UVC Science - UVC Light Kills Germs

UVC light has been proven to be an affordable, efficient and effective solution for reducing or eliminating unwanted surface and airborne pathogens. To understand how UVC disinfection works, it’s important to understand the science of UVC light.

A century of evidence that UVC light kills germs.

In 1877 Downes and Blunt discovered sunlight’s ability to prevent microbial growth. In 1930, Gates published the first analytical bactericidal action spectrum noting peak effectiveness at 265 nm, very near the 254 nm output of germicidal lamps. Since then, multiple research studies have confirmed that UVC light is effective in inactivating or eliminating viruses, bacteria, and spores.

Today, news reports show that UVC light is being used to disinfect hospitals, subways, airports and other places where people gather. With the global SARS-CoV-2 pandemic, virtually every industry is looking at UVC as a means to safely, quickly and effectively disinfect surface and airborne pathogens to create safe spaces.

The fascinating science of UVC disinfection.

Ultraviolet light is part of the electromagnetic spectrum, falling between visible light and x-rays. It’s classified into three primary groups based on wavelength: Ultraviolet A (UVA), Ultraviolet B (UVB) and Ultraviolet C (UVC). UVC light has a wavelength range of 100 – 280 nanometers (nm) and is widely acknowledged as the most effective light to eradicate germs. Accordingly, it is sometimes referred to as Ultraviolet Germicidal Irradiation (UVGI).

UVC Science Electromagnetic Spectrum Graphic

UVC irradiation is a physical process that disrupts and damages the nucleic acid (DNA and RNA) of harmful organisms such as viruses, bacteria, and fungi. The UVC light produces electromagnetic energy that causes a photo-chemical reaction, triggering the formation of specific thymine or cytosine dimers in DNA and uracil dimers in RNA. This alteration of the DNA and RNA strands leaves the organisms sterile, rendering them unable to function or reproduce. In scientific terms, a sterile organism is in essence a dead organism. Since they can’t reproduce, the organisms can’t spread, and the pathologic effect has been eliminated.

When exposing microorganisms to UVC light, the light penetrates through their cell wall and disrupts the structure of their DNA molecules, prohibiting reproduction.

How does UVC light affect DNA? Slide the bar below to see DNA before (left) and after (right) exposure to UVC light. Notice the bulging of the outer sugar phosphate backbone, and the breaking and reformation of the base pairs.

DNA changes exposed to UVC Light Before ImageDNA changes exposed to UVC Light After Image

How UVC disinfection is measured.

Log Reduction Reduction Factor Percent Reduced
1 10 90%
2 100 99%
3 1,000 99.9%
4 10,000 99.99%
5 100,000 99.999%
6 1,000,000 99.9999%

The extent to which UVC light can inactivate pathogens is dependent on the dose (intensity x time), wavelength of radiation (measured in nm), and sensitivity of the specific type of organism. Different pathogens have unique resistances to UV light; some are very susceptible, while others are more resilient and require more UVC exposure for inactivation. For example, because SARS-CoV-2 (the specific coronavirus that causes the COVID-19 disease) consists of single-strand of RNA, it’s highly susceptible to UVC light.

Most experts agree it’s not necessary to completely kill pathogens, but rather apply enough UVC light to prevent the organisms from replicating. A number of research studies have produced widely-accepted UVC dose requirements to inactivate common microbes. The level of inactivation achieved is quantified in terms of a Log Reduction Value (LRV). Log reduction is a mathematical term used to express the relative number of microbes eliminated by disinfection.

Why UVC is unequalled for disinfecting.

In today’s environment, traditional cleaning protocols are no longer enough. Even though they’re beneficial, topical germicides typically clean less than 50% of surfaces, and may include harmful chemicals and unpleasant odors. In contrast, UVC effectively eliminates 99.9% of pathogens within its line of sight. Using both topical germicides and UVC technology can provide the optimal cleaning solution.

Benefits of UVC Light Disinfection

  • There are no harmful sprays or chemicals
  • It doesn’t require the storage of hazardous materials
  • It doesn’t produce by-products, toxins or VOC emissions
  • It won’t affect smell or taste in water and food disinfection applications
  • Rooms can often be disinfected in minutes
  • It inactivates or kills up to 99.9% of targeted pathogens
  • Microbial cells can’t build up resistance to UVC light

For more information about the science of UVC, visit our FAQ page.

To learn about Safeology products, visit our UVC Tower page.