The Problem With CIE’s CRI

Reasons why CIE's CRI is wrong:

CRI is outdated and inaccurate for modern light sources.
CRI only applies to lights below 5000K.
CRI does not measure a light source’s ability to render color faithfully.
CRI does not work with modern LED technology because it penalizes lights that can fully saturate colors especially those that contain blue and green.
A score of 100 can be achieved with light sources which can illuminate the 8 low saturated colors used in the test, but fail to render bright colors accurately. For instance, an incandescent lamp will score 100, but the light makes an object appear dull.
Manufacturers like GE and Sylvania in an attempt to offer full color rendering to their incandescent lamps are adding rare-earth phosphors to add blue and green/yellow spectra.

CQS Color Quality Scale
“ Color rendering: Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant „ —CIE 17.4, )
International Lighting Vocabulary, (Schanda 2002)

CQS is being developed by NIST (National Institute of Science) to replace the outdated CRI measurements

The human eye works optimally when objects are illuminated with noonday sunlight (6500K). The white light from the sun includes all the light spectra from Blue to Red in equal proportions. We see the spectra an object reflects and does not absorb. If a light source does not have the full spectrum of the sun then objects do not appear their natural color.
CQS will replace CRI. Some of the CRI procedures will be retained but the test will test for a light to saturate the colors at the end of the spectrums. Light that score well on the CRI test will suffer under the CQS test.
Solid State Lighting technology using High Brightness white LEDs score very high on CQS and low on CRI. LEDs can be made to score well under the CRI test but must sacrifice at least 20% of the efficiency to do so, and then would no longer render color as well.
Is it reasonable to use CRI as a measure of a Solid State Light? Silescent Lighting will provide whatever the customer wishes, but if efficiency and good color rendering is desirable then CQS is the preferred standard.

Posted in LED Lighting Articles.