HOW DO WE SEE COLOUR ? As explained earlier , in Colour Perception , objects do not actually have colour . What we see as the colour of an object is due to the way that the object interacts with light and ultimately reflects it to our eyes .
An object contains atoms that might be capable of selectively absorbing one or more frequencies of the visible light that strikes it . When visible light strikes an object and a specific frequency is absorbed , that frequency of light will never make it to our eyes . Only the visible light that strikes the object and becomes reflected or transmitted to our eyes will contribute to the colour appearance of that object .
DO COLOURS BEND ? Light traveling through a medium , propagates in a straight line and at a relatively constant speed , unless it is disturbed in some manner . This depends on two key concepts : » the optical density of the medium » the frequency of the light wave
☼ The optical density of a medium is the medium ’ s ability to slow down the light which passes through it . More optically dense materials will cause light to travel slower , and less dense materials will cause it to travel faster .
The optical density of a medium is not the same as its physical density . The physical density of a medium refers to the mass / volume ratio . The optical density of a material relates to the sluggish tendency of the atoms of a medium to transfer energy between each other . In every medium , other than a vacuum ( a perfect particle free medium ), there is a relative time delay as this energy is passed along .
If a ladybug shell absorbs all of the frequencies of visible light except for the frequency associated with red light , then the ladybug will appear red . If a leaf absorbs all of the frequencies of visible light except for the frequency associated with green light , then the leaf will appear green .
This relative speed is quantified in what is called the index of refraction ( n ), ie ., the number of times slower that a wavelength will travel in a given medium in comparison to a vacuum ( which has the lowest possible optical density ). For example , the refractive index of water is 1.3 , meaning that light will travel 1.3x slower in water than in a vacuum .