There are three types of UV rays, classified according to their wavelengths and measured in ‘Nanometers, nm’. All three differ in terms of their biological activity and their penetration levels to our skins. UV’s with shorter wavelengths are the most destructive and dangerous, although they are completely filtered by the atmosphere level, and do not reach the earth’s surface.
Here is how the sun’s UV affects life on earth. When the sun comes up, its’ energy is emitted at different wavelengths. What we see is visible light. There are also infra-red (felt as heat) and ultraviolet (UV) rays (which we do not see or feel). Let us consider the three basic types: UV-A UV-B and UV-C.
UV-A has a long wavelength (315-399nm) and reaches the earth all the time. It makes up about 95% of UV radiation reaching the earth’s surface. It helps generate vitamin D for living things. In recent studies, prolonged exposures UV-A is known to enhance skin cancer development.
UV-B is not as long as UV-A (280-314nm). Because it is shorter, it is more damaging to human and plant cells. Not all UVB reaches the earth, as some of it is filtered by the ozone layer. The little that reaches earth causes sunburns and can also damage our cells and DNAs (DNA is the basic building blocks of our cells). This is why it can cause skin cancer and cataracts in our eyes. The amount of UV-B that reaches us on earth depends on factors like the time of the day, the time of the year and the amount of stratospheric ozone available to block it. It is also known that altitude, weather conditions and reflective surfaces such as sand, snow and water reflect some of the UV radiation, and that means shady areas can have higher UV effect.
UV-C has the shortest wavelength (100-279nm). It is the most dangerous but all of it is usually absorbed by the ozone layer.