Colour temperature is measured in in units known as Kelvins and is related to the light that is radiated when a metallic incandescent light source is heated to various temperatures (Hicks, 2005). The range of colours we go through is roughly red, orange, yellow, white and through on to blue. On the Kelvin scale the temperatures run from approximately 2000K to 16000k with neutral white light coming in at around 5500K
White is generally considered to be the visual standard and this can be found in the middle of the day. We are likely to find the lower temperature red (2000 - 3500K) in the early morning and late afternoon . A blue cast (7000K) can be found in the shadows on a sunny day, at dusk or in cloudy weather.
Also of importance is the colour temperature of indoor tungsten lighting which is around 2900K to 3500K, so in the orange/red area. For the sake of this exercise we will not include florescent lighting as this is not classed as incandescent light and can therefore not be measured in Kelvins.
Armed with this knowledge we can proceed with the exercise. The camera has settings for Auto, Shade, Cloudy, Sunlight, various artificial light sources and custom white balance. We are going to see how well some of these settings work for given situations.
The first group of pictures were taken under sunny conditions. In this sequence the difference between auto and cloudy seems difficult to detect but both seem a little lighter than the sunlight shot. Maybe cloudy has added a little more exposure? The sunlight setting appears pretty close to how I remember the scene. The 'shade' white balanced version appears the most different. The camera processor has added orange/yellow to the image. The amount that has been added has made the image much warmer than the sunlight setting. This makes perfect sense. The camera has assumed that I have photographed something in the shade so has added orange/yellow to compensate for the blue cast mentioned above. Unfortunately I lied to the camera and the orange/yellow has been added to a normally daylight balanced photo!
|Auto white balance, F4 @ 1/ 2500 200 ISO.|
|Cloudy white balance, F4 @ 1/ 2500 200 ISO.|
|Sunlight white balance, F4 @ 1/ 2500 200 ISO.|
|Shade white balance, F4 @ 1/ 2500 200 ISO.|
The camera has mistakenly added yellow to compensate for the non existing blue cast!
|Shade white balance, F5.6 @ 1/125 100 ISO.|
|Auto white balance, F5.6 @1/125 100 ISO.|
|Sunny white balance, F5.6 1/125 100 ISO.|
|Cloudy white balance, F5.6 1/125 100 ISO.|
|Cloudy white balance, F8 1/40 200 ISO.|
|Auto white balance, F8 1/40 200 ISO|
|Daylight white balance, F8 1/40 200 ISO|
|Shade white balance, F8 1/40 200 ISO|
I shoot RAW all of the time and this is one reason that makes this worthwhile. The white balance can be tweaked in software after the shot has been taken. On important shoots I have also started using a grey card for the same reason.
The final part of this exercise asks us to compare settings for an image shot partially in natural light and incandescent light. To make this picture I shot from within a room with the light on through a window to the natural light outside.
|Auto white balance, F1.8 1/60 100 ISO.|
|Daylight white balance, F1.8 1/60 100 ISO.|
|Tungsten white balance, F1.8 1/60 100 ISO.|
Pushed to make a choice, I think I would choose the daylight balanced version. There is no main subject to focus on so it is purely a matter of what feels right. I like the warm interior and natural lighting on the other side of the window and can identify with the colours this way. I feel there is little difference between this and the second shot but that the tungsten balanced photo is too cold.
Hicks, N, "The photographers guide to light", David & Charles.