New colour rendering method spells end for CRI

A new way to measure colour rendering that is set to replace the traditional CRI metric has been unveiled and has won the backing of the US Government.

If adopted, it’s set to be the biggest change in methodology in the lighting industry in a generation and spells the end for the current Colour Rendering Index, whose history stretches back to the 1930s. The CRI method has come under increased criticism for its inability to accurately describe how well LEDs render colours. For instance, an LED can have a relatively high CRI but render red badly.

The new system has been developed by scientists for the respected Illuminating Engineering Society, and is commonly called TM-30 after the numbering system for its technical documents.

TM-30 is based on a reference set of colour samples that is more representative of objects in the real world than the pastel samples used for the CRI method.

Instead of the traditional Ra, lighting engineers would have to get used to the new Rg measure, which evolved from research into what’s termed the Gamut Area Index.

The new method has won the backing of the highly influential US Department of Energy, which effectively means the end of the CRI method in America and If the International Commission on Illumination (CIE), the standards body behind CRI, agrees with the new method, it will effectively become the global standard.

However, some years ago, the CIE refused to adopt another proposed alternative called the Color Quality Scale.  The organisation says it ' has a strong intention to revise CRI' and that it has two technical committees actively working on the problem, one developing a new colour fidelity metric to update the CRI, and another investigating other aspects of colour quality for possible preference-related metrics.  

Additionally, many manufacturers don’t welcome TM-30. This week the Global Lighting Association – which represents 5,000 lighting equipment makers – said it would support an additional colour quality metric, such as one based on colour saturation,  ‘that represents a significant and meaningful improvement’ but only in conjunction with – rather than a replacement for - the existing CRI system.

The organisation is also opposed to the establishment of regulatory or other minimum performance requirements for a colour rendering index of greater than 80 for indoor lighting applications.

In a statement, it said: ‘Currently the colour rendering index Ra is the internationally accepted and standardised metric for colour fidelity…. Significant research effort over the past years on colour fidelity, however, has failed to deliver a single new meaningful metric for fidelity that can be used by the lighting industry and replace the existing Ra metric.’

- The new TM-30 colour rendering method will be explored in a special presentation at the LuxLive 2015 event in London in November. To register, visit www.luxlive.co.uk

- A special Lux webinar on colour rendering in association with Erco takes place at 1pmBST/8amEST/2pmCEST on 14 October. To be notified of registration opening, email events@luxreview.com with the subject line 'colour rendering'.

  • Internet of Things-based lighting control, data capture and security will be a key theme of LuxLive 2017, which takes place on Wednesday 15 November and Thursday 16 November at ExCeL London. For more information, and to register for free, click here.

Comments 2

There are several issues here. First, the CIE is not organized to "agree" with standards published by other organizations. It could at best issue a position statement on TM-30, but this is unlikely, given that CIE TC 1-69, "Colour Rendition by White Light Sources," was unable to agree on a final report regarding color rendering metrics. This included a number of metrics in addition to the NIST CQS, including two that were forerunners of the TM-30 color fidelity and color gamut metrics Rf and Rg. Second, the Global Lighting Association position statement (http://www.globallightingassociation.org/library) calls for an undefined "color saturation" metric, while stating that "colour saturation can only be changed by increasing the difference between the reference source and the test source, which unavoidably lowers the Ra value." By this, the GLA presumably means spectral power distributions with spikes that enhance *perceived* color saturation -- in other words, a "color preference" metric. This is a necessarily ill-defined metric, as human preferences vary with the observed objects. (This issue is currently and presumably being addressed by CIE TC 1-91, "New Methods for Evaluating the Colour Quality of White-Light Sources.") Third , the GLA position statement reads, "Significant research effort over the past years on colour fidelity, however, has failed to deliver a single new meaningful metric for fidelity that can be used by the lighting industry and replace the existing Ra metric." After decades of research and over two dozen proposed color rendering metrics, it is difficult to accept this claim without supporting evidence. Fourth, the GLA position statement concludes with, "It is the view of the Global Lighting Association that in the near future an additional colour quality metric should be adopted that represents a significant and meaningful improvement in conjunction with the currently used fidelity metric Ra." What the GLA is saying is that while the CIE General Colour Rendering Index Ra has acknowledged shortcomings, it must remain as the industry standard. The only logical reason for this is that some major lamp manufacturers do not want to see their products possibly downgraded by another metric. (The same argument was presented by at least one major lamp manufacturer to the CIE TC 1.69 committee.) Finally, the GLA position statement makes no reference whatsoever to IES TM-30-15. While it was released five weeks after TM-30 was publicly released, there is no indication that the GLA was commenting specifically on these two new TM-30 metrics, Rf and Rg. (On the other hand, the article above was published two days before the GLA position statement was publicly released.)

Very interested in this seminar - which day is it on?

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