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The Science of Ultraviolet (UV) Light

Fast Facts on Ultraviolet (UV) Light

  1. "Beyond" violet
    Ultraviolet means "beyond violet" (ultra meaning "beyond" in Latin), and violet being the color of the shortest wavelength of visible light.
  2. Ultraviolet (UV) light is electromagnetic radiation
    UV light has a wavelength that is shorter than that of visible light, but longer than x-ray light. It is invisible to the human eye.
  3. Categorized by wavelength
    UV can be subdivided based on its wavelength, as measured in nanometers. It is typically divided into near UV (200-380nm) and extreme or vacuum UV (10-200nm)
  4. The sun is the greatest source of UV light
    The sun emits ultraviolet light in both near UV and vacuum UV wavelengths, but because of absorption in the atmosphere's ozone layer, 99% of the ultraviolet light that reaches the Earth's surface is 315-380nm (UV-A).
  5. Proven and trusted
    UV is widely used to disinfect drinking water and wastewater worldwide, and has been for many years. UV is also extensively used for industrial applications including food & beverage, pharmaceutical, and semiconductor manufacturing.

How Does UV Disinfect?

Unlike chemical approaches to disinfection (like chlorine), UV provides rapid, effective inactivation of microorganisms through a physical process. When talking about disinfection in terms of microorganisms, means a reduction of at least 3 log (or 99.9%).

When bacteria, viruses and protozoa are exposed to UV light, the UV energy destroys the genetic material (DNA) within, eliminating their ability to reproduce and cause infection - this process is known as thymine dimerization. Unable to multiply, the microorganisms are "inactivated", and no longer pose a health risk.

When bacteria, viruses and protozoa are exposed to UV light, they are rendered incapable of reproducing and infecting

UV light has demonstrated efficacy against pathogenic organisms, including those responsible for health risks such as cholera, polio, typhoid and hepatitis. It also inactivates E.coli, Cryptosporidiym and Giardia.  

Note that disinfection is not sterilization.

Categories of UV Light

UV Light can be subdivided by wavelength, as measured in nanometres, ranging from 10 nanometers (nm) to 400 nanometers (nm).

These are the main UV Light Categories:

  • Vacuum UV: 10-200 nm
  • UV-C (Short Wave UV): 200-280 nm
  • UV-B (Middle Wave UV): 280-315 nm
  • UV-A (Long Wave UV): 315-400 nm 

Light Spectrum depicting categories of UV Light

The energy employed for UV water treatment is categorized into 254 nm and 185 nm, where nm = 1/1000 of a micron. For disinfection and ozone destruction applications, the 254 nm wavelength is utilized.

UV Technology and Water Treatment

Ultraviolet (UV) light treatment is a widely recognized and proven method of disinfection of water. It is a physical treatment, not chemical, so it doesn't alter the water chemistry.

UV doesn’t add color, odor, taste or flavor to the water and doesn’t generate harmful by-products like pH.

UV Applications

While the most common application of UV in water treatment is UV disinfection, it is also used for these applications:

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