Photocell Working and Its Applications

Basically, the photocell is one kind of resistor, which can be used to change its resistive value based on the light intensity. These are inexpensive, simple to obtain in numerous sizes as well as specifications. Each photocell sensor will perform differently compare with other modules, even if they’re from the same family. Actually, the changes in this can be higher, large, etc. Because of these reasons, they cannot be used to decide exact light levels within mill candela otherwise lux. This article discusses an overview of the photocell which includes working, circuit diagram, types, and its applications.

What is Photocell?

A photocell can be defined as; it is a light-sensitive module. This can be used by connecting to an electrical or electronic circuit in an extensive range of applications like sunset to sunrise lighting that mechanically turns on whenever intensity of light is low. These are also used in other applications like intruder alarms and also automatic doors.

The photocell is one kind of sensor, which can be used to allow you to sense light. The main features of photo-cell include these are very small, low-power, economical, very simple to use. Because of these reasons, these are used frequently in gadgets, toys, and appliances. These sensors are frequently referred to as Cadmium-Sulfide (CdS) cells. These are made up of photo resistors and LDRs.


These sensors are apt for light-sensitive applications such as light otherwise dark out. If the block light is there in front of the sensor, if there something disrupting a laser light, sensors which have the majority of light hitting.

Photocell Construction

The construction of a Photocell can be done by an evacuated glass tube which includes two electrodes like collector and emitter. The shape of the emitter terminal can be in the form of a semi-hollow cylinder. It is always arranged at a negative potential. The shape of the collector terminal can be in the form of a metal which can be arranged at the axis of the partially cylindrical emitter. This can be constantly kept at a positive terminal. The evacuated glass tube can be fixed over a nonmetallic base & pins are offered at the base for exterior connection.

Photocell Working

The working principle of a photocell can depend on the occurrence of electrical resistance & the effect of photoelectric. This can be used to change light energy into electrical energy.


When the emitter terminal is connected to the negative (-ve) terminal & collector terminal is connected to the positive (+ve) terminal of a battery. The frequency radiation will be more than the material’s threshold frequency in the emitter, and then photo ton emission will occur. The photon electrons are involved in the direction of the collector. Here the collector terminal is the positive terminal with respect to emitter terminal. Therefore, the flow of current will be there within the circuit. If the radiation intensity is enhanced, then the photoelectric current will be increased.

Photocell Circuit Diagram

The photocell used in the circuit is named as dark sensing circuit otherwise transistor switched circuit. The required components to build the circuit mainly include breadboard, jumper wires, battery-9V, transistor 2N222A, photocell, resistors-22 kilo-ohm, 47 ohms, and LED.

The above photocell circuit works in two conditions like when there is light and when it is dark.

In the first case, the resistance of photocell is less, and then there will be a flow of current through the second resistor like 22Kilo Ohms & photocell. Here, transistor 2N222A works like an insulator. So the lane which includes LED1, R1 & transistor will be off.


In the second case, the resistance of photocell is high, then the lane of the circuit will change. So the low resistance will be there toward the base of the transistor or through the photocell.

Whenever the base terminal of the transistor gets power, then the 2N222A transistor works like a conductor. The lane including LED, R1 & the 2N222A transistor will be ON & the LED will blink. So, if the base terminal of the transistor gets power, then the transistor will perform like a conductor then the LED will ON.

Types of Photocells

Photocells are available in different types

  • Photovoltaic
  • Charge-Coupled Devices
  • Photoresistor
  • Golay Cell
  • Photomultiplier

1). Photovoltaic Cell

The main function of a photovoltaic cell is to change the energy from solar to electrical. A usable current can occur whenever photons beat electrons over the cell into a high state of energy.

2). Charge-Coupled Devices

A charge-coupled device can be used by the community of scientific because these are very consistent & exact photosensor. When the charge generated by photo-sensitive sensors can be used to examine a variety of things from galaxies to only molecules.

3). Photo Resistor

LDRs are one kind of sensors devices whose resistivity can be reduced with the sum of exposed light. The camera light meters & several alarms utilize inexpensive photoresistors in their applications.

4). Golay Cell

A Golay cell is mainly used to sense IR radiation. A blackened metal plate cylinder is filled with xenon gas on a single end. IR energy which falls over the blackened plate will heats-up the gas within the cylinder & twists the elastic diaphragm over the other ending. Here, the motion is used to find out the energy source’s output.

5). Photomultiplier

The photomultiplier is a very sensitive sensor. The unclear light can be multiplied by 100 million times.

Applications of Photocells

The applications of photocells include the following.

  • Photocells are used in automatic lights to activate whenever it gets dark, and the activation/deactivation of streetlights mainly depends on the day whether it is day or night.
  • These are used as timers in a running race to calculate the runner’s speed.
  • Photocells are used to count the vehicles on the road.
  • These are used instead of photovoltaic cells & variable resistors.
  • These are used in lux meters to decide the light intensity.
  • These are used as switches as well as sensors
  • These are used in burglar alarms to protect from a thief.
  • These are used in robotics, wherever they direct robots to hide from view in the dark, otherwise to follow a beacon or line.
  • These are used in exposure meters which can be used with a camera for knowing the correct time of exposure to get a good photo.
  • Photocells are used in the sound reproduction which can be recorded on a movie film.
  • These are used in Dusk-to-Dawn lights.

Thus, this is all about an overview of Photocell. The main function of this is to detect light when a light is on, otherwise whenever the sun is out. Here is a question for you, which metal is used in photocell?