What is Ra or CRI in LED lighting?

Ra, also called CRI, says how natural colours look under a lamp. The scale runs to 100, and daylight is the yardstick. Above Ra 80 is fine for most rooms; above Ra 90 you see the difference on skin, wood and food.

How the number is arrived at

The method is set out in CIE 13.3. Fourteen test colours are placed under the lamp and compared with the same colours under a reference source of the same colour temperature. The smaller the shift, the higher the score.

An important detail: the number you see on the packaging is the average of only the first eight, and those are all soft pastel shades. The other six do not count.

The gap in the measurement is called R9

R9 is saturated red, and it is not in the average. Two lamps can both score Ra 90 while one renders red properly and the other makes it look grey.

You notice that exactly where it counts: meat in a kitchen, skin tones in a bathroom mirror, a wooden floor or a red sofa in the living room. If you are wondering why your new lighting makes everything look slightly washed out while the Ra figure is good, R9 is usually the cause.

The trade therefore increasingly works with TM-30, which uses 99 colours and gives two numbers: Rf for fidelity and Rg for saturation. That is more precise, but you rarely see it on consumer packaging.

What you actually need

The European Ecodesign requirements keep light sources at Ra 80 minimum. So everything you can legally buy is already at that level, and that settles a hallway, a store room or a garage.

Above Ra 90 it gets interesting in rooms where you look at things rather than just walk through:

• Kitchen, because colour tells you whether something is cooked or fresh
• Bathroom, because you judge yourself in the mirror
• Living room, because wood, textiles and art otherwise look flat
• Workspace where colour matters, from paint to sewing

What we carry

We list the Ra figure per product, and the differences are big enough to choose on. At the top: the Lesto 5W in chrome at more than Ra 97, the Vigo and the Cavo in silver at more than Ra 95.

Below that sits a middle group around Ra 90 to 93, including the Lesto, the Marlo and the Quaro. And there is a group at Ra 80, such as the Movo and the Lyvo, which works excellently where colour is not decisive.

The trade-off you are making

High colour rendering costs light output. To render red better you need more red in the spectrum, and that comes at the expense of lumens per watt. You see that in our range: every spot with energy label G sits at Ra 90 or higher, while the F group mostly sits at Ra 80 to 84. The Quaro is the exception that combines both.

So it is not a fault but a choice. In a living room or kitchen that choice is easy, because you sit under it all evening. In a crawl space it is not.

Also take care not to mix within one room. Two spots with the same colour temperature but different Ra figures give a visibly different feel side by side. More on that interplay in What is the difference between kelvin and lumens? The range is at recessed spotlights.