VISION
The human eye and brain work together to translate light into colour . The signals that lead to colour vision come from your eyes but it is your brain that makes sense of them , allowing you to see grass as green , the sky as blue , and a banana as yellow .
For a ripe banana , wavelengths of 570 to 590 nanometers are reflected off its surface . These are the wavelengths of yellow light . When you look at the banana , the light waves reflect off the peel and enter your eye through the cornea , the outermost part of the eye . The cornea bends light toward the pupil , which controls the amount of light that hits the lens . The lens then focuses the light on the retina , the layer of nerve cells in the back of the eye .
Lens
Cornea
Pupil
The retina has two different types of cells that detect and respond to light . These specialized cells are called photoreceptors . There are two types of photoreceptors in the retina : cones and rods .
Cones are responsible for colour vision . There are three kinds of cones , each with a distinctive pigment . Roughly , 64 % ( red ) absorb long wavelengths , 33 % ( green ) absorb medium wavelengths , and 2 % ( blue ) absorb short wavelengths .
The reflected light reaching the retina stimulates all three types of receptors to varying degrees . As per the “ trichromatic theory of colour vision ” , the pattern of their responses determines the colour perceived .
Rods contain only one type of lightsensitive pigment , transmitting mostly black and white information to the brain . They are therefore not useful for colour vision . Rods mainly provide information about contrast and movement .