What is the Colour Rendering Index?
Take two lamps that measure the same with a colour-temperature meter. Let one of the lamps meet a formal standard and compare the other to it. To compare them, measure the lamps’ reflectance off eight colour pataches, using a meter that is calibrated to “see” colours as the Standard Observer would see them. The CRI is a calculation of the similarity of these readings, expressed as a percentage. A CRI of 93 purports to indicate that the lamp in question has an accuracy of 93%. This is a little like measuring the distance from Toronto to Vancouver to the nearest kilometer but the number does gives a rough-and-ready idea of whether a lamp will tend to make colours look reasonable or bizarre. In the graphic arts business, a CRI of 90 is usually deemed acceptable for comparing colours.
