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Home Latest Articles PC Monitors Kagoo Explains: Light Part 1 - Colour Temperature

Kagoo Explains: Light Part 1 - Colour Temperature

Updated 14 October 2020
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Welcome to ‘Kagoo Explains’ - a series of short articles de-mystifying some of the confusing terminology used to describe tech. Today we’ll be looking at colour temperature, and how ‘warmer’ and ‘cooler’ colours affect your monitor or TV.

Visible light is a surprisingly complicated subject. The light we see is only part of a wide spectrum of electromagnetic radiation - one that includes everything from radio waves to x-rays. Visible light is approximately in the middle of this range, as a narrow band of electromagnetic radiation we are capable of perceiving naturally.

This article will look at an overview of visible light & energy. For a detailed discussion on Blue Light, see Kagoo Explains: Light Part 2 - Blue Light

Catching Some Waves

All of these different sections of the ‘Electromagnetic Spectrum’ - radio waves, visible light or x-rays - have different wavelengths & frequencies, which are concepts that will need a bit of explanation. When we talk about ‘waves’, we mean that all these different signals regularly move (oscillate) between a high point and a low point, like a pendulum swinging from left-to-right in a grandfather clock. There are 2 important concepts connected to this:

  • Wavelength: The distance between ‘crests’ in a wave - i.e how long it takes to complete a full movement to return to the same point again
  • Frequency: How many times the wave repeats in a set period of time.

These two are closely connected - if a wave has a longer wavelength, then it will have a smaller frequency, since it’ll take longer to complete each repetition. On the other hand, if a wave has a shorter wavelength, it’ll have a higher frequency, since it can fit more repetitions into the same amount of time. This is known as an ‘inverse correlation’.

Why is this important for light and colour temperature? Electromagnetic waves carry energy - and higher the frequency of the waves, the more energy is capable of being carried over a set amount of time. Slower waves - such as radio waves - therefore carry far less energy than much faster waves such as x-rays. The same thing happens at a smaller range with visible light - colours on the red-brown end of the spectrum carry less energy than blue-violet colours.

This difference in energy is the cornerstone of understanding why different lights feel ‘warmer’ or ‘cooler’ to us - also known as Colour Temperature.

Warmer… Warmer… Colder...

Colour Temperature is measured in ‘kelvins’ (K), a unit that measures absolute temperatures. It measures how much energy the various sections of the visual spectrum are capable of carrying. And since heat is a transfer of energy from one source to another, the level of energy is directly related to the temperature.

Stop thinking about vodka - ‘Absolute’ in this context means the temperatures are measured directly against the energy they give off. So the lowest absolute temperature is one with the lowest possible energy level. This is Absolute Zero: 0K or -273.15 Celsius. That’s pretty cold!

Colour temperatures range from browner ‘warmer’ shades (around 2000-3000K) to white-blue ‘cooler’ shades (5000K+). So a harsh white fluorescent light would be an extremely cool shade, while a candle flame would be far warmer.


While this may not seem too important, the choice of colour temperatures you surround yourself with has significant hidden effects. Everything from the choice of bulbs in your room to the setup of your PC monitor changes how much of a certain temperature colour you are exposed to, and this all affects your body’s internal clock, the Circadian Rhythm.

Feel the Rhythm! Feel the Rhyme!

Circadian Rhythm’ is the internal sleep/wake cycle we naturally conform to. It tells our bodies when to feel drowsy & sleep, and when to wake up & be alert. Numerous factors control this rhythm, but light is one of the biggest. Sunlight has a very high concentration of blue-white light, so when your body perceives light on the cooler end of the spectrum, it releases chemicals to help you feel energetic & awake. On the other end of the scale, comfortable brownish light and warmer colour temperatures are perceived by the body as signs that it is nighttime, and so it releases chemicals to make you feel drowsy and sleepy.

By now you’re probably thinking “This is all backwards! Why are the scientifically warmer temperatures considered ‘cooler’, and the cooler temperatures considered ‘warmer’?” It’s a fair question - and the answer is that ‘warm’ and ‘cool’ are named because of our historical perception of such colours. Warmer colours mimic the comfortable glow of fires and candles in the evening, while cooler colours evoke cold sensations like snow and ice. In this case the psychological connection to the colours has proven more resilient than scientific accuracy.

The choice of colour temperature is therefore very important when calibrating your TV, PC monitor or smart phone - many of these will have special modes to transition the colour temperature from cooler to warmer shades as the day progresses, helping keep your body in its natural rhythm. This also helps reduce the amount of blue light you receive from viewing screens. The use of a correct colour temperature can help reduce eye strain and headaches if you view screens a lot during the day.

Hopefully this helps give a better understanding of what colour temperature means, and how some colours are ‘warmer’ than others. If you want to know more, look at our followup article on Blue Light!

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