Without the sun, there is no life, and naturally there will be no health. Daylight includes ultraviolet light, visible light and infrared light, which are extremely important for human health. Sunlight can be sterilized to oxidize the polluted atmosphere and has a clean atmosphere. Ultraviolet rays can kill bacteria and viruses and can be used for disinfection of air and water. Sunlight is also important for human skin. Ultraviolet rays help to control and kill harmful bacteria on the surface of the skin. It also converts melanin in the skin into melanin through the action of oxidase, which protects the skin from pigmentation. The skin and the effect of preventing internal tissue from overheating. In addition, ultraviolet light can stimulate blood regeneration and enhance the immunity of the body (including the skin). Infrared to the body, mainly heating performance. Long-wave infrared rays are absorbed when they come into contact with the skin to produce a warming effect. Short-wave infrared has a strong penetrating power, which can increase the temperature of deep tissues, dilate blood vessels and congestion, promote metabolism and cell proliferation, and thus improve blood circulation and nutrient supply.
But excessive exposure is equally harmful. Sun dermatitis and sun rash are common in summer, but they are harmless. Another type of non-inflammatory sun damage, such as solar keratosis, solar granuloma, etc., is proliferative and may become cancerous if it is out of control. Excessive sun exposure is also an important cause of conversion of benign pigmented nevus to malignant melanoma. Ultraviolet rays can induce tumors of many animals (skin scaly and skin cancer, fibrocarcinoma, etc.). Excessive ultraviolet radiation can cause loss of elasticity of the skin, rough skin, premature wrinkles, and long-term, can lead to skin cancer. Ultraviolet light not only converts normal cells into cancer cells, but also prevents the host from destroying cancer cells due to interference with the immune system. In addition, in the summer season, strong sunlight can also cause the body to overheat and cause heat stroke.
Therefore, the role of sunlight has advantages and disadvantages. Ultraviolet-B is very energetic and can penetrate the inside of the skin, easily causing capillary congestion, destroying proteins, damaging the elastic fibers of the dermis, and making the skin inelastic. Therefore, preventing light radiation actually means preventing ultraviolet B radiation. Ultraviolet-B is irradiated to the ground through the ozone layer in the atmosphere. When the sun is in the oblique direction, the medium-wave ultraviolet rays that illuminate the ground through the ozone layer are the most and strongest. This time is before 10:00 and after 15:00. Trying to avoid the sunlight during this time has practical significance for reducing and reducing light hazards.