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New colour rendering method spells end for CRI

The TM-30 method measures how LEDs render colours better than the traditional CRI technique

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

– 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 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.