Your camera’s light meter is a reflected light meter.

Here’s how it works. And you need to simply accept and remember the following:

The in-camera light meter is designed to give a good reading when aimed at a mid-gray (“18% grey”) subject.

By implication, this means that when you aim at a non-midtone subject (like a dark subject or a light subject) the image will be incorrectly exposed.

In other words, because the camera “thinks” that it is looking at mid-grey it will try to render the subject as mid-grey.

One solution is to set your exposure manually while looking at a grey card; then using that exposure for your subsequent pictures taken in that light. That way I get pictures that are right regardless of the subject’s brightness.

Like these two taken at yesterday’s Sheridan College class, of two of my students:

[1] Darker subject, coat, camera:

[2] NBow a lighter subject, dress, wall:

Both were correct at the metered settings of 1/125th second, f/2.8, at 800 ISO. Which I measured off a gray card!