Those who have been around photography for a while are familiar with 18% gray, but for those who are still learning, this can be an easily overlooked concept.  So we're going to try to break it down into some easier to understand concepts (nothing fancy here, folks). The way your camera's meter works is that it reads reflected light off of the objects in front of it.  Since different objects have different reflectance, camera manufacturers decided to use the reflectance