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Article By MG Cooling Solutions In UVGI - June 3, 2021

Ultraviolet germicidal irradiation (UVGI) is now widely accepted as an infection control strategy to reduce the spread of airborne pathogens. The ability of disinfection of UVGI technology is based on the principle of ultraviolet(UV) radiation produced by the sun in the natural environment. UVGI devices employ UV-C radiation because of their ability to kill microorganisms with their short wavelength. The principle of UV disinfection is to use UV radiation that results in photolysis and denaturation of bacterial protein leaving them unable to reproduce. The specific wavelength responsible for these reactions are situated between 240 nm to 280 nm with a peak wavelength of 265 nm

The effectiveness of UV light in killing microorganisms is estimated by calculating UV dosage which will be delivered to the microbial population. The UV dose applied by the UV system is very important in understanding the level of protection that will be offered by the UVGI devices. The UV dose is the amount of germicidal UV energy that is absorbed by a microbial population over a period of time, the higher the UV dosage the greater will be the level of protection. The inactivation rate of a specific microorganism depends on the UV dose given by the UVGI devices and the susceptibility of that microorganism. If the UV dosage under a specific condition is known thence can relate the inactivation capacity and disinfection performance of the UVGI devices.

The UV dose is the product of intensity and the exposure time, intensity is the overall power of the lamp and the exposure time is how long the UV light is ON and delivering UV to a surface. It is expressed as,

UV dose = UV intensity (W/cm2) x Exposure time (seconds)

The value of the above calculations will be expressed in WSec/cm2. The UV dose is commonly expressed in millijoules per square centimetre (mJ/cm2)

1mJ/cm2 = 1000 micro Watt second/cm2

The relationship between the dose and the destruction accomplished of a target microorganisms can be expressed as follows: –

N/No = e-KD


N = initial number of target organisms

No = number of target organisms after treatment 

K = constant associated with target organisms 

D = dose

It is derived from the above relationship doubling of the UV dose will increase the destruction of microorganisms by a factor of 10. Therefore doubling the UV dose needed for 90% destruction will produce 99% destruction of the target organism, tripling the UV dose will produce a 99.9% destruction of the target organism and so on. The dosage required to kill 90% of most bacteria and viruses ranges between 2000 and 8000 W.s/cm2.

Several factors that impact the UV dose are: –

  • LAMP INTENSITY- It is the measure of how much light is produced by the lamp per unit of the lamp surface area. Lamp intensity is usually depending on the type of lamp technology that is used.
  • FOULING– various organic and inorganic compound that eventually fouls the quartz sleeves protecting the UV lamp. Fouling of the quartz sleeves can decrease the transmittance of UV light through the sleeve into the surrounding environment. Heavier the degree of fouling the lower the UV dose.
  • FLOW RATE- The duration of time that an organism spends in front of a UV lamp is directly related to the airflow rate through the UVGI system. The faster the flow rate the less time the organism will spend in front of the lamp and the lower the UV dose.

MG COOLING SOLUTION is a leading HVAC enterprise providing UL certified highly efficient UV lamps that will protect against airborne infections. We provide UVGI solutions that are environmentally friendly and effective on the pathogen and safe to use.

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