The cells which are present in the retina of eye and these are responsible for the vision in dim light.these are photo receptor cells.these contain a pigment called "rhodospin". 

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Rod cells are photorecepter cells and are used and they need very less amt. of light (lesser intensity of light)  in order to function. The are concentrated in the outer edges of the retina and so helps in peripheral vision. The are responsible mainly for night vision and they have only one sensitive light pigment (rhodospin) and so have very little role in coloured vision.
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