The information below is extracted from the research paper: "Fluence (UV Dose) Required for up to 99% disinfection from Viruses, Bacteria, Protozoa and Algae" that can be downloaded also on our website at the links below:
The effectiveness of sterilization or disinfection with UV light depends on the exposure, time, wavelength and irradiance.
- Exposure or fluence (sometimes called dose) is measured in mJ/cm2 (where 1 mJ/cm2 = 10 J/m2)
- Exposure time is measured in seconds (s), minutes (m) or hours (h)
- Irradiance is the flux of radiant energy per unit area, in other words how much of the UV radiation power (measured in W = 1000 “miliwatts” mW = 1.000.000,00 “microwatts” μW ) reaches the surface. Irradiance is measured in mW/cm2 or W/m2 (1 mW/cm2 = 10 W/m2) and is dependent on the radiant power, distance and dispersion of the radiation emitted by the lamp source.
Many studies that show the effectiveness of UV light in disinfection or sterilization present in their findings the inactivation of virus or bacteria for a given Exposure in an amount of time, for a given UV wavelength. However, it is difficult to centralize or build a database with so many variables. The most common solution to this problem is to present the fluence required to achieve a log reduction from 1 to 5.
Log reduction explained
"Log reduction" is a mathematical term (as is "log increase") used to show the relative number of live microbes eliminated from a surface by disinfecting. For example, a "5-log reduction" means lowering the number of microorganisms by 100,000-fold, that is, if a surface has 100,000 pathogenic microbes on it, a 5-log reduction would reduce the number of microorganisms to one, equal to 99.999% kill rate.
- 1 log reduction means the number of germs is 10 times smaller (101)
- 2 log reduction means the number of germs is 100 times smaller (102)
- 3 log reduction means the number of germs is 1000 times smaller(103)
- 4 log reduction means the number of germs is 10,000 times smaller(104)
- 5 log reduction means the number of germs is 100,000 times smaller(105)