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Color Rendering Index

The Color Rendering Index (CRI), simply put, is the measurement of a particular light’s accuracy in illuminating colors. This is measured on a numerical scale going up to 100, which is the CRI of a reference light. Known to color scientists as a “black body radiator”, a reference light is either traditional incandescent light or natural sunlight. Prior to the introduction of fluorescent lighting, the accuracy of lighting illumination was not very well studied since practically all forms of commercial, industrial and consumer lighting were incandescent. It should be noted that CRI is independent of Coordinated Color Temperature (CCT), which is measured in kelvins and relates to the actual color of light produced, not the accuracy of that lights illumination.

During the middle of the 20th century, color scientists began to explore the abilities of artificial light to reproduce colors accurately. The International Commission on Illumination, known as the CIE from its French title (Compagnie ivoirienne d’électricité), was formed in 1900 to promote cooperation and an exchange of information on all matters related to the science, technology and art of lighting. The CIE developed the CRI standards used today, based on extensive research into the criteria for determining a light’s accuracy in showing color. Their method of measuring, known as CIE (1995), is the industry standard throughout the world for measuring the accuracy of artificial light.

Definitions

CRI – Color Rendering Index – The scale used by color scientists to measure the accuracy of lighting illumination.

CIE – International Commission on Illumination – The commission formed to study the art and science of lighting. Meets periodically to come up with new standards and scientific methods.

CCT – Coordinated Color Temperature – The measurement of the actual color of a light source using a scale in Kelvins.

ColorChecker Chart – A color calibration target with squares of painted samples for testing color rendering accuracy

Fluorescent Light – A low pressure mercury vapor gas discharge type lamp that produces light by running electricity through mercury vapor and phosphorus, causing it to glow. Up until recently, it has been considered the standard for industrial and commercial lighting.

Incandescent Light – The original artificial light, which generates its glow from running electricity through wound tungsten filament. This is the original type of light bulb, invented by Thomas Edison in 1879 at his Menlo Park Laboratory, which is now located at the Henry Ford Museum’s Greenfield Village.

LED Light – Light produced by LEDs (Light Emitting Diode), which is the most recent innovation in lighting. This is fast becoming the dominant choice in retrofit and new construction lighting, due to its high CRI and exceptional energy efficiency.

How CRI Works

The CIE has developed a specific method for measuring CRI, which is now the industry standard for lighting. This method involves comparing the color rendering of a test source to a perfect source with a CRI of 100, which is referred to as a black body radiator. There are ten primary reference samples used as perfect sources to calculate general color rendering index. The source selected will depend on the color temperature of the light being measured. These sources are categorized using a ColorChecker chart, established by CIE (1999), which organizes them numerically starting with TCS01 and ending with TCS10. The closer the test source matches with the perfect source, the higher the CRI number.

Different types of artificial illumination fall into certain general ranges of CRI ratings. As mentioned previously, traditional incandescent lighting and natural sunlight has a CRI of 100, which all other sources of illumination seek to achieve. Generally speaking, sodium and HID lamps have the lowest CRI of all currently used lighting options, with an effective CRI of near zero for low pressure sodium lamps, ranging up to 60 for HIDs. Fluorescent lamps, which have been the most popular lighting choice for decades throughout the world, have an average CRI of around 70, which is a significant improvement over HIDs. LED lamps vary considerably, however they have an average CRI of 80-95. There are exceptions to these generalizations, however they are considered accurate representations of the CRI ratings one should expect from these lighting options.

Chart showing the Color Rendering Index ranging from 0 to 100 from low quality dark red light all the way up to excellent quality white light

Why is CRI Important?

It may be obvious by now that CRI is an important measurement in determining a lights performance and is a major factor in today’s lighting marketplace. There are several distinct benefits of having a light with a higher CRI rating, which help to improve not only safety, but productivity and efficiency of a commercial environment. Generally speaking, any CRI of 80 or above is considered good for overall commercial purposes.

One of the largest benefits of higher CRI lighting is the improvement in safety due to increased visibility. A low CRI light, such as a traditional fluorescent light, does not accurately show true colors, making it harder to distinguish between colors in things such as warning labels, safety zoning, etc. The improvement in visibility from a high CRI light, such as an LED, helps to alleviate these issues and will reduce the number of workplace accidents and mistakes.

Another benefit of lighting with higher CRI is the improvement in workforce productivity. Higher CRI lighting creates a more pleasurable environment for workers and employees by reducing stress, headaches, depression, eye strain and improving mood. All of this contributes to increased productivity. This is notable, because it has a direct impact on a company’s bottom line and improves profitability.

For retail environments, high CRI lighting has an additional benefit – improved sales. Retail customers prefer higher CRI lighting, for the same reasons as employees and workers. Higher CRI lighting has been proven to improve sales in practically all types of retail environments, due not only to a more pleasurable shopping experience but also the improved illumination of products which makes them more visually appealing.

In Summary

High lighting accuracy is of the utmost importance in today’s lighting marketplace, due to the numerous benefits previously discussed. The most noticeable benefit for most is the significant improvement in quality of life for users due to the higher accuracy in color rendering making it easier on the eyes. Another benefit that is more apparent to business owners and building operators is the noticeable improvement in safety and efficiency due to increased visibility.

Out of all the major types of lighting, LEDs have become the dominant choice over the past several years for those looking for the best color rendering. Many lighting manufacturers are now exclusively using LEDs in their fixtures, not only because of their high CRI ratings but also due to their energy efficiency. This bright future of lighting is something that all businesses and industries have to look forward to.