ultraviolet wavelengths less than 200 nanometers, x-rays, and gamma rays, are collectively called ionizing radiation since the energy in any such light quantum is high enough to 'kick' an electron out of an atom. this is why these kinds of radiation are dangerous to life. ultraviolet light is subdivided into three main bands. uv-c has the shortest wavelengths and is dangerous ionizing radiation. nitrogen and oxygen absorb the uv-c from solar radiation. uv-b has medium wavelength and is less dangerous to living things. the earth's ozone layer absorbs most of it. uv-a from the sun gets through the atmosphere entirely. it has wavelength almost as long as visible light, and many animals can see it but humans cannot.