What are the Applications and Types of Light Dependent Resistor?

Most of the outdoor lights, street lights, as well as some indoor home appliances are usually maintained and operated manually in so many occasions. It isn’t just risky; it results to power wastage with personnel negligence or rare circumstances for the control of the electrical appliances OFF and ON. Therefore, we can make use of the light dependent sensor for the automatic switching OFF. This is based on the intensity of the daylight by working with light sensors.

In this article, we will be discussing briefly what a light dependent resistor is. We will them go further to explain how to make the circuit of a light dependent resistor as well as its applications.

What is a Light Dependent Resistor?

A Light Dependent Resistor or LDR is called a photocell, photoresistor, or a photoconductor. This is a resistance whereby there is a change in the resistance. This depends on the quantity of light that falls on the surface. There is a change in the resistance whenever light falls on this resistor.

The resistors are usually useful in many different circuits whereby sensing the presence of light is very necessary. In addition, these resistors have different resistance and functions

How does a Light Dependent Resistor Work?

The Light Dependent Resistor functions with the help of the photo conductivity principle. Anytime light hits or falls on the surface, there is a reduction in the material conductivity. Also, the valence band’s electrons present in the device become excited to its conduction band. Furthermore, the photons present in this incident light have to possess an energy that is higher than the semiconductor material’s band gap.

Furthermore, this will make the jumping of the electrons from its valence band to the conduction. All these devices are dependent on light. Anytime the light falls or drops on the light dependent resistor, there is a decrease in resistance, leading it to increase anytime it is dark. Also, anytime the LDR is placed in dark areas, it has a high resistance, and anytime this Light Dependent Resistor is kept in light, then the resistance will reduce or decrease.

What are the Different Types of the Light Dependent Resistor?

A Light Dependent Resistor is classified or grouped with respect to the materials that are used.

Intrinsic Light Dependent Photo Resistors

These light dependent resistors are usually pure and semiconductor devices such as germanium or silicon. Anytime the light falls on top of the light dependent resistor, then there is an excitement of the electrons from its valence band onto the conduction band. Also, there will be an increase in the charge carriers.

Extrinsic Light Dependent Photo Resistors

The devices here are all doped with different impurities. All these impurities help in the creation of some new energy bands that are above your valence band. Furthermore, you will fill these bands with electrons. Therefore, this will decrease the gap of the band and there is a small energy needed to move them. All these photo resistors are majorly useful for the long wavelengths.

Describing the Circuit Diagram of the LDR – Light Dependent Resistor

Full pcb manufacturing

In the light dependent resistor’s circuit diagram, anytime there is a low light intensity, then there is a high LDR resistance. What this does is stopping of the current flow onto the transistor’s base terminal. Therefore, the LED doesn’t light. Moreover, anytime the light intensity on the light dependent resistor is high, then there is a low LDR resistance.

Therefore, current will flow onto the first transistor’s base and then to the next or second transistor. This makes the LED to light. In this case, a preset resistor is used in turning down or up to help in decreasing or increasing the resistance.

What are the Applications of the Light Dependent Resistor?

The light dependent resistors come with a low cost as well as a simple structure. Most times, the resistors are useful as light sensors. Also, the resistors are majorly used whenever you need to check the presence as well as the absence of the light like the alarm clock, burglar alarm circuits, etc.

Furthermore, the LDR resistors majorly deal in different electronic and electrical projects.

Security System which is controlled by the Electronic Eye

For this security system, an electronic eye controls it with respect to the photo sensing arrangement. This proposed system makes use of the 14-stage ripple binary counter that helps in sensing the light intensity using a light dependent resistor (LDR). Furthermore, the o/p helps in making a buzzer and relay for the necessary action.

The project here makes use of the light dependent resistor. Anytime light falls on your light dependent resistor sensor, then there is a decrease in the sensor’s resistance. This then goes on to activate the alarm to alert or notify the user. The project is great in offering lockers security system, cash boxes usually found in banks, jewel shops, and shopping malls.

Light Intensity Control (LDR Based) for the Street Lights

For this system, highway lighting is usually achieved via HID lamps. This is because, these lamps have high energy consumption.

The project makes use of LEDs in overcoming HID lamps drawbacks. The project explains the use of LEDs (light emitting diodes) serving as the source of light.

Lighting Switch

The lighting switch for sunset to sunrise is to help in controlling the illuminated light onto LDR sensors. The LDR sensor resistance changes anytime there is a change in light intensity falling on the light dependent resistor. The sensor’s output is given to the IC 555 timer that is connected in the bistable mode.

Furthermore, the IC 555’s o/p is useful in controlling the load prompting via a TRIAC. Therefore, the circuit helps in switching on the load during sunset and then switches it off automatically during sun rise.


We hope that this article has created enough information concerning what the light dependent resistor (LDR) is. What the LDR types are, how it works, as well as its applications.

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