Ultraviolet index grade

The forecast grade of ultraviolet index is divided into five grades.

The first index value is 0 to 2, usually cloudy or rainy. At this time, the ultraviolet intensity is the weakest, and the secondary index value is 3 to 4, which is generally cloudy. At this time, the ultraviolet intensity is weak, and the third index value is 5 to 6, which is generally cloudy. At this time, the ultraviolet intensity is strong, and the fourth index value is 7 to 9, which is generally cloudless. At this time, the ultraviolet intensity is very strong, the fifth finger value reaches or exceeds 10, and it is mostly sunny in summer.

Ultraviolet index refers to the degree of possible damage to human skin caused by ultraviolet radiation in the sun rays reaching the ground when the sun is at the highest position in the sky in a day (usually around noon), and is expressed by a number from 0 to 15. The greater the ultraviolet index value, the more serious the damage to human skin, and the stronger the damage to skin in a short time. The ultraviolet index at night is 0, and in tropical and plateau areas, the ultraviolet index in sunny days is 15.