Light and Human Colour Vision

Sunlight

White light from the Sun is fundamental to human colour vision, but it can be split into all the colours of the rainbow. The light waves are refracted (bent) as they enter and leave the prism. The shorter the wavelength of the light the more it is refracted, so the colours are split – technically its called dispersion. Our eyes can see around seven distinct colours in the light from the prism.

Taking one colour and putting that through another prism still gives a single colour, the prism is not able to split the light any further. But we now know that light can be split into its individual wavelengths or frequencies using equipment such as diffraction gratings or spectrographs.

Light and Vision Primary Colours

The primary colours of light for human vision are Red, Green, and Blue, mixing all three makes white light.

Additive colour mixing illustrated above

Light visible to the human eye

We see only a small part of the full electromagnetic spectrum. We see is less than a 10 trillionth of what’s out there! Some snakes can sense some infrared, and honeybees include ultraviolet in their view of the world, giving them an advantage when viewing flowers etc.

Why Do We See Colour At All?

White light strikes an object and the colour we see is due to the light that is reflected into our eyes. Objects absorb some of the colours from the light falling on them and we see the light that is not absorbed.

A green object such as a leaf absorbs all colours from the light except the green light. A white object absorbs very little light and reflects most of it into our eyes. Black object absorb most of the light falling on them and so they are often hard to see in high detail, unless the illumination is very good.