What is Ultraviolet Light?
Ultraviolet light is a natural component of sunlight. Ultraviolet rays are electromagnetic wavelengths of radiation which are just shorter than those of visible light. The sun’s radiation contains many ultraviolet rays.
Higher energy wavelengths of UV rays have the unique ability to destroy harmful microorganisms in water. UV light destroys these microorganisms by disrupting their genetic information (DNA), rendering them harmless and unable to reproduce. Of all current methods of water disinfection, UV disinfection is the most efficient, economical and environmentally safe system.
There are four types of UV light within the electromagnetic spectrum which includes electromagnetic waves of various frequencies (measured in cycles per second) and wavelengths (measured in meters or nanometers). Wavelength and frequency are inversely proportional, with shorter wavelengths having higher frequencies, and therefore more energy. The regions of the UV spectrum that have a germicidal effect are known as UV-B and UV-C.
Short-wave UV-C lies between 200 and 280 nanometers (nm). This is where germicidal effects occur. Because short-wave UV is screened out by the earth’s atmosphere, naturally occurring UV-C is rarely found at the earth’s surface.
Ultraviolet Dosage
Ultraviolet dosage is measured in micro-watt seconds per square centimeter (μWs/cm2). The higher the micro-watt, the higher the dosage; the longer the exposure time, the higher the dosage; the more area exposed to the ultraviolet radiation, the higher the kill.
Ultraviolet disinfection of water generally employs low pressure mercury vapor lamps. These lamps generate short wave ultraviolet in the region of 253.7 nanometers, which is lethal to microorganisms including bacteria, protozoa, viruses, molds, yeasts, nematode eggs and algae.
Approximate dosage rates to kill:
- Bacteria 2,500 – 26,400 μWs/cm2
- Yeast 6,600 – 17,600 μWs/cm2
- Algae 11,000 – 330,000 μWs/cm2
- Viruses 2,500 – 40,000 μWs/cm2
The U.S. Public Health Service published a policy stating the dosage requirement for drinking water should be approximately 16,000 μWs/cm2. This statement has formed the basis for a World Wide Standard. Every ENLIGHT™ UV unit emits in excess of 30,000 μWs/cm2,which is more than double the recommended dosage of the U.S. Public Health Service.