UV irradiation has been known to break down microorganisms for over 100 years. Ultraviolet light at short wavelengths, 254nm, breaks down the molecular bonds in the microorganism’s DNA. The use of UV light for sterilization is referred to as UVGI, ultraviolet germicidal irradiation. UVGI is currently used in hospitals and laboratories where sterile environments are necessary. UVGI is also used in closed water holding tanks where the water is recirculated past the UV light and is considered a highly effective method of destroying microorganisms. In parts of ventilation systems where condensation can occur UVGI prevents the development of mold and the growth of bacteria. The wavelength of light which breaks down the DNA of microorganisms is also harmful to humans. Exposure will cause a sunburn and can cause inflammation of the cornea. Earth’s atmosphere filters our this radiation from the sun before it reaches the earth. When the UV light is used to sterilize laboratory items such as pipets and goggles and the surfaces of biological safety cabinets, a safety mechanism must be in place to ensure the laboratory personnel are not exposed to the light. Longer wavelengths of UV light which do come through the earth’s atmosphere can also sterilize with prolonged exposure. Solar Water Disinfection or SODIS is used in developing countries at the household level to produce safe drinking water. The water is placed in clear clean PET bottles and the bottles are exposed to at least 6 hours of full sun. This solar exposure kills all the microorganisms in the water and makes it safe to drink.