Measuring device with measuring head and using the measurement apparatus in a method of assessing the efficacy of the photocatalytic surfaces

The invention relates to a measuring apparatus and a method for assessing the efficacy of the photocatalytic surfaces. The presented measurement device includes an optical measuring head which comprises a hollow Messkopfumhausung having an outwardly open side with an edge. The rim includes a flexible, resilient element or consists thereof. Characterized a light-tight contact can be produced at surfaces of all types to the optical measuring head. In addition, the measuring head contains an indicator of known concentration, is placed in the measuring head that has at a contact of the measuring head with a surface to be measured of the indicator to the surface of a specified defined distance. As a result, an indicator-related contamination damage to the surface to be measured can be avoided and the comparability of the measurement results obtained with the measuring device can be improved.