The balcony in the north is well lit, but the sun doesn't shine. There is ultraviolet light.

If you don't expose yourself to the sun, you will receive ultraviolet rays. What you receive is scattered ultraviolet light, but the intensity of ultraviolet light is different.

On cloudy days or rainy days, ultraviolet rays are sometimes particularly strong, because clouds mainly reflect visible light and ultraviolet rays are not reflected, so the ultraviolet rays on cloudy days or cloudy days will not be weakened much. Summer is coming, and more and more people are aware of the harm of ultraviolet rays to the skin. However, there are ultraviolet rays from the sun every day, but the intensity is different. You can be exposed to ultraviolet rays in cloudy days, sunny days, summer, winter, outdoors and even indoors.

Ultraviolet light is invisible to the naked eye. It can be divided into three types: long-wave ultraviolet (UVA), medium-wave ultraviolet (UVB) and short-wave ultraviolet (UVC). There are two main sources of ultraviolet rays, one is natural radiation source, that is, electromagnetic radiation caused by sunlight, and the other is artificial radiation source. Anything heated above 2500K will start to be released ... So at night, in the environment with strong lights, the skin in dance halls and other places will also be exposed to ultraviolet rays.