The SUN emits many types of radiation. At the earth's surface we receive mostly VISIBLE RADIATION (light) and INFRARED RADIATION (heat) ULTRAVIOLET RADIATION (UVR) is also present but we cannot see it or feel it. Ozone in the atmosphere absorbs much of the UVR before to CAUSE SUNBURN as well as more serious HEALTH PROBLEMS.
The ultraviolet index or UV Index is an international standard measurement of the strength of UVR from the sun on the ground at the particular time. As the UV Index increases the hazard increases. There are a number of categories ranging from low exposure to extreme as shown in the table: