12 Jun 2018 | Sean Keenan, PE

The Science of Light: An Investigation into Color Temperature

In a previous blog post, I introduced the Bialosky Lighting Laboratory and started to investigate the science of light and its integral role in design. Today, I’d like to delve deeper into the topic of color temperature.

Color is not an intrinsic property of light or objects: it is a perceptual phenomenon that is part of the visual experience. The spectrum of the light source affects how we perceive the colors we see in the lighted environment.

Color is one of the most definitive examples of where simple lighting choices can have dramatically different effects on how space is visually experienced by its users:

  • The color of the light source – whether the appearance is warm or cool.
  • The color rendering of fabrics, objects, and finishes – whether the colors appear attractive and are rendered accurately.
  • The color appearance of skin tones – whether faces look pale, flush, jaundiced, etc.
  • Color contrast – describing the visibility of the task detail against its background.


The metrics used to quantify the color appearance of a light source are chromaticity, dominant wavelength, correlated color temperature (CCT) and color rendering index (CRI). We will examine CRI in a future blog, but let’s now explore the role of color temperature and its requisite role in design.

CCT is measured in Kelvins (K), a temperature metric similar to Celsius with equally sized degrees, but starting at absolute zero. 0 degrees Kelvin  =  -273 degrees Celsius. A theoretical reference source called a black body radiator is used which when heated and glowing will shift in color with heat continuously along the visual spectrum. This body is black at room temperature, but as electrical current passes through the body, it heats to a red-orange glow. As the temperature increases, the color shifts to yellow and along the spectrum to a bluish light. A temperature measurement of the body can be taken at any time and that value corresponds to the color of the light. Light sources that employ disproportionate levels of each wavelength are measured by CCT which compares to the black body radiator.

Light sources are loosely classified as “cool” (4000 K or greater – blue appearance) or “warm” (3000 K or less – yellow appearance), while “neutral” lies in the middle (3500 K – white appearance).

Warm sources include red and orange wavelengths, accentuating skin tones and enriching the appearance of red and orange in objects. Cool sources include blue and green wavelengths, enriching the appearance of blue and green objects. 

CCT plays a large role in controlling our circadian rhythm as well. The use of cooler CCT stops the production of melatonin in the body, increasing alertness. Lighting designs have used this recent discovery to improve health and wellness in the areas of education and healthcare, along with helping control the symptoms of Alzheimers and Autism.

Because the paramount purpose of lighting is to serve the needs of humans, color temperature becomes another factor designers employ to predict the impact of different sources. The importance of color to the application must be weighed by the designer. Some light sources display poor color characteristics, but higher efficacies (lumens of light output per watt of energy). Other light sources offer preferable color quality, but drive up the installation cost. Designers gauge the needs of the application and then compare light sources (weighing potential trade-offs in appearance, color, efficacy, cost and overall performance) in choosing the most appropriate source for the application.

Now when we are selecting fabrics, room finishes and colors, we can closely examine them under light with the same color temperature as the lamps being proposed for the space.

Color temperature is one of the most influential mood-setting features of a space. Our lighting laboratory allows us to explore the effects of color temperature on our design, deliberately creating moods and enhancing architecture.

For those design professionals, building owners, clients, and students interested in learning more about experimenting in the lighting lab first hand, contact Sean Keenan through our contact form online or at 216 752 8750.