Some reasonable methods which estimate the number of germicidal lamp fixtures necessary for air sanitation of rooms or air ducts have been suggested.
Referring to the experimental data, the simple formulas calculating the fixtures are derivered as follows:
The number of fixtures (N) for ultraviolet disinfection of air with an air duct are proportional to theside length of cross-scetion of the duct which fixtures are mounted on (C) in meter, and the air speed.(J) in meter per minute.
The amount of N required for 99% disinfection of micro-organisms and viruses having a relatirelylow ultraviolet resistivity as well as E-coli may be calculated as
N=0.23 CJ/G
Where G is the effective output rating at the mean value of the germicidal flux throughout the lamp' life for the fixture in watt, and depends on type of the fixture. This formula will be recommended for general use in such places as office, working-shop, theater, etc.
If higher sanitatry condition is called for in such places as the working-shops of foodstuff and pharmacy, next formula may be recommended in order to make the condition of 99% disinfection against air-borne bacteria.
N=0.90 CJ/G
In case of air disinfection in a closed room by installing the fixtures such as the upper space irradiation, it is supposed that the air in the room continuously diluted with disinfected air which passed through the assumption duct having the size of irradiated space.
The number of fixtures (N) required for environmental air sanitation of a working-shop may be proportional to the volume of the room (V) in cubic meter, and inversely proportional to the distance. from fixture to ceiling (H) in meter, therefore the formula may be
N=0.05V/GH
It makes the condition of 90% disinfection against air-borne bacteria within ten minutes for the air in the room theoretically.
In case of sanitary ventilation of a living room in order to protect the respiratory infections for persons, the number of required fixtures (N) may be proportional to the square of occupants, but. inversely proportional to H and V. Thus the formula may be
N=4P²/GHV
It makes the condition of 63.2% disinfection against the most of infectious bacteria or viruses per minute for the recommended amount of sanitary ventilation theoretically.
For the purpose of effective air disinfection, the instructions about the mounting of fixture in air duct, fixture choice and protection against harmful ultravilolet radiation in the upper space irradiation of the room have been described.

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