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— Light: Sensitivity of the Human Eye —

Scotoptic: Rods

The rods are the brightness sensors of the eye and reside in the peripheral regions of the retina. The density is about 150,000 rods per mm2. Maximum efficiency is at about 594 THz at some green variety near the colour cyan.

Photoptic: Cones

The cones are responsible for the colour view. They are concentrated in the fovea (center of field of vision) and there are about 10,000 cones within a diameter of 0.3 mm — the density is about 1,000 cones per mm2. The maximum efficency is at 545 THz at a green variety near the yellow. There are three different colour cones:

Cone Type (Wavelength) Colour max. Sensitivity at Quantity 100%
S (short) Blue 660 THz 11%
M (medium) Green 570 THz 30%
L (long) Red 480 THz 59%

Efficiency of View

Because the distribution of the cones is about 150 times less dense than the one of the rods, the night view is colourless (In the night, all cats are grey, as the saying goes). Since the rods are not in the center of vision, you have to look in the dark slightly off the target to be able to see it better, e.g. a faint star at night.

  © 2004 - 2017 by Horo Wernli.