Why R9 is important in high CRI value?

If we aim to determine the right light quality of your art-work, we may understand how important the high color rendering index (CRI) is. Color Rendering Index (CRI) is the value scale from 0 to 100 for evaluating how well a light renders colors of the objects. General CRI value (Ra) is a simple and direct parameter to help you imagine how realistic or accurate your objects’ color vision or your final footage will be under the lights.

Ra is the average value of R1-R8, other values from R9 to R15 are missing in Ra calculation, including R9 Saturated Red, R13 Skin Color (Light), and R15 Skin Color (Medium), which are all difficult colors to faithfully reproduce.
R9 is a vital index in high CRI lighting as many applications require red lights, such as film and video lighting, medical lighting, art lighting, etc. However, in general CRI (Ra) calculation, R9 is not included. Therefore, this value often forgets by customers.

What is R9 Color Rendering Value?

R9 is one of the numbers of Ri refers to Test Color Samples (TCS), which is one score in extended CRI. It is the number rates the light source’s color revealing ability towards TCS 09. And it describes the specific ability of light to accurately reproduce the red color of objects. Many lights manufacturers or retailers do not point out the score of R9 while it is a vital value to evaluate the color rendition performance for film and video lighting, as well as any applications that need high CRI value. So, generally, it is regarded as a supplement of color rendering index when evaluating a high CRI light source.

Ri is the value calculated according to each TCS spectrum. Likewise, R9 is calculated depends on the TCS 09 spectrum, which shown in the picture below.

What we can notice is that TCS 09 spectrum almost ranges from about 580nm. We regard it as red part in the spectrum. To put it simply, if the test lights do not have enough red light part, the red color of objects will be unnatural or inaccurate in your eyes or cameras.

For example, the spectrum in blue below compared to D50 standard light spectrum, it does not include much red part spectrum above 660nm. According to the test report, the CRI value of it is about 80, while its R9 scores at a minus value.

Why R9 is important for film, video and DSLR Lighting?

R9 value, TCS 09, or in other words, the red color is the key color for many lighting applications, such as film and video lighting, textile printing, image printing, skin tone, medical lighting, and so on.

Besides, many other objects which are not in red color, but actually consists of different colors including red color. For instance, the skin tone is impacted by the blood under the skin, which means the skin tone also includes red color although it looks much like close to white or light yellow. So, if the R9 value is not good enough, the skin tone under this light will be more paleness or even greenish in your eyes or cameras.

This will be a big issue for film making and medical operation. So, when searching for high CRI lights, please do not forget R9 index.

Skin tones accurate color is a crucial factor need to be considered carefully in the footage. The blood or the hemoglobin in our blood is one of the determinants of skin tones color. The blood reflectance spectrum is as the picture below.

Resource: http://wtamu.edu/~cbaird/sq/2015/07/16/is-human-blood-ever-any-color-other-than-red/
TCS 09 (The spectrum determines R9 color rendering value)

Compare blood reflectance spectrum and TCS 09 spectrum, we can see that they are fairly similar. Therefore, if R9 value is low, the light is not able to reveal the natural color of skin tones. It would probably result in odd hues of skin tones in cameras.

What is good R9 color rendering value?

Although we know R9 is important, while it is difficult to achieve a high score to maximum.

The Department of Energy (ENERGY STAR) has regulated a standard of Ra ≥ 80 and R9 > 0.

In this regulation, the R9 value is poor.

The California Energy Commission defined Ra ≥ 90 and R9 > 50, in which the R9 value is acceptable “Medium”

NHK Science & Technology Research Laboratories and Panasonic Corporation recommend Ra ≥ 90 and R9 ≥ 80 for white LED Lighting. The R9 value is good enough.

For MM’s High CRI Lighting products, we announce that the R9 value of our lights is mostly above 90, with a guarantee of R9 ≥ 80.