Colour rendering – there’s more to light than the CRI index

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June 6, 2016

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The Colour Rendering Index (CRI) has been a useful tool in the development of ways to measure the effectiveness of lighting but it has limitations.

In fact, there’s a new system pushing for global adoption called TM-30 developed by the Illuminating Engineering Society and uses a set of colour samples more closely representative of real-world objects compared to the pastel samples that CRI references.

While that adoption process progresses, it’s useful to know what CRI is and how it’s being used.

What is CRI?

CRI is the recognised standard for measuring how well a light renders colours underneath it.

Colour rendering is about how true to life an object’s colour appears under an artificial light source. A lamp which is good at rendering colours will show objects underneath it as if they were in daylight.

A lamp which is bad at rendering colours will make an object underneath it appear the wrong colour. For example, a green object can appear brown under a light with a low CRI score.

A light is given a score on the CRI index from 0 to 100. Anything below a score of 80 is below average for LED and will not render colours well.

A score of 80 to 85 is about average for LED and will render colour well. A score of 95+ is very good and colours underneath a lamp with this score will appear very similar to the colours under sunlight.

Why it is the CRI index useful?

The CRI index is really useful as an immediate indication of how well a lamp renders colours. The scale from 0 to 100 gives a very clear and definite answer. Any manufacturer can claim their lamps render colours well, but a score above 95 will prove as much.

On the other hand, a manufacturer who claims great colour rendering with a score of only 75 cannot support that claim.

CRI is also an industry standard measure so you can be confident that the claim is not being fabricated. You can therefore trust that the performance of the lamp will be faithful to the score.

Why is the CRI index limited?

The CRI index measures a broad range of all the different colours, but only one type of each colour. The CRI index focuses on pastel colours. That means it is possible that a lamp with a high CRI index score could perform disappointingly at rendering bold colours.

For the index, colours in the light spectrum are given numbers and have R at the beginning, for example. R1, R2, R7, etc.

The problem with the CRI index is that it only measures colours R1 through to R8, whereas there are colours beyond R8: R9 through to R14.

R9 to R14 are the same colour groups as those in R1 to R8, but the colours represented by R9 and above are much bolder, richer tones of that colour. R1 to R8 are pastel tones.

Manufacturers have an interest in getting the best possible score in the standard measures. This sometimes leads to manufacturers neglecting colour rendering at R9 and beyond because the majority of customers don’t understand the difference.

Soraa

Soraa have trail-blazed a movement to have superb colour rendering above and beyond the CRI index.

Their Vivid range delivers exceptional colour rendering in the R9 to R14 range and so bold colours are rendered beautifully underneath them. This makes Soraa the choice for numerous high-quality establishments. Jewellers in particular are very fond of Soraa.

The colour rendering of Soraa’s Vivid range, in addition to the several other advantages explained on our Soraa brand page, make them the market leader.

You can read more on the developing TM-30 index here.

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