Why can owls see well at night?

The night vision of owls is 100 times as keen as that of human beings, because their eyes are especially adapted for seeing in the dark. But most are almost colourblind and the pictures they receive are slightly blurred. This is because their eyes contain more rod-shaped receptor cells than cone-shaped ones. Owls have exceptionally large eyes and can control the amount of light entering by expanding or contracting the pupil. Their eyes are so large that they supported by thin, bony, tubular structures called sclerotic rings. Because of this the eyes are almost immovable and nature has compensated for this by giving owls extremely flexible necks, which enable them to turn their heads through an arc of 270degrees.(questions and answers)