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pls help me on it. I do not know if it is right but why do we only see black colour while there is no light.

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  • $\begingroup$ Are you really just wondering why black is associated with no light, as given in Swike's answer? Or are you looking for something deeper involving the biophysics of the vision process, noise in photon detection, etc.? $\endgroup$ Commented Aug 20, 2020 at 11:52
  • $\begingroup$ Does this answer your question? Explanation about black color, and hence color $\endgroup$
    – Brick
    Commented Aug 20, 2020 at 14:59
  • $\begingroup$ There are optical illusions where you will see black even when the true color is not black, so I think your statement as made is false. It also works the other way - You can sometimes see colors when there was really only black and white. Closest open-source example I could find of the former: en.wikipedia.org/wiki/Checker_shadow_illusion. Example of the latter: en.wikipedia.org/wiki/Benham%27s_top $\endgroup$
    – Brick
    Commented Aug 20, 2020 at 15:14
  • $\begingroup$ I’m voting to close this question because this question lacks basic prior research. $\endgroup$
    – user258881
    Commented Aug 21, 2020 at 5:45

3 Answers 3

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Technically, nobody see only black when there is no light, this is an oversimplification of phenomenology. If you put yourself in complete darkness, you will see things, part hallucinations, part residual neural excitation, part noise, depending on your mental state. Color is a neurobiological phenomenon, not a physical one. You can see colors by stimulating parts of your nervous system. But there is no color outside, just electromagnetic radiation.

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Color in physics is all about the frequency of light. Higher frequencies yield "bluer" colors and lower frequencies "redder". You can have the entire rainbow of colors by changeing just this property of light.

But be aware, we commonly define color in a much diverse way. For example we have tagged purple and magenta to things we perceive as colors separated from the rest, but these do not exists in the frequency spectrum of light. In a fundamental way the color purple is a combination of red and blue light. In the same way, we say white is a color but it is not located anywhere in the visible spectrum (since in reality is a combination of all visible frequencies at the same time). In a similar way we say black is a color, but fundamentally it has again little to do with the concept of color as a frequency of light.

In fact the color we perceive as black is fundamentally the absence of any light frequencies of the visible spectrum. Black is the absence of light by definition. That's why there is black when there is no light and why when there's no light there can only be black.

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  • $\begingroup$ So yes, black if associated with no light. But I think there is something more interesting and deeper here, but it might need more biology to fully understand. It really comes down to reliability of how our vision works. Why does something else not happen when no light hits our eyes? Why is there a considerably small amount of noise present when there is no signal so that we do in fact perceive black? I think the question needs to be improved, but I think there is more to be said than just "black is the absence of light" $\endgroup$ Commented Aug 20, 2020 at 11:51
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    $\begingroup$ For the general science questions, it's important to keep a distinction between "color" in the physics-slang sense of a single frequency and "color" in the broader sense of the perceptual experience. This answer kind of mixes them up. More to the point of the question, I think, at the perceptual level there are known optical illusions where you perceive color of something that is black in the physical sense or perceive black for something that is not. The last paragraph is factually wrong with respect to the perceptual experience of "black". $\endgroup$
    – Brick
    Commented Aug 20, 2020 at 15:18
  • $\begingroup$ Pure spectral colors are not the only colors that should be called "colors". Our perception of color depends on how much each of the three different types of cone cells in our retinas are excited. If you really wanted to talk about a "pure" color it should be a color that excites only one of the three cone cell types. But no such color exists because the response functions of the three cone cell types overlap. $\endgroup$
    – The Photon
    Commented Aug 20, 2020 at 17:20
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If I understand your question correctly, you are essentially wondering why we perceive the absence of light as black? Please correct me if I am mistaking your question here.

That is actually an intriguing question, we cannot truly and satisfactorily answer, as the necessary mechanisms that translate physical sensory signals (such as a photon of specific wavelength impinging onto our retina at the back of our eyeball) to our conciousness through a highly intricate neurobiochemical machinery in general are very poorly understood.

However, we are in luck (or not, since our mind is actually always faking and tweaking the actual reality to some degree), there is no need to answer the question in this way! Colours do, in fact, not exist - they are a fabrication of our neurological grey matter that has its rudimentary roots many hundreds of million years ago (i.e. when evolution invented 'seeing').

So, if we 'see' or rather perceive something as black, this simply means that the lack of sensory signals in the retina is interpreted as 'no light/photons come from here', albeit every 'black surface' is not perfectly black (see, e.g. Vantablack). But our optical sensors pick up no or too little, and that signal is forwarded to our conciousness as 'black colour'. It could be green as well, or orange, if the past biological evolution would have resulted into a different-wired brain.

If you are more interested into The Neuroscience of Reality, I was recalling a same-named article from Scientific American whicho elaborates on our brain 'faking' our perception of colours as real, although they are not (this is why so many biologists wonder, how the world looks like to all the other species that can 'see'):

Anil K. Seth: SciAm092019

and a short extract from the online article linked above, relevant to this answer:

Take, for example, the experience of color—say, the bright red of the coffee mug on my desk. The mug really does seem to be red: its redness seems as real as its roundness and its solidity. These features of my experience seem to be truly existent properties of the world, detected by our senses and revealed to our mind through the complex mechanisms of perception.

Yet we have known since Isaac Newton that colors do not exist out there in the world. Instead they are cooked up by the brain from mixtures of different wavelengths of colorless electromagnetic radiation. Colors are a clever trick that evolution has hit on to help the brain keep track of surfaces under changing lighting conditions. And we humans can sense only a tiny slice of the full electromagnetic spectrum, nestled between the lows of infrared and the highs of ultraviolet. Every color we perceive, every part of the totality of each of our visual worlds, comes from this thin slice of reality.

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