Introduction: Fully Automatic Night Light


When we talk about automatic Night lamp first thing comes to our mind is LDR (Light Dependent Resistor).

If we would like to go with LDR ,as it's resistance changes in proportion to light intensity the effective change in resistance is some what slow which results in relay chattering.No matter either you use circuit with transistors or with 555 timer ,we'll face the problem.

Instead , we can use solar panel itself as a sensor ,as the output from the panel is reliable and stable.


1. No Relay chattering problem.

2. IC s are not required.

3.Less component count.

4.Either solar panel or power supply value is specific,you can go with any value of your choice.

4.Good isolation between AC and DC.

Step 1: Components

we need

1. Solar panel 10v,any wattage

2.Two general purpose Transistors like BC 547

3.2.2 Kohm-- 1

4.1 Kohm--1

5.10 kohm---1

6.18 kohm--1

7.100 uf----1

8.12v,7A relay

9.stable 12V power supply

10 ac LED lamp

Step 2: Circuit

Connect components according to the circuit provided.

During the day time, solar panel produces voltage around 10 v,as this positive voltage is given to base of T1 it's going to on,T2 going to be off so the relay.

In the night time ,voltage at the base is "0".So T1 is going to be off,T2 goes into on state which in turn switches ON the relay .

The RC network at the base of the T1 provides the buffer time for the transistor for reliable operation of the relay.

Step 3: Simulation Results

You can test this circuit by applying 10v and 0v ,when base is given with 10v realy should be in OFF state and it should ON in second case i.e with 0v.

This one tested with 10v solar panel & working to my satisfaction.

Note: 1.we need to make common negative terminal by joining both solar panel's and 12v power supply's negative terminal.

2.You can use any solar panel ,but you need to adjust resistor values at base of T1.

Thank you.

Step 4: Finished Circuit