photovoltaic exposure meter

Photovoltaic exposure meters are an older type of photographic device that measures light intensity to determine the correct aperture and shutter speed for a photograph. These meters use a selenium element that converts light directly into an electric current. A microammeter then measures this current to indicate light intensity, allowing photographers to set their camera's exposure settings based on film sensitivity.1

While effective, selenium cells required to be relatively large for adequate sensitivity. They have largely been replaced by photoconductive meters, which use silicon photodiodes or cadmium sulfide cells connected to a battery. These modern meters are more sensitive and compact, and many are now built directly into cameras.12