Color Rendering Index in Lighting

Home / Blog / Color Rendering Index in Lighting
Color Rendering Index in Lighting - Light falling on orange wall
Photo by marra on Unsplash


Hi, and welcome to this blog about CRI, or Color Rendering Index in lighting.

Firstly let’s think a little about color. When I say green what shade or green do you think of. Probably a different one from me. So how do we define what is the color we are talking about.

Moreover, unless we are staring into the sun all light is reflected. In general from non-white surfaces. And that is how we see color. One exception is rainbows where the light we see is refracted rather then reflected.

Measuring Color Reflection

In order to measure the quality of the color we see the CIE (Commission Internationale de l’Eclairage or International Commission on Illumination) developed a test. And that test is the Color Rendering Index.

In brief it works by taking an artificial light. In this case an LED light bulb. And shining it on eight different color swatches. The the frequency of the light reflected is measured and compared to what is reflected by natural sunlight.

So, a score of 100 CRI would be exactly like sunlight and 80 CRI would be mostly like sunlight, but with a 20% difference. The CRI is the average score across all eight different color swatches.

Eight pastels used in CRI
Color Swathes used in the CRI testing

R9 – Red

If you look at the eight color swatches used in the CRI test you may notice something. To point out, none of the swatches is red. Lots of greens and blues and purples, but no reds. Additionally a lot of light sources do not produce much red light. So taken together this can mean that a light source has a high CRI but is very poor at reproducing reds.

In order to combat this possible issue there is an additional test, the R9 test. Similar to the CRI test it checks the reflection of light from a color swatch. In this case a red swatch. So this is the ninth color watch, which is where the name comes from.

Why is Color Rendering Index in Lighting Important

There are many reasons we want accurate colors produced under artificial light. Firstly, if you have decorated your house in bold or bright colors, you want these to look good not just in the daytime, So a high color rendering index in your lighting choice is important.

Secondly your furniture, particularly upholstery will look more natural under lighting with a high CRI. Also, it is particularly important for painting where the color is a key factor.

Finally if you ever take an indoor photo and use artificial light. Photography is particularly sensitive to color reproduction, and red is a key component of many skin tones.

High CRI LED Light Bulbs

If you are interested in LED light bulbs that have a high CRI rating then we review seven on the best ones here.


National Institute of Standards and Technology – Color Rendering Light Sources

LED Lights: What is CRI and Does it Matter?