What is white balance?

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Mixing light temperatures. Kilmainham Gaol, Dublin.
As mentioned in my last module under ‘Newton’, white light is made up from a mix of red, green and blue light. White balance is all about the variations in the behaviour of each of these colours within white light.  These variations give us different ‘colours’ of white light, otherwise known as  ‘light temperature’.  
Our eyes struggle to tell the difference in temperature of white light in all but the extremes of lighting situations, i.e. at sunset and on overcast days.  When different light sources are placed side by side it is easier to identify the differences (Hunter,2012:18). A camera sensor is much more sensitive to the temperature of white light and we need to use various automatic and manual white balance settings to ensure we capture the correct light temperature.  If we fail to remember to change the white balance settings we will open the images in post production and find nasty blue or yellow colour casts in our images. I know this from my own mistakes and experience.
Photographers talk of light temperature measurement in terms of Kelvin scale .   This link is a superb chart that demonstrates Kelvin scale and the best camera settings.
 
Oddly, at the upper end of the Kelvin scale is the ‘hotter’ light is made up of predominantly ‘cool’ blue light and the ‘cooler’ light is made up of the ‘warm’ red light (Hunter,2012:18).
References:
Meyer, J. (2012). What Is Colour Temperature. Available: http://www.digitalcameraworld.com/2012/05/23/what-is-color-temperature-free-photography-cheat-sheet/. Last accessed 24/01/2014.
Hunter,F, et al. (2012). Light: The Raw Material of Photography. In: Unknown, Light, Sience and Magic. 4th ed. Kidlington: Focal Press. 18 – 19 .
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