Cleaning of a cleanroom is expensive and requires extra people to work in the cleanroom. Therefore smart cleaning can reduce costs as well as the level of cleanliness reached in a cleanroom. The change of surface contamination can be measured by PDM equipment in automatic mode or in regular intervals. Upon the results found can be acted by the facility managment. Periods of extra deposition can be noticed and additional cleaning can be planned. Likewise low activity may lead to a lower change of the cleanliness level thus allowing deferred cleaning. Deferred cleaning based on measurements is not the same as deferred maintenance which is often the result of cost reduction.