Light, vision and colour,

Visible light is part of a much broader span of radiation called the electromagnetic spectrum. This spectrum ranges from very short wavelength gamma rays (~10−12m) to very long radio waves (~1000m). Visible light is in the wavelength range 380 (violet) to 770 (red) nanometres or nm (where a nanometre is 10−9m). This range of wavelengths is recognised and interpreted by the eye-brain system to produce the sensation of vision. The choice of this spectral range for vision is evolutionary – the sun’s spectrum at sea level is most intense at these wavelengths, and so the eye-brain system has adapted to work most effi ciently in this wavelength range (see Figure 14.1).