According to different biological effects, ultraviolet rays are divided into four bands according to wavelength:
The classification of ultraviolet rays includes UVA, UVB, UVC and UVD. Among them, UVC has been absorbed and scattered by the ozone layer in the atmosphere because of its short wavelength, so it cannot reach the ground. The wavelength of UVB is among the three, and the wavelength can only reach the epidermis of the skin, while the longer UVA will penetrate deep into the skin, damage the dermis layer of the skin, and cause skin aging.
The UVC band, with a wavelength of 200-275nm, is also called short-wave sterilizing ultraviolet light. Its penetrating ability is the weakest, unable to 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. Short-term exposure can burn the skin, and long-term or high-intensity exposure can also cause skin cancer. The ultraviolet germicidal lamp emits short-wave UVC ultraviolet rays.
The UVD band, with a wavelength of 100-200nm, is also called vacuum ultraviolet.
UVA is the terrible sunshine killer. UV light intensity meter is used to test the uv intensity of different bands. Linshang LS125 UV light intensity meter can be equipped with 9 probes which can test uv-a, uv-b, uv-c bands.
UVA is a terrible killer of sunlight. With its relatively long wavelength and strong penetrating ability, it can penetrate the surface of the skin and penetrate deep into the tissues below the dermis. It can destroy the fine structure of the skin such as collagen and elastic fiber tissue, resulting in wrinkles and Fine lines make the skin sagging and aging. This is medically called photo-aging.
In the energy distribution of ultraviolet rays in the sun, UVA is 15 times that of UVB, which is the main reason for skin tanning. It can reduce the water-bound hyaluronic acid content in the skin, dry the skin, accelerate the formation of melanin, and darken the complexion. It is also an important cause of skin cancer.
UVA wave band, wavelength 320～420nm, also known as long-wave black spot effect ultraviolet rays. It has 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 of the skin, destroy elastic fibers and collagen fibers, and tan our skin. UVA ultraviolet rays with a wavelength of 360nm conform to the phototaxis response curve of insects, and can be used to make insect trap lamps. UVA ultraviolet rays with a wavelength of 300-420nm can pass through a special colored glass tube that completely cuts off visible light, and only emit near-ultraviolet light centered at 365nm, which can be used for ore identification, stage decoration, currency verification and other places. In October 2009, German and Italian scientists discovered that [Astaxanthin] can effectively eliminate [ultraviolet UVA] damage to skin cells.
UVB band, wavelength 275～320nm, is also called medium wave erythema effect ultraviolet. Medium penetrating power, its shorter wavelength part will be absorbed by transparent glass, and most of the medium-wave ultraviolet rays contained in sunlight are absorbed by the ozone layer, and only less than 2% can reach the surface of the earth, which is particularly strong in summer and afternoon. UVB ultraviolet rays have erythema effects on the human body, can promote mineral metabolism 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. The ultraviolet health care lamp and the plant growth lamp are made of special transparent purple glass (not transmitting light below 254nm) and phosphor with a peak near 300nm.
The ozone layer can block and weaken ultraviolet rays.
PPD is used in European and American systems to extend the multiples of the UVA tanning time for the skin to represent long-term tanning. After 2 hours of UVA exposure, the skin is still tanning. It is the most practical protection factor to prevent dark spots. PPD can best reflect the long-term tanning effect of sunscreen products on UVA. PA is adopted by the Japanese system to reflect the effect of UVA tanning, expressed by the number of plus signs: