The effectiveness of ultraviolet (UV) sterilization depends mainly on the wavelength of the UV light and the irradiation dose. UV can be divided into three main segments: UVA (320-400 nm), UVB (280-320 nm) and UVC (100-280 nm). Of these, UVC wavelengths have the strongest germicidal ability because they are able to damage the DNA and RNA of microorganisms, thus preventing them from replicating.

For UVC sterilization, the following are some general guidelines: Microorganisms are usually best sterilized at wavelengths between 240 and 280 nanometers, and are especially effective at 253.7 nanometers. The germicidal effect is proportional to the dose of UV irradiation, i.e., the product of the intensity of UV radiation and the duration of irradiation. In order to effectively kill an average bacterial colony, an irradiation dose of up to 10,000 microWatt-seconds per square centimeter (10,000 μW-s/cm²) is usually required. For more tolerant microorganisms, such as bacterial spores, doses of up to 100,000 μW-s/cm² may be required.

The resistance of viruses is intermediate between that of bacterial propagules and spores, whereas fungal spores may be more resistant and sometimes require higher doses of irradiation, e.g., 600,000 microwatt-seconds per square centimeter (600,000 μW-s/cm²). To achieve these irradiation doses, the intensity and duration of the UV light must be appropriate. For example, if the UV intensity is 100 μW per square centimeter (μW/cm²), then in order to achieve a dose of 10,000 μW-s per square centimeter, an irradiation of 100 seconds (approximately 1 minute and 40 seconds) is required. However, dose calculations in real-world applications can be more complex, as the effects of reflection, absorption and other environmental factors are also taken into account. In practice, the intensity of UVC lamps varies depending on the design, quality and ageing of the lamp. The intensity of a new lamp may range from 100 to several thousand microwatts per square centimeter, but may decrease by 30 to 50 percent with increased use. Therefore, regular monitoring and maintenance of UVC light sources is critical to ensure sterilization effectiveness.