Before digital became the medium by which we made photographs the control of colour temperature was something that only professional photographers considered seriously. We had colour temperature meters that would read the colour of the light, not the brightness. From that we could deduce the colour correction filters we needed to adjust the colour of light to match the film we were using. Since the advent of digital cameras we use the White Balance controls to manage colour temperature. This article on the Lightstalking site By Jason Row explains this process
“Lord Kelvin, AKA William Thomson has a lot to answer for. It was this Glasgow University based physicist that developed the scale of measuring temperature that we use in photography today. So why does a scale of temperature have relevance in photography? Well the Kelvin scale also measures the colour of light. The science of this is somewhat complicated but put in it’s simplest terms, if you have a pure black radiating object and heat it up until it is glowing, when the temperature is below 4000K it will appear reddish, above 7500K it will seem bluish.
So why is this important to us photographers?
Well, light at different times of the day and under different conditions will have different colours. Our eyes are so highly developed that we do not see this change, our brain quickly adapts to the difference but colour film and more recently digital sensors cannot adapt.
In terms of film, it can only be set to one color temperature, usually 5500K which is the average colour of the shade on a sunny day at noon, or, 3200K which is the temperature of tungsten light, for example the average household light bulb or professional photoflood studio lights. Digital sensors can be set to a range of colour temperatures but rely on one of two things to get the right white balance – the camera’s metering system or the user setting it manually.
Neither of these are entirely infallible so if we can understand a little of what the colour of the light is in a given scene, we can improve the colour rendition of our images.”.….MORE