The accuracy of the colour of lighting and the colour of objects in lit scenes is critical to both lighting designers and those who are marketing lighting. Unfortunately inaccurate colour reproduction can be a common problem when photographing lighting, particularly if the picture is taken by someone who does not understand both lighting temperature (CCT) and white balance setting in cameras and image processing software. It becomes especially important if you are trying to show the benefits of a new technology or upgrade to a lighting installation.
Confusion often arises because the scale used for white balance adjustment appears to be the opposite way round to the values of CCT. When a photo is taken on a digital camera the data is captured using a sensor which is recording red, green and blue photons. The camera and its image processing software use the same black body model as the CIE 1931 colour space diagram. The white balance temperature you set is the temperature of the black body radiator that illuminated the scene. Often this setting is done automatically by the camera. If you were photographing a scene lit by direct sunlight and the actual temperature is 5500k and the white balance is set to the same value then the scene appears neutral and as you would expect. However if the camera or photographer chooses the wrong setting say 6500K then the camera is assuming that the scene was illuminated with a higher temperature (i.e a more blue light source) than it actually was. As a result the photo will look more red or warmer than it actually was, because there is not the expected amount of blue light (higher temperature). If we then wanted to correct this photo in image processing software such as photoshop we would then adjust the temperature to add in more blue. We are adjusting the assumption about the black body temperature of the light in this example to a lower temperature value – to add more blue, which is the reason why the scale in photoshop and similar software shows blue having low values (2000K). Conversely if the white balance temperature had been set to 4000k then the assumption the processor is making is that the scene is lit with a light source that contains more red so it overemphasises the blue channel and under emphasises the red. Consequently to correct it you would increase the white balance colour temperature to add in more red.
In practical terms camera sensors can often get fooled as they expect that the overall scene will contain an average “colour” light source. Photos taken on smart phones or point and shoot cameras are highly prone to this problem as there is no opportunity to manually adjust the settings. When you are photographing a scene where there is a very dominant light source for example sodium lighting (orange) or rooms like a bathroom which have highly reflective surfaces of one colour (white tiles for example), then it will be necessary to manually adjust the white balance of the camera to ensure an accurate rendering of the illumination. This can be done by photographing a reference point such as a grey card or measuring the colour temperature at the scene. Most professional photographers will know how to do this and make the adjustments and avoid the pitfalls that a camera’s auto white balance setting might create.
In conclusion if you want to get the best shots of your lighting make sure you work with someone who understands these kind of issues. At Great Impressions we have a background in both lighting technology and photography so why not give us a call on 07557 780336 when you want to have photos taken of your next lighting project or new product. Click here for more.