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What Is Color Rendering?

Color rendering is the measure of a light source’s ability to accurately display colors in their truest, most realistic forms. It is a huge factor in deciding which light source to use for a project. The color rendering index describes how well natural light appears to the human eye and how it represents the various shades of every color.

How Does the Color Rendering Index Work?

Color rendering is measured on a scale called the color rendering index (CRI), which runs from 0 to 100 percent and indicates the accuracy of a light when compared to a reference light source. A reference light source, such as incandescent or daylight, is used as a benchmark for the accuracy and suitability of the light. The closer the CRI is to 100 percent, the more accurate the light source will render a color’s true appearance. For example, a CRI of 95 represents considerable value, while a low CRI rating indicates that some colors will not appear as vividly when illuminated.

CRI and color temperature are similar in that they are both often measured by their ability to render colors. The color rendering index is an independent method of describing certain characteristics of light, for example, and is different than the measurement of Kelvins (warm and cool light).

How Is the CRI Used?

Munsell Color Chart

We have now established that a high CRI is better than a low CRI, but three questions immediately follow: What exactly is measured, how are those measurements taken, and is there value in having a CRI as high as 95? The color rendering index is a commonly recognized metric that is currently the only means available for accurately evaluating and reporting the color rendering of light sources. While CRI is based on eight defined common color samples, the results of a CRI evaluation are found mathematically. The predefined color chart is used to evaluate the appearance of specific colors and compare it to the reference light source (discussed above).

The eight defined colors used to measure CRI are selected from the Munsell color wheel. To run accurate color comparisons, the color temperatures of the reference light source and the test light need to be identical. For example, it is a misconception that a light source with a high CRI will produce light similar to a bright sunny day, making your home look like the sun is beaming inside. This is incorrect. CRI measures how accurately a light source compares to a similar light source of the same color temperature.

Kelvin Temperature Chart

Other Ways to Measure Color Rendering

Aside from CRI, another common way of measuring light is by correlated color temperature (CCT). CCT is a form of measuring a light source using Kelvin (K) temperature. Kelvin temperature specifies the warmth or coolness of a color’s appearance. A low Kelvin temperature will be softer and warmer, while a higher Kelvin temperature will be a cooler light. For example, 3000K is considered warm white because it falls more toward the yellow end of the white-light spectrum and is typically used to instill a sense of comfort (it is often used in homes and restaurants). 4000K can be considered neutral white and is one of the most popular Kelvin temperatures for sports courts. Lastly, 5700K, or cool white, falls close to the blue end of the white-light spectrum and offers a crisp and clean color often compared to daylight.

While CCT classification of a light source gives an overall positive representation of the appearance of a lamp, this isn’t always the case. Two lamps may have the same CCT, but when used for their intended purpose the colors may be quite different. This is because it is rare that a color is made up of just one solid, defined color. More likely than not, the application you are using will have many colors and shades, thus why something with the same CCT can result in different results.

Another way of measuring light is by color quality scale (CQS). Traditionally, we have measured light sources using CRI, however CQS is a new method of measurement and is said to eventually eliminate CRI. The main reason behind this movement is the challenge of measuring LEDs with CRI. CRIs measurement gets more complicated when you consider that its natural light source is a black body radiator and, as mentioned previously, is based on eight colors. Incandescent bulbs receive a CRI of 100, yet they are far from ideal color rendering. And, vice versa, a light source can receive a poor CRI score even if it works well with bright colors. For example, LEDs can accurately illuminate bright or saturated colors, but not always unsaturated colors. A low CRI for LED lighting can be misleading. CQS is an alternative method that uses 15 colors that span a wider range of object colors. Additionally, CQS takes factors such as chromatic discrimination and human preference into consideration.

Applications That Require a High CRI and Fixtures That Deliver High CRI

Access Fixtures offer a wide range of high CRI fixtures, such as those in the APTA, APTI, and APTU/APTO families. These fixtures come standard in 70+ CRI but are available at 80+ CRI and 90+ CRI at a minimal extra cost. APTA and APTI fixtures are high-powered pole lights that are used for sports lighting applications, park lighting, and anywhere a maximum amount of footcandles is desired. APTO and APTU fixtures are full cutoff wall packs in two different designs.