A World of Grays

Although you live in a splendid world of many colors (the computer monitor I’m looking at right now can discern and display millions of them), your light meter interprets the world as a single gray value — tragic from the perspective of human imagination and vision perhaps, but a very efficient model when it comes to accurately measuring light. By assuming the world is a single tone of gray, your meter ignores the gaudy trappings and distractions of color, and measures just one thing: how much light is reflecting from the scene that you are pointing it at. And in reality, that is all the basic information you need to create a good exposure.

Regardless of the type of light meter you’re using, all of them are calibrated on the following two premises: first, that everything in front of them is (and should be recorded as) 18-percent gray or medium gray, as it’s often referred to, in tone; and second, that this is just fine with you. All meters are designed to see the world as 18-percent gray because gray represents a tonality that is exactly halfway between pure black and pure white. It doesn’t matter what colors your subject contains or what lighting is illuminating it; your meter is going to give you an exposure recommendation that records that subject as a medium tone.