Can you match lights or lighting sources using x,y coordinates? – Newsshooter

September 2, 2022 by No Comments

Matching lights is really hard to do, especially if you are using lights from different manufacturers. The problem becomes even harder when you try and match RGBW/RGBWW/RGBAW/RGBACL lights. You can’t just dial in a different CCT and make +/- G/M adjustments to get a closer result. Because an RGBW/RGBWW/RGBAW/RGBACL fixture is creating white light by mixing many different colored LEDs you introduce a lot more variables into the equation.

Color temperature is not a good metric to use with RGBW/RGBWW/RGBAW/RGBACL fixtures. A much better metric is the CIE 1931 xy coordinate system. This system allows every specific color to be assigned a unique set of x,y coordinates. This essentially means that any color temperature you want to create can be assigned x,y values instead of a CCT value.

One way of making RGBW/RGBWW/RGBAW/RGBACL lights match more closely is to look at their x,y coordinate values and then assign those values manually to another light.

In 1931 in Cambridge, the International Commission on Illumination (CIE) established an international system of trichromatic colorimetry, which is the basis for the CIE System which is still in use today. The primaries of the CIE chromaticity chart were specified and the color vision characteristics of a reference observer were defined by extensive tables that gave coordinates of points on the locus of spectral radiation in the chromaticity chart and the distribution coefficients for light with an equal-emergy spectrum were adopted as the standard for white light.

In Laymen’s terms, the CIE is just a way to define how perceived color is viewed using chromaticity coordinates.

You would have seen a CIE chromaticity chart before, as it is commonly used when showing color spaces such as rec.709 and Rec.2020, etc. A CIE chromaticity chart is based on what the human eye can see when it comes to colors and that is why it is a strange-looking horseshoe shape and not a 360-degree circle like you would see on a color picker.

For lighting, it is important to look at the Planckian locus, or Planckian curve that it is sometimes referred to, which is the path that the color of a black body takes as the blackbody temperature changes. It is depicted as a curved black line that you can see on the CIE chart above. Perfectly reproduced Kelvin color temperatures follow this curve. If you get a reading that is above the curve then the light will lean green, if it falls below the curve it will have extra magenta. This curve is one of the tools we can use to judge how well lights are able to replicate a perfect lighting source. The further away readings are from this curve the less accurate a light will be. In saying that, small discrepancies are not going to make a huge difference and as long as the reading from the light stays close enough to the Planckian locus then it will produce decent results.

Ok, so what does this have to do with matching lights to lighting sources or other lights? Well, as I mentioned earlier if you take two different lights and try to get them to produce the same exact same color temperature that won’t always work because of the different types of LED emitters that are being used. Certain lights have the ability to display CIE x,y coordinates. If you have two different lights that have …….



Leave a Comment

Your email address will not be published. Required fields are marked *