Please note that many variables (air flow, humidity, distance of microorganism to the UV light, irradiation time) take place in a real world environment that make actual calculating of the UV dosage very difficult. However, it is proven that UV light will kill any DNA-based microorganism given enough UV dosage. UV breaks down DNA on a cumulative basis. Therefore, as air circulates through the ductwork of an HVAC system containing an UV light, the UV light continuously disinfects the air. If a microorganism is not effectively deactivated on the first pass through the ductwork, the UV light will continue to break its DNA down on subsequent passes. Microorganisms do not sit in a static environment in HVAC systems except on coils which can be exposed to UV light also. Microorganisms multiply rapidly if not controlled. The UV light helps to reduce airborne microorganisms from the indoor environment.
The following are incident energies of germicidal ultraviolet radiation at 253.7 nanometers wavelength necessary to inhibit colony formation in microorganisms (90%) and for 2-log reduction (99%):
Tests confirmed that the 14" high output UV lamp used in the American-Lights® units produces 800µW/cm² @ 1' with 534FPM air flow at 55º F. UV dose = UV intensity x time in seconds. To compute time needed to inactivate germs in the following chart at 1' distance by one American-Lights unit divide the UV dose by 800.
Example: for 90% kill factor of Bacillus subtilis spores: 11,600 divided by 800 = 14.5 seconds.
Energy Dosage of Ultraviolet radiation (UV dose) in µWs/cm2 needed for kill factor