Reflection

This is the property of materials to reflect light. There are different types of reflection, such as mirrored, mixed, fully diffused and irregularly diffused reflection. Indoor lighting uses diffused reflection almost exclusively.
 
The reflective behaviour of a material is expressed by the reflection factor r. This is the ratio of the luminous flux reflected by the material to the luminous flux incident on the material (r= F/ F₀). The reflection factor (reflectance) is specified in most cases for diffused incidence of light (r_dif) or quasi-parallel incidence of light under 80 (r). In lighting technology the value mostly used is r_dif. In theory, the maximum value for r and rdif is 1 (100%).

 

This table shows the reflectances of the most common colours and materials:

Colour r Material r White 0,8 Plaster 0,8 Light yellow 0,7 Tiles, white 0,7 Light green, pink 0,4 Maple, birch 0,6 Sky blue 0,4 Light oak 0,4 Light grey 0,4 Concrete 0,3 Light brown 0,3 Dark walnut 0,2 Mid-grey 0,2 Dark oak 0,2 Dark red 0,1 Red brick 0,2 Black 0,1 Breeze block 0,1