The operation of bactericidal lamps is characterized by radiometric values. The main ones are bactericidal dose and bactericidal efficacy. The degree of disinfection of air or surfaces depends on the bactericidal dose. In a bactericidal dose (dose of ultraviolet radiation) or exposure, one should understand the density of the bactericidal radiation energy, or the ratio of the energy of the bactericidal radiation to the area of the irradiated surface (surface dose, J / m2) or the volume of radiation (volume dose, J / m3) .
The effectiveness of exposure to microorganisms, or bactericidal (antimicrobial) effectiveness is the level of reduction of microbial contamination of the air environment or on any surface as a result of exposure to ultraviolet radiation. This value is estimated as a percentage – as the ratio of the number of dead microorganisms to their initial number before irradiation. The bactericidal efficacy of lamps depends mainly on the dose of radiation (DUV, J / m2) supplied to microorganisms:
DUV = I * t (1)
Where, I – is the average intensity or dose, J / cm2;
t – is the exposure time, s.
The application of this simple-looking equation is quite difficult when considering the dose for a particle passing through a device with a variable flux density. The equation describes the process of irradiating a fraction with the dose received in one pass through the device. With repeated exposure to radiation on microorganisms (recirculation), bactericidal efficacy doubles.
The survival rate of microbial or colony forming units (CFU) exposed to bactericidal exposure exponentially depends on the dose:
S = e k D U V, (2)
where k – is the constant of deactivation (inactivation), depends on the specific type of CFU m2/J;
The obtained coefficient of inactivation of the fraction of one of its passage (η) through the radiation field is used as an indicator of the total radiation efficiency and shows the percentage or proportion of CFU inactivated after one passage through the radiation field, and also depends on S and is always less than 1:
η = 1-S. (3)
The value of the parameter k for many types of bacteria, fungi, mold, obtained experimentally, and can differ from each other by several orders of magnitude. This is due to the methods and conditions of measurements: in the air stream, in water or on the surface they are made. The readings k is strongly affected by the error in measuring the survival rate of the microbial culture. In this regard, it is very difficult to choose the correct value of k for the design conditions of bactericidal irradiation systems, and, as a rule, the average or maximum of the known values of k depending on the goals of disinfection is taken to apply equation 2.