Color Temperature

Color Temperature

Characteristics of Light

 

In this article series, we will have a closer look at the characteristics of light. Since photography is a way of painting with light, it is important to understand these attributes to make the most of them. The five main characteristics are:


  • Color Temperature
  • Direction
  • Intensity
  • Contrast
  • Hardness/Softness

Today we’ll be looking into the color temperature of light.

What is the color temperature of light?


The temperature of light has nothing to do with how warm or cold it is outside, it is a way to describe the appearance of the light. It is measured in Kelvin (K) on a scale between 1000K and 10000K. The color temperature of a light source is an indicator of what the look and feel of the produced light will be. Lights in the range between 2000K and 3000K provide a warm white tone with a red to a yellow color case. Lights in a range of 3100K and 4500K produce a cooler white tone, while lights in a range between 4600K and 6500K produce a light that is similar to daylight.

The most common light sources range from about 1600K (candle lights) to about 9000K (the blue hour). A 1600K cool color would be red, while a 9000K warm color would be a blue tone. 

The human brain is somewhat smart about color temperature, it translates the brightest color into a plain white, no matter what the light source is. You can try this by taking out a sheet of white paper. It looks white, doesn’t it? Or can you spot a color cast? Now, take out a sheet of white paper from a different vendor. If you are looking at one at the time, it will look plain white, but if you compare them instead one might have a slight color cast. Now look at them using a different light source, do they look any different?
With your camera’s White Balance setting, you can counteract the light’s temperature and neutralize it, so that a plain white would look plain white and not white with a tint of magenta.

How to use the White Balance settings?


The White Balance (WB) setting tells your camera what color the light has that you are photographing in. Your camera will use this temperature setting to calculate how much more red/blue is needed to neutralize the color cast of your light source. A neutral color would have a temperature of about 5500-6000K.
So let’s say you dialed in a WB setting of 4000K. Consider the last section, what would your camera add to the recorded color values? More blue (higher color temperature) or more red (lower color temperature) to neutralize the color in your image?

Now imagine you are photographing a candle-light scene, but you want to keep the photo looking as if it was candlelight and not as if it was a neutral light. What kind of color temperature would you use as your white balance? A cooler one or a warmer one?

Yes, I know it sounds complicated at first. 
Remember the following: 
The White balance setting, in general, neutralizes the light source’s color temperature. So you would dial in the light source’s color temperature for your WB setting. If however, you want to get a colder color recorded you would have to warm up your WB setting. Think about it: your camera will use the (warmer) setting to calculate how to neutralize it. So if you are taking a photo at midday outside in bright sunlight (neutral color temperature of 5500K) and you wanted the image to look colder, what would you do? Yes, you would dial in a warmer color temperature into your WB, so that your camera would counteract the extra warmth by cooling it down. To record a photo that looks warmer, you dial in a colder temperature so that the neutralization would warm the color up.

Imagine you had a partner and you could only tell him if you were cold/hot/ok with the temperature in the room. You would expect him to change the thermostat to make you feel ok in the resulting room temperature. You cannot say “make it warmer”/”make it cooler,” but only “I am hot”/”I am cold”/”I am ok.” So you want your partner to make it warmer…what do you tell him how you are? This is what you are doing with your camera: With your WB setting you are telling your camera “I am using a warm/cold/neutral light, please neutralize it for me.”

Auto White Balance

Typically the Kelvin area that the Auto White Balance (AWB) setting can cover is restricted to about 3000-7000K. This means that on a cloudy day or during the blue hour, for example, you would get better results if you set your color temperature either completely manually or used one of the predefined values. You need to bear in mind, that you can fool the AWB even on a sunny day. Set your camera to AWB and point it toward a strong colored object, maybe a blue car. Your camera would interpret the blue car as a color cast and would try to remove that, cooling the temperature into a more amber tone. If you pointed your camera at a red object the opposite would happen. Your camera would interpret the red as a color cast and would try to warm your image up to a higher color temperature.

Examples

The following images are all taken in the morning, roughly around 7:30a.m. in April one and a half hours after sunrise. My camera is pointing toward the South, so I have the sun behind me to the left. There are only a very few clouds in the distance.
What would you set your White Balance to in order to take the photograph?

What if you chose the “wrong” WB setting?


The result depends on what you are shooting in. If you are taking JPEGs only, you have a minimal range to change the White Balance after the file is created. If you are, however, shooting in RAW, you will be able to change the White Balance after you have made your image.
The reason for this is that JPEGs are fully developed images. Not only is the exposure hardcoded in the photo but also settings like the image style or the results of digital filters that you have activated in the camera are coded in the JPEG-file. The RAW file, however, is considered a digital-negative. While you cannot change the depth of field in a RAW image, other settings as the image style, the digital filters but also the White Balance are not saved (permanently) with the RAW file and can be changed after the fact.

RAW files are like the recipe you use to bake a cake. Your post-processing software is able to read and interpret that recipe and present you with an image based on it, but you can, in the software, make an adaption to that recipe and change the outcome. JPEGs are like the finished cake, you can add icing or cut some burned parts away after the cake is made, but you cannot change the ingredients of the cake after baking it.

Color temperatures of different light sources

Light source Light temperature (K)
Candle Light 1600-2000
Oil lamp 2300
Light bulb 2600-3000
Sunrise/Sunset 2000-3000
Tungsten/halogen 3200
Right before/after sunrise 3500
Fluorecent 4000
Moonshine 4100
Morning/Evening 5000
Daylight Lamp D50 5000
Midday daylight / Flash 5000-6000
Daylight 5500-6500
Haze 6500
partly cloudy 6500
open shade 7500
cloudy 7500
blue hour 9000

Exercises

  1. Find out how to change the White Balance for your digital camera. (The manual of your camera describes how to do so.)
  2. You have dialed in a color temperature of 7500K, will your photo be colder or warmer if you use this setting at midday on a bright sunny day without clouds?
  3. You have dialed in the color temperature of Tungsten and are photographing at midday in bright sunlight. Will your photo have a color cast? If so will it be a red or a blue one? Why?
  4. Take a JPEG photo of a landscape scene with all these different WB settings:
AWB, Shade, Cloudy, Tungsten, Flash, Daylight, Lightbulb.
 Is there a difference in the resulting photos? Explain what happened why.
  5. You are in a cozy room, lit by the warm light of candles. In your photo, you want to preserve that warm color cast, what White Balance setting would you use? A warmer one or a colder one? Explain why and test your result with your camera taking a photo.

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