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Amount of single photons to make white light?

  1. Nov 13, 2015 #1
    First off I hope I'm putting this in the correct forum. My question is more than just the minimum amount of photons to make a single blip of white light, but more so the base photons in the visible spectrum of light. We have all seen a prism split light into violet, blue, cyan, green, yellow, orange, and red waves of light, but what are the colors possible from a single photon of light. Example cyan is really a mixture of blue and green light, so I'm guessing a single photon could be blue or green but not cyan?

    I feel like I'm starting to ramble on with all of my thoughts about this, but my real question is what are the colors a single photon of light can be?


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  2. jcsd
  3. Nov 13, 2015 #2
    This is a little vague. Color is human perception, and there is no universal consensus on the finer color boundaries. You can always unambiguously refer to the frequency of a photon (in a particular frame) though, and since frequency ultimately determines the color the human eye sees, it seems like a good quantity to use instead of color.
     
  4. Nov 13, 2015 #3

    mfb

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    There are no "base photons". The spectrum is continuous without gaps or steps, classifications like "green" and "yellow" are arbitrary and have no physical relevance.

    "White" is a subjective perception, you can generate that impression with light of three wavelengths (computer monitors do that), but you can also generate it with four, 100, or the full continuous spectrum. You certainly need more than a few photons, however, because our eyes are not sensitive enough.
     
  5. Nov 13, 2015 #4
    So is it possible for a single photon to be any wavelength/color in the visible spectrum of light?
     
  6. Nov 13, 2015 #5

    sophiecentaur

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    The colours you see are almost never due to a single frequency, but combinations of different frequencies. (Where would you find a natural monochromatic source of light?)
    BTW, for someone to perceive an actual colour you need a lot of photons. It's easier to talk in terms of light flux than photons here. Rod receptors are claimed to be able to detect the presence of individual photons but just as a brief 'twinkle'.

    Again.not strictly true, in practice, because the phosphors used (and specified) are not monochromatic and, particularly with the green phosphor, are a significant distance from the spectral curve. It's a matter of compromise to have good, bright phosphors that are near enough to the spectral curve on the CIE chart to encompass as many displayed colours as possible. It's really best never to confuse colour and wavelength.
     
  7. Nov 13, 2015 #6

    mfb

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    Every wavelength is possible. As I said, there are no steps or gaps.
    It is not. Unless you confine the photon to be between two mirrors, for example, then you can get similar energy levels.
    A collection that excites the color-sensitive receptors in the eye in some fraction that is similar to the fraction we get from the sun. That is more biology than physics.
     
  8. Nov 13, 2015 #7

    Nugatory

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    Color is how our brain interprets the signals it receives from our optic nerves when the cells of of the retina are stimulated by incoming light, so when someone says "red light", they're using those words as a convenient shorthand for the more precise "light of a wavelength that most people (but not necessarily those with some forms of colorblindness) will perceive as red".

    Generally this is OK, but it can confuse us into thinking that light has a color - it doesn't, it has a wavelength and frequency. Light in the 500-520 nanometer wavelengths stimulates the retina and is interpreted by the brain the same way as a mixture of light in the 430-500 and 520-565 wavelengths.
     
  9. Nov 13, 2015 #8

    sophiecentaur

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    Biology is crammed full of interesting Physics.
    One photon can only stimulate one receptor so you would need enough photons for enough of the cone receptors to produce a statistically significant set of signals that the optical processing could 'decide' what colour to recognise / categorise - on the basis of the proportions of each receptor group excited.
     
  10. Nov 13, 2015 #9

    sophiecentaur

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    Light is usually a mixture of frequencies and not just one. It's only the 'colours' of monochromatic light that correspond to particular frequencies. It is very limiting to equate colour and frequency. eg Pink = ?, bottle green = ?, purple = ?
     
  11. Nov 13, 2015 #10
    While that is true, it does not seem to address the OP's question here:
     
  12. Nov 13, 2015 #11

    sophiecentaur

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    Possibly but it's helpful to re-phrase a question when necessary in order to give a proper answer, (imo.)
    I gave an answer to the OP. The answer was that it couldn't be perceived as a colour.
     
  13. Nov 13, 2015 #12

    phinds

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    The answer to that is simple and has been given. None. A single photon does not impinge on the optic nerves sufficiently to produce any perception of color.

    If the question is what frequency can a single photon have, then that has also been answered. Anything you like.
     
  14. Nov 13, 2015 #13

    Nugatory

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    This is correct - it would only be under artificial conditions (a well-tuned laser comes pretty close) that we might encounter true monochromatic light, let alone superpositions of monochromatic light. Just about all the cyan that I'll ever see, including the color I saw when I smashed a used inkjet printer cartridge just to see what was inside it, is a mixure of frequencies that my brain is interpreting as a single color.

    (In writing that post you're quoting I was soooooo hoping not to have to go there.... :smile:)
     
  15. Nov 13, 2015 #14
    Is this specifically directed towards me, or are you just answering the OP?
     
  16. Nov 13, 2015 #15

    phinds

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    Both.
     
  17. Nov 13, 2015 #16
    Thanks everyone for your responses. The current IOS game we (www.tapgods.com) are designing is centered around your character (a photon) and involves a lot of physics involving light and you all have helped greatly in our rough design.

    Our site is currently getting a bit of a facelift. Some things may be misbehaving
     
  18. Nov 13, 2015 #17
    Um, thanks for giving me those facts, but I sorta knew them already.
     
  19. Nov 13, 2015 #18

    Nugatory

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    Good point.... The color-sensitive cone cells in our retina aren't triggered by the amount of energy carried in a single photon of visible light. The rod cells, which are more binary off/on in their behavior can be triggered by a single photon, and this is why we lose color vision in dim light.
     
  20. Nov 13, 2015 #19

    phinds

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    Since you say the character will be a photon, I'm assuming you are not planning on using real physics, right? I mean, there is no such thing as "the point of view of a photon".
     
  21. Nov 13, 2015 #20
    It is to early in the production to release to many details. I can say certain aspects of the game will use correct or close to correct physics and others will be completely fantasized.
     
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