Light comes in many different colours. Daylight changes colour throughout the day and through the seasons, and in different parts of the world. Artificial light also varies in colour from the deep orange of candlelight to the green tinge of fluorescent lights.
The human eye barely notices the changes, but the camera does.
The colour of light is measured using the Kelvin scale. At the lower end, colours are red/orange (e.g. candlelight), while natural daylight averages between 5,000K and 6,000K.
Measuring White Balance
For the most precise white balance, it’s best to set it manually. This usually involves pointing the camera at something white or neutral such as a sheet of paper (or a grey card) in your scene and pressing the button. The camera then measures the colour and adjusts the white balance till your target area has no colour bias.
Manual Temperature Selection
In addition, there is usually a mode that lets you dial in a specific Kelvin setting. This can be handy if you know what the specific colour temperature is (for instance, when using studio lighting) or when you want to go down the Kelvin scale incrementally till you get a colour balance that you like the look of.
In some situations there may be more than one light source – you may have both tungsten and daylight, for example – in which case the camera will either try to set something in between, or go with the dominant source. Neither option may be satisfactory to you, so you’ll need to set your white balance carefully.
Cameras apply their white balance settings to the image while it’s being processed into a jpeg, and can’t be changed later on. But if you shoot in raw mode you will have the opportunity to change the white balance setting in your raw processing software later on if you choose.
White Balance Pre-sets
Digital cameras measure the colour temperature of the scene and, in the default Auto White Balance mode (AWB or, simply, AUTO), adjusts the settings to ensure neutral colours.
This sytem, while generally okay, is by no means infallible. Luckily, cameras also offer a selection of preset white balance settings to cover most shooting situations, as well as a manual mode so you can set the precise white balance for the prevailing lighting.
Setting any of these fixes the white balance at a particular setting, so you must remember to change it if the light conditions change.