LUMIGHT BLOG POST
TOPIC: CONTRACTOR’S GUIDE TO COLOR AND CRI
Contractors Guide to Color, CCT & CRI
By Craig DiLouie
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 what is Color?
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.
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.