Lighting accuracy is critical in today’s residential, commercial and industrial markets. This is measured and quantified using the Color Rendering Index (CRI), which is the industry standard for measuring a particular light’s accuracy. CRI runs on a scale going up to 100, which is the CRI of a black body radiator reference light. This reference light is either an incandescent type artificial light or natural sunlight, which are the most accurate light sources available. It is worth noting that CRI is independent of Correlated Color Temperature (CCT), a term often used in conjunction with CRI when describing the properties of light. CCT measures the actual color of the light produced in Kelvins and does not have anything to do with the light’s illumination accuracy.

What is the Color Rendering Index (CRI)?

A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in color-critical applications such as neonatal care and art restoration. It is defined by the International Commission on Illumination (CIE) as follows:

Color rendering: Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference or standard illuminant.

The CRI of a light source does not indicate the apparent color of the light source; that information is given by the correlated color temperature (CCT). The CRI is determined by the light source’s spectrum. An incandescent lamp has a continuous spectrum; a fluorescent lamp has a discrete line spectrum, implying that the incandescent lamp has a higher CRI.

The value often quoted as “CRI” on commercially available lighting products is appropriately called the CIE Ra value, “CRI” being a general term and CIE Ra being the international standard color rendering index.

Numerically, the highest possible CIE Ra value is 100 and would only be given to a source whose spectrum is identical to the spectrum of daylight, very close to that of a black body (incandescent lamps are effectively black bodies), dropping to negative values for some light sources. Low-pressure sodium lighting has a negative CRI; fluorescent lights range from about 50 for the basic types, up to about 98 for the best multi-phosphor type. Typical white-color LEDs have a CRI of 80, 90, or more.

Spectral Power Distribution

The visible part of the electromagnetic spectrum is composed of radiation with wavelengths from approximately 400 to 750 nanometers. The blue part of the visible spectrum is the shorter wavelength, and the red part is the longer wavelength with all color gradations in between.

Spectral power distribution graphs show the relative power of wavelengths across the visible spectrum for a given light source. These graphs also reveal the ability of a light source to render all or selected colors.

Below see how a typical spectral power distribution graph for daylight.

Notice the strong presence (high relative power) of ALL wavelengths (or the “full-color spectrum”). Daylight provides the highest level of color rendering across the spectrum.

Compare the daylight spectral power distribution with that of a LED light.

The most obvious difference is the generally lower level of relative power compared to daylight – except for a few spikes. All wavelengths (the full spectrum) are again present but only certain wavelengths (the spikes) are strongly present. These spikes indicate which parts of the color spectrum will be emphasized in the rendering of color for objects illuminated by the light source. This lamp has a 2700K color temperature and a CRI of 82. It produces a light that is perceived as “warmer” than daylight (2700K vs. 5000K). Its ability to render color across the spectrum is not bad, but certainly much worse than daylight.

How does color works?

Light sources can be divided into either artificial or natural light sources. In most situations, we are concerned about the color quality of artificial forms of lighting, such as LED and fluorescent lamps. This is compared to daylight or sunlight – a natural light source.

Natural light, such as sunlight, combines all the colors of the visible spectrum. The color of sunlight itself is white, but the colors determine the color of an object under the sun that it reflects.

A red apple, for example, appears red because it absorbs all colors of the spectrum except red, which it reflects.

When we use an artificial light source such as an LED lamp, we attempt to “reproduce” the colors of natural daylight such that objects appear the same as they do under natural sunlight.

Sometimes, the reproduced color will appear quite similar, other times quite different. It is this similarity that CRI measures.

Our example above shows that our artificial light source (an LED lamp with 5000K CCT) does not reproduce the same redness in a red apple as natural daylight (also 5000K CCT).

But notice that the LED lamp and natural daylight have the same 5000K color. This means that the color of light is the same, but the objects still appear different. How could this be?

If you look at our graphic above, you will see that our LED lamp has a different spectral composition than natural daylight, even though it is the same 5000K white color.

In particular, our LED lamp is lacking in red. When this light bounces off the red apple, there is no red light to reflect.

As a result, the red apple no longer has the same vibrant red appearance that it had under natural daylight.

CRI attempts to characterize this phenomenon by measuring the general accuracy of various objects’ colors when illuminated under a light source.

CRI is invisible until you shine it on an object

As mentioned above, the same light color can have a different spectral composition.
Therefore, you cannot judge a light source’s CRI by simply looking at the color of the light. It will only become evident when you shine the light onto various objects with different colors.

How is CRI measured?

CRI is measured using the industry standard method developed by the CIE. This involves the comparison of a test source’s color rendering to a reference source known as a black body radiator with a perfect CRI score of 100. For this testing, there are fifteen primary reference samples used to calculate the general CRI rating. The sample selected for the reference source is dependent on the color temperature of the light being tested. The ColorChecker chart, established by CIE (1999), categorizes these reference sources and organizes them numerically starting with TCS01 and ending with TCS15. The closer the source being tested matches with the perfect reference source, the higher it will rank in CRI.

We compare the reflected colors and formulaically determine each color swatch’s “R” score.

The R value for a particular color indicates the ability of a light source to faithfully render that particular color. Therefore, to characterize the overall color rendering capability of a light source across a variety of colors, the CRI formula takes an average of the R values.

Ra is the average value of R1 through R8.

AvgR is the average value of R1 through R15.

Special value: R9

Ra is the average value of R1–R8; other values from R9 to R15 are not used in the calculation of Ra, including R9 “saturated red”, R13 “skin color (light)”, and R15 “skin color (medium)”, which are all difficult colors to reproduce faithfully. 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 the general CRI (Ra) calculation, R9 is not included.

R9 is one of the numbers of Ri that 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 capacity of light to reproduce the red color of objects accurately. Many light manufacturers or retailers do not point out the score of R9. At the same time, it is a solid value to evaluate the color rendition performance for film and video lighting and any applications that need a high CRI value. So, generally, it is regarded as a supplement to the color rendering index when evaluating a high-CRI light source.

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 are not in red color, but actually consist of different colors, including red color. For instance, the skin tone is impacted by the blood under the skin, which means that 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.

What about non-daylight color temperatures?

For simplicity, we’ve assumed a 5000K color temperature for our examples above and compared it to a 5000K natural daylight spectrum for CRI calculations.

But what if we have a 3000K LED lamp and want to measure its CRI?

The CRI standard dictates that color temperatures 5000K and greater use a daylight spectrum, but for color temperatures less than 5000K, use the Planckian radiation spectrum.

Planckian radiation is essentially any light source that creates light by generating heat. This includes incandescent and halogen light sources.

So when we measure the CRI of a 3000K LED lamp, it is being judged against a “natural” light source with the same spectrum as a 3000K halogen spotlight.

(That’s right – despite the awful energy efficiency of halogen and incandescent bulbs, they produce a full, natural and excellent light spectrum).

The importance of CRI

It should be clear now that CRI is a vital measurement for determining the performance of artificial light and is a crucial purchasing consideration in today’s lighting market. Building managers, decision-makers, and purchasers have recognized the essential benefits of using lights with higher CRI ratings. This includes an improvement in workplace safety and the productivity and efficiency of a commercial environment. These benefits are most noticeable, with lights having a CRI of 80 or above, suitable for general commercial and industrial purposes.

The most readily apparent benefit of lights with higher CRI ratings is the improvement in safety due to increased visibility. Lights with lower CRI ratings, such as sodium lamps and fluorescent lights, do not accurately show true colors, making distinguishing between colors difficult. This can affect the ability to read or notice warning labels, safety zoning, or other crucial safety-related information such as bright colors to draw attention to risks and danger. Improvements in visibility due to a higher CRI light source such as LEDs reduce these risks and the number of accidents, mistakes, and related issues.

Productivity is another benefit of higher CRI lighting, often overlooked on paper. A workplace illuminated with high CRI lighting produces a far more pleasant environment for workers and employees. Higher CRI ratings reduce stress, headaches, tension, depression, and eye strain and improve overall mood, which boosts productivity. This improvement is especially notable over time due to its direct impact on a company’s bottom line and profitability.

In the retail world, lighting with a high CRI has the additional benefit of improving sales performance. As mentioned previously, customers shopping in retail stores prefer high CRI lighting for the same reasons as employees and workers. There is such a preference for this that retail locations that have switched to high CRI lighting have seen significant improvements in sales numbers afterward. This is due to a more pleasurable shopping experience and the improved illumination of products, which increases their appeal.

What are common CRI values and what is acceptable?

80 CRI (Ra) is the general baseline for acceptable color rendering for most indoor and commercial lighting applications.

For applications where color appearance is essential for the work being done inside or can contribute to improved aesthetics, 90 CRI (Ra) and above can be a good starting point. Lights in this CRI range are generally considered high CRI lights.

For professional reasons, types of applications where 90 CRI (Ra) might be needed include hospitals, textile factories, printing facilities, or paint shops.

Areas where improved aesthetics could be necessary, include high-end hotels and retail stores, residences, and photography studios.

When comparing lighting products with CRI values above 90, it can be beneficial to compare the individual R values that make up the CRI score, particularly CRI R9.

Applications of CRI

Residential Lighting

High Color Rendering Index (CRI) values are integral in residential settings as they significantly impact living spaces’ ambiance and visual comfort. With a high CRI, the colors of interior decor, furnishings, and even food appear more vibrant and true-to-color, creating a more aesthetically pleasing environment. Moreover, accurate color rendering aids in daily activities such as cooking, reading, or makeup application, where color differentiation is important. High CRI lighting can transform a home by enhancing the natural colors, thus contributing to a warm and welcoming atmosphere, which is essential for relaxation and comfort at home.

Commercial Lighting

Commercial spaces such as retail stores, showrooms, and restaurants benefit immensely from high CRI lighting. Accurate color rendering is crucial for showcasing products in their true color, enhancing the appeal and encouraging customer purchases. In fashion retail, for instance, customers must see the accurate color of clothing, which influences their buying decision. Similarly, high CRI lighting in restaurants can make food appear more appetizing. Additionally, well-lit spaces with accurate color rendering create a pleasant environment that can enhance customer satisfaction and brand perception. Investing in high CRI lighting is a practical move towards creating a visually appealing commercial space that can positively impact business performance. More information, please check Commercial Lighting: A Definitive Guide.

Industrial Lighting

In industrial environments, accurate color rendering is a critical aspect of ensuring quality control and safety. Industries such as automotive, electronics, textiles, and printing require precise color differentiation for various tasks. High CRI lighting aids in accurate color matching and detection of defects, ensuring that the products meet the required quality standards. Additionally, better visual clarity can enhance the efficiency and productivity of workers, reducing the likelihood of errors. The right lighting environment also contributes to better safety, ensuring that signs, labels, and potential hazards are clearly visible. Therefore, high CRI lighting is an essential component in creating a conducive and safe working environment in industrial settings. More information, please check A Comprehensive Guide To Industrial Lighting.

Special Lighting (Photography, Art Galleries)

The significance of high CRI lighting is paramount in photography and art galleries where accurate color representation is essential. Photographers and videographers rely on high CRI lights to capture their subjects’ true essence and color, ensuring that the output is as close to natural appearance as possible. In art galleries, accurate color rendering allows for the authentic representation of artworks, preserving the artist’s original intent and the pieces’ integrity. High CRI lighting enhances the viewing experience, enabling audiences to appreciate the nuances of color and texture in each artwork. Investing in high CRI lighting is fundamental to ensuring that the visual arts are presented in the best light possible. More information, please check Art Gallery Lighting: The Definitive Guide.

Factors Affecting CRI

Light Source

The type of light source plays a pivotal role in determining the Color Rendering Index (CRI). Different lighting technologies, such as LED, fluorescent, incandescent, or halogen, have varying spectral distributions, influencing how colors are rendered. For instance, LEDs have advanced significantly, now offering high CRI values suitable for color-critical applications. It’s crucial to select a light source with a CRI value that aligns with the space’s specific needs to ensure accurate color rendering.

Material of the Object

The material’s color, texture, and reflective properties significantly impact how colors are perceived under different lighting conditions. Materials can absorb, reflect, or transmit light differently, affecting the color rendering outcome. Understanding the interaction between materials and light is essential for achieving desired color rendering results, especially in color-critical industries like fashion, interior design, and art.

Distance and Angle

The distance and angle light hits an object can alter color perception. As distance increases, light intensity decreases, which can affect color rendering. Similarly, the lighting angle can create shadows or highlight textures, impacting color perception. It’s imperative to consider the placement and orientation of lighting fixtures to achieve optimal color rendering.

Benefits of High CRI

Visual Comfort

High Color Rendering Index (CRI) lighting significantly contributes to visual comfort. It creates a pleasant and natural atmosphere, making indoor spaces feel more like the outdoors. High CRI lighting minimizes strain on the eyes, making it easier to perform tasks that require a keen eye for color differentiation. The naturalness and clarity of light with high CRI values enhance visual comfort, essential in residential and professional settings.

Improved Aesthetics

High CRI lighting brings out objects’ true colors, enhancing a space’s aesthetic appeal. Whether it’s a living room, a retail store, or an art gallery, high CRI lighting enriches the environment by rendering colors vividly and accurately. It accentuates the aesthetics, creating spaces that are appealing and inviting. The enhanced color accuracy contributes to better representing interior designs, artworks, and merchandise, making spaces look more attractive and engaging.

Enhanced Productivity

Quality lighting with high CRI values can enhance productivity, especially in work environments. Good color rendering allows for better visual clarity, which is crucial in tasks that require color accuracy. It helps in reducing errors improving the accuracy and efficiency of work. High CRI lighting also improves mood and alertness, further boosting productivity. In design studios, workshops, or any professional setting where color differentiation is key, high CRI lighting is indispensable.

Drawbacks of Low CRI

Poor Color Accuracy

Lighting with a low Color Rendering Index (CRI) distorts colors, making them appear unnatural or washed out. This poor color accuracy can be misleading and unsatisfactory in both residential and commercial settings. For instance, in retail environments, products might look different under low CRI lighting, potentially leading to customer dissatisfaction.

Strain and Discomfort

Low CRI lighting can cause eye strain and discomfort over time. The harsh lighting and inaccurate color rendering can make it difficult to focus, especially during tasks that require a keen eye for color differentiation. This could lead to fatigue and a decrease in productivity and comfort.

Reduced Quality of Work

In professions where color accuracy is crucial, low CRI lighting can significantly reduce the quality of work. It hampers the ability to make accurate color judgments, which is detrimental in fields like graphic design, painting, photography, and other color-critical tasks.

CRI VS CQS

The Color Rendering Index (CRI) and the Color Quality Scale (CQS) are both metrics used to evaluate the color rendering capabilities of light sources. However, they differ in their approaches and the aspects of color rendering they measure.

CRI primarily focuses on color fidelity, the accuracy with which a light source renders colors compared to a reference light source, usually natural daylight. It measures how “true” colors appear under a light source.

On the other hand, CQS is a more recent metric that was developed to address some limitations of CRI. Unlike CRI, CQS considers other aspects of color rendering, including color saturation and color preference. While CRI only measures color accuracy, CQS provides a holistic view of color rendering quality. It evaluates how pleasing the colors appear to the human eye under a light source, including factors like saturation that could make colors appear more vibrant.

Here’s a comparative table illustrating the differences between CRI and CQS

The CQS may be more advantageous in particular applications where both color accuracy and appeal are crucial. For example, in environments such as retail spaces or art galleries, where the vibrancy and allure of colors can significantly impact the viewer’s experience and satisfaction.

CRI VS TM30

The Color Rendering Index (CRI) has been the standard metric for evaluating color rendering of light sources for many years. However, its limitations, especially in evaluating modern lighting technologies like LEDs, led to the development of TM-30.

TM-30 is a more recent and comprehensive method for evaluating color rendition. Unlike CRI which only focuses on color fidelity, TM-30 provides a detailed analysis of color fidelity and color gamut. Color fidelity in TM-30 is about the accuracy of color rendering, similar to CRI, but it also includes color gamut which evaluates color saturation and hue change.

Here’s a comparative table illustrating the differences between CRI and TM-30:

TM-30 is particularly useful in applications that require a high degree of color accuracy and consistency. It provides a fidelity index (Rf) which is similar to CRI but also a gamut index (Rg) which gives information about color saturation and hue change, making it a much more informative and versatile tool for understanding and evaluating color rendering in lighting.

Full Spectrum Lighting and SunLike Natural Spectrum LED Technology

Full Spectrum Lighting aims to simulate natural sunlight, providing a balanced spectrum of light that encompasses the entire color spectrum visible to the human eye. This kind of lighting is particularly beneficial in indoor environments, helping to create a more natural and comfortable lighting atmosphere which can have positive effects on mood, productivity, and overall well-being.

Seoul Semiconductor has taken a significant stride in the domain of Full Spectrum Lighting with its SunLike Natural Spectrum LED Technology. This technology is designed to closely mimic the spectrum of natural sunlight, thereby offering a more natural and comfortable lighting solution.

Spectrum Reproduction:

SunLike technology reproduces the spectrum curve of natural sunlight by matching the intensity of each wavelength across the color spectrum including red, orange, yellow, green, blue, navy, and purple​​.

Applications:

The SunLike Series LEDs have found applications in various fields. For instance, they’ve been adopted for horticulture LED lighting by Fiberli, achieving a full spectrum of light wavelengths from 380nm to 740nm, similar to the spectral curve of natural sunlight, with a color temperature of 5000K optimized to daylight spectra and color properties of CRI97, CQS97, TM30=100​​.

Technological Collaboration:

The SunLike Series natural spectrum LEDs were co-developed through a combination of Seoul Semiconductor’s optical semiconductor technology and Toshiba Materials’ TRI-R technology​​.

High Color Rendering Index (CRI):

The SunLike LEDs boast a high color rendering index (CRI) of 98+, implying that they can render colors very accurately, which is particularly beneficial in settings where color accuracy is crucial​​.

Benefits:

The resemblance to natural sunlight not only creates a comfortable lighting environment but also has been noted to improve learning abilities such as memory, correct answer rate, and speed of learning​​.

Seoul Semiconductor’s SunLike Natural Spectrum LED Technology is a notable advancement in the realm of full spectrum lighting, offering a blend of technological innovation and practical benefits, which makes it a favorable choice for various applications aiming to replicate the natural light spectrum indoors.

How to Choose the Right CRI

Know Your Needs

Understanding the lighting needs of a space is crucial in selecting the right Color Rendering Index (CRI). Different applications necessitate varying levels of color accuracy. For instance, an art gallery or a retail store would require high CRI values to ensure accurate color representation, while other areas like warehouses might not have such stringent requirements. Assess the specific needs of a space, considering the activities that will be carried out there, and the importance of color accuracy in those activities.

Check Labels and Specifications

It’s essential to check the labels and specifications for the CRI value before purchasing. High CRI values, typically above 80, indicate better color rendering, making colors look more true-to-life. Reading the specifications will clearly understand the light source’s color rendering capabilities. It’s advisable to go for reputable brands and suppliers who provide accurate and reliable information on CRI and other lighting specifications.

Test Before You Buy

Testing the lighting in the intended environment before making a purchase can be beneficial. It allows for a hands-on assessment of the color rendering quality and the overall lighting performance. This step can save time and resources in the long run, ensuring the chosen lighting solution meets the required standards for color accuracy and visual comfort. Testing might include checking the color rendering of various objects or materials, assessing the visual comfort, and ensuring the lighting complements the aesthetics of the space.

Historical Evolution of the Color Rendering Index (CRI) Standard

The development and evolution of the Color Rendering Index (CRI) as a standard has been influenced by continuous advancements in lighting technology over the years. Originating in the mid-20th century, the CRI was devised to measure the color accuracy of artificial lighting. Over time, with the advent of new lighting technologies, the methodology to calculate CRI has been refined to represent color fidelity better. Additionally, new standards like TM-30 have been introduced to address the limitations of CRI. This historical context underlines the industry’s efforts to achieve accurate color rendering, which is vital for various applications, from interior design to retail and art preservation.

Global Standards and Regional Variations in CRI Standards

The Color Rendering Index (CRI) is a globally recognized standard used to measure the color rendering capabilities of light sources. However, different regions may have variations in how CRI standards are applied or interpreted due to local lighting conditions, cultural preferences, or regulatory frameworks.

Regulatory Frameworks: Some regions may have specific regulatory frameworks that dictate the minimum CRI values for certain applications, influencing the utilization and perception of CRI standards.

Cultural Preferences: Cultural preferences may lead to variations in desirable CRI values. For example, certain cultures may prefer warmer or cooler lighting, which could influence the importance of high CRI values.

Local Lighting Conditions: The natural lighting conditions in a region could also influence the application of CRI standards. Regions with less natural daylight might emphasize artificial lighting with high CRI values to compensate.

Understanding these regional variations is crucial for manufacturers, designers, and other stakeholders in the lighting industry to ensure compliance with local standards and meet the preferences and needs of different markets.

Future Trends: Evolving Metrics and Technologies

The lighting industry continually evolves with emerging technologies and metrics. While CRI has been a reliable standard, newer metrics like TM-30 and CQS are gaining traction for a more holistic view of color rendering. Additionally, advancements in LED technology and smart lighting systems influence how color rendering is evaluated in the future.

Conclusion

In conclusion, the Color Rendering Index (CRI) is a measure of how well a light source can render colors compared to a reference light source. CRI is an important factor to consider when choosing lighting for various applications, especially in environments where color accuracy is critical, such as in art galleries, museums, and hospitals. A higher CRI value generally indicates better color rendering performance. However, it is important to note that CRI is not the only factor that affects color perception, and other factors such as color temperature and illuminance should also be considered. By understanding CRI and its importance, consumers and businesses can make informed decisions when selecting lighting that best suits their needs.

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