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Beams A and B are of different colors.

I am trying to understand how both the lights would impact each others' wavelength.

So Color IS EQUIVALENT TO Wavelength

What will be the color of the areas labelled C,D and E?

 \   \          /   /
  \   \        /   /
   \   \      /   /
    \ A \    / B /
     \   \  /   /
      \   \/   /
       \  /\  /
        \/C \/
        /\  /\
       /  \/  \
      /   /\   \
     / D /  \ E \

What will be the final color of C,D and E?

Will C be a mixture of A and B? If yes, then how.

Will D and E have the color B and A respectively?

Answers with citation or proof of practical demonstrations shall be given more preference over those which do not have them.

Nephew of Stackoverflow
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  • C is an area? That's just where the beams pass each other. D will be the color of B and E will be the color of A. Nothing will change, as far as linear optics are concerned. –  Oct 30 '19 at 15:15
  • What will be the final color of C,D and E? Will C be a mixture of A and B? If yes, then how. Will D and E have the color B and A respectively? – Nephew of Stackoverflow Oct 30 '19 at 15:21
  • Why would you anything at C? Is there dust in the air? Are these laser beams? –  Oct 30 '19 at 16:40
  • Like if you cross two flashlights with different color filters, they won't interact, they just show up on the wall at different spots, like the other wasn't there. If they meet on the wall, then yes their colors will blend into a new one in the reflection off the wall. –  Oct 30 '19 at 16:42
  • So they won't give different colors if matter/any surface isn't present? – Nephew of Stackoverflow Oct 30 '19 at 17:25
  • @user47014, Careful when explaining stuff to newbies: The only place where "blending" happens is in the observers brain after the photons of different colors have reflected off the same spot on the wall, and exited different receptors in the observer's eyes. – Solomon Slow Oct 30 '19 at 17:25
  • @SolomonSlow True that, so will they blend in my mind, assuming I am looking at C from the top or do I need a surface to be able to see it? – Nephew of Stackoverflow Oct 30 '19 at 17:29
  • @Solomon Slow Yeah I forgot to mention it is in what we see, though maybe I thought it's implicit enough –  Oct 30 '19 at 17:30
  • @user47014 Can u answer my question? – Nephew of Stackoverflow Oct 30 '19 at 17:32
  • @Nephew of Stackoverflow You generally need a surface to see commonly used light, unless a lot of dust is in the air or it's a really strong beam. So if you put a surface at C, the reflection will look like a blend of colors in your eyes, but something like a spectrometer could still differentiate them. Otherwise the colors won't change, like at D or E, from what they came from. –  Oct 30 '19 at 17:33
  • So if it were a strong beam, would I see a mixture of those two colors or something else altogether? – Nephew of Stackoverflow Oct 30 '19 at 17:36
  • @NephewofStackoverflow you would see some of A bouncing off some dust or water particles, and some of B, and then your eyes and brain mix them exactly as they would with any other surface. – A_P Oct 30 '19 at 17:57

1 Answers1

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What will be the final color of C,D and E?

"Color" is something that only happens in your brain. Photons have energy/wavelength.

The photons that pass by E are the same photons that earlier passed by A. They are completely unaffected by the crossing of the beams. Likewise, the photons that pass by D are the same photons that earlier passed by B, and they too are unaffected.

If you place a white card at any one of those places, photons will reflect off of it in all directions. Some of them will enter your eyes, and you will see a bright, colored spot on the card.

Photons reflected form a card at A, or E will cause you to see one color, and photons reflected from a card at B or D will cause you to see a different color.

At location C, the card will reflect photons of both wavelengths. The photons still are unaffected by each other, but when photons of the two different wavelengths come from the same location (the spot on the card) and enter your eyes together, your brain will perceive a third color, different from the other two.

Solomon Slow
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  • Well, not only in your brain... Color can have actual physical meaning because it corresponds to a specific frequency of light waves. And two waves could interfere to cancel each other out, but the OP's question is too broad. –  Oct 30 '19 at 17:39
  • Yeah that's what I meant. – Nephew of Stackoverflow Oct 30 '19 at 17:40
  • So will the wavelength at C change? – Nephew of Stackoverflow Oct 30 '19 at 17:41
  • @S V light does not cancel each other out, they make interference patterns if they do interfere, but you won't see that with like two color filtered flashlights on a wall. –  Oct 30 '19 at 17:51
  • @NephewofStackoverflow Note that not all colors are from single wavelengths. For example, white light has a distribution of photons of different wavelengths. When we see photons from this distribution fast enough, we perceive white. – BioPhysicist Oct 30 '19 at 17:55
  • So do the photons of beam A and B influence each others' wavelength at C? – Nephew of Stackoverflow Oct 30 '19 at 18:02
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    @NephewofStackoverflow No, they would not – BioPhysicist Oct 30 '19 at 18:04
  • So why do they get influenced when a surface is introduced? – Nephew of Stackoverflow Oct 30 '19 at 18:05
  • @Nephew of Stackoverflow They aren't influencing each other with a surface either, your brain just perceives that they are mixed when they come from the same spot. –  Oct 30 '19 at 18:07
  • @Nephew of Stackoverflow Think if you got a bunch of yellow leaves and brown leaves and broke them into tine little bits, and put them in a pile. The pile may look beige to you eyes, but you know that it's actually a mix. –  Oct 30 '19 at 18:12
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    @SV, There is no mapping from the space of colors to wavelength or frequency. Color space* is three dimensional. Any given color corresponds to the levels of excitation of three different kinds of color receptor cell in the retinas of your eyes. There may be a single wavelength that you call "yellow", but there also are infinitely many different blends of reddish and greenish wavelengths that would appear to you as exactly the same "yellow." Also, there are colors (e.g., magenta) for which there is no single wavelength. – Solomon Slow Oct 30 '19 at 18:12
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    * That is, for human color vision. Most non-primate mammals perceive a two dimensional color space. Birds perceive a four dimensional color space. Some arthropods perceive even more dimensions of color than that. – Solomon Slow Oct 30 '19 at 18:14
  • So I don't need a surface to see the mixture of the 2 colors? – Nephew of Stackoverflow Oct 30 '19 at 18:14
  • @NephewofStackoverflow, In order for you to "see" a mixture of two different wavelengths, they must both converge on the same spot on your retina. Because of the way your eyes work, that means they must both enter your eye from the same direction. Reflecting both beams off a white card is a cheap and easy way to accomplish that. You might also achieve the same effect with some complex optical instrument that has a beam splitter. Or you might achieve it by looking at two different light sources that are so close to each other that you can't tell them apart. – Solomon Slow Oct 30 '19 at 18:17
  • @SolomonSlow that is very interesting, I do remember seeing something like that in a Vsauce video called "this is not yellow". But for the particular question the OP is asking I think the idea is in reverse. You can map a frequency into color space (the inverse doesn't exist, though)... and you can also map a superposition of frequencies (probably... at least if the superposition is only 2 of them). This being said, the OP's question says nothing about frequencies, just color... but we could assume that it means just a single frequency and probably be safe, no? (like in a laser beam). –  Oct 30 '19 at 18:19
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    @SV, Re, "two waves could interfere..." Interference is what we call the stationary patterns of intensity-in-space that are caused by the superposition of different wave fronts that have exactly the same wavelength. – Solomon Slow Oct 30 '19 at 18:19
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    @SV the original question depends upon whether two different light beams are changed in any way when they cross each other. The simple answer to that is, No. They are not changed in any way by the crossing. – Solomon Slow Oct 30 '19 at 18:21
  • @SolomonSlow thank you for the answer, optics is really not my forte. I thought that the electromagnetic fields could affect each other in some way but I really don't know enough of the subject. What you mentioned about color is very interesting though. –  Oct 30 '19 at 18:23
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    @SV https://physics.stackexchange.com/questions/351154/can-electromagnetic-fields-interact-with-each-other – Nephew of Stackoverflow Oct 30 '19 at 18:29