What is Light Dependent Resistor?

What is  Light  Dependent  Resistor?

Photoresistor definition

Photoresistor is a kind of semiconductor device based on internal photoelectric effect, and its resistance value depends on the change of incident light intensity. With the increase of incident light intensity, the resistance value of photoresistor decreases, the incident light weakens, and the resistance value of photoresistor increases. The photoresistor has no polarity, and an external voltage in any direction is applied at both ends when it is used, and the intensity of the incident light can be reflected by measuring the current in the loop.

Basic structure of Photoresistor

• Insulating substrate

• Photosensitive layer

• Electrode

How photoresistor works

The working principle of a photoresistor is based on photoconductivity. Photoconductivity occurs when the electrical conductivity of a material increases after absorbing photons (light particles) with sufficient energy. When light hits a photoresistor, the photons excite electrons in the valence band (the outermost layer of the atom) of the semiconductor material, causing them to jump to the conduction band. This process creates more free electrons and holes to carry current, reducing the resistance of the photoresistor.

Parameter characteristics of photoresistor

• Photocurrent, bright resistance

• Dark current, dark resistance

• Sensitivity

• Spectral response

• Illumination characteristic

• Volt-ampere characteristic curve

• Temperature coefficient

• Rated power

• Frequency characteristic

Factors affecting photoresistance

• The wavelength and intensity of incident light

• Band gap of semiconductor materials

• Doping levels of semiconductor materials

• The surface area and thickness of the photoresistor

• Ambient temperature and humidity

Photoresistor classification

• Intrinsic photoresistor

• External photoresistor

Photoresistor applications

• Security systems: Photoresistors can be used to detect the presence or absence of light, for example in camera meters, burglar alarms, or electronic eyes.

• Lighting control: Photoresistors can be used to control the brightness or color of lights, such as street lighting, outdoor lighting.

• Audio compression: Photoresistors can be used to smooth the response of an audio signal by reducing the dynamic range, such as in a compressor, limiter, or noise gate.

• Optical communication: Photoresistors can be used to modulate or demodulate optical signals, such as optical cables, lasers, or photodiodes.

• Measurement and instrumentation: Photoresistors can be used to measure or indicate light intensity, for example in photometers, spectrometers, or photometers.

Advantages and disadvantages of photoresistor

Advantage

• Low cost and easy to use

• Wide range of resistance values, sensitivity levels

• No external power supply or bias required

• Compatible with many circuits and devices

Shortcoming

• Low accuracy and precision.

• Slow response and recovery time

• It is easily affected by temperature, humidity and aging environmental factors