What is the Kelvin Temperature Scale?

We are going to dive a bit deeper into the science of light and what it is that your camera is doing when you adjust the white balance. To understand this however, you need to first understand what kelvins are. The Kelvin temperature scale was the brainchild of Belfast-born British inventor and scientist William Thomson — also known as Lord Kelvin – in 1848. It is one of the three best-known scales used to measure temperature, along with Fahrenheit and Celsius. Each unit on this scale, called a Kelvin rather than a degree, is equal to a degree on the Celsius scale. For this reason, just the K, not the degree symbol, is used when reporting temperatures in Kelvin. There are no negative numbers on the Kelvin scale, as the lowest number is 0K. During his research, Kelvin heated a block of carbon, progressing from a dim red light, increasing to a brighter yellow as the temperature increased and ultimately a bright blue-white glow at the highest temperatures.

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All light sources have a specific measurement on the color temperature scale, known as Kelvin scale, which ranges from around 1000 Kelvin to 10.000 Kelvins. Not all light sources have an equal color temperature. If you think of bright light like normal daylight, or studio lights, they tend to have a temperature around 5.500K, which is about halfway up the scale. A candle flame has a warmer, redder light, and is about 1.850-1.930K. At the other end of the scale is pure blue sky from a north-facing source. This comes in at 10.000K. It’s easier to think of the scale as going from dark, warm orange at the lower end to bright, cold blue at the higher end.

Our brain automatically adjusts to these changes in color temperature. If you looked at a white piece of paper under a fluorescent light, then took it outside in the sun, you’d still see a white piece of paper. A camera doesn’t have that ability, which is why we need to tell it what color temperature the light is so that it can accurately adjust the colors to show true white – regardless of whether you’re shooting in candlelight or in bright blue daylight. Yes, you can choose auto white balance mode on your camera, but sometimes it’s not good at judging the color temperature and that is when you end up with a horrible blue or orange cast to your images.

To see the differences on the Kelvin scale through the camera, we will have to select K in the menu where we can find the white balance settings, since it is the manual white balance mode. Then, we can choose in which Kelvin number we want to shoot. When increasing this kelvin number, the camera understands that the light in the frame is cooler, therefore the photo becomes warmer. When decreasing, it understands it is cooler and it will make the photo warmer. Basically, by choosing one or other number, you are telling the camera what temperature the light is and how it should be read. But you have to be careful and don’t go pass the setting for the light type you’re using, because you could make your photo too warm or too cold.

This is kind of a cool way you can adjust your Kelvins and really fine-tune what you want your white balance to be. Maybe you don’t want your image to be fully perfectly natural-looking, maybe you want it to be a little bluer or a little orange, you can adjust these Kelvin numbers to get that exact look that you’re trying to get.

This might seem like just a bunch of random numbers, but by understanding Kelvins can make you better understand what you are doing when you or your camera sets the white balance. You’ll be a better photographer if you can quickly see the lighting in your frame and know what the white balance setting should be and how to play with it do add a more creative tint or look to your image. Also, by knowing what your camera is registering as true white, you will be able to better understand how the rest of the colors in the image will come out. This is very important when you start mixing light sources in an image.

Nevertheless, you could just change your white balance in post-processing – if you shoot in RAW format. You can change the white balance to any that you like best in Lightroom, because a RAW image stays unprocessed by the camera, and any settings it applies are for reference only, they do not affect the actual image.

One of the advantages of shooting RAW files is that you can apply different white balance settings to the image to see which give the most natural, or most attractive, results. The original RAW file remains unchanged. All the work is done on copies of the RAW file, which means that you can return to the RAW file and try again if the initial results are not what you want.

If you shoot JPEG’s, however, you can’t change it in post. You can try, but you won’t like the results. So, you’ll have to learn to white balance for any given lighting situation. Although shooting in RAW format almost exclusively, always set your white balance before a shoot. It just saves time in post-processing, and you can see the colors rendered accurately as you shoot on your LCD or tethered PC screen.

 

Continue to lesson 45: White balance modes & auto white balance