LDR sensor (photoresistor light-dependent resistor, and the latter is abbreviated as ldr) or photoconductor, is commonly made of cadmium sulfide, as well as selenium, aluminium sulfide, lead sulfide and bismuth sulfide. These fabricated materials have the characteristics of rapid reduction of resistance under the irradiation of specific wavelength light. This is because the carriers generated by light are all involved in conduction, and it will cause drift under the action of an applied electric field, and electrons run to the positive pole of the power supply, and holes run to the negative pole of the power supply, so that the resistance value of the photoresistor sensor decreases rapidly.
Usually, LDR photoresistor is made into thin sheet structures to absorb more light energy. When it is irradiated by light, the electron-hole pairs are stimulated in the semiconductor sheet (photosensitive layer) to participate in conduction, which enhances the current in the circuit. In order to obtain high sensitivity, comb pattern is often used in the electrodes of the LDR sensor. It is formed by evaporating gold or indium on the photoconductive film under a certain mask. LDR light sensor is usually composed of photosensitive layer, glass substrate (or resin moisture-proof film) and electrodes. LDR sensors are usually represented by the letters "R" or "RL" and "RG" denotes that LDR sensors are usually made of cadmium sulfide (CdS). It is divided into two types: epoxy resin packaging and metal packaging, which belong to the wire type (DIP type). According to the diameter of ceramic substrate, the idr sensor of the epoxy resin package can be divided into Ø3mm、Ø4mm、Ø5mm、Ø7mm、Ø11mm、Ø12mm、Ø20mm、Ø25mm.