The effect of walls on colour rendering

Colour rendering indices are characteristics of light sources, but nothing is said about the influence of the room where they are used. The walls' effect is analysed using the parametric approach of colour rendering. This formulation affords the possibility to classify the spectral reflection factors. Particularly green and red colours tend to change colour rendering more than blue or yellow ones do. The walls' effect really exists as it is shown in two examples. If it is unwanted, a method is proposed to avoid it by changing the light source or the colour of the walls.