Can you guys tell me that when we close our eyes for a long period of time and then we open our eyes we see colour blue why?
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That's a nice question! Allow me to begin with a little bit of info about our eyes.
Our eyes work by means of millions of receptor cells; when light falls on any one of them, our brain gets the message of it being turned "on" and thus millions of such signals, refreshed about 24 times a second, give us our vision. However, all of these receptors aren't the same.
We have two types of cells: Rods and Cones. The Rods sense the intensity (brightness/unit area) of incoming light, while the Cones sense the colour of the incoming light (by sensing the wavelength). Cones require a certain minimum amount of light to function, because their response time is very fast and they are much fewer in number than rods (this is important so remember this). This is why we can't see colours when it's very dark, all we see is black and 'not black'. Vitamin A deficiency causes night blindness, because it affects the Rods - which are the only functioning cells in the dark.
The Cones are further subdivided into three, depending on the wavelength to which they respond - short (S), medium (M) and long (L). Each type of cell responds only to its own characteristic wavelength. The Sun emits light of all wavelengths in the visible spectrum, and thus from outer space, the Sun looks white. However, the atmosphere scatters light, and the extent of scattering is inversely proportional to the fourth power of wavelength. Thus, blue region (440 nm) is scattered 4-5 times more than the red-orange region (650 nm) and so we see the Sun as yellow-orange.
Now, when you look at the Sun for a few seconds, extremely intense light falls on your Cone cells, specifically the M and L cone cells. Thus, those cells, to avoid damage by overexposure, create a certain "resistance" to input signals. When you look away, the M and L cells remain in this state of high resistance for a few seconds while the S cells are working fine. As I said, the cones need more than a certain minimum amount of light to function, and so when you look away, the M and L cells report being "off". Thus, your eye tells the brain that everything around you is bluish - it is just blocking out the red-yellow region.
Note: A similar thing happens when you use your cellphone in the dark at night. Keep one eye covered in a dark room, and use your cellphone for about 3-5 mins. Now, turn the screen off and look around, one eye after the other. The eye that was open will be near-blind, but the closed eye will be able to see. The logic is same, that the rods in the open eye develop a resistance, and so when the light is turned off suddenly, they go in the "off" state.
Our eyes work by means of millions of receptor cells; when light falls on any one of them, our brain gets the message of it being turned "on" and thus millions of such signals, refreshed about 24 times a second, give us our vision. However, all of these receptors aren't the same.
We have two types of cells: Rods and Cones. The Rods sense the intensity (brightness/unit area) of incoming light, while the Cones sense the colour of the incoming light (by sensing the wavelength). Cones require a certain minimum amount of light to function, because their response time is very fast and they are much fewer in number than rods (this is important so remember this). This is why we can't see colours when it's very dark, all we see is black and 'not black'. Vitamin A deficiency causes night blindness, because it affects the Rods - which are the only functioning cells in the dark.
The Cones are further subdivided into three, depending on the wavelength to which they respond - short (S), medium (M) and long (L). Each type of cell responds only to its own characteristic wavelength. The Sun emits light of all wavelengths in the visible spectrum, and thus from outer space, the Sun looks white. However, the atmosphere scatters light, and the extent of scattering is inversely proportional to the fourth power of wavelength. Thus, blue region (440 nm) is scattered 4-5 times more than the red-orange region (650 nm) and so we see the Sun as yellow-orange.
Now, when you look at the Sun for a few seconds, extremely intense light falls on your Cone cells, specifically the M and L cone cells. Thus, those cells, to avoid damage by overexposure, create a certain "resistance" to input signals. When you look away, the M and L cells remain in this state of high resistance for a few seconds while the S cells are working fine. As I said, the cones need more than a certain minimum amount of light to function, and so when you look away, the M and L cells report being "off". Thus, your eye tells the brain that everything around you is bluish - it is just blocking out the red-yellow region.
Note: A similar thing happens when you use your cellphone in the dark at night. Keep one eye covered in a dark room, and use your cellphone for about 3-5 mins. Now, turn the screen off and look around, one eye after the other. The eye that was open will be near-blind, but the closed eye will be able to see. The logic is same, that the rods in the open eye develop a resistance, and so when the light is turned off suddenly, they go in the "off" state.
Riyapathak:
you helped me thanks
Ur wlcm
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