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Why is it neccessary that if there is no light then everythimg is black and when we close our eyes we see everthing black usually when we are in black room??

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    $\begingroup$ Is your question: "why does the absence of light (from the physically shielding of our pupils from taking in light) appear black?" or "why do we perceive darkness as the color black? (vs., say, all white?)?" ? $\endgroup$ – theforestecologist Dec 1 '18 at 23:56
  • $\begingroup$ Am I unusual? Because when I close my eyes in a dark room, I don't see complete black, but darkness with some random "light shows" going on, for instance random dots of a slightly orange-tinted grey. $\endgroup$ – jamesqf Dec 3 '18 at 5:16
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The mechanism of sight is as follows (ref. 1). This was shown in the 1100s by Ibn al-Haytham (ref. 2), except the 4th step which may have been proposed by Galen in the 100s (ref. 3).

  1. Light comes from a light source
  2. The light then hits an object
  3. The light then bounces off the object into your eye
  4. Your eye sends a signal to your brain. Your brain then figures out what you're seeing

So in order for us to see, you need light getting into your eye (step 3). If you're in a dark room you have no light source, so no sight (no step 1). If you shut your eyes, you're stopping light from getting into your eye (no step 3). When there's no light getting to your eye, the eye tells this to your brain. So your brain just sees black (the absence of light).

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References

  1. Duree, G. (2011). Optics for Dummies. p. 67.

  2. Adamson, Peter. (7 July 2016). Philosophy in the Islamic World: A History of Philosophy Without Any Gaps. p. 77.

  3. Reeves, C. and Taylor, D. (2004). A history of the optic nerve and its diseases. p. 1097.

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