What is germicidal UV-C light?
Before we define germicidal UV-C light, we need to define ultraviolet, or UV, light. We also have a whole blog post on the basics of UV here.
Ultraviolet light is a type of naturally present electromagnetic radiation that is in sunlight and actually makes up approximately 10% of the total light generated by the sun. UV light is electromagnetic energy with wavelengths shorter than visible light but longer than x-rays. The wavelength of this light ranges from 10nm to 400nm and is classified into three sub-bands; UV-A, UV-B, and UV-C.
UV light with wavelengths less than 290nm are considered to have “germicidal” properties. Germicidal means that the light can kill (inactivate) pathogens, just as it sounds. 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. Germicidal UV-C light is commonly used to inactivate or kill microbes on surfaces, in air, and in water. When implemented properly, UV-C lighting can kill up to 99.9% of pathogens.
Germicidal ultraviolet light kills pathogen 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. (source)
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Brief History of UV Light Disinfection
The disinfection properties of ultraviolet lighting have been known for over 140 years, since Downes and Blunt discovered the antibacterial effects of the shorter wavelengths of sunlight. Shortly thereafter, it was proven that the UV portions of the light spectrum were able to destroy microorganisms.
After confirming UV lighting’s ability to kill pathogens, the next step was to find a way to replicate the UV wavelengths that would result in the disinfection of surfaces, air, and water. The first UV quartz lamp was invented in 1904 and resulted in the germicidal lamp.
Germicidal lamps are a type of lamp that produce the wavelengths of ultraviolet light (UV-C; 200nm to 280nm) that have disinfection properties, like the ones used in this study to reuse N95 masks during the coronavirus pandemic.
Below are a few image examples of UV disinfection lighting at work: