a. There are two systems for taking light readings:
Calculator dial of a typical light meter
(1) Incident light readings measure the amount of light falling on
the subject. They take no account of the subjects or tonality. An incident
reading for a black cat would be exactly the same as a reading for a white
house. The only thing that matters is the amount of light falling on the
subject and to some extent its direction.
It's easy to recognize an
incident meter, because it has a hemispherical cover of translucent plastic
(or dome) over the light sensor.
In some meters, the dome looks exactly
like a ping pong ball that has been sliced in half and glued over the
element. The dome (called a "photosphere") collects the light and diffuses
it toward the inside, causing a response from the sensor.