Applying CRI and CCT

Posted on August 19, 2013 Category: Interior Lighting Design Articles

As LED lighting becomes more popular in homes and businesses, lighting and interior designers are examining lighting temperature to find out which colors are best for various locations.

In order to do this, they use two scales: Correlated color temperature (CCT) and color rendering index (CRI).

Correlated Color Temperature (CCT)
According to the Illuminating Engineering Society, CCT is a specification of the color appearance of white emitted light. This is measured by comparing it to the color of a reference source when it is heated to a particular temperature as measured in degrees Kelvin. When metal is heated up, it starts by turning red in appearance. It then transitions to orange, yellow, white, blue-white and then, ultimately, it will change to deeper colors of blue.

Counterintuitively, as the metal gets higher in physical temperature, we consider its color to become cooler.

For example, "soft white" tungsten halogen lights generally are measured at around 3000K, "neutral white" linear fluorescents are near 4200K, high pressure sodium lights are around 1900K and "warm white" compact fluorescents come in at 2700K. "Daylight White" is considered to be around 6500K.

While this light measurement gives a good indication for the light's general appearance, it does not provide a description of its specific spectral power distribution. Therefore, two lights could be described as having the same CCT rating, even while their effects on the colors of objects may be noticeably different.

According to lighting designer Randall Whitehead, incandescent light has longer wavelengths and therefore will render red colors the most effectively. LEDs and fluorescents with the same CCT rating have more powerful short wavelengths, and therefore make blues stand out more.

Because of this variation, the CRI rating was developed.

Color Rendering Index (CRI)
The CRI is a measurement of the accuracy of a light source in rendering different colors as compared to a reference light source that has the same correlated color temperature. The highest CRI possible is 100, meaning it has the best possible color reference and provides the best visual perception of colors.

Generally, a high CRI rating is preferred, but is not always necessary. Incandescent lights tend to have a higher CRI, but the color is invariably on the warmer end of the spectrum and is much less energy efficient than other alternatives.

Now that houses and condos tend to be designed with an open plan concept where the kitchen and dining room or living room tend to flow through the same space, Whitehead told Residential Design that he prefers a high-efficiency, high CRI light that will unify the whole area. Using LEDs in this space not only creates the desired ambiance, but also helps houses comply with energy efficiency standards, like those in California which requires that 50 percent of the lighting in the kitchen must come from high-efficiency sources.

However, when it comes to lighting spaces like closets, laundry rooms and other places where color matching is important, he prefers to have light with a warmer CCT as well as a high CRI.

Another option that can be used anywhere in the home is White Adjustable LED Lighting. These lights allow homeowners to adjust their lights to any CCT from 2700K to 6500K, generally by using a remote or wall mount panel. This level of control allows users to adjust their lighting as needed to always provide the perfect ambiance.

With advancements like those of LED dimmers and White Adjustable LED Lighting, LEDs provide both energy efficiency and the quality of light expected by consumers. Even Whitehead told Residential Lighting that he prefers to use hard-wired LED recessed adjustable features throughout the entire home to make sure the lighting matches across the house.

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