White balance has been discussed to death, and there are plenty of sources available online that discuss how you can best white-balance your photographs. That's all good and well, but I often get questions from frustrated readers. Why? Because all the fantastic resources on-line omit to mention that there are lighting situations where white-balancing your photographs properly is impossible.
This would never happen to your eyes, but your camera can be fooled – in this case, I had my camera set to a manual white balance for indoor photography, which is why this image of Norman Jay came out looking all blue.
The reason that white balance exists at all is because brains and cameras work slightly differently. Our brains are truly astonishing at interpreting different situations, and determining what "white" is.
Per definition, 'pure grey' is a colour where all the colours of the rainbow are represented in equal brightness. Out in the real world, this rarely happens. The colour of the sun changes throughout the day: it's 'warmer' -- or more red -- in the morning and evening, and 'cooler' -- more blue -- in the middle of the day. Artificial light also comes in a variety of different colour tones.
The good news is that your camera can compensate for the different colors of light, by mixing the colors. In automatic white balance, if your camera discovers the picture is too 'cool', it can mix the colors differently, adding in more reds and removing some blues – which results in a well-balanced image.
Of course, you can just use a Gray card and shoot in raw to guarantee that your photos are colour balanced -- but that only works if you're dealing with a single light source. As soon as you add multiple light sources, you're in for a nasty surprise...
This photo is white-balanced for the outside scene; but the wine bottle looks distinctly wrong.
White-balancing on the outside world makes the wine bottle look way too 'warm' – but if you white-balance on the bottle, everything else looks far too 'cold'. In situations like this, you can't win – part of the photo is going to look off.
In many lighting situations, you'll find that you have a series of different light sources. You may be sitting in a restaurant, lit by candle light, with a light-bulb above the table, and some halogen light spots in the background, and fading sunlight outside. These are all different-colored light sources. Unless you're going to do some extremely high-tech photo retouching, you're never going to be able to get them all to look the same.
You can use different light sources for creative effect: White-balancing for the white rose inside a restaurant gave a beautiful, dramatic blue background, even though in reality, it was just a normal, sunny day.
Sometimes, the best you can do with mixed light sources is to colour balance for one of them, so at least part of your photo looks 'natural' – and consider the rest of the photo a mood-lit background.
Haje Jan Kamps is a prolific photography blogger who has written a small stack of books about photography. He also developed the Triggertrap camera trigger and has been known to travel the world a bit. If you’re of the tweeting kind, try him on @Photocritic!