Is Higher CRI Always Better?

In our previous article, we explored Spectral Power Distribution (SPD) and explained that every LED has its own spectral composition. The spectrum determines which wavelengths are present in the light and ultimately how objects appear when illuminated.

This naturally raises another important question.
If the spectrum influences colour appearance, how do we measure the quality of that light?
The most widely recognised metric is the Colour Rendering Index (CRI). It is often treated as the benchmark for light quality, and many specifications simply state CRI >90 or CRI >95 without further explanation.

But does a higher CRI always mean better lighting?
The answer is no.

What is CRI?

The Colour Rendering Index evaluates how accurately a light source reproduces colours compared with a reference source of the same correlated colour temperature. The result is expressed as an average score on a scale from 0 to 100, where higher values indicate better colour fidelity. A light source with a CRI of 90 will generally reproduce colours more faithfully than one with a CRI of 80.
For many applications, this single value provides a useful first indication of colour quality.

However, CRI has an important limitation. It reduces a complex characteristic of light to one average number.

What CRI does not tell you

The commonly quoted CRI value, known as Ra, is calculated using eight relatively unsaturated test colours.
These samples provide a broad indication of general colour fidelity, but they do not represent the full range of colours found in real environments.
Strong reds, skin tones, artwork, fabrics, food and natural materials can all respond differently to the same light source.
As a result, two LEDs with exactly the same CRI 90 can still produce noticeably different visual results.
One may render red objects with exceptional richness, while another makes them appear flatter and less vibrant. Yet both satisfy the same CRI specification.
This is because CRI evaluates the visual result using a limited set of samples. It does not describe the complete spectral composition that produces that result.

Is higher CRI always better?

Not necessarily. The appropriate CRI depends on the application and the visual objective.

For offices, schools and general commercial spaces, CRI 80 is often sufficient. A higher CRI can improve colour fidelity, but it may also reduce luminous efficacy and increase cost.
In museums, galleries and healthcare environments, where accurate colour differentiation is more important, CRI 90 or above is often preferred.
Retail lighting presents a different challenge. The objective is not always perfect colour fidelity. In many cases, the aim is to present products in the most attractive and natural way.
A bakery may benefit from a spectrum that strengthens warm golden and brown tones. Jewellery lighting may aim to improve brilliance and sparkle. Fresh meat can appear more appealing under a spectrum with stronger deep-red wavelengths.

In these applications, the most suitable light source is not necessarily the one with the highest CRI. It is the one with the right Spectral Power Distribution for the intended purpose.

Looking beyond CRI

As LED technology has developed, lighting professionals have recognised that one average value cannot fully describe colour quality. Additional metrics are therefore used to provide a more complete assessment.

R9 evaluates the rendering of a saturated red test colour. It is particularly relevant for skin tones, food, textiles, artwork and other applications where red colour rendering is important.

TM-30 provides a broader analysis of colour fidelity and saturation across a much larger set of colour samples. It can show not only whether colours are reproduced accurately, but also whether specific colour regions become more or less saturated.

These metrics reveal differences that CRI alone cannot show.

Colour quality begins with the spectrum

Ultimately, colour rendering begins with the Spectral Power Distribution of the light source.

The spectrum determines which wavelengths are available to be reflected by objects. Colour-rendering metrics such as CRI and TM-30 evaluate the visual result produced by that spectrum.

Professional lighting design therefore requires looking beyond a single number.

• CCT describes how warm or cool the light appears.
• Δuv describes its subtle tint relative to the Planckian Locus.
• SPD describes the wavelengths that create the light.
• CRI and TM-30 evaluate how that light affects colour appearance.

Together, these parameters provide a more complete understanding of light than the Kelvin value or CRI alone.

At Light4U BV, we believe that selecting the right light source requires understanding the complete picture. By considering colour temperature, spectral distribution and colour rendering together, lighting designers and engineers can choose the light that best supports the intended application.