While simply structured micro-organisms are very sensitive to UVC rays, i.e. can be easily neutralized in a extremely short time, considerably greater energies are needed to kill more complex organisms like spores or algae.

The effectiveness of a UV disinfecting process lies directly in connection with the used dosage (meaning the product of Time x Intensity) in the deactivating of micro-organisms. High intensity during a short time or low intensity over a longer time can more or less be interchanged and are equally effective in disinfecting. The dose is usually given as µW*s/sqcm (microwatts per second and square centimetre), but often also as J/sqm (Joule per square metre).