New colour rendering method spells end for CRI
An article in Lux review looking at an alternative way to meaasure colour rendering. Published on 16th September 2015.
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Improved colour rendering from LED
Continued developments in LED technology and new testing standards are putting more emphasis on how good or otherwise LED is at rendering colour. To be clear, we’re not talking here about how warm or cool any given light is. Colour rendering looks at how accurately a light source shows different colours and is typically measured on a CRI scale of 0-100.
Colour rendering measures the accuracy with which colours are shown across the spectrum. LEDs have a tough time rendering reds like the tomatoes in the banner for this page. A blue LED treated with phosphor sits at the heart of most white LED light sources. As a consequence LEDs have rendered blue better and struggled more with reds. That’s in contrast with incandescent sources like halogen that render colour across the spectrum effortlessly. This uneven rendering of colour might not be particularly noticeable to the naked eye (though it can be very evident with poor quality LEDs) However there are applications where you might want the best colour rendering you can get and the good news is LED is improving in this area.
Why is good colour rendering important?
Think about the applications where you want the best rendition of a colour. Makeup lighting really needs accurate colour rendering and there is a lot of red in the colour of human skin even before you’ve considered the cosmetics. So as well as good shadow-free lighting, you should have accurate colour rendering on your wishlist.
Food preparation is another area where good colour rendering is important. We want our tomatoes to look like tomatoes not olives so if you’re considering kitchen lighting take heed of the Colour Rendering Index (CRI).
A higher CRI figure is one indication of superior colour rendering. A fitting with a CRI of 95 is going to have a better average rendition of the sample colours that go into the CRI standard than one with a CRI of 85. We’re using downlights with higher CRI in bathrooms and kitchens as well as in commercial applications like restaurants and we’ve a range of LED fittings with a 95 CRI option available here.
CRI is an accepted and useful standard but it’s not without its critics.
Not least because the standard eight colours sampled in the CRI average don’t include a saturated red which can be measured as a separate standard. It’s possible we’ll see an alternative measurement supplement and potentially replace CRI in the future. There is momentum behind a testing system TM-30-15 which samples a wider range of colours said to be more representative of the colours we see in everyday life.
If you’re interested in learning more have a look at the Lux article here on TM-30-15 here which is a good and not overly techy introduction.
Standards are useful but we find it useful to supplement the bare figures with physical testing against specific finishes or materials. We’ve tested against brick, marble, different granites, artwork and even strawberry tarts. After all, if you’re lighting the cakes in one Yorkshire’s iconic tea rooms, you don’t want your raspberries to look like kumquats.
The great news for buyers is that choosing LED now doesn’t mean abandoning good colour rendering. Like so much about LED lighting, it’s more complicated than the light sources it replaces. However with careful design and specification it’s possible to experience both great colour and all the efficiency and lifespan benefits that makes LED so attractive.
