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Figure 3: Frequency graph
As seen by the above equation the energy of the photon of light depends on the frequency of the light.
Thus the working principle of photodiode can be explained in the opposite of LED working principle. The photodiodes are the semiconductors with conduction and valence energy bands. Electrons at the valence band cannot move hence no current flows through the material. However a small voltage can make the electrons move from the condution band. When a photon with energy E(as described above) strikes the photodiode, the photon is absorbed. The energy of the photon is absorbed by the electron, it gets excited and is able to move thus producing the electrical signal. This is how light power- a number of photons times a photon's energy per unit of time is converted to electrical signal or current which can be explained in Figure 4.
Figure 4: Principle of operation Photodiode
References
- Encyclopedia: Definition of:laser, Accessed:27.3.2014
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