What Is the UV Index?

Ultraviolet index refers to the possibility that when the sun's position in the sky is the highest (usually around noon, that is, from 10 am to 3 pm), the ultraviolet radiation in the sun's rays reaching the surface of the earth can affect human skin. degree of damage. The range of UV index change is expressed by a number of 0-15. Generally, the UV index at night is 0, and the UV index in tropical, plateau, and sunny days is 15. When the UV index is higher, it means that the degree of erythema damage to human skin is worsened by UV radiation. Similarly, the higher the UV index, the greater the damage to the skin in a shorter period of time. ^[1]

Ultraviolet index refers to the possibility that when the sun's position in the sky is the highest (usually around noon, that is, from 10 am to 3 pm), the ultraviolet radiation in the sun's rays reaching the surface of the earth can affect human skin. degree of damage. The range of UV index change is expressed by a number from 0 to 15. Generally, the UV index at night is 0, and the UV index is 15 in tropical, plateau, and sunny days. When the UV index is higher, it means that the degree of erythema damage to human skin is worsened by UV radiation. Similarly, the higher the UV index, the greater the damage to the skin in a shorter period of time. ^[1]

The UV index is expressed as a number from 0 to 15. Generally, the UV index at night is 0. In tropical and plateau areas, the UV index is 15 when there are no clouds on a sunny day. The larger the UV index value, the more severe the erythema damage to human skin caused by UV radiation. Similarly, the larger the UV index, the stronger the damage to the skin in a shorter period of time. When the UV index is 0, 1, and 2, it means that the amount of ultraviolet rays in the solar radiation is the smallest, and this amount has no effect on the human body. When the UV index is 3 or 4, it means that the amount of ultraviolet rays in the solar radiation is relatively low, which is harmful to the human body. The possible impact is also relatively small; when the UV index is 5 and 6, it means that the amount of UV is medium intensity, and it also has a medium intensity damage effect on the human skin; when the UV index is 7, 8, and 9, it means that there is a strong UV The intensity of irradiation, at this time, the possible impact on the human body is relatively large, and corresponding protective measures need to be taken; and when the UV index is greater than 10, it means that the ultraviolet exposure is very strong and has the greatest impact on the human body, and protective measures must be taken. ^[2]

UV index forecast is a very useful forecast in daily life. According to the UV index released by the forecast, you can take some measures to prevent UV rays. Of course, UV rays are not a very scary thing. Don't be one-sided. The ground is dominated by UV forecasts. According to the published UV index, it is necessary to take effective measures to prevent excessive exposure to UV rays and to effectively use UV rays in a suitable period of time. The intensity of UV irradiation is not constant throughout the day and is most needed during the day. The time to pay attention is from 10 am to about 3 pm. Of course, according to the weather, the amount of ultraviolet radiation also changes, so you should also pay attention to the daily weather changes, and pay attention to which time period according to the weather changes. Special care should be taken. ^[1]

The standard method for calculating the UV index proposed by the World Meteorological Organization and the World Health Organization is to measure the solar UV intensity at different wavelengths up to 400nm, multiply the solar UV intensity at different wavelengths by the corresponding weighted value in the "erythema effect spectrum curve" to reflect Human skin's response to ultraviolet light. Add up the results of the multiplication above to get the total UV intensity , weighted by the erythema spectrum, in milliwatts per square meter (mW / ). Then multiply the total UV intensity of the erythema spectrum by 0.04 to get the UV index (25 mW / UV index per unit) ^[4]

UV is

Ultraviolet rays can be divided into three parts according to their wavelengths: A ultraviolet wavelengths are between 0.32 and 0.40 microns. The effect of A ultraviolet rays on us is to promote the synthesis of vitamin D, but excessive A ultraviolet rays can cause photocoagulation. Suppresses the function of the immune system, too little or lack of A ultraviolet radiation is also prone to erythema and cataract; B ultraviolet wavelength is between 0.28 ~ 0.32 microns, the effect of B ultraviolet on us is to make the skin red and reduce vitamin D Generated and long-term acceptance may cause skin cancer, cataracts and suppress the immune system function; C ultraviolet wavelength is between 0.01 ~ 0.28 microns; C ultraviolet rays are almost all

In recent years, due to the increasingly severe destruction of stratospheric ozone, the amount of ultraviolet radiation received on the ground has increased, causing widespread concern. For this reason, environmental scientists around the world have reminded people to pay great attention to the harm of ultraviolet radiation to the human body and take necessary precautions.

When the skin is irradiated with ultraviolet rays, the melanin cells in the human epidermal layer begin to produce melanin to absorb ultraviolet rays to prevent skin from being damaged. Prolonged UV irradiation will cause a large amount of melanin to deposit in the epidermal layer and become permanent "tanning" marks.

It is now generally recognized that excessive exposure to ultraviolet radiation can easily cause skin cancer and cataracts.

It is reported that the incidence of skin cancer is 800 in 100,000 in Australia; 250 in 100,000 in the United States; it is estimated that there are currently 5 in 100,000 in Japan. And medical experts warn people that maybe soon, Japan will also reach the incidence of skin cancer like Europe, America and Australia, it is only a matter of time before this dangerous situation occurs. In China, although there is no exact estimate and report of the incidence of skin cancer so far, foreign experiences and lessons tell us that we must pay full attention to this.

In addition, ultraviolet radiation will promote the accelerated chemical decomposition and aging of various organic and inorganic materials; plankton in the ocean will also be affected or even killed by ultraviolet radiation; ultraviolet radiation will affect various animals, including people, Plant physiology, growth, and development bring serious harm and impact.

According to different wavelengths, ultraviolet radiation can be divided into three bands of UV-A (315 ~ 400nm), UV-B (280 ~ 315nm) and UV-C (below 280nm). Because the atmospheric ozone layer absorbs very little UV-A, the change in the amount of UV-A radiation has basically nothing to do with the change in the ozone layer; while UV-C is completely opposite to UV-A, it is almost completely absorbed by the ozone layer, so It basically does not reach the ground; the amount of UV-B radiation is closely related to changes in the ozone layer. Therefore, the direct measurement and analysis of UV-B can be used to study the changes in the atmospheric ozone layer and the impact of ultraviolet radiation on the environment and human body.