Colour Rendering

The Colour Rendering Index (CRI) is a number between 0 and 100. It might be considered as a measure of the colour quality of lighting. A higher number tells us that the light source or luminaire is rendering colours more accurately. It is calculated based on how well a light source or luminaire renders 8 CIE defined basic colours (and latterly an additional 7 that can be used) in comparison to under natural daylight.

CRI figures are sometimes expressed as Ra, e.g. CRI Ra 96. This expresses average colour rendering index of the 8 reference colours. It is common to have some of the 15 reference colours represented individually too, very often the RED which is the 9th reference colour, e.g. R 980 as red rendering can be challenging for lower quality light sources.

Whilst CRI values are still commonly used there are methodologies that look at a larger palette of reference colours that can be considered a more comprehensive approach such as TM-30-15. Whilst we will provide CRI figures for all products in specification documents it can also provide TM-30-15 information.

Stoane Lighting believe that the quality of light is hugely important to many of the applications of our products. All products are available with 95+CRI options and some with 90+CRI too where that is sufficient.

Colour quality and luminaire efficacy are inextricably linked. As the CRI increases, the efficacy typically decreases. Stoane Lighting can advice on light source choice to get the balance right depending on the application.

We will provide information based on the data provided to us by our light source manufacturer suppliers. We can also assess the relative performance when in luminaire by carrying out photometric (spectrometer) measurement in our lab, in some cases filters, diffusers or even colours parts are painted can have a small impact, if this is a concern on a bespoke product it can be assessed.

 

TM-30-15 (TM-30-18 and TM-30-20)

These ANSI/IES standards can also be used as a metric for the colour rendering quality of light sources and luminaires. The -18 and -20 are later revisions of those standards released in 2018 and 2020 but the methodology is still based on an assessment of a selection of reference colours larger than CRI. In this case there are 99 reference colours which provides a larger sample of more common colours on which to aggregate performance numbers.

With this methodology, results are presented with two figures: Rf (fidelity) and Rg (gamut).

The Rf (fidelity) metric is similar to the CRI Ra (average) figure and scores closer to 100 represent the most accurate rendering of colours

The Rg (gamut) metric represents the other important human perception of colour, saturation. Again, accurately saturated colours will get a score closer to 100. Over saturation will give figures over 100 whilst under saturated colours will get figures under 100.

TM-30 information is often presented in other useful graphical ways such as colour vector graphs in our detailed photometric reports which are based on measurement of products in our lab and are available on request.