Photosensitivity

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Photosensitivity is the amount to which an object reacts upon receiving photons of light. Devices that are photosensitive include the human retina and photographic film. Film is photosensitive because it has a chemical reaction when struck by light. The same process is used in the electronic device known as a photocathode, which is a surface that emits electrons when struck by light. An electron tube called a photocell can be constructed with an anode and such a photosensitive cathode, both enclosed in a vacuum. When this is inserted in an electrical circuit it will allow current to flow when the cathode is illuminated with light.

Typical substances that are photosensitive are alkali salts, such as silver halide.

See also

• Heliotropism