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CRI, Color Temperature and New Lighting Quality Metrics

Aug. 19, 2019

Color temperature and the Color Rendering Index are dependable ways to measure light quality. Here’s how to use them in your project and why. 

Lighting is about more than illumination. It impacts the room’s mood, contributes to comfort and makes it possible to get an accurate look at the work you’re doing there.

Energy-efficient light sources allow you to deliver that light wherever it’s needed without overspending.

Today’s commercial LED lighting is highly efficient, but two equally efficient light sources could have radically different effects on the quality of lighting in a space.

Because efficiency isn’t the whole story, it’s crucial to compare lighting quality before you purchase. The primary tools used to describe and quantify quality of light are color temperature and the Color Rendering Index (CRI).

Here’s why you need to compare both quality indicators to determine your best LED lighting solution.

How Is Lighting Quality Measured?

Both color temperature and the Color Rendering Index have been around for many years and describe different aspects of light quality. 

Color temperature

Measured in degrees of Kelvin (K), color temperature quantifies the color of white light. Lower color temperatures appear visually “warm” and have more of a red-yellow tint—think of a classic incandescent light bulb, which typically has a color temperature around 3000K.

Mid-range color temperatures between 3500 to 4100K have a more neutral and true white appearance because the color wavelengths of the light are more balanced. At the other end of the scale are high color temperatures above 4100K, which have a cool, blue-tinged look.

Color Rendering Index

CRI measures a light source’s ability to display the color of objects relative to the color rendering abilities of a specific light source, such as a phase of daylight or a black body radiator (an object that absorbs all electromagnetic radiation regardless of its frequency or angle).

A CRI rating above 80 is considered generally accurate at rendering, though some LED lighting manufacturers have products with CRIs in the 90s.

[Related: How Lighting Controls Can Mimic the Sun]

New lighting quality metrics

The existing color rating systems have shortcomings, explains John Yriberri, North American market leader at Modular Lighting Instruments. That’s why the Illuminating Engineering Society (IES) developed a more comprehensive replacement for the CRI, called the IES-TM-30-15

“Because TM-30-15 is somewhat new and requires a more in-depth understanding of color, CRI continues to be used throughout the industry and will likely continue for some time to come,” says Yriberri. “Since CRI only addresses eight color samples—none of which are saturated in nature—for many applications using LED sources, it is important to also evaluate the R9 value.”

R9 is not one of the test color samples used to calculate CRI, so it's important to evaluate it in addition to the CRI value. It represents how accurately a light source will reproduce deep red, which is more difficult to create with LEDs than colors with shorter wavelengths like blue, green, yellow and orange.

Consider asking manufacturers about R9 data so you can make sure your commercial LED lighting can render the red tones in your facility accurately. 

Many of these metrics require specialty lab equipment to measure, so it’s crucial that you know manufacturers are relying on certified labs to collect and report these measurements, Yriberri says. 

What CRI and Color Temperature Do I Need?

Finding the right commercial LED lighting for your project requires an in-depth knowledge of what you need to accomplish in each application. Different spaces need different color temperatures and Color Rendering Index ratings. 

“CRI and application requirements are very closely linked,” says Yriberri. “For example, the light quality required in the utility room of a hotel is different than what should be used in the restaurant or bar.

For a utility room, the primary objectives might be brightness for doing detailed tasks and energy savings, whereas the primary objectives for a restaurant/bar might be color rendition and ‘comfortable’ light, both in intensity and color.” 

A CRI of at least 80 would be fine for the utility area in this example, Yriberri explains, but the restaurant and bar area would need a CRI of 90 with an R9 (deep red content) of 50, because the color rendition of people and objects is so much more important in the restaurant.

“Like CRI, color temperature is also very dependent on the application,” Yriberri says. “The utility room would benefit from a cooler light source, especially if detailed tasks will be performed, so minimum 3500K should be selected.

[Related topic: Connected Buildings Increase as Companies Prioritize Advantages]

For the restaurant or bar, the idea would be to create a cozy environment, so a warmer light source like 2700K should be selected.”

He adds, “Color temperature can influence not only how a space looks, but also a person’s subconscious behavior. In the bar/restaurant example, using a light source that is too cool can make the place look sterile, which translates to more like a hospital-type setting.

Subconsciously, this can make a person feel uneasy and more likely to leave the space, even though the person may not directly realize that the lighting is creating this unpleasant environment.”

Other Important Light Quality Considerations

Yriberri recommends weighing each application to see if you could benefit from dimming controls. The utility room example may not have much need for dimming, but a hospitality space like a bar or restaurant may use several different color temperatures and dimming levels throughout their open hours.

“The dimming should be free of flicker and stroboscopic effects,” says Yriberri. “In regard to dimming and flicker, a responsible manufacturer will have a dimmer compatibility list or chart for each product.

This chart requires testing to ensure performance and is highly recommended to match the dimming system and the luminaire to ensure that the performance is going to meet expectations.”

Today’s commercial LED lighting marketplace can leave you spoiled for choice, but examining the tasks that will be performed in each space will help you narrow down the right color temperature, CRI and other metrics to include in your specification.

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About the Author

Janelle Penny | Editor-in-Chief at BUILDINGS

Janelle Penny has been with BUILDINGS since 2010. She is a two-time FOLIO: Eddie award winner who aims to deliver practical, actionable content for building owners and facilities professionals.

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