What is sunlight composed of?
Sunlight is composed of a spectrum of rays: visible light, ultraviolet (known as UV) and infrared light. The light is measured in wavelength units – nanometers (nm) and millimeters (mm). Each of the different rays of the light in the spectrum has a different wavelength.
Visible light accounts for around 50% of the sunlight spectrum, and as the name suggests, it is the only part of the light detectable by the human eye. Its wavelength ranges from 400 to 760 nm.
Ultraviolet light is invisible to the human eye and it comes in three forms: ultraviolet- A (UVA), ultraviolet – B (UVB) and ultraviolet - (UVC) rays. UV light has shorter wavelength than visible light. UVA and UVB rays have wavelength between 280 nm and 400 nm, with UVA having longer wavelength than UVB rays. Together, they make up around 5% of the sun rays.
UVA rays account for 90 -95% of the UV light rays which reach the Earth’s surface and they are:
ess intense than UVB rays, but penetrate deeper in the skin layers.
may cause signs of premature aging of the skin, such as wrinkles, and also skin diseases (cancer and pigmentation).
their action is continuous throughout the day and the year.
UVB rays account for 5-10% of the UV light rays which reach our skin and they:
affect the superficial layers of the skin.
contribute to creation of vitamin D, and their action is limited to the surface of the skin by activating melanocytes which produce mela nin.
cause initial skin damage, such as burns, the prematurely aged skin effect as well as various skin diseases (cancer and pigmentation)
UVB radiation is most intense during the summer months, with the peak intensity reached in early afternoon.
UVC radiation is the most threatening. However, it is absorbed in the ozone layers, which prevents it from reaching the surface of the Earth and consequently affecting our skin.
Infrared A- and B- rays have longer wavelength, ranging between 760 and 1,000 nm (1m), and just as the UV rays, they are invisible to the human eye. They make up the remaining 40% of the sunlight.