have no angular dependence) at the "cost" of having the observer perceive an angular dependence to the radiant intensity of light reflected by a uniformly-lit planar Lambertian Reflector. Why is the observer "privileged" in such a manner by Lambert's Cosine Law?
67533
I know that the light is reflected from a object to my eyes, but I don't understand exactly how. The photons appear from the light source and disappear in my eye! Can someone explain the phenomenon of where the photons go and do to allow us to see?
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I was readng Wikipedia article (English one) about radiation pressure because there is something I still cannot figure out. As I understand it, radiation pressure emerges from conservation of momentum. Photons or electromagnetic waves possess momentum and when they are absorbed, reflected or even emitted, the aborber/reflector/emitter experiences a pressure that is proportional to the irradiance (in watts per square meter). OK. In the case of a perfect reflector that does nothing but reflecting incoming radiation, it would seem the reflector is pushed and the radiation is reflected in opposite directions. But the radiation has not lost anything, it has only changed direction. And I do not understand how something can be set in motion (the reflector), which amounts to do work, yet the source of this work does not lose energy. I mean, if the radiation, after a U turn, meets a second reflector, it would have pushed two reflectors a way, yet it would continue in its original direction as if nothing happened...? What am I missing here? Should not photons lose something?
34027
Why do polarized sunglasses remove (most) reflections on car windows?  I know that both lenses of polarized sunglasses are polarized in the same direction and I can see that reflections in my own windshield and the windows of other cars appear, disappear, or change depending on how I tilt my head, but why?  Why is the light in those reflections polarized?  edit: And why is most of the light in the various reflections on the interior of my own windshield and various windows/windshields at what seem like a variety of angles all polarized in a sufficiently narrow set of ways as to make polarized sunglasses work?
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This example purports to show reflection of light rays from a spherical mirror. It looks good, until you try to draw a ray from the tip of the candle flame, then through the focal point, $F$, and then emerging parallel to the optic axis $(CF)$.  Go ahead, draw it on your computer monitor screen, or print this page and draw it on the paper. Whoops! This ray should then pass through the image of the tip of the candle flame, but it doesn't!  Here's what you get when you draw the third light ray (in red) from the candle flame. It comes nowhere near the image of the candle flame. As soon as you draw some of the "missing" rays, you discover that the diagram becomes inconsistent.    According to me, the diagram seems to be perfect. From where did this anomaly come from? Please help.
25321
Why are characteristic impedances of traces not considered when the traces are shorter than half a wavelength? I've had the same issue with light diffraction, which happens when pinholes are smaller than half a wavelength - it sort of makes sense somehow, but I can't "see" it, I don't understand how wavelengths are related to reflections (which I assume are the only reasons why we care about impedance matching). I'm trying to make the ocean wave analogy work but... Well, the fact that I'm asking this says it all.
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Consider this picture of sun beams streaming onto the valley through the clouds.    Given that the valley is only (at a guess) 3km wide, with simple trigonometry and the angles of the beams, this gives the result that the position of the light source is being a few tens of km away at most.   What is wrong with the analysis?
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The  treatment of circular apertures yields a diffraction pattern of circles, with the first minimum (dark ring) at an angular radius of $\theta$ where $\sin(\theta)=1.22\lambda/b$, where $b$ is the diameter of the circular aperture.     But this same result is extrapolated to lenses, to calculate its limit of resolution. But in the case of lenses, there is no opaque material which blocks of the light coming out from everywhere except the aperture.      In the absence of this opaque obstacle, how can diffraction take place,   since according to the , the wavefront which would   produce the secondary wavelets still extends everywhere and not just   to a confined region, which is how the diffraction pattern arises, by   confining secondary sources to a finite region or confining it from an   "edge" till infinity?* In other words, Why does putting a circular lens in the path of plane wavefornt produce the same effect as allowing only a circular portion of that wavefront to propagate?      And even if there is diffraction, will the same formulae apply? will   not the presence of light elsewhere change the case?
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I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
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I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object (or material) that refracts/reflects it. But a light ray should be part of an electro-magnetic wave, is this correct? If it is so, it should obey to the  and this doesn't seem to me to describe a straight line ray.  I'm having problems visualizing how light is emitted and how it relates with the wave equation. Can someone with a clear understanding of the problem explain it to me in simple terms?
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Why does the apparent size of an object change when it is farther away from me compared to when it is closer to me?  Can someone perhaps explain this through an optics perspective?
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I was looking at  on why  and emission lines don't cancel out:      An experiment shining light on the material and looking at the   reflected spectrum will see absorption lines at those frequencies,   because the relaxation of the excited electrons will emit back   radiation all around randomly, whereas the reflected spectrum is at a   specific angle.   However it is not totally convincing to me. The photons that get emitted towards the center of the Sun (by the electrons in higher energy states that absorbed a photon earlier) would get absorbed again when they hit a different electron (and then re-emitted) and would eventually make it out. So why don't absorption and emission lines cancel out in our Sun?
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When light (composed of photons with different frequency and wavelength) falls on a material, some of it gets absorbed and some get reflected depending upon the color of the material on which it strikes. And the material reflects the light of its own color only, thereby absorbing all the other colored light. So, my questions are:  How would a photon with certain wavelength (say 400 nm) decide to get reflected after striking the material of red color?   What is the actual mechanism behind the reflection of various colored light by the material of different color?
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This is something that I have wondered for a long time. How come when I walk around why do I not see random black spots where light has collided destructively and bright spots where it has collided constructively?
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Take a look at the following picture:   Why does the light at the bottom of the water form this pattern? I have also seen the same phenomenon in all the swimming pools I've ever visited, of whatever depth they may be. How does this happen?
81639
I am currently reading about the interactions between light and matter, but I keep coming across conflicting explanations.  My initial understanding (using classical electrodynamics) was that light (EM) waves do not actually travel through glass. Instead, they are absorbed by the atoms and/or electrons within the glass, which then emit new EM waves. The new EM waves emitted by the energised particles make up the forward-radiation, which is the light observed from the opposite side of the glass. So it appears as if light is travelling through the glass, but it's actually being absorbed and then re-emitted with (mostly) the same properties.  The article  by Chad Orzel, based on a related SE question, confirms the above:      To understand the propagation of a wave through a medium, you can   think of each component of the medium– atoms, in the case of a glass   block– as being set into motion by the incoming wave, and then acting   as a point source of its own waves.   But an answer to a different but related question,  conflicts with the above:     the electrons in glass are tightly bound to atoms so they are not free   to move like the electrons in a metal and therefore they do not absorb   the photons.   I know the above is referring to the quantum electrodynamics understanding, but I think it still conflicts as it claims that EM waves are not absorbed by the electrons in glass because they are too tightly bound to their atoms.  Also, the  provides a small explanation of the mechanics behind refraction within glass, which kind of conflicts with both of the above:     In the case of dielectrics such as glass, the electric field of the   light acts on the electrons in the material, and the moving electrons   generate fields and become new radiators. The refracted light in the   glass is the combination of the forward radiation of the electrons and   the incident light. The reflected light is the combination of the   backward radiation of all of the electrons.   From my understanding, the above claims that some of the light is absorbed and re-emitted by the electrons (which conflicts with the linked answer), and that the rest of the incident light travels through the glass (makes up the rest of the refracted light) (which I think conflicts with the linked article, claiming the light is absorbed (although the article doesn't technically state whether all of the light is absorbed and re-emitted, so maybe that's where I'm going wrong(?))  I'm sure this is my misunderstanding, so I would be very grateful if you could clear it up for me:  When a light wave is incident on a sheet of glass, do the particles that make up the glass absorb the waves and re-emit them in the forward direction? Or do the light waves manage to travel through the glass, without being absorbed and then exit the glass?
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The blue color of light of the sky is due to Rayleigh scattering.  But the sun itself appears yellow in color whereas the scattered sunlight itself appears blue.  Why does this happen? Should the sun then not also appear blue in color?