Ultraviolet radiation is electromagnetic radiation of a wavelength shorter than that of the able to be seen region, but longer than that of soft X-rays. It can be subdivided into near UV and tremendous or vacuum UV.
When allowing for the effects of UV radiation on human health and the surroundings, the range of UV wavelengths is often subdivided into UVA, also called Long Wave or "black light"; UVB, also called Medium Wave; and UVC, also called Short Wave or "germicidal". See 1 E-7 m for a list of objects of similar sizes.
In photolithography, in laser technology, etc., the term cavernous ultraviolet or DUV refers to wavelengths below 300nm.
The name means "beyond violet", violet being the color of the unswerving wavelengths of able to be seen light. Some of the UV wavelengths are colloquially called black light, as it is imperceptible to the human eye. Some animals, including birds, reptiles, and insects such as bees, can see into the near ultraviolet. Many fruits, flowers, and seeds situate out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Many birds have patterns in their plumage that are imperceptible at usual wavelengths but seen in ultraviolet, and the urine of some animals is much easier to spot with ultraviolet.
The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of amalgamation in the atmosphere's ozone layer, 99% of the ultraviolet radiation that reaches the Earth's surface is UVA.
Ordinary glass is see-through to UVA but is opaque to shorter wavelengths. Silica or quartz glass, depending on quality, can be see-through even to vacuum UV wavelengths.
The onset of vacuum UV, 200 nm, is defined by the fact that normal air is opaque below this wavelength. This opacity is due to the strong amalgamation of light of these wavelengths by oxygen in the air. Pure nitrogen is see-through to wavelengths in the range of about 150–200 nm. This has wide practical significance now that semiconductor manufacturing processes are using wavelengths shorter than 200 nm. By working in oxygen-free gas, the apparatus does not have to be built to withstand the pressure differences necessary to work in a vacuum. Some other scientific instruments, such as circular dichroism spectrometers, are also normally nitrogen purged and operate in this spectral region.