Colour consistency metric proposed for LED lighting

The aim is to produce a single number which sums up how even a beam will appear when shone on to a white surface, allowing different LED and optical combinations to be compared.

“It is very difficult to quantify the quality of colour because everyone has a different way to perceive colour,” according to Gaggione. “We found it necessary to create a unit of measurement that enables the quantification of the quality of colour mixing in a scientific way.”

The resulting ‘colour consistency index’  is based upon physics, colorimetry and a standard deviation calculation.

To increase the chances of broad adoption, the firm has chosen to extended generally-understood ‘Macadam ellipse’ concept, where the likelihood of someone noticing that two light sources are different increases with the number of Macadam ellipses they are apart on the CIE colour chart – with one Macadam ellipse indicating the two sources are generally indistinguishable to most people, and four Macadam ellipses indicating that almost all will see that they are different.

In Gaggione’s case, when a nominally white beam is projected onto a white wall, a score of Macadam ellipse in its CCI scale will indicate no mottling or other colour variation visible to most people, and so on.

“Our CCI measurement protocol gives a result expressed in MacAdam Ellipses steps deviation, already being an industry standard for LEDs binning,” said Gaggione. “From now on, all of the colour mixing solutions published on our standard products selection tool have a CCI.”

Can other people use CCI?

Yes, if you are a luminaire maker.

“The technique was initially developed for RGBW colour mixing applications, but it also works with tunable white luminaires as well as white static luminaires. If you can define a colour correlated temperature for your luminaire, then you may characterise it with the colour consistency index,” said the firm.

But, what if you are another maker of optics?

“Initially we developed the CCI in order to compare our optics with the optics from our competitors with a scientific and objective tool,” Gaggione optical design manager Jean-Pierre Lauret told Electronics Weekly. “So we would be very happy if the other optics makers use the CCI as well.”