Components of solar radiation
The solar radiation that reaches the earth consists of 3% ultra-violet rays (UV), 55% infra-red radiation (IR) and 42% visible light.
These three components of solar radiation each correspond to a range of wavelengths. Ultra-violet extends from 0.28 to 0.38 µm (nanometres), visible light from
0.38 to 0.78 µm and infra-red from 0.78 to 2.5 µm. The overall energy distribution of solar radiation, as a function of the wavelength between 0.3 and 2.5 µm (spectrum), for a surface perpendicular to this radiation, is represented by the curve shown below. This spectrum draws on definitions provided in BS EN 410 and certain atmospheric constants concerning the characterisation of the air and the diffused radiation.
Visible light, or daylight, is the range of wavelengths of the electromagnetic spectrum between 0.38 µm and 0.78 µm.
The combined wavelengths of the visible spectrum when acting on the eye, result in the physiological effect known as vision.