Understanding the Limitations of the Color Rendering Index (CRI) and the Emergence of TM-30-15
- By Ledrise Led Professional
- Jan 25, 2023
Introduction to the Color Rendering Index (CRI)
In 1974, the International Commission on Illumination (CIE) introduced the Color Rendering Index (CRI) to compare the color rendering of artificial light sources to a reference standard illuminant modeled after daylight. The CRI aimed to express the quality of white light produced by various types of gas lamps available in the market at that time.
Over the past 40 years, the CRI index has become deeply ingrained in the lighting industry and among professionals. However, it remained relatively unknown to most consumers since it wasn't particularly relevant to their decision-making when purchasing lighting. Manufacturers produced most lamps based on their CRI value for specific applications, ensuring that the choice of lamp could not be wrong. For instance, office or linear lighting typically used Tri-Phosphor linear fluorescent tubes with a CRI over 80. Homes relied on incandescent lamps and halogens with a CRI of 100, while retail spaces utilized metal halide lamps with a minimum CRI of 85.
The Impact of LED Technology
The emergence of LED technology in the 2000s revolutionized the lighting industry. LEDs became the first truly multipurpose light sources, with applications ranging from lighting fixtures, light bulbs, linear tubes, flashlights, cove lights, floodlights, and more. LEDs offer a full spectrum of performance and quality, including the ability to accurately reproduce colors across various levels of quality.
The makeup of some fixture types for common applications, such as down-lighting, spot-lighting, office-lighting and street-lighting. All can use LEDs.
When LEDs are installed directly into luminaires or lamps, the CRI value of the light source becomes the CRI of the light fixture, which cannot be changed later. This increased product complexity has rendered the CRI index and its eight test colors insufficient as an optimum quality test, given the vast array of technologies, wavelengths, and color temperatures available today.
One key limitation of the CRI index is its inability to prevent designing a light source that specifically targets a good score for the eight test colors while neglecting the overall color spectrum. This is where the TM-30-15 color index steps in to address these limitations.
Introducing the TM-30-15 Color Index
The TM-30-15 color test, proposed by the Illuminating Engineering Society (IES) and the US Department of Energy (DOE), features a Color Fidelity Index that substantially enhances benchmark precision by increasing the number of test colors from 8 to 99. This increase in test colors makes it almost impossible to cheat, as only light sources with a high similarity to daylight or standard light can achieve a score higher than 90 or 95 across the entire spectrum.
The TM-30-15 also incorporates the Gamut Index, which indicates if a light source is designed to saturate specific colors, such as red. A Gamut Index (Rg) of 100 signifies that the light source does not under- or over-saturate a color palette. For index values ranging from 101 to 140, progressive over-saturation of color occurs, while values from 100 to 60 indicate de-saturation. A color graph is also recommended to accompany the numerical index.
The TM-30-15 also incorporates the Gamut Index, which indicates if a light source is designed to saturate specific colors, such as red. A Gamut Index (Rg) of 100 signifies that the light source does not under- or over-saturate a color palette. For index values ranging from 101 to 140, progressive over-saturation of color occurs, while values from 100 to 60 indicate de-saturation. A color graph is also recommended to accompany the numerical index.
The graph shows that many test light sources, mainly LEDs and narrowband fluorescent, have a Fidelity Index below 80, while scoring at least 80 on the Color Rendering index.
The level recommended as minimum required for general lighting is 80, thus by using the new Fidelity Index only those truly suitable lamps for the application will be of choice.
In addition, TM-30-15 includes the Gamut Index to shows if a light source is designed to saturate particular colors, such as red for example.
A colorful graph is also suggested as accompaniment to Gamut Index number.
Using the TM-30-15 with its Fidelity Index (FI) and Gamut Index (GI) makes it significantly easier to select LED lights with the optimal light spectrum.
Currently, the highest CRI values for LEDs come from the new technologies such as Nichia Optisolis and Seoul Semiconductor SunLike, both with almost day-like spectrum and maximum scores for all the CRI test colors. They also have similar high scores with the Fidelity Index.
The comparison of their spectrum to sunlight and other light sources can be seen below:
In conclusion, the traditional CRI index, while still valuable, has limitations when it comes to evaluating LED light sources. With the advent of LED technology and its wide range of applications, the TM-30-15 color index offers a more comprehensive and accurate measure of color rendering performance for these modern lighting solutions. By utilizing the TM-30-15's Fidelity Index and Gamut Index, consumers, designers, and lighting professionals can make better-informed decisions when selecting LED lights that best suit their needs.
With innovative technologies like Nichia Optisolis and Seoul Semiconductor SunLike, the LED lighting industry is continuously evolving to provide even better color rendering and higher quality light. These advancements help ensure that spaces like homes, offices, museums, retail shops, and more benefit from lighting that closely resembles natural sunlight, enhancing visual comfort and accurately representing colors.
In summary, while the CRI index has served the lighting industry well for many years, it is essential to recognize its limitations and adapt to more advanced metrics like TM-30-15 for a more accurate evaluation of LED light sources. By embracing these new methods and innovative technologies, designers and professionals can continue to push the boundaries of lighting design and create spaces that truly enhance the human experience.
At Ledrise can find Sunlike or Optisolis LED strips and modules: