If thinking of skipping this page, there is a Summary of Flash
Metering Principles below. There are two types of light meters,
reflected meters (at left) aimed at the subject from the camera
or from the camera direction, which reads light reflected from
the subject. And incident meters (at right) aimed at the camera
from the subject position, which reads the actual direct light
incident upon the subject - at the subject, but totally
independent of the subject. Since cameras are not located at the
subject, they can only use reflected meters. Reflected meters
are aimed at the subject from camera, and read the light
reflected from the subject. A black dress will read much lower
than a white dress, so, we must realize what we are metering.
Incident meters instead read the actual light source (aimed at
camera, away from the subject), and are usually close to
correct, because incident measures the actual light, which is
independent of the variable reflection from the subject. Meters
like the Sekonic L-358 or L-308S