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Knowledge Introduction of the LDR Sensors

Knowledge Introduction of the LDR Sensors

With years' experience, Senba Sensor has high-quality photoresistors for sale. This article is a brief introduction of the light dependent resistor.

LDR sensor has no polarity. It is purely a resistor device. It can be used with either DC voltage or AC voltage. LDR photocell sensor is a photoelectric element made of semiconductor material and operated by internal photoelectric effect. Under the action of light, its resistance often decreases. This phenomenon is called photoconductive effect. Therefore, LDR sensor is also called photoconductor. When a voltage is applied between the metal electrodes at both ends of the LDR sensors, a current passes through it. When illuminated by light of appropriate wavelength, the current increases with the increase of light intensity, thus realizing photoelectric conversion.


Semiconductors such as metal sulfides, selenides and tellurides are the main materials used to manufacture LDR sensors. Usually, thin LDR sensors and comb-shaped ohmic electrodes are fabricated on insulating substrates by coating, spraying and sintering methods, and then lead wires are connected and packaged in sealed shells with transparent mirrors to avoid dampness affecting their sensitivity.


In dark environment, its resistance value is very high. When illuminated, as long as the photon energy is larger than the forbidden band width of semiconductor material, the electron in valence band can absorb the energy of a photon and then transit to conduction band, and produce a positive charge hole in valence band. This pair of electrons and holes produced by illumination increases. The number of carriers in semiconductor materials decreases the resistivity, resulting in a decrease in the resistance value of LDR sensors. The stronger the illumination, the lower the resistance. When the incident light disappears, the electron-hole pairs generated by photon excitation will gradually recombine, and the resistance of the LDR sensors will gradually restore to its original value.


The main parameters of LDR photocell are bright resistance (RL), dark resistance (RD), maximum operating voltage (VM), bright current (IL), dark current (ID), time constant, temperature coefficient sensitivity, etc.

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