Continuous Colour from Red to Violet

Look carefully at the diagram at the top of the page. Now check out the following questions (and answers)!

1. Is visible light a form of electromagnetic radiation?
2. Do different wavelengths of light correspond with different colours seen by an observer?
3. How many different colours can the human eye see in ideal conditions?
4. Name two colours with the longest wavelengths?
5. Name two colours with the shortest wavelengths?

Introducing the diagram! Read back and forward between the image at the top of the page and the explanation below!

This diagram is about the visible spectrum and which wavelengths of electromagnetic radiation correspond with the different colours we see in the world.

• It shows that a human observer can distinguish between colours corresponding with thousands of wavelengths of visible light.
• The visible spectrum (a rainbow for example) can be thought of as six bands of colour or as being made up of light rays of different wavelengths, each distinguished by its measurement in nanometres.
• The visible spectrum is made up of an infinite gradation of wavelengths and colours. The total number of colours in the world is limited only by the sensitivity of human vision and the size of the units of measurement used to calculate wavelength.
• The list down the left of the diagram represents the visible spectrum as bands of wavelengths and bands of colour.
• The scale along the bottom marks out the visible spectrum in nanometres with the corresponding colours shown above.

Remember that:

• Objects appear to be different colours to an observer depending on their wavelength.
• The name given to light that contains all wavelengths of the visible spectrum is white light.
• When all wavelengths contained in white light reflect off a neutral coloured surface then the object appears white to an observer.
• When a narrow band of wavelengths reflect off a neutral coloured surface then the object appears coloured to an observer.
• The colour an observer sees depends on the wavelengths of visible light emitted by a light source and on which of those wavelengths are reflected off an object.
• Although a human observer can distinguish between many thousands of wavelengths of light in the visible spectrum our brains often produce the impression of bands of colour.