Colour Rendering Index (a.k.a. CRI or Ra) is a lighting metric that is often forgotten about, assumed or frankly deceiving. It is a numerical measure of a light sources ability to accurately represent, or render colours, with reference as to how they would appear under the sun.
In basic terms, this means that a low CRI light source can make colours appear different from how they were intended, and as a result of this, they can look flat and dull. On the other hand, High CRI light sources can represent colours much truer to how they were intended, but ( and there is always a but), this technology can sometimes come at a premium or traded off against luminaire efficiency.
Why is CRI important?
As designers, we want our spaces to feel natural, to feel familiar. Luminaires with a poor Colour Rendering Index can make our spaces disorientating, even down to how we see each other! A low CRI can make spaces feel dull, and make people look unhealthy with very washed-out skin tones. And why do we allow an interior designer to make bold choices with texture, pattern and colour if the lighting will undo all of this hard work?
CRI is especially important in colour-critical & human-centric applications. Think clothes shops, fruit and veg shops or meat counters (a dull steak isn’t very appealing!) Think retail and showrooms all the way to restaurants, offices and meeting rooms.
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What do we cover in the full version?
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Why do we reference the sun?
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But LEDs look pretty good, right?
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So how do we really know if our luminaire has a good CRI?
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CRI CASE STUDY: EAGLE HOUSE, Bristol
CRI Top Tips
- Look at the R9 (Saturated Red) value – if reds are important in your project, make sure this is high
- Re (extended CRI value) will give you a much better idea of how the LED will perform over Ra (which just tests the first 8 colours)
- Look for specialist LEDs for your application – some luminaires can be specified with specially engineered chips to light specific items, for example, denim, meat, cheese etc.