see Colour rendering index

Reflectance value

Ratio of the luminous flux reflected by a surface and the luminous flux incident on said surface. The reflection behaviour of reflective surfaces, e.g. road surfaces, is expressed by the luminance coefficient and reflection factors and is internationally standardised for road surfaces C1 and C2 (see also standards). In the past, the road surfaces R1, R2, R3 and R4 were used in some European countries, including Germany.


In contrast to control, which depends on external parameters, regulation means manipulating a variable using measurements  in a way that causes it to permanently adjust itself to a constant nominal value (see also chapter “daylight-dependent control”).

Reflection factors

(S1, S2, κp): The reflection factors describe the “gloss level”, i.e. the reflective properties of a reflecting surface. In combination with the luminance coefficient they describe the reflection behaviour of road surfaces, for example.