Color rendering in LED lighting
When it comes to lighting, we often look first at light color (Kelvin) and light output (lumens). Yet another factor largely determines how pleasant and realistic a room is perceived: the color rendering of the light source.
Natural
Color rendering determines how faithfully colors are rendered under a given lamp. This may seem like a detail, but the difference can be significant. Products, materials and skin tones can appear vibrant and natural under one light source, while they may appear dull or unnatural under another. In applications such as retail, hospitality, museums and healthcare environments, this plays an important role.
What is the Color Rendering Index (CRI)?
The most commonly used measure of color rendering is the Color Rendering Index, commonly abbreviated as CRI or Ra. This index compares how colors look under a light source compared to a reference source, such as daylight or a traditional incandescent lamp. The value ranges from 0 to 100. The higher the value, the more faithfully colors are rendered. The CRI is calculated on the basis of eight reference colors (R1 to R8). These are relatively soft pastel colors. The average of these colors forms the well-known Ra value.
What do CRI values mean in practice?
|
CRI |
Color rendering |
Application |
|---|---|---|
|
90 – 100 |
Very true to nature |
Retail, hospitality, museums |
|
80 – 90 |
Good color rendering |
Offices, schools |
|
< 80 |
Limited color reproduction |
Industry, technical lighting |
CRI does not tell the whole story
Although CRI gives a good indication of color quality, the Ra value does not tell everything. This is because the index is based on only eight relatively soft colors. In addition to these first eight test colors, additional reference colors exist: R9 through R15. These are more saturated colors. Especially R9, which stands for saturated red, is important for how we experience light.
Why R9 is important
A high R9 value ensures that red tones are faithfully reproduced. This is important for skin tones, meat and fresh produce, clothing and textiles, and wood materials, among other things. So a light source can have a CRI of 90 but a low R9, which means that red tones are still less well rendered.
* A comparison between a spotlight with CRI 80 and a spotlight with CRI 98 (the value of our spots with the best color rendering).
Other ways to measure color rendering
In addition to CRI, there are other methods for assessing the quality of light.
Gamut Area Index (GAI)
The Gamut Area Index looks primarily at the saturation of colors. A higher GAI means that colors are often rendered more vividly or powerfully.
Color Quality Scale (CQS)
The Color Quality Scale was developed as a more comprehensive method for assessing color reproduction. This method uses fifteen color samples and also takes into account how the human eye perceives colors.
TM-30
The TM-30 method is increasingly being used in the lighting world. This involves analyzing as many as 99 color samples. This method gives two important values:
- Rf – color fidelity
- Rg – color saturation
This provides a much more complete picture of the quality of a light source.
Color rendering in retail lighting
In retail environments, color rendering plays a major role in the presentation of products. Fabrics, materials and colors should be displayed as naturally as possible. A light source with a high CRI and a strong R9 value ensures that products retain their true color. This makes the presentation more attractive and helps customers judge colors better. This is why light sources with a CRI of at least 90 are often chosen in retail lighting.
Ultimately, everything revolves around the light spectrum
The quality of color reproduction is ultimately determined by the spectral distribution of light. This describes how different wavelengths in light are distributed. The more balanced this spectrum is, the better colors are rendered in a room. Thanks to modern LED technology, manufacturers are increasingly able to control the light spectrum. As a result, high-quality LED luminaires today can achieve color quality comparable to, and sometimes even better than, traditional light sources.