CRI Comparison1


The colour rendering index (CRI) of a light source is the measure of its ability to reproduce colours of various objects faithfully in comparison with an ideal or natural light source. In general terms, CRI is a measure of a light source’s ability to show object colours “realistically” or “naturally” compared to a familiar reference source, either incandescent light or daylight.

CRI is significant because it has been the most difficult metric for incandescent replacement light bulbs to match (while maintaining high efficiency) and therefore the most frequently ignored. For that reason, bathroom mirror lights and LED light bulbs with a high CRI can be worthy replacements for incandescent light bulbs. Most LED lights do not have a CRI above 90.

CRI is calculated from the differences in the chromaticities of eight CIE standard colour samples (CIE 1995) when illuminated by a light source and by a reference illuminant of the same correlated colour temperature (CCT), commonly measured in Kelvins, indicating the light colour produced by a radiating black body at a certain temperature; the smaller the average difference in chromaticities, the higher the CRI. A CRI of 100 represents the maximum value. Lower CRI values indicate that some colours may appear unnatural when illuminated by the lamp. Incandescent lamps have a CRI above 95. Cool white fluorescent lamps have a CRI of 62, however fluorescent lamps containing rare-earth phosphors are available with CRI values of 80 and above.

The CRI measure in use today was developed by the CIE in 1974 and slightly updated in 1995. The measure has two main flaws. Its colour differences are measured in a hardly uniform colour space. Its colour sample set has just 8 items, which is much too few to test lights with complex spectra. A light manufacturer can tune its spectral power distribution to the sample set to achieve an unrealistically high CRI. In 2015 the IES (Illumination Engineering Society) produced a modern replacement to the CRI measure. It uses a newer colour space and 99 colour samples. In 2017 the CIE published an almost identical measure, but it did not depreciate its 1995 CRI measure.

At UNILED we source only the highest standard of LED, put through thorough testing standards, to ensure the best possible quality.


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