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light-dependent resistor , LDR , are also known as  photo-conductive cell.. It is a passive component that decreases resistance with respect to receiving luminosity (light) on the component's sensitive surface. The resistance  of a photoresistor decreases with increase in incident light intensity;  it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits and light-activated and dark-activated switching circuits acting as a resistance semiconductor  . In the dark, a photoresistor can have a resistance as high as several megaohms (MΩ), whereas n the light, a photoresistor can have a resistance as low as a few hundred ohms.

If incident light on a photoresistor exceeds a certain frequency. photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons conduct electricity, in this way they lower resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. photoresistors may react differently to photons within certain wavelength bands.