Applications, Advantages of [LDR] Light Dependent Resistor

Light Dependent Resistor(LDR)

The main application of the  Light Dependent Resistor(LDR) is that it is used as a variable resistor in electronic circuits as well as electrical circuits whose resistance varies with the brightness of light falling upon it.

There are huge important applications of LDR are available so we will discuss all the important and interesting applications, advantages, and disadvantages of LDR with examples and circuit diagrams.

LDR Symbol

LDR Basic Construction

As you see in the below figure a light-sensitive material having a snake-like structure is placed on an insulating substrate. The light-sensitive material is made of Cadmium Sulphide(CdS) film and the insulating substrate is made of ceramic material. The length of the light-sensitive material is decided depending on the power rating and the resistance rating of the LDR.

The whole structure is placed on a plastic or resin case. When the LDR is placed in a dark place, it gives very high resistance(in MegaOhm). But when light falls upon the LDR its resistance decreases and conductivity increases.

LDR Characteristics

The characteristics of LDR shown in the below graphical structure.

You can see in the above figure, the changes in resistance are taken along the 'Y' axis and the illumination of the light falls upon the LDR is taken along the 'X' axis.

The above graphical structure also shows how the resistance of LDR changes with the changing of illumination of the light that falls upon the LDR.

Light Dependent Resistor(LDR) Applications

The important applications of LDR are,

1. LDRs are used in Light Sensors

2. LDR is also used in some cameras to detect the presence of light.

3. LDRs are used in Ligh Intensity measurement meters.

4. In the manufacturing industry, LDR is used as a sensor for the counting of the packets moving on a conveyor belt.

5. LDRs are also used in Light Activated Control Circuits.

6. LDRs are used in Street Lights which are automatically turn ON in the night time.

7. LDRs are used in Burglar Alarm Circuits.

8. LDRs are used in Photosensitive Relays

9. LDR can be used in simple Fire alarm circuits.

10. The Light Dependent Resistors are used in modern televisions, and computer screens for automatic brightness and contrast control.

These are some important and useful applications of Light Dependent Resistors(LDR)

Advantages of LDR

1. LDRs are very low-cost devices.

2. LDRs are very small in size.

3. LDR is a very simple device.

4. The connection of LDR is also very simple.

Disadvantage of LDR

1. LDR is not so much a sensitive device.

2. LDR gives inaccurate results if the working temperature changes.

The application of LDR in Automatic Night Lamp Circuit

Here a circuit diagram of the Automatic Night lamp circuit using LDR is given below. You can make this circuit for your home night lamp.

The working of the circuit is very simple. A 230V night lamp is connected to the 230V power supply through a relay. During the night time, the resistance of the LDR will be decreased so a current will start flowing through the LDR and Transistor T1. When the transistor T1 is activated, it will activate the transistor T2. When the transistor T2 is activated then a current will flow through the Relay coil and the Relay becomes NC to NO. Therefore the night lamp will be turned ON.

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