Demystifying CCT & the Colour of White Light.
Every day we move through spaces filled with white light – our homes, our offices, stores, restaurants, gyms, and of course the great outdoors. As you experience these different environments are you aware of how the colour of the white light changes? Have you noticed that your home and restaurants are usually a “warmer white”, your office is a “neutral white” and stores and gyms can often be described as “cool white”? This difference in the colour quality of white light is known as Colour Temperature and understanding its metrics and general effects is a key tool in architecture and lighting design.
Almost everyone has spent time by a fire; whether outdoor summer camping, indoor winter relaxing or all season barbeque cooking, fire is the common element. If you look at the fire you’ll notice that it varies in colour - from deep red glowing coals to flickering yellow and orange flames to intense blue flame cores. The difference in these colours is produced by the physical temperature of the burning gas; the blue flame cores are the physically hottest temperature, while the glowing red embers the physically coolest. This counterintuitive temperature-to-colour relationship, wherein the cool colours are hot temperatures and the warm colours are cool temperatures is the foundational concept for understanding colour temperature.
Our next step is to apply a metric to this concept. Temperature is measured in degree scales. We are all familiar with Celsius (°C) and Fahrenheit (°F) from our daily weather forecasts. What may be unfamiliar is a third temperature scale called Kelvins (K). Named after the British inventor Lord Kelvin, his scale differs from the others in that there are no negative numbers. Rather, 0 Kelvin represents “absolute zero” where it is so cold molecules no longer move. To translate this into common terms, 0 Kelvin equals -273°C / -459°F – brisk to say the least.
The lighting industry uses the Kelvin scale to quantify the colour temperature of the white light. Relating back to our example of the fire, the higher the temperature in Kelvin, the cooler the white colour produced. For specificity the lighting industry applies the Kelvin scale to a theoretical “black-body radiator” – a good real world analogy is a coiled heating element on an electric stove top. When unheated the black body radiator (stove coil) is black, representing no colour. As heat is applied it begins to glow with low heat producing deep reds and higher heat shifting to orange and yellow. Moving beyond our analogy we can continue to heat our theoretical radiator until we reach temperatures producing our various colours of white light. The black body radiator allows us to correlate the colour of white light emitted to specific temperatures on the Kelvin scale. This correlation gives us our official term of Colour Temperature or CCT for short.
Now that we understand what CCT means, we should discuss how to use this information in our designs and buildings:
With all that said, it should be noted that these typical CCT examples are basic guidelines to assist with understanding colour temperature concepts. Architects, Lighting & Interior Designers are encouraged to consider deviating from these basics and trying other CCT options where unexpected. When executed well the results can be striking in providing inhabitants with a different memorable experience – see the below example of 8th Street SW in Calgary Alberta for a successful use of CCT juxtaposition.
Further, new LED technology is allowing us to change the CCT within a light. This exciting break-through known as “Tunable” or “Dynamic” white adds complex new options for our clients and designers to consider for their projects. The Wirecast will definitely be discussing this topic in the near future.
SMP Engineering has extensive experience providing state-of-the-art lighting design solutions and would be pleased to partner with you on your next project. Should you have any questions regarding the content in this post, please contact our office.