Light meters measure the amount of light falling on the subject. If you desire a certain ISO, shutter speed, or aperture setting, you can input this information into a light meter, take a “reading,” and the light meter will calculate the appropriate corresponding settings for your camera. When using a light meter, your camera should be in manual mode.
Light meters average the amount of light in the scene, taking into calculation the light and dark areas, and provide a reading that would be appropriate if the entire scene was an average of the two, or a medium gray. For brightly lit scenes or dark scenes, you will want to take into consideration methods that were discussed on page 168.
In-camera light meters measure the light reflected from the subject and are referred to as reflected-light meters. Any meter that is held from the camera location and aimed at the subject is called a reflected-light meter.
Incident-light meters measure the amount of light falling on the subject and are held near the subject and pointed toward the camera. This is the most common type of hand-held meter and produces a much more accurate reading.
Spot meters measure the light falling in a very precise area, where light measurement is critical. —CWN