How do we recognize colours? Why are some people called colour blind?


Retina of our eye is made of light sensitive cells that are shaped like a rod and cones. These rod-like cells respond to the intensity of light and give information about the brightness or dimness of the object to the brain. It is the conical cells that respond to the colour and give information about the colour of the object to the brain. Brain processes these received information and we get to see the actual image of the object. While, the rod-like cells respond to faint light the conical cells do not. Thus, we perceive colours only in bright light. The cone cells can respond differently to red, green and blue colours. When red colour falls on the eyes, the cells responding to red light get excited more than those responding to other colours and we get the sensation of red colour. Some people lack the conical cells that respond to certain colours. These people are unable to recognize those colours or distinguish between different colours. These persons are said to be colour blind. Other than their failure to distinguish between different colours, their eyesight is normal.

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