• how the eyes see color

How Does the Eye See Color?

The won­der­ful pre­ci­sion instru­ment that is the human eye can do some pret­ty remark­able things in coor­di­na­tion with the brain. Adapt­ing to see in the dark, being able to process depth per­cep­tion and the abil­i­ty to dis­tin­guish even the slight­est vari­a­tions of col­or are some the very things that the eye and brain can do. The way our eye sees and process­es col­or is con­cep­tu­al­ly sim­ple but very impor­tant.


The brain and eyes are con­nect­ed by the optic nerve, which trans­ports the images of the world we see to the brain for pro­cess­ing. In the eye, there are two dif­fer­ent types of pho­tore­cep­tors- rods and cones. The job of the rods are to allow some capa­bil­i­ties of see­ing in dim light con­di­tions or at night, the cones, on the oth­er hand, are used in bright light con­di­tions and to see col­or. We as humans have three types of cones for short, medi­um, and long wave­length light. So when light enters the eye through the pupil and pass­es through the lens it becomes focused on the back of the eye­ball where the rods and cones are. The light that enters the eye is of spe­cif­ic wave­lengths, which is what deter­mines the col­or of the object that we can see. The vis­i­ble light spec­trum for the human eye is from about 390nm to 700nm, just beyond the spec­trum lies ultra­vi­o­let light which is too short of a wave­length and infrared with is too large of a wave­length to process. The object itself actu­al­ly deter­mines which wave­length is reflect­ed back to our eye.


When we look at an orange, all wave­lengths of the vis­i­ble spec­trum are absorbed by the mate­r­i­al except for the spe­cif­ic wave­lengths that we process as orange, which are reflect­ed back to our eyes. To sim­pli­fy how it depends upon arrange­ment of elec­trons in the atoms of the mate­r­i­al is that when light, which car­ries ener­gy, strikes an object and some of it is absorbed and some is not depends upon the elec­tron struc­ture of the mate­r­i­al. We see an orange as orange because the elec­trons in the atoms of the orange peel absorb all oth­er wave­lengths of the vis­i­ble light except orange, which are reflect­ed back to the eye. Once the orange wave­lengths reach the eye, the cones that cor­re­spond to that wave­length are then stim­u­lat­ed to a cer­tain degree and then that infor­ma­tion is passed to the optic nerve to the brain to be processed by the visu­al cor­tex into the “col­or” orange that we per­ceive.


While we are much bet­ter at dis­tin­guish­ing vary­ing col­ors and degrees of col­or than most mam­mals, some crea­tures have four types of cones that allow them to see parts of the light spec­trum we are unable to. Some insects, birds and fish have been found to see some degrees of ultra­vi­o­let light, which have too short of wave­lengths for us to see.


How many col­ors can the human eye see? Despite not being at the top of the evo­lu­tion­ary vision chain, humans are still able to see and process quite a range of col­or.  

January 18th, 2016|Comments Off on How Does the Eye See Color?

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