Automatic Street Light using 555 Timer

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Automatic Street Light using 555 Timer

The Automatic Street Light using 555 Timer is a small project to switch ON/OFF street lights automatically. It can switch ON the street lights during night time and switch them OFF during day time.

This can help us in saving lot of energy due to its automated approach.

Manual way of controlling street lights wastes a lot of energy. That adds to the shortage of electricity.

Due to which, we have to face power cuts during peak summer and winter seasons. This small project can solve this problem smartly and economically.

How to Make an Automatic Street Light using 555 Timer?

Image of an LDR

This circuit is based on a special type of resistance called LDR (Light Dependent Resistance).

As the name suggest its resistance depends upon the amount of light falling on it.

During the daytime when the sunlight is in plenty. The resistance of LDR is low and thus it drops a very little voltage across it.

And as a result, the voltage across Resistor R2 is nearly Vcc. Since we know that 555 Timer needs a negative going pulse to get triggered.

So, when the daylight is sufficient, the trigger pin is hold nearly at Vcc supply voltage.

However when night comes, the amount of light falling on the LDR reduces. As a result, its resistance increases and it begin to drop a high amount of voltage across it.

Consequently, the voltage appearing at R2 also drops significantly and it causes the 555 timer to get triggered.

Circuit Diagram

This is the Circuit Diagram of the Automatic Street Light using 555 Timer

Automatic Street Light Circuit using 555 Timer
Automatic street light circuit using 555 timer

Parts List for Automatic Street Light Circuit

Part NameDetailsQuantity
ICIC 555 Timer1
R1LDR (Light Dependent Resistance)1
R210 KΩ, Potentiometer (Variable Resistor)1
R31 KΩ, 0.5 W1
R4330 Ω, 0.5 W1
D1LED (Light Emitting Diode), any color1
Power12 V Power Adaptor or Battery1
Wires for connection
Parts List for Automatic Street Light Circuit

Working of the circuit

In this circuit, a light depend resistance (LDR) is used with a 555 timer to form a photo sensitive circuit for switching on a light at sun set and off at sun rise.

If you have read our basic article on IC 555 Timer or you have some previous knowledge about IC 555 Timer.

You may notice something very different about this circuit. There is no timing capacitor involved in this circuit, Why?

This is due to the fact that here 555 timer is used as an Flip-Flop.

From the above circuit diagram, You can see that R1 and R2 are connected in series forming a voltage divider. Thus R1 and R2 divide Vcc according to the ratio of their resistances.

Now, here is the catch, resistance of the LDR keeps changing according to the amount of light falling on it.

When there is a bright sunlight, its resistance falls. While, during the night, its resistance increases.

So, the voltage across R2 and at Trigger input of the IC 555 keeps changing.

In this Bistable (Flip-Flop) mode, the 555 timer switches ON and OFF according to the intensity of light.

This is the way the Automatic Street Light Circuit functions.

Note : While making this project, please make sure to shield LDR from the Light of the LED and any other light source during the night.
Otherwise, the LDR will sense light and 555 timer will starts oscillating due to feedback. It will cause the Street Light to ON/OFF very fast.
Also, install it away from trees, otherwise the shadow of the tree leaves will stop it from functioning properly.
Ideally, it should be placed upwards facing the sky. And installed on the top of the street light itself.

Testing the Circuit

Automatic Street Light using 555 Breadboard Circuit
Light OFF during DayTime

Actual Working of the Automatic Street Light Circuit. When there is enough light, the LED remains OFF. On covering the LDR with sheet of paper, the LED switches ON instantly.


So Friends, I hope you found the Automatic Street Light using 555 Timer very useful and helpful for your projects.

In this article, ‘Automatic Street Light using 555 Timer’ we made a model street light that can be switched ON/OFF automatically.

In this circuit an LDR is used to keep the trigger pin voltage above 2/3 Vcc during day time to switch OFF the Street Light.

And during night, the resistance of LDR increases causing the voltage at trigger pin to fall below the 1/3 Vcc, thus triggering the 555 timer to switch ON the Street Light.

The Automatic Street Light Circuit has many benefit such as saving electricity and saving in manual labor cost. And, Reduction in Power cuts etc.

I hope you found this article Automatic Street Light using 555 Timer quite useful and valuable for your projects. Did you found it useful?

Please let me know through the comment section.

And if you think there is some mistake or typo error in the text, please let me know that also. So that I can make it better in future. I will be very glad to hear about the projects you made using 555 timer.

If this article arouse your interest in 555 timer, you can read more interesting articles about 555 timer IC on this website.


LDR (Light Dependent Resistance) : An LDR is also known as photo sensitive cell, photoresistor and photoconductor.

Basically it is an passive electronic component whose resistance depends on the environmental light conditions.

When light falls on an LDR its resistance decreases drastically to a few hundred ohms.

On the other hand when it is exposed to darkness its resistance rises to several Mega ohms.

It is a must have component for building light-dependent projects such as automatic ON/OFF lights and in lazer based security systems.

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