Despite the lack of it, color is very important in Black and White Photography.
White Balance (or Color Balance) is one of most commonly used tools (it's actually two: temperature and tint) in color photography to modify the warmth and tint of an image.
It is overlooked by many when it comes to Black and White imagery, but we'll see why you might want to add this tool to your monochrome editing workflow.
Some colors are brighter than others
Black and White is all about the brightness: how white and how black something is. We could believe that a yellow and a blue flower would convert to the same shade of grey, given the same brightness for both.
However, our eyes don't see colors that way: yellows appear brighter than reds, and reds brighter than blues.
Editing software tries to mimic this behavior. This is how colors convert in Lightroom using the default Adobe Monochrome profile:
As you can see, yellow is brighter than green, green is brighter than red, and red is brighter than blue.
Warmth affects the brightness of an image
We can dramatically change the colors of our image by modifying the Color Balance. If we increase the temperature, we are effectively putting more greens and reds while subtracting blues, and the other way around. Look at how the histogram changes:
A direct result of this is that warm images will be brighter than cool images when we convert them to Black and White. That's because, again, red and yellow tones are brighter than blue tones.
We start to see how Color Balance can be used to change the exposure of our photographs.
As opposed to the exposure slider which affects all colors in the image the same way (changes the brightness of all of them), the White Balance setting is more selective as it affects the brightness of colors in a different way:
Think of White Balance as an advanced or more selective way to change the brightness in our images.
We can even use it in combination with the B&W Mixer Sliders (which allow us to change the brightness of individual colors) to further increase our ability to modify how colors render in Black and White.
Color Balance in Black and White Film Photography
What about B&W film? Color Balance is set in the film stock itself and can't be changed afterwards (we lose all information about colors when shooting Black and White film). Each stock treats colors in a specific way, that's why different Black and White films render differently. The only way we have to change the Color Balance when shooting film is to use color filters.
A creative tool
Despite being disregarded often as simpler and easier, Black and White photography is very complex. I love it because as artists we can get really creative with all the tools that it provides. White Balance is just another one.
Next time you are converting a raw file to Black and White, try playing with the Color Balance and see how it changes your image. At the very least, keep it in mind as yet another tool to tweak the exposure and contrast of your photographs.