Why should we stop using CRI and TLCI ratings in LED lighting and adopt the SSI rating in advanced cinematography?

As directors of photography and cinematographers, we always take special care of the nature and quality of the lighting that we use in our work, given our awareness of the importance of the quality of lighting and its impact on the quality of our work. Given this, we give great importance, when we purchase or use a certain type of lighting, to the values ​​of both CRI and TLCI classifications and to ensure that there are high values ​​in that lighting. But there are important problems related to these classifications, and with these problems, some lighting manufacturing companies resort to using the confusion surrounding these classifications to promote their goods in an incorrect and misleading manner, so in today’s article, we will talk in detail and technically about the differences between these classifications, the problems behind them, and why they cannot be adopted in the field of cinema in our current era, and we will learn about a new evaluation that was approved by experts in lighting and cinema worldwide. This article was built based on a study Scientific collaboration between the Academy of Motion Picture Arts and Sciences (Oscar.org) and the International Federation of Cinematographers. Well, let us begin by answering the first question: What is the CRI classification? The CRI (color rendering index) classification, or color rendering index for a specific set of colors, is a mechanism to measure the quality of light according to what our eyes as humans see. When we see a color, that color is light rays reflected from the surface of an object. Objects in our world have their own color, so they absorb or reflect light rays according to their color. Water, for example, absorbs long-wave light rays more than short-wave light rays.

Therefore, the red part of sunlight is absorbed after several meters under water, and then orange, yellow, and green, while the blue color is reflected from the surface of the water, and that is why we see the sea as a blue color. So the color spectrum is the result of the reflection and absorption of different parts of sunlight, so when we see color, we see the reflected part of the light from the body that is present to the human eye only. We see this term in all lighting, and it is usually accompanied by a number to represent the quality scale, where 0 is the lowest value and 100 is the highest. These numbers are called Ra. The CRI scale shows us how well any given light source shows the colors of a surface as they are compared to daylight (sun), which contains the full color spectrum with optimal representation quality. Most lighting production companies compete by providing lighting with high CRI values ​​of up to between 96 and 98 RA, which is always mentioned when introducing a new lighting product to the market and promoting through the CRI value of that light. We spoke briefly about the CRI classification in a detailed article that was previously published in 2019. You can access it from here. Where is the problem with the CRI classification?

This type of classification is used with lighting used in clothing and jewelry stores, etc., as this classification depends primarily on the human eye and the way it deals and reads the colors resulting from that light. Therefore, adopting this classification in the field of filmmaking is illogical, since the classification takes into account the human eye as a mechanism for reading colors and not modern electronic cameras, and here lies the basic problem. The most important problem is that this classification deals with a specific group of colors only, not the entire color space. It deals with measuring eight colors only, to determine whether the quality of light is sufficient or not. The color meter, or what we call the Color meter/Spectormeter, measures each of the six colors separately, with a value represented by one RA. Then it collects all those values and extracts the standard rate for their sum, which is supposed to simulate the white color. Then the apparent value from this rate is what determines the quality of light, of course. Later, scientists realized that it is not enough. To determine the quality of the measured light, we collected 8 samples to extract the average color rendering scale. Therefore, a wider range of colors was produced, including 7 new colors to ensure the collection of more samples and to ensure the availability of most colors in the testing phase. The most important of these colors was an increase of two colors over the colors that represent the skin, red and blue, so the color group was as follows: Here there was a need to create a new one instead of Ra for the measured number and replace it with Re to clarify that this number is issued by a measurement of the expanded color group, so a problem began to appear. It is a low quality rate, due to the large number of colors being tested. Not all of these new colors are produced with acceptable quality, which creates problems in reading some colors such as blue R12, red R9, and colors that mimic skin color, which are symbolized by R13 and R14. Here lies the problem of relying on the CRI scale and the extended CRI scale. The first problem here, which is a very serious problem, is that some companies that produce LED lighting show the CRI value for the first eight colors only, which means that the color rendering number will be high, misleading the buyer that the lighting is good enough, without the companies talking about the total of 14 colors.

The second problem if we adopt the CRI color rendering scale in our use of lighting is that if we use two different types of lighting with the same CRI value, each of the two lights may produce different colors because we have ignored the rest of the colors on the expanded scale, especially the colors we talked about: blue R12, red R9, and the colors that mimic skin color, which are symbolized by R13 and R14, green R13, and light green R11, which affect our lighting. For chroma. Let us also remember what we mentioned at the beginning of the article about talking about relying on the human eye as a viewing tool, not cameras, and here also lies a big problem, as our eyes can correct some color errors and differences automatically, which the cameras we deal with today cannot do.

What about TLCI classification?

The TV Lighting Consistency Index (TLCI) is considered a development of the CRI classification, as it samples 18 colors from the light spectrum. The colors are followed by six graduated colors between white and black with medium gray in the middle. We can find all of these colors in the Color Checker card as shown in the figure below: This classification is considered more reliable in analyzing how the color display is performed in the sensors of television broadcast cameras, which use an imaging system known as: three-CCD (3CCD), which depends on separating light into three channels: red, Blue, green, then combining them together again to form the television image, so this classification is used when talking about television broadcasting in the days when there were three-CCD cameras.  

(3CCD) is used for broadcasting. In lighting, which is the most important point in our conversation, the TLCI rating is measured from 0 to 100, but if we measure a certain light and the result is 99, this does not necessarily mean that this light is good from a practical standpoint, which is the biggest problem with this rating. Notice the test that filmmaker Sherif Mokbel did on his channel The DP Journey, in which he showed how the NANLITE 300B lighting beat the ARRI Orbiter lighting in the TLCI scale, but in In fact, the lighting of the ARRI Orbiter is considered much better compared to the NANLITE 300B, due to its ability to produce more colors, according to what is shown in the table below: Not to mention that, as we mentioned above, this classification is a classification intended for television broadcast cameras that are based on shooting in the color space appropriate for the television, Rec709, while cinema cameras today shoot in color spaces much wider than Rec709, which confirms the necessity of paying attention to the extent to which light produces colors properly. Enough to cover the color space. The SSI classification approved by the Academy of Motion Picture Arts and Sciences (Oscar), according to the study presented by the General Academy of Motion Picture Arts in a recently published technical article, and the article published by the International Federation of Cinematographers, we must adopt natural sunlight and tungsten lighting, and study the quality of the colors they produce over the entire color space, then compare that result with the result that the LED light will give us. This comparison is called a classification: SSI: SPECTRAL SIMILARITY INDEX The scientific paper presented within the study mentioned above (which is a set of scientifically detailed files that you can access from here), the study stipulates that there are two values that must be considered: The first value is the value that measures the illumination of tungsten. If the value is 80, the illumination is considered acceptable, while an illumination value of 90 is considered very excellent, and what is in between, then the illumination is considered good.

The second value is the daylight value. If the value is 75, the lighting is considered acceptable, while a lighting value of 80 is considered good lighting, and from a value of 80 to 90, the lighting is considered very excellent and may be rare. How can I check all of this? The above values ​​can be verified by a Sekonic spectromaster, manually checking the lighting and comparing the lighting kit to each other, especially when renting a lighting kit. You can also check with the manufacturer if they have declared the actual value of the lighting they produce.

What problem do we face in the lighting market? One of the most important problems that we suffer from when talking about the above classification is that manufacturers sometimes refrain from mentioning this classification, and even deliberately show the values ​​of the CRI and TLCI classifications that we talked about at the beginning of the article to mislead the buyer into thinking that the lighting is excellent. Days after the publication of Oscar.org and the International Federation of Cinematographers' research paper, some lighting manufacturers have begun to talk about the terminology and highlight it to buyers, such as Aputuer and IFOOTAGE, and it appears that more companies are about to talk more and more about this classification.

But we must pay careful attention to this classification, whether when we purchase lighting or when carefully calibrating the lighting we are working on. I would like to remind you that if you find any questions, you can also send your inquiries by clicking on  Contact Us, and you can also follow us through our account at 

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