The Difference in Color Temp and CRI in Billboard Lights

William Hall, Tuesday, November 29, 2016

Imagine you are looking at two billboards. The graphics on one are clear, crisp, and true to color.

The other, however… The clarity is still present, but the light source gives everything a slightly yellowish glow.

If someone were to survey you about these two billboards, you would probably point to the first as the most effective. Even if the content of the first isn’t as appealing as the second, that yellowish glow lends a cheap feeling to the billboard.

This scenario demonstrates the importance of quality lighting in your billboards. Good lighting can’t overcome bad content, but it can certainly weaken good content.

Two qualities you need to consider in the lighting for your billboards are color temperature (color temp) and the Color Rendering Index (CRI).

colortemp1Color Temp

According to “Discover Lighting,” a document produced by the Illuminating Engineering Society, a light source’s color temp is the “numerical measurement of its color appearance.”

Essentially, the color temp compares the color of the light emitted by a source to the color we would expect to see in an object heated to that temperature.

We know fire changes color as it gets hotter. Red and orange flames aren’t nearly as hot as blue and white ones. In terms of lighting, the cooler the light, the higher the color temp assigned to it. Color temp is measured in kelvin.

Including Color Temps over the spectrum, with real world items, would help i.e. Candlelight, Sunlight, LCD monitor.


The CRI refers to how closely light resembles the colors you would expect to see when viewing an object in sunlight, or color accuracy.

On a scale of 1 to 100, the higher the number, the closer that light source mimics natural lighting. You’ll learn that scores of 90 and above are considering excellent (also called high CRI).

However, such a high score is unnecessary for your billboard. Since it’s unnecessary, billboard lights do not go above 80. Good design means your content already contrasts enough for easy readability. Being able to pick apart colors is unnecessary. An example of when high CRI is needed is in a retail store where customers are comparing objects similar in color.

The Lighting Research Center says, “CRI is calculated from the differences in the chromaticities of eight CIE standard color samples (CIE 1995) when illuminated by a light source and by a reference illuminant of the same correlated color temperature (CCT); the smaller the average difference in chromaticities, the higher the CRI.” [CIE refers to the International Commission on Illumination.]

Choosing a Billboard Light

Check the color temp and CRI on all billboard lights you are considering. While some lights, such as incandescent bulbs, have a high CRI, the color temp may be low. This leaves you with that yellowish glow.

For billboard lights, you may find higher color temp more important to the appearance of your billboard than a high CRI. Higher color temp seems brighter overall, while high CRI simply allows you to tell the difference between colors more easily.

No matter what lighting you choose, be sure your content is easily visible at great distances.

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