COLOR VISION

The image of objects is formed on light sensitive Retina in our eyes from where it is transmitted through the optical nerve to the brain. The retina has a large number of  light sensitive cells which are of two types:

i) Rods (which are Rod shaped)

ii) Cones(which are Cone shaped)

These have different functions.

The Rods are sensitive to the intensity of light and detect the degree of brightness of light. The cones are sensitive to colors of light.

They are responsible for ability of human eye to see colors.

There are infact 3 types of cones

i) one corresponding to Red
ii) one corresponding to Green
iii)one corresponding to Blue 

COLOR BY TRANSMITTED LIGHT

The colors of transparent objects is determined by colors of light transmitted by them.

A transparent red filter held against White light appears red as it absorbs all colors except Red which is transmitted to the eye.

If a Red filter is held against Green light it will appear black as it absorbs the Green light.

If a Red flower is viewed through a Green filter, it will appear black since the Red light from flower is not transmitted by Green filter.

Thumb Rule: If there is a common color in the incident light and the filter, then the filter will appear to be of common color. Otherwise it will appear black. 

Colors of objects in colored light

The color of an object as seen by us is affected by the color of light in which it is observed.

A Red flower if observed in blue light will appear black since it absorbs the blue light. It will appear black in Green light also. In Red light it will appear Red since Red light is reflected.

A magenta object when viewed in yellow light will appear Red. This is because Yellow light consists of Red and Green lights and a magneta object will absorb Green light but will reflect Red light.

Thus, if there is a common color in the incident light and the object, the object will appear to be of common color. If there is no common color, the  object will appear black.

Colors of objects in white light

The color of an opaque object depends on colors of light  reflected by it.

An object appears white in day light if it reflects all colors. 

An object appears black if it absorbs light of all colors and does not reflect any color.

An object appears Red in day light if it absorbs all the colors of white light except Red, which it reflects.

An object appears Yellow in day light if it absorbs all colors except Red and green which it reflects. These combine to produce the effect of yellow.

 

What is color addition?

The mixing of coloured lights is called colour addition. When lights of different colours are mixed, different colour effects are observed.

Primary Colors are those which combine to produce white light and which can be used to produce light of all other colours.

The three primary colours are Red, Green, and Blue.
                     Red+Green+Blue = White
                     Red+Green =Yellow
                     Red+Blue=Magenta
                     Blue+Green = Cyan
The colours Yellow, Magenta and Cyan produced when two primary colours mixed are called "Secondary Colors".

The combination of coloured lights to give different colours is represented in below figure.