As an installer or maintained person for lighting products having a good understanding of color is important. Today’s popular light sources (LED) are an artificial light source and how the human eye perceives it is quite different that natural light (Sunlight) or older obsolete lighting such as incandescent bulbs.  This is particularly true when it comes to the actual color of the lamp. With this difference a different language has evolved. Electrical Contractors and maintenance personal need to have a good understanding of color in today’s technology to be successful in their jobs. So, welcome to your Lumight contractor's guide to color, CCT and CRI.

 

SO WHAT IS COLOR?

 

Lumight's Contractor's Guide

 

 For the eye to perceive an object as being a certain color, that color must be present in the object and in the light striking it. As a result, designers can to an extent control how colors are perceived in a space through light source selection. In the lighting field, color quality is evaluated using two metrics. Adjusting these metrics can have a big impact on how spaces look. These are CCT and CRI.

Correlated color temperature (CCT): Color temperature or CCT is Measured in degrees Kelvin. Kelvin is an actual temperature similar to Celsius but instaed of starting at zero degrees it starts at -273 degrees Celsius (Absolute Zero). The CCT is the approximation or the color a “black body” needs to be heated to glow the same color. This is the physics of it.

 

In lighting CCT is more a measure of the color tone of the light source and its light emission compared to an ideal reference light source (sunlight or sometimes incandescent lamps). Light sources are considered cool (>4000K, appearing bluish-white); neutral (3000-4000K, appearing white); or warm (<3000K, appearing orangish-white). Warm sources tend to enrich warmer colors such as red, orange and flesh tones. Blue sources tend to enrich cooler colors such as blues and greens. Daylight, for example, is a very cool light source (4500-10,000+K).

 

Color rendering index (CRI): Measured on a scale up to 100, CRI is a measure of color fidelity, or how closely a light source renders 8-14 pastel test colors compared to an ideal reference light source. Comparing the CRI of two light sources is only relevant if they have the same CCT.

 

color-rendering-index LEDlightsindia  Image source: ledlightsinindia.com

 

While CRI has endured for decades, it is based on color science going back to the 1930s. The advent of the LED, with its unique color characteristics, made its flaws more pronounced. In 2006, the International Commission on Illumination (CIE), which maintains the CRI standard, attempted a revision but couldn’t come to agreement. In 2013, the Illuminating Engineering Society (IES) published TM-30-15, a new method for evaluating color rendering. To be clear, TM-30 is not a standard; it was published to be used alongside CRI and vetted as a possible new standard. CIE is currently investigating it.

 

TM-30 introduces three new tools

 

Fidelity Index: This metric functions the same way as CRI but is based on an average fidelity score across 99 color samples instead of 8-14. The intent is to improve accuracy when predicting color fidelity.

 

Gamut Index: This metric indicates the average level of saturation and desaturation compared to an ideal reference light source. A score higher than 100 means the light emission procures an average increase in saturation. Lower than 100, an average decrease. The intent is to address the fact that two light sources can have the same CRI but result in different visual appearance due to saturation.

Individual color distortion: Using data produced based on TM-30, color distortion graphics can be generated that reveal which colors are specifically saturated or desaturated. This delivers significantly more information about color.

By understanding the metrics involved and what the application needs, specifiers can select the right light source for the job.

 

What is important for contractors and maintenance people to know is that all light fixtures of the same wattage are not created equal, even if they have the same light output (Lumens). The CCT and the CRI can have a dramatic effect on how a space looks like when illuminated. If you have any questions about Color, CCT, or CRI please contact Lumight and we will be happy to assist you.

 

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