Secret Diagram: Automatic Night Light using LDR

Wednesday, 18 January 2017

Here is the simple Automatic Night Light circuit using LDR.

Components Required:

1) Breadboard

2) 470 ohm resistor
3) 22 Kilo ohm resistor

4) LED (Any Color)
5) 15 Kilo ohm Light Dependent Resistor (LDR)
6) 3904 NPN Transistor

6) 9Volt Battery

Procedure:

Connect the circuit as shown in the circuit diagram below.
During day time the brightness will be more, which lowers the resistance of the LDR.
Therefore the current is grounded, as current prefers only low resistance path.
Hence there is no base current to forward bias the 3904 NPN transistor and the LED remains OFF.
During night time the brightness goes down, which increases the resistance of the LDR.
Therefore the current will not be grounded and prefers a alternate path to flow.
Hence there is enough base current to forward bias the 3904 NPN Transistor and the LED glows.

Circuit Diagram:

Figure 1: Automatic Night Light using LDR Circuit simulation made in Multisim

Figure 2: Automatic Night Light using LDR