How is light detected?

Light carries energy, so a light detector must convert light energy to another form of energy. In most cases light is converted into electrical energy. In the eye, which will be discussed more thoroughly later in this chapter, light strikes a molecule called an opsin. The absorption of light changes the shape of the molecule, which results in an electrical signal sent on the optic nerve. In detectors used in digital cameras when light is absorbed in a semiconductor one or more electrons are released. The charge they carry produces a voltage that is then converted into a digital signal. In photographic film molecules consisting of silver and chlorine, bromine, or iodine are used. When light strikes these molecules it transfers its energy to electrons. The molecules are broken apart and a tiny crystal of metallic silver remains.


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