White balance and overall colour

White balance is a very important setting on our cameras.  It is often overlooked because we are unaware of the neutral, colourless ambient light present in our images.

This is because our eyes adapt quickly to the changes in the colour of light.  For example, there is a difference in the colour of sunlight when the sun is high in the sky to when it is setting.  Tungsten and flourescent lighting have a orange/red and green hue respectively.  Our eyes do not notice this colour because our brains process and 'neutralise' these colours.

The camera's sensor will record all these colours.  This means that we need to consider changing the white balance in different lighting situations.

Our visual standard for colour is sunlight and in the middle of the day it is 'colourless' which we refer to as white.  This is our benchmark for normal lighting.  From this white in the middle of the day sunlight takes on a reddish hue at sunset and sunrise.  This is often seen as yellow or orange in a weak sunset/sunrise.  A very strong one however would make for a very red sky.  In the shade on a sunny day the light takes on a bluish colour.  We refer to these colours as the colour temperature scale and this is measured in degrees Kelvin.



In general, the cooler the Kelvin temperature the warmer the colour.  Therefore we need to be careful when describing reddish colours as warm because in fact they are cooler on the Kelvin scale.

Let's think about why colours have a 'temperature' briefly.  If we were to heat something that wouldn't easily burn like iron, it first becomes reddish, then yellowish and then white.  In hotter temperatures materials can become blue.

As we can see from the above scale, midday sun has a temperature of about 5400 to 5500 Kelvin.  When the sun lowers in the sky the temperature drops to about 4000K in the afternoon to below 3000k at sunset.

Reflected light from a blue sky can be as high as 6500K.  This is shaded areas.

D90 white balance settings

• Auto - this generally makes a good guess at the white balance.  I have found it to be pretty reliable in most situations and tend to shoot mostly using this setting. 
• Incandescent - tungsten.  Makes images very blue - use indoors with conventional tungsten lighting.  You can also use it to make your images have an arctic feel to them say in landscapes etc.  
• Fluorescent - makes images taken with fluorescent less green.  I generally prefer to use the Auto setting for these situations because I haven't found this to have a noticeable positive effect on my images. 
• Direct sunlight - midday sun.  
• Flash
• Cloudy - produces warmer than direct sunlight.  I tend to use this for sunsets when I want warmer colours.
• Shade - adds a bit of orange to your image to tone down the blue associated with shooting in the shade.  
• K to choose a colour temperature.  5400K for direct sun, 7500K for shade.  
• Presets - I can save 5 presets on my camera.  You can use a white piece of card or paper to set the white balance using presets. Place the white card in the same light as your subject and then press the WB button.  The camera will automatically record the correct temperature for you to use in that particular setting.

Within each of these I can adjust the white balance to fine tune the settings.