Context

Scientists are studying the use of ultraviolet germicidal irradiation (UVGI) to detect the virus in schools, restaurants and other public places. Through this method, ultraviolet (UV) lights would be able to disinfect contaminated public spaces to stop the transmission of the virus

About

• Ultraviolet germicidal irradiation (UVGI) is the use of ultraviolet (UV) energy (electromagnetic radiation with a wavelength shorter than that of visible light) to kill or inactivate viral, bacterial, and fungal species. 
• UVGI is a method of disinfection that uses short wavelength ultraviolet light (UV-C) to inactivate or kill microorganisms and pathogens.
• Essentially, UVGI is the use of UV light with sufficiently short wavelengths to disinfect surfaces, air, and water.

The effectiveness of germicidal UV light depends on the length of time a microorganism is exposed to UV, as well as the intensity and wavelength of the UV radiation.

What is UV light?

• Ultraviolet light from the sun has shorter wavelengths than visible light and, therefore, is not visible to the naked eye.
• The full spectrum of UV radiation is sourced from the sun and can be subdivided into:
  • UV-A rays
  • UV-B rays
  • UV-C rays

• In this spectrum, UV-C rays are the most harmful and are completely absorbed by the Earth’s atmosphere.
• Further, while both UV-A and UV-B rays are harmful, exposure to UV-B rays can cause DNA and cellular damage in living organisms.
• UV light kills cells. Increased exposure to it can cause cells to become carcinogenic, thereby increasing the risk of getting cancer.
• In fact, it is the increased direct exposure to UV rays from the sun that most commonly causes skin cancers.
• UV light with wavelengths less than 290nm are considered to have “germicidal” properties (more on this later).
• Earth’s atmosphere absorbs ultramagnetic radiation with wavelengths less than 290nm, meaning that most of the UV-C and UV-B generated by the sun is blocked by our planet’s ozone. 

How does UV Light Kill Viruses and Bacteria?

• Ultraviolet light kills cells by damaging their DNA. 
• Exposure to the electromagnetic radiation (light) at certain UV wavelengths modifies the genetic material of microorganisms and destroys their ability to reproduce.
• The UV energy triggers the formation of specific thymine or cystosine dimers in DNA and uracil dimers in RNA, which causes the inactivation of microbes by causing mutations and/or cell death as well as failure to reproduce. 

How does UVGI work?

• Ultraviolet germicidal irradiation (UVGI) uses destructive properties of UV light to target pathogens.
• It is thus considered effective in disinfecting the air and helps in preventing certain infectious diseases from spreading.
• UVGI replicates UV wavelengths that disinfect contaminated spaces, air and water.
• It is a promising method for disinfection but the efficacy of it depends on its dose.

Are UV Lighting and UVGI the same thing?

• UVGI is a specific method of sterilization that uses UV lighting. In essence, UV lighting is a component of UVGI.
• UVGI is just one method of sterilization/decontamination using lighting.

Can it prevent infection?

• UVGI is most effective in preventing infections that are chiefly spread through smaller droplets and not by direct contact or larger respiratory droplets.
• While using UVGI, it is important to consider factors such as the sensitivity of microorganisms to UVGI, the dose of UVGI required to kill them, humidity and weather conditions.
• Further, UVGI relies on air circulation in a room, which means the circulation of air needs to be such that air from below the room, where the pathogen is generated reaches the upper-portions of the room, where the UVGI can trap the pathogen.
• Even so, using UVGI on a mass-scale, in public spaces such as schools, universities, restaurants and cinema halls may not be the most cost-effective way to approach disease prevention.