Monday, August 10, 2009

Why Can We See Different Colours?

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The retina of our eye is packed with a layer of tiny cells called rods and cones. These cells contain coloured substances that react when light falls on them, triggering a nerve impulse.

Rods are slim cells, which can help in black and white vision. Cone cells give us colour vision. They contain different light sensitive substances that respond to either red, yellow-green or blue-violet light.

Thus, cone cells give us the coloured picture of the object we see. The cone cells only work in bright light making it difficult to see and distinguish colours in a dim light.


Below Cone Cells info from Wikipedia (

Cone cells, or cones, are photoreceptor cells in the retina of the eye that function best in relatively bright light. The cone cells gradually become sparser towards the periphery of the retina.

A commonly cited figure of six million in the human eye was found by Osterberg[1] in 1935. Oyster's textbook (1999) cites work by Curcio et al. (1990) indicating an average closer to 4.5 million cone cells and 90 million rod cells in the human retina.[citation needed]

Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods.[2] Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, they have trichromatic vision. Being color blind can change this, and there have been reports of people with four or more types of cones, giving them tetrachromatic vision.

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