What's the difference between CCT and CRI?

This article helps explain and distinguish between two of the color and light terms that are often confused with each other - CCT (correlated color temperature) and CRI (color rendering index).

What is CCT, or Correlated Color Temperature?

CCT is a number, measured in degrees Kelvin, which helps to describe the relative warmth or coolness of a light source. Most light products will range from 2700K (warm, incandescent color) to 5000K or higher (crisp, white daylight color).

For most residential applications, 2700K and 3000K are preferred color temperature options as they both create a nice, warm appearance that creates a relaxing environment.

For retail or commercial applications, 4000K is a popular color option as it provides for a crisper, more energetic shade of white. For industrial or task-oriented applications, 5000K or even 6500K is a preferred color option, as these color temperatures best match natural daylight.

What is CRI, or Color Rendering Index?

The CRI value of a light source describes how accurately a light source illuminates colors of an object. It is scored on a scale with 100 being the best. Most standard bulbs have a CRI value of 80, while high CRI products have a CRI value of 90 or higher.

For example, a painting shown under a 70 CRI light source may exhibit colors that don't appear correct, or accurate. When seen under a 95 CRI light source, however, the colors of the painting will likely look accurate and natural.

The difference between CRI and CCT explained

As explained above, CCT and CRI measure two different aspects of color. CCT tells us the color of the light emitted by the light product, and is immediately visible to the casual observer by looking directly at the light source.

On the other hand, the CRI value does not tell us the color of the light itself. Rather, it tells us about the color appearance of objects under the light source. You cannot determine a light product's CRI value by looking at the light itself. Instead, a light product's CRI can only be estimated to the naked eye by looking at the colors of an object illuminated by the light product. 

The only way to measure a light source's CRI value is by using specialized spectral measurement devices. Lighting manufacturers rely on data from these devices to publish and guarantee color rendering related metrics.