What is Correlated Color Temperature in Lighting, and How Do You Choose?

Anthony Di Domenico, Sr. IEC Lighting Product Manager talks about how to use color temperature in industrial LED lighting design:

Many industrial lighting customers are starting to think more and more about color temperature options in lighting, and how to choose the best one for their site application. What follows are the basics of color temperature, the common options available for industrial/hazardous luminaires and, some techniques used around designing with color temperature.

Correlated Color Temperature (CCT) is a measure of how warm or cool a light source appears to the human eye. It is measured in degrees Kelvin. The CCT is defined by the proximity of the light source’s color appearance coordinating to a blackbody radiator – think of the color of steel or iron when removed from a forge. 

It is important to note that CCT does not tell you anything about the color rendering index (CRI) or brightness (lumens) of a light source. Color temperature options allow a lighting designer, or end user to make choices about illuminating their locations that previously weren’t available before LED luminaires.

Typical industrial/hazardous lighting color temperatures range from 3000K (warm white) to 4000K (neutral white) to 5000K or 6000K (cool white). LED lighting has allowed Appleton to provide these options within practically any luminaire design. Previously manufacturers were limited to the natural color temperature of the light source, whether that be high intensity discharge (HID) or fluorescent lamps.

Each CCT range allows a lighting designer, or end user to make focused decisions on the color appearance they need to safely and effectively light their space. A chart below shows the benefits to choosing one color temperature over another. Those benefits revolve mostly around mood or time of day, the application you are lighting, or the presence of humans or wildlife in the area.

A common misconception is that a cooler color temperature, like 5000K, is much brighter than a warmer CCT of 3000K. This is an effect commonly called, “perceived brightness”. Perceived brightness is a trick our eyes play caused by the increased presence of blue in the color spectrum of 5000K luminaires. The 5000K CCT is crisp and similar to daylight, and our eyes see the light in such a way as to make you feel as if the light is brighter. Meanwhile, the lumen difference between a cool light source and warm light source is minimal, and is more due to the manufacturing process for creating color temperature in LEDs.

Color temperature variations are created at the individual LED chip level. The basic construction elements of an LED include: a substrate, a semi-conductor chip, and a phosphor coating. The semi-conductor chip emits a highly efficient blue LED light. The conventional white color temperatures are created by layering a yellow phosphor coating on top of this chip. The warmer the color temperature, the more phosphor is required. The result is the warmer LEDs require a little more wattage to power and have about 5-10% less light than much cooler LEDs. The light loss is rarely noticeable, especially in high output luminaires. Instead of having color temperature choices revolve around the amount of lumens required for an application, other lighting design decisions should be taken into consideration.

One lighting design technique that can be used with color temperature is highlighting. Highlighting creates visual contrast between one area of a site and another. This can be used to provide attention to an important piece of equipment, or give visual contrast between different areas, like a process area and a walkway. Color temperature variations can also be used at varying height levels, as cooler white CCT luminaires could be desired at higher mounting heights, away from eye lines.

In summary, correlated color temperature (CCT) is an important aspect to take into consideration when making a luminaire choice. Behind brightness, it is arguably one of the top choices you could make when designing a lighting layout for a site. We have covered some of the basics here around CCT options and why a lighting specifier would choose one over another. What are some of the ways you think color temperature could best be used to enhance a lighting layout design?