Sunlight has many benefits to the human body, especially for children, women and the elderly. Among them, ultraviolet light has many benefits for preventing myopia in children, strengthening bones, killing bacteria and beautifying the skin. But overdose will backfire. Therefore, scientific monitoring of ultraviolet light intensity is the most effective sunlight value. Since the impact of ultraviolet rays on the human body is accumulated over many years, it is necessary to pay attention to prevention from an early age.
In recent decades, due to the increasingly serious destruction of atmospheric stratospheric ozone, the amount of ultraviolet radiation received on the ground has gradually increased, and the impact of ultraviolet rays on human health (mainly skin) has attracted more and more attention. The meteorological department also makes timely UV index forecasts for people to take defensive measures when traveling to avoid and reduce the immediate and far-reaching damage of ultraviolet rays to the skin.
1. The wavelength of ultraviolet light
Ultraviolet rays in sunlight are invisible light. The wavelength of ultraviolet light is shorter than visible light, but electromagnetic radiation is longer than X-rays. Ultraviolet light has a wavelength in the range of 10-400 nm in the electromagnetic spectrum. This range starts at the short-wave limit of visible light and overlaps with the wavelength of long-wave X-rays. Ultraviolet light is divided into A ray, B ray and C ray (abbreviated as UVA, UVB and UVC), and the wavelength ranges are 400-315nm, 315-280nm, and 280-190nm respectively.
Ultraviolet is divided into 3 sections according to the wavelength:
The UVA area, long-wave ultraviolet rays, accounts for about 10% to 20%. It is the main reason for premature skin aging. It can penetrate the dermis layer, make the skin tan, cause lipid and collagen damage, and cause skin light. Aging or even skin cancer has a slow and lasting effect and is cumulative, so it is called "age ultraviolet rays" and is not blocked by windows, umbrellas, etc., even if it rains on a cloudy day.
UVB area, medium-wave ultraviolet rays, accounts for about 80% to 90%. It can reach the dermis, causing skin to be sunburned, causing skin peeling, erythema, tanning, etc., but it can be blocked by glass, umbrellas, clothes, etc. .
UVC area, short-wave ultraviolet, it cannot reach the ground because it has been absorbed when passing through the ozone layer.
2. UV index calculation
The UV index refers to the possibility that the ultraviolet radiation in the sun rays reaching the surface of the earth will affect human skin when the sun’s position in the sky is highest (usually around noon, that is, from 10 am to 3 pm) degree of damage. The variation range of the UV index is represented by a number ranging from 0 to 15. Generally, the UV index at night is 0, and the UV index at tropical, plateau and sunny days is 15. The higher the UV index, the more severe the erythema damage caused by ultraviolet radiation to human skin. Similarly, the higher the UV index, the greater the damage to the skin in a shorter period of time.
The standard method for calculating the UV index recommended by the World Meteorological Organization and the World Health Organization is to measure the solar UV intensity of different wavelengths up to 400nm, multiplying the solar UV intensity of different wavelengths by the corresponding added total UV intensity in the "erythema effect spectrum curve" , The unit is milliwatt/square meter (mW/㎡). Then multiply the total UV intensity after the weighted erythema spectrum by 0.04 to get the UV index (UV index per unit is 25 mW/m²). After the total UV intensity, the unit is milliwatt/square meter (mW/㎡). Then multiply the total UV intensity after the weighted erythema spectrum by 0.04 to get the UV index (UV index per unit is 25 mW/m²). After the total UV intensity, the unit is milliwatt/square meter (mW/㎡). Then multiply the total UV intensity after the weighted erythema spectrum by 0.04 to get the UV index (UV index per unit is 25 mW/m²).
3. Interpretation of UV Index
The ultraviolet index is an internationally accepted calculation index. In order to facilitate the public to remember, understand and use, the China Meteorological Administration has standardized the forecast level of ultraviolet rays. The relationship between the UV index value UV Index and the forecast level is as follows.
UV index generally starts from 0 and ends at 10 (including greater than 10). According to these values, the Meteorological Bureau divides the forecast levels of the UV index into five levels.
UV index value is 0 to 2, usually overcast or rainy, when the ultraviolet intensity is the weakest, the forecast level is level one;
UV index value is 3 to 4, generally cloudy weather, at this time the ultraviolet intensity is weak, the forecast level is second;
UV index value is 5 to 6, generally in the weather with little cloud, when the ultraviolet intensity is strong, the forecast level is three;
UV index value is 7 to 9, generally sunny and no clouds, at this time the ultraviolet intensity is very strong, the forecast level is four;
The UV index value reaches or exceeds 10, mostly on sunny days in summer, the ultraviolet intensity is particularly strong, and the forecast level is five.
It needs to be explained that the above index value and intensity level are based on the unified regulations of the China Meteorological Administration based on the average UV index and intensity monitored for 4 hours from 10 am to 14:00 every day. Generally speaking, the maximum value of ultraviolet rays appears around 12 noon. People should avoid outdoor activities during this period as much as possible in their daily life (especially in summer). Even if they are in the sun in winter, they should choose before 10 am and afternoon. "Prime time" after 3 o'clock.
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