What do UVA, UVB, UVC, and UVD mean in ultraviolet light?

According to different biological effects, ultraviolet rays are divided into four bands according to wavelength:

The UVA band, with a wavelength of 320 to 400 nm, is also known as the long-wave black spot effect ultraviolet. It has a strong penetrating power and can penetrate most transparent glass and plastics. More than 98% of the long-wave ultraviolet rays contained in sunlight can penetrate the ozone layer and clouds to reach the surface of the earth. UVA can directly reach the dermis layer of the skin, destroy elastic fibers and collagen fibers, and tan our skin. The 360nm wavelength UVA ultraviolet rays conform to the phototaxis response curve of insects, and can be used to make trap lights. The 300-420nm wavelength UVA ultraviolet light can pass through a special colored glass lamp tube that completely cuts off visible light, and can only radiate near-ultraviolet light centered at 365nm, which can be used in ore identification, stage decoration, banknote inspection and other places.

The UVB band, with a wavelength of 275-320nm, is also called medium-wave erythema effect ultraviolet. Moderate penetration, its shorter wavelength part will be absorbed by transparent glass, most of the mid-wave ultraviolet rays contained in sunlight are absorbed by the ozone layer, and less than 2% can reach the surface of the earth, which will be particularly strong in summer and afternoon. UVB ultraviolet rays have a erythema effect on the human body, which can promote the metabolism of minerals and the formation of vitamin D in the body, but long-term or excessive exposure will cause the skin to tan and cause redness and peeling. Ultraviolet health care lamps and plant growth lamps are made of special transparent glass (which does not transmit light below 254nm) and phosphors with a peak near 300nm.

UVC band, wavelength 200～275nm, also known as short-wave sterilization ultraviolet. It has the weakest penetration ability and cannot penetrate most transparent glass and plastics. The short-wave ultraviolet rays contained in sunlight are almost completely absorbed by the ozone layer. Short-wave ultraviolet rays are very harmful to the human body. They can burn the skin in a short period of time. Long-term or high-intensity irradiation can also cause skin cancer. The ultraviolet sterilization lamp emits UVC short-wave ultraviolet.

The UVD band, with a wavelength of 100 to 200 nm, is also called vacuum ultraviolet.