As the name suggests, an automatic night lamp is for turning ON and OFF the lamp automatically without the need for human interventions. It senses the light intensity from surroundings and finds whether it's day or night. And it automatically turns ON when the surrounding is dark, and it turns OFF when it receives light from surroundings. A sensor called LDR is used to detect the light intensity. This project finds wide outdoor applications in streets, gardens, and public places where it finds difficult to appoint a person to operate the lights.
Components Required
1. LDR (Light Dependent Resistor).
2 BT137 TRIAC (Triode for Alternating Current)
3. 220k Resistor
4. 220V Bulb and wires
What is LDR?
LDR(Light Dependent Resistor) is also known as a photoresistor. It is a device whose resistivity is a function of the incident electromagnetic radiation. That's why they are light-sensitive devices.
Semiconductor materials like PBS and InSb
What is TRIAC?
Triode for Alternating Current (Triac)
It's a bidirectional device and has controlled in both of the direction.
Unlike SCR (Silicon Controlled Rectifier) or thyristor, TRIAC can trigger in both directions.
Working Principle of LDR
Light Dependent Resistor (LDR) works on the principle of photoconductivity.
Photoconductivity is an optical phenomenon in which materials conductivity is reduced when light falls, and photons fall on the device. The electron in the valence band of the semiconductor material is exited to the conduction band. These photons in the incident light should have energy greater than the bandgap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence, when light having enough energy strikes on the device, more and more electrons are excited to the conduction band, resulting in a large number of charge carriers. Hence, the resistance of the device has been decreased. And in the daytime, when there is light in the surrounding, the LDR conducts and as given in the circuit diagram. It is connected with the terminals of TRIAC (Triode for Alternating Current).
Therefore we can say that there is no potential difference between the terminals of T1and T3, or you can say less voltage difference than the breakdown voltage of TRIAC (Triode for Alternating). As a result, the switch is open, and TRIAC does not conduct when there is light in the surrounding.
Now, as the darkness came into existence, the LDR stops conducting, which results in some voltage difference greater than the breakdown voltage of TRIAC, and the TRIAC turns on. After turning on, the current flows from the gate, and the light bulb glows, clearly shown by the circuit diagram.
LDR advantages, disadvantages, and applications
LDR is a small and inexpensive device.
Easy to use.
Its connection is simple.
In stable materials, it responses very slowly.
Light Dependent Resistors are simple and low-cost devices. These devices are used where there is a need to sense the presence and absence of light are necessary. The application of LDR mainly includes alarm clocks, street lights, burglar alarm circuits.
With the help of LDR, light energy will be saved.
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