It is through the perception of contrasts that we see the world around us. Discrimination between objects and surfaces is the easier, the greater the contrast. If contrasts are weak, illuminance has to be increased in order to ensure good discrimination.

  • Contrast (C) is a measure of how clearly an object is set off (and therefore recognisable) against its background. Contrast can be calculated from the Luminance of the illuminatedobject and that of the background:

    LH = Luminance of the (normally lighter) background
    LD= Luminance of the (normally darker) background
  • Balanced contrast is needed to achieve a stimulating and interesting distribution of brightness, which has a great influence on the impression made by an interior. The luminance ratio between the focus of work and its immediate surroundings should not exceed 3:1, with a maximum of 10:1 for the general background. Stark contrasts make a harsh impression and are tiring, as the human eye has to keep adapting to different levels of brightness. A lack of contrast, on the other hand, is also dissatisfying, creating a soft and flat impression which is also tiring.
  • The loss of contrast deriving from reflected glare can be quantified with the helpof the Contrast Rendering Factor (CRF) (LiTG Publication No. 13, CIE 29/2).