What is the effect of UV germicidal lamps related to?

Ultraviolet does radiation illuminance x exposure time

Ultraviolet sterilization is jointly determined by two parameters: sterilization dose: ultraviolet radiation illuminance exposure time (seconds); bacteria type and environmental conditions.

Currently, most ultraviolet germicidal lamps on the market use low-pressure mercury lamp technology. According to my country’s current national standard 'GB19258-2012 Ultraviolet Germicidal Lamps

From this, we can see that the actual UV sterilization wavelength of the low-pressure mercury lamp is 253.7nm, which is the most effective ultraviolet sterilization wavelength for artificial ultraviolet light sources currently on the market, and it is also the internationally popular standard sterilization band for ultraviolet sterilization lamps. 

According to the requirements of the national standard 'GB19258-2012 ultraviolet germicidal lamp' for germicidal lamps: ultraviolet radiation illuminance is used as a unit to indicate the radiation intensity of the ultraviolet germicidal lamp. The test distance is required to be 1000mm, which is the distance from the surface of the lamp tube to the surface of the measuring instrument. The dose of ultraviolet light directly affects the sterilizing effect of the ultraviolet germicidal lamp, and the sterilizing power of ultraviolet light is also related to the specific bacteria type, temperature, humidity, and exposure time.

In general, the bactericidal power of ultraviolet rays for each type of bacteria depends on the bactericidal dose, that is, the irradiation time of ultraviolet radiation illuminance (seconds). Generally, if the irradiation time is doubled, the same sterilization effect can be obtained even if the ultraviolet illuminance is halved. The sterilization effect is affected by the irradiation time, distance, and the irradiance of the ultraviolet germicidal lamp. In the case of the same irradiation time and distance, the greater the irradiance, the better the sterilization effect.