Understanding the Kelvin temperature scale is another scientific or technical bit of knowledge that will help you take better digital photography. Named after a Scots scientist of the 19th century, the Kelvin scale is another way to measure temperature like Fahrenheit or Celsius. The difference is that the Kelvin scale starts at absolute zero, which is –459.67 degrees Fahrenheit or –273.15 Celsius. This was important information when the only photographic medium was film. Some film was manufactured to be used only outdoors (or indoors with a flash) or only indoors (without a flash). If you shot the indoor film outside, all your pictures would have a blue cast.
Light consists of various colors, as you can see when light passes through a prism. The Kelvin scale measures the light in terms of whether it trends toward the orange or blue. Once you understand what kind of light (or color) is orange, blue or somewhere between, you can make the necessary adjustments when shooting your digital photos.
The deep blue sky of the tropics is about as blue as possible, and is designated as 10,000 Kelvin. An intense sunset goes almost completely orange on the Kelvin scale to a 2,500 reading. Obviously, as the Kelvin number increases, the bluer is the color. It’s difficult for your eyes and mind to distinguish the various levels of blue or orange as accurately as your camera will, meaning the color in your digital photos may look different than you thought they would.
The time of day and the lighting conditions will determine how your camera reproduces colors. When you understand how the time of day and the lighting conditions have that effect you can make some camera adjustments to compensate. For example, on a typical day, the light starts as quite orange at sunrise, progresses through various shades of blue, depending on cloud cover, and then becomes orange again at sunset; in fact, so orange, it becomes red.
If your camera has an automatic white balance feature, or AWB, then it can make whatever adjustments are necessary, so your camera can reproduce the colors accurately. Your camera may also have a custom white balance setting, which allows you to choose “daylight” for standard daylight, “overcast” for less light, etc.
Indoor lighting or street lamps, signage lights, etc. will trend toward orange, but it won’t be visible to you. To compensate, use the “indoor” or “artificial light” setting when shooting inside and use the flash, which produces a very blue light, for any artificial light sources outside.
It most cases, the AWB feature of your camera will make the necessary adjustments automatically, but there are some situations where understanding color temperature and the Kelvin scale will help you shoot digital photos with better color balance.