How does UVC light destroy germs?
The high energy from short wavelength UV-C light is absorbed into the cellular RNA and DNA, damaging nucleic acids and preventing microorganisms from infecting and reproducing. UV-C is strongly absorbed by RNA and DNA bases which leads to photodimerisation, the damaging of the molecular structure. This results in virus inactivation since the germs can no longer replicate and cause disease.
The strength of inactivation correlates with the intensity and duration of the UV-C dose. The further an object is from the light source, the less UV-C it will be exposed to. When the distance doubles, only a quarter of the UV-C remains.
The UV light emitted by a source is expressed in watts (W) and the irradiation density is expressed in watts per square meter (W/m2). The correct dose is required for germicidal action to take place. The dose is the irradiation density multiplied by the time (t) in seconds and expressed in joules per square meter (J/m2).
One of the most efficient ways to generate enough UV-C radiation is to use a low-pressure mercury discharge lamp. On average, 35% of input watts is converted to UV-C Watts. The radiation generated is almost exclusively at 254nm viz. at 85% of the maximum germicidal effect and 80% on the IES curve. Radiation wavelengths below 240 nm form ozone (O3) from oxygen in the air. This is highly reactive and toxic to humans, so precautions must be taken to avoid exposure to both life and certain materials.
Brands such as Phillips, found in our own Sterilon UV-C Lights, produce low-pressure tubular fluorescent ultraviolet (TUV) lamps that have an envelope of special glass which filters ozone-forming radiation. This results in almost zero formation of ozone while maximising the production of UV-C radiation.
Unlike other techniques, UV-C photolysis produces a minimal amount of potentially dangerous by-products. Air has a low absorption coefficient, thus allowing UV-C to attack any microorganisms present. Although UV-C radiation has proven to be effective against the entire Coronavirus family, every method has pros and cons that must be addressed.