Colour Temperature

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"Camera Blindness"

"Colour Temperature?" - What has temperature got to do with colour?

Have you ever noticed how much redder things look outside in the early morning or late evening when compared with mid-day?

On a cloudy day, some colours appear more blue than when the sun is shining.

The sun is consistently the light source and yet, depending on the time of day and the amount of water in the atmosphere, it’s effect on the colour of things changes - like a rainbow.

Indoor lighting also has it’s effect. Fluorescent lighting casts a greenish colour, tungsten bulbs make things appear more orange and candle light turns colours redder still.

At the red end of the spectrum colour temperature is low, at the blue end it is high. It’s curious how we think of red as a warm colour and blue as a cool one - the exact opposite of the way it is measured.

Feel free to skip over this next bit unless you are keen to know why.

The colour temperature model is based on the relationship between the temperature of a theoretical standardized material, called a black body radiator, and the energy distribution of its emitted light as the radiator is brought to increasingly higher temperatures, measured in Kelvin (K).

Although this radiator does not exist, many metals behave very similarly to a black body so we can take a metal pot as an example.

Colour Temperature

In this illustration the metal pot is first heated to a temperature of about 900 K (pot on the left), where it begins to glow a dull red. As the temperature is increased to between 1500 and 2000 K, the pot (second to the left) turns a yellowish to brighter red colour.

As the temperature is further increased above 3000 K the colour turns to a yellow-white (the third pot from the left), and at 5000 K and above (the pot on the far right), a bluish-white color appears.

(Explanation and Illustration courtesy of Olympus Corporation)

All light affects the way we see colours but we compensate and mentally adjust the colours back to what we are used to. We see a Caucasian's skin as flesh pink, no matter what colour the light source changes it to, but when it comes to photography lighting -

A camera does not have the capability to automatically compensate for colours.

It has to be told the colour of the light source if it is to record colours accurately. Modern cameras have clever means of estimating the colour of the light but all cameras can be fooled so it’s worth knowing how to set it correctly.

Unless your camera is completely automatic and you cannot change its settings, your instruction book will tell you how to adjust for the colour of the light source.

Colour Temperature

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