Rainbows and spectra

Red
Orange
Yellow
Green
Blue
Indigo
Violet

When he directed each colour separately on to a prism, no further splitting took place.

Light and colour

To see colour we need light. Without light there can be no colour.

In 1666, Isaac Newton (1642-1727) demonstrated that light was composed of different colours by directing a narrow beam of sunlight on to a glass prism in a completely darkened room. The light was refracted on its entry and exit of the prism and produced a spectrum of coloured light. Newton identified seven colours

However, when all the colours were directed together on to the prism, he found that they recombined to form white light.

At the beginning of the nineteenth century, Thomas Young (1773-1829) investigated the effect of mixing coloured lights and found that almost all colours, including white could be produced using only three: red, green and blue, which he called primary colours.