The Color Rendering Index (CRI) is a scale from 0 to 100 that measures how accurately a light source renders colors compared to natural daylight. While CRI provides a general assessment, it doesn't fully capture the accuracy of rendering certain colors, particularly saturated reds. This is where R9 comes into play.
 
R9 is a specific component of the CRI system that measures how well a light source renders saturated red colors. It is part of the extended CRI scale, which includes values R1 to R15, each representing the rendering ability of a particular color sample. R9 corresponds to the test color sample TCS09, which is a strong red hue. Unlike the general CRI, which averages the scores of R1 to R8, R9 is not included in the CRI calculation but is crucial for applications requiring accurate red color reproduction.


High R9 values indicate that a light source can accurately reproduce vibrant red colors, which is essential in various settings:
 
Healthcare: Accurate red rendering is vital for assessing skin tones and blood flow.
Retail: Enhances the appearance of red products, making them more appealing to customers.
Art and Photography: Ensures that artworks and photographs are displayed with true-to-life colors.
Food Industry: Improves the visual appeal of red foods, influencing consumer perception.
 
In these applications, a high R9 value is often more critical than a high general CRI, as it directly impacts the accuracy of red color reproduction. The significance of R9 values varies depending on the application. In residential lighting an R9 value of 25 is generally considered acceptable. In retail and art displays, an R9 value above 75 is often required to ensure vibrant and accurate red colors. Within the area of healthcare and photography ann R9 value close to 100 is ideal for precise color rendering.
 
To achieve high R9 values, manufacturers can use phosphor-conversion techniques and advanced LED chip technologies. Selecting LEDs with high R9 values ensures that red colors are rendered accurately, enhancing the overall color quality of the lighting.
 
When selecting LED lighting for applications where accurate red color rendering is essential, it has to be ensured that the LED product specifies its R9 value. By considering R9 values alongside general CRI, it is possible to select LED lighting that meets the specific color rendering requirements of lighting applications.