White Balance - Understanding Exposure

"Tokyo Train Platform, with multiple white balances" Tea L

I find that White Balance is often a concept that is a bit confusing to beginners. Is white balance exposure? No. But do you usually deal with it at the same time as exposure? Yes. So what is it exactly? Well let’s demistify it. 

For quick reference

Here are your basics for review, but if you are seeking to understand, continue on.

• White balance is measured in Kelvin (i.e. 3200K) if you want to assign it manually.  

• Most cameras have an auto white balance setting as well as multiple presets for sun, shade, indoors, fluorescent, etc which will set the correct kelvin value for you. 

• I would personally suggest choosing an appropriate preset (Day, Cloudy, Shade, Incandescent) or a kelvin setting for white balance, if you think you can manage it. 

• This is because the auto function can sometimes vary wildly in various situations where it detects (or thinks it detects) multiple color temperatures of light.

The colors of white light

White light is a spectrum of different colors, but it also is not universal. What appears as white light to our eyes is largely dependent on context. The perception of light as “pure white” is less about what light comes into our eyes and more about how our brain interprets that light. This is something our brains are extremely good at, it turns out. 

If you walk from one distinct lighting environment to another, you may notice a momentary hitch in our brain's interpretation of white. Walking outside in the middle of the day after being in an artificially lit room, you might notice things might seem extremely blue for a few minutes.

Why is this? It’s because light approaching white can vary a lot in two defining characteristics Temperature and Tint. 

image credit: Synergy Creativ

Color Temperature

Color temperature is based in mathematical / scientific observation, I am not going to describe that here as I think it confuses a lot of people. For simplicity sake, we can say that white light exists on a spectrum between “warm” orange tones and “cool” blue tones.

This spectrum is described as temperature and is measured in Kelvins (K). 

Incandescent lightbulbs (i.e. classic bulbs with a filament) produce “warm” orange light, which is also the color temperature that modern “warm” led lights seek to approximate. This typically exists in the range of 2400K to 2700K. Old school incandescent film lights sit at a "cooler" tone of 3200K. 

The sky, however, is on the other side of the equation*. Full daylight is often in a range between 5000K and 6500K, firmly towards the “cool” blue tones.

Other forms of daylight can be far bluer than that, ranging over 10,000K. 

*The wrinkle in this is that there are conditions where sunlight changes its color temperature, notably sunset and sunrise, otherwise known by photographers as "Golden Hour". Here its color temperature drops matching firelight, going as low as 1700K.

When operating a camera, we instruct the camera what color temperature to expect, more on that in a few. 

Color Tint 

The other spectrum we tend to look at with white light is Tint, which ranges from Magenta to Green. This is less often compensated for in camera and more often compensated for during color correction in editing, as the changes are usually very slight. 

However, most cameras do compensate for this in their fluorescent presets, as fluorescent tubes and lights have a tendency to cast more of a green tint. 

The main effect of tint on the image is that magenta is found in human skin tones, so if the light source falling someone’s skin is very green it can leave the looking sickly.

image credit: Oh My Camera

How do we deal with this in camera?

This impacts your camera because the camera is standing in for your brain. It needs to make the judgement as to what part of the spectrum the “white” in your image should be calibrated to at any given point. 

This can be done one of three or four ways: 

1. Auto White Balance: The processor in the camera looks at your image and continuously attempts to determine what the color temperature should be and adjust to that temperature. 

2. Presets: Cameras typically have a number of presets that are fairly intuitvely labeled with words or pictograms. Sunny, Partly Cloudy, Shade, Flourescent, Incandescent (light bulb) maybe even underwater moders (fish). The appropriate preset for your situation can be selected from the list. 

3. Kelvin (Manual): You know the Kelvin scale well enough to dial it in on your own. This allows you to roll through the values and see the effect in real time. 

4. Custom: This varies by camera but involves the camera taking an image capture and using the auto white balance system to set a static white balance. So, once it is set it does not change. 

   
   

Any and all of these can and do work, but here are the two common pieces of advice I would give people. 

1. Avoid auto white balance if you can, it will help you in post. Due to the continuous nature of the auto mode, it can shift over time even in the same lighting conditions. It can be somewhat difficult for new editors to color balance different shots in editing, but it will be extremely difficult to correct multiple changes in a single continuous shot. By using any of the other options, you assure that you do not run into this problem. 

2. If you are shooting with multiple cameras, use Kelvin. All cameras have presets for the same scenarious like shade. However, these presets are not always uniform across different models or makes. As such, if you are going to edit multiple cameras together, it will make your life much easier if they are all the exact same temperature, hence Kelvin.