Ultraviolet (UV) radiation is a part of the electromagnetic spectrum that extends from the end of visible light through to X-rays. This part of the spectrum is undetectable to the naked eye, with only a few insects capable of seeing it, but it’s indirectly visible to us via fluorescent objects, which emit the radiation at a lower energy level.
The spectrum of ultraviolet light lies between the wavelengths of 400 nanometres (near-visible light) through to just ten nanometres (near-X-ray). This spectrum is divided into four major categories: near (400-300 nanometres), middle (300-200 nanometres), far (200-100 nanometres) and extreme (100-10 nanometres). It’s also split into ten subtypes, which possess different qualities for various applications.
UV radiation is produced by high-temperature surfaces, such as stars, and is emitted in a continuous spectrum. On our planet, for example, the majority of UV light is found in light rays emanating from the Sun, where it constitutes about ten per cent when in the near-vacuum of space. However, the vast majority of this UV radiation is absorbed by ozone in the Earth’s atmosphere, with only limited quantities of the ultraviolet A (UVA) subtype reaching the surface.