Photography A - Z the Easy Way: K -
Kelvin or Colour temperature
By Eric Hartwell

Kelvin? Colour temperature? What is it all about?

The first thing to say, is don’t worry yourself about it too much except to realise that light has different colours. Some bright spark made up a “temperature chart” in “degrees Kelvin”. This is basically a way of measuring how orange or blue light is.

For example:

A beautiful sunset is very “orangey” and has a Kelvin temperature of about 2500. However, a blue sky has a Kelvin temperature of 10,000. The bigger the number the “bluer” the colour.

What does this mean to you? Not a lot and certainly you can switch off when people start harping on about Kelvin. For your purposes, when people talk about Kelvin, they are saying how blue or orange the scene or image is.

Your eyes can deceive, and frequently do. What you see before you will not always be the same as what turns out on the final image because your brain makes adjustments.

What you therefore need to be aware of is the different colours or “temperatures” at different times of the day and in different situations. Pure blue sky is blue (no surprises there). Shade from a blue sky is still blue but not “as blue”. If the sky is overcast then it is even “less blue” and in the early afternoon it is positively “more yellow”. As the day wears on it becomes “more orangey” and then “more red”.

That’s under sunlit conditions and even then you can be fooled as the light in the early morning is positively orangey in overall hue (provided there is sunlight).

To the practical bit. Your pictures will look different depending on what time of day it is and what type of light is illuminating your subject. Your camera will have AWB (Automatic White Balance) which will compensate for excesses of colour in your shots and any “colour cast”.

But, for best results you should use custom white balance if your camera has it. In this way you switch to “daylight” for normal daylight, “overcast” for cloudy or overcast etc.

Other situations can be allowed or compensated for. Artificial indoor or cityscape lights will be overall orange in hue (but you can't see it with your naked eye). Flash from a flashgun is very “blue”. The answer to the problem is simple – switch to “indoor” or “artificial light” for the former and “flash” for the latter.

Don’t worry if you don’t understand it all. First, you don’t need to and second, AWB on you camera will cover all the most likely situations pretty well.

Eric Hartwell runs the photography resource site http://www.theshutter.co.uk and the associated discussion forums as well as the regular weblog at http://thephotographysite.blogspot.com.

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