Pulsar Knowledge – Colour Temperature Series Pt. 1


What is Colour Temperature?


Colour temperature is a way to measure the colour of the colour of white light. But wait, isn’t white light just one colour? The short answer is no. In the 17th century, Isaac Newton showed that white light is a combination of many different colours. Later, Max Planck, another physicist, showed that the exact mix of those different colours is determined by temperature. White light comes in many different shades, from the warm glow of a fire or tungsten bulb to the cool clarity associated with daylight, or a laboratory. Here, temperature refers to how hot you’d have to heat up a material (this could be a filament) to create that specific colour of white light. Lower colour temperatures tend to be closer to amber, and higher colour temperatures become bluer.

Why do we consider these colours to be white, rather than amber and blue? This is simply because these light sources still give out a full spectrum of light, rather than just one colour. When plotted on a graph, the colour temperature scale forms a line known as the Planckian Locus (see image below).

Colour temperature is measured in Kelvin (k). This measurement represents the temperature that you would have to heat an imaginary perfect material (known as a black body radiator) to create the same light colour.

Why colour temperature?


Why use colour temperature as a measurement of light colour? Could we use a different scale? Nearly all the light sources that exist in nature emit light by heating something up, and so fall along the Planckian Locus. This means that colour temperature has many useful reference points and is easily transferrable across many different disciplines of science, design, and art.


Why is colour temperature so important?


Because colour temperatures exist in nature, certain colour temperatures are very powerful at evoking emotions. Warm colour temperatures, such as the light cast by a fire, a candle or a tungsten light bulb provide a welcoming, cosy feel. Cool colour temperatures like daylight are energising and encourage clarity.

Colour temperature is a subject of much research right now, and the science shows that colour temperatures play an important role in how the body produces melatonin, and can have profound psychological and photobiological effects.


What do different colour temperatures look like?


See the images below for an idea of how different colour temperatures look in an architectural lighting context. This represents the typical range of colour temperatures used in architectural lighting design.

If you’d like to read more about colour and lighting, check out our article on colour mixing from the link below.