What is CRI R9 and why is it significant?

CRI R9 is a test color sample (TCS) utilized in the computation of extended CRI. Numerous manufacturers will solely disclose the general CRI, omitting the CRI R9 value. CRI R9 is frequently a valuable supplementary metric for evaluating a light source's color rendering capability, particularly regarding objects with reflectance spectra that include red wavelengths.
An in-depth examination of the calculation of R9, together with its associated test color sample (TCS9), is frequently advised for individuals seeking to understand the color quality of a light source.

What is the CRI R9 value?

R9 is the metric that indicates the fidelity of a light source in reproducing vibrant red hues.
"Accurate" is characterized as resembling daylight or incandescent bulbs, contingent upon the color temperature.
The R9 value is determined by calculating the reflected color from a theoretical object characterized by the reflectance profile designated as TCS9, similar to the calculations for each of the CRI R values.
The TCS9 spectrum is predominantly comprised of red light. In terms of spectrum, we observe this as wavelengths exceeding 600 nm.
This indicates that insufficient red light in the light source will cause red hues to appear distorted or altered.
The LED exhibits a significant deficiency of red light emission at wavelengths over 600 nm.
The CRI R9 rating for this LED is -1.4. (Indeed, a negative integer!) This occurs despite the general CRI (Ra) being 79.
 

What is the significance of CRI R9?

CRI R9 is a crucial statistic, as numerous light sources may exhibit deficiencies in red content, a fact obscured by the averaging of CRI estimates that exclude R9.
In the context of the broader CRI Ra criteria, an LED exhibiting subpar red color reproduction may still get an 80 CRI (Ra) grade.
An examination of the R9 value, however, indicates that the light will exhibit subpar performance for red hues specifically.

 

What constitutes an acceptable CRI R9 value?

While the maximum attainable value of R9 is also 100, it should be evaluated somewhat differently than average CRI values.
Mathematically, R9 presents significantly greater difficulty in attaining a high score relative to the other R values used in the CRI computations and exhibits heightened sensitivity to spectrum fluctuations. An R9 score of 50 or higher is deemed "good," whereas a R9 score of 90 or more is regarded as "excellent."
Consequently, you will see that the majority of lighting products on the market hardly state the R9 value, and when they do, they rarely assure a value over 50. We stipulate R9 > 80 or R9 > 90, and cannot assure any value exceeding R9 > 95 due to this sensitivity.
This occurs because CRI use the CIE 1960 uv color space, which is distorted to amplify color disparities in the red section of the chromaticity diagram. As CRI evaluates the color discrepancies between a light source and a reference source, a greater estimated color discrepancy will lead to a more significant reduction in the R score.

 

What makes red a significant color?

Red is an essential hue for various uses, including photography, textiles, and the representation of human skin tones.
Numerous things that do not exhibit a red hue are, in fact, a composite of various colors, including red. Skin tones are significantly impacted by the underlying redness of the blood beneath the skin.
Consequently, light devoid of red will render an individual appearing pale or even greenish. This may provide challenges for medical applications where color perception is essential for precise diagnoses. In fields like photography, aesthetic quality is paramount and often cannot be rectified during post-production or digital editing.

When seeking a high color quality LED, ensure to question about the CRI and its R9 value.