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43 Colour rendition The colour rendition of light determines whether colours appear dull or bright in the light. It is important for good visual results and pleasant viewing experiences. Light that contains all spectral colours – such as day light – makes the colours of objects look natural. Colour rendering is neutral, and therefore particularly favourable for judging colours. The colours of objects tend to look unnatural in light with an unbalanced colour spectrum. The quality of the colour rendering of a light source is assessed by the colour rendering index (CRI). It is derived from com- mon test colours and indicates how naturally colours are rendered. Depending on the visual task, the appropriate colour rendition should be chosen. To ensure a relaxed and positive visual experience, the colour rendering index should not be less than 80. This aspect can be safely ignored in spaces where precise colour rendition is not crucial, such as living rooms and bedrooms. Here lights can be selected according to the mood to be evoked. Only an indirect relationship exists between light colour temperature and colour rendition. The currently best meth- od uses the principle of "luminescence conversion" and is used both for LED and fluorescent lamps. In this method the original blue LED light is transformed into white light by a very thin layer of phosphor material. Currently, CRI values of up to over 90 can be achieved with this method. Lighting basics