LIGHTING LEDS


SHADE


PUTTING CRI IN THE


C


The colour rendering index does not measure up as a metric for LEDs. Jill Entwistle reports on its likely successor – the colour quality scale


olour rendering, put simply, describes the effect that a light source has on the colour of a surface, and therefore the


quality of illumination that the source produces. The first CIE (International Commission on Illumination) colour rendering scale devised to measure it appeared in the 1960s, and was designed in response to the appearance of the fluorescent lamp. The system in use today is defined in


CIE document number 13.3, published in 1995. Even that, of course, was long before the widespread use of white LEDs, the technology that has put a question mark over the colour rendering index (CRI) as a suitable metric. In fact the CIE positively recommends that it is not used with white light LEDs. ‘The conclusion is that the CIE CRI


is generally not applicable to predict the colour rendering rank order of a set of light sources when white LED light sources


32 CIBSE Journal June 2012


The arrival of LED technology put a question mark over the colour rendering index


www.cibsejournal.com


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