Question: What is the 'wavelength of visible light?'

Susan Skelton answered on 20 Nov 2013:

Hello u12tsangv,

This is a great question! Simon has partly answered your question, but there are mistakes in his answer, which I’ll put right here.

If we imagine our light beam to look like waves on the ocean, the wavelength is the distance between the peaks of two waves next to each other. The wavelength of light is very very small and is usually measured in nanometres (or ‘nm’ for short). One nanometre is equal to 0.000000001 metres, or one billionth of a metre – so very small indeed!

Visible light is not one wavelength, but it covers a wide range. The range that is visible isn’t some absolute value though; it depends on who is looking!

Human eyes, for example, can detect wavelengths ranging from about 400nm (blue light), past 500 nm (green light) up to about 700 nm (red light).

This range is very useful for us to see in the daylight, however its not much use at night-time! At night, when there is not much light, it’s much better to use wavelengths longer than 700 nm – the infrared. All warm objects send out light waves with wavelengths longer than 700 nm, all the time. Unfortunately our eyes are not very good at seeing these wavelengths, so we have developed special devices called ‘night vision’ that allow us to detect these wavelengths and see in the dark!

Different animals have developed sensitivity to different ranges of light wavelengths. Snakes and some bugs can detect infrared light, so they’re much better at seeing in the dark than we are. Other creatures like insects are better at seeing ultraviolet light (wavelengths less than 400 nm).