Sunlight is More than What We See Ultraviolet light is classified into three categories: UVA (long wave, black light, 315 to 400 nm) which causes tanning, UVB (medium wave, 280 to 315 nm) which causes sunburn, and UVC (short wave, germicidal, 100 to 280 nm) which is filtered out by the atmosphere and does not reach us. Incidentally, the ozone layer absorbs 97–99% of the UV from about 200 nm to 315 nm wavelength, which potentially damages exposed life forms on Earth. Not everything UV light does to you is bad, ultraviolet light (between 270 nm and 300 nm) reaching our skin breaks down 7-dehydrocholesterol flowing in the bloodstream, converting … Continue reading UV exposure, aging and our remedy: UV Repair Cream