Colour Rendering – Explained

Colour rendition is a crucial but often misunderstood aspect of any lighting installation. There are a few methods of measuring colour rendering, including TM-30, the Colour Quality Scale (CQS) and others, but this article will focus on the Colour Rendering Index (CRI) as this venerable system is still by far the most commonly used.

What is colour rendering?

Put simply, colour rendering is a measure of how accurate the colour of objects illuminated appears to be, when compared to a reference source. Things illuminated with a high CRI light source can be expected to look very similar to how they would in daylight, for example.
What colour rendering doesn’t do is tell you anything about the colour of a light source; that’s instead determined by the colour temperature (CCT). It also doesn’t tell you the range of colours that can be seen under the light source- something known as the gamut area.

How does CRI work?

CRI is based on a set of eight test colours, which are distributed evenly across the range of visible colours. The colour rendering of each of these test colours is determined against a reference source (an incandescent lamp). A blackbody radiator (considered a perfect colour rendering source) will have a CRI of 100; as such, incandescent lamps and sunlight are CRI 100.

The more that a light source diverges in terms of colour rendition, the lower the CRI will be. Below are a few examples of typical/approximate CRI values for different lamp types:

Low Pressure Sodium:         <0 CRI

High Pressure Sodium:        20-25 CRI

Mercury:                                 50 CRI

Fluorescent:                           50-90 CRI

Metal Halide:                         80-85 CRI

LED:                                        65-95 CRI

Incandescent:                        100 CRI

Sunlight:                                100 CRI

Why is this important?

Why does colour rendering matter? There are numerous reasons; in the workplace it contributes to perception of detail, and creates a more comfortable environment to work in. In retail, it increases the perception of quality of your product. Additionally there are government schemes that help you to buy LED lighting for your business, which require certain CRI levels to be achieved. At Pulsar we can make lights at up to 95 CRI using some of the best colour rendering LEDs available, and our team can advise you on the best solution for your project.


Article by Hallam Smith.