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Lighting quality: The key to true colour


The lighting we use in our homes and workplaces plays a significant role not only in our visual comfort, but also in the way we perceive the world around us. The correct colour rendering of light sources is fundamental to the visual authenticity of our surroundings. So what is the difference between the two key light quality indicators: CRI (Colour Rendering Index) and Ra?

Colour Rendering Index (CRI)

CRI is a measure that determines the ability of a light source to reproduce colours faithfully when compared to natural daylight or a well-chosen artificial alternative. CRI values range from 1 to 100, where 100 indicates perfect colour reproduction, similar to that offered by a high-quality halogen bulb. A high CRI indicates that colours are reproduced naturally, which is crucial for visual comfort.

Measure of Perfection: How do we assess the quality of light?

To the human eye, the higher the CRI of a light source, the better and more naturally the colours are rendered. Emitters with a CRI above 90 are considered very good, values around 80 are good sources and below 70 indicate poor quality. CRI values below 70 are nowadays considered a low-quality product.

Quality of Colour Reproduction, or CRI

The main challenge for LED manufacturers, especially the cheaper ones, is to achieve a high quality of red reproduction. In order to achieve a high CRI, it is necessary to balance the spectral characteristics of the light source so that its emission is evenly distributed throughout the visible range, from violet to deep red. Optimal radiant power distribution (SPD) requires precise selection of the luminophore components, and the most challenging is the red component, which is the most expensive and difficult to convert efficiently.

CRI or Ra - Which better characterises the light source?

Although both refer to the colour rendering quality of light sources, there is a subtle difference between the two. CRI is calculated from a broad set of test colours, giving a more comprehensive picture of a source's ability to reproduce colours. Ra, the arithmetic average of CRI values for the eight primary test colours, is considered a more general measure.

The CRI therefore provides more detailed information, taking into account a larger number of colours, including the red colour (R9), which is critical for light quality. This makes a high CRI, especially with good red reproduction, preferable in applications where colour authenticity is crucial, such as art galleries and fashion shops.

Why CRI matters?

Understanding the differences between CRI and Ra and their impact on lighting quality is essential for making an informed choice of light source. A high CRI provides better visual quality and comfort, especially in areas where faithful colour reproduction is crucial. When choosing lighting for your home or workplace, it is therefore worth paying attention not only to parameters such as brightness or energy efficiency, but also to CRI to ensure the highest quality of visual perception.