Automatic Street Light Circuit using LDR

In this post we learn how to build an automatic street light circuit using LDR and relay.

Saving energy is important, so many places are using special street lights with LEDs that turn on by themselves!

These lights sense darkness using a light sensor called an LDR which helps save power.

This article explains how to build a circuit with this LDR sensor to automatically turn on a regular street light 230V at night, so you do not even need a switch.

Circuit Working:

Parts List:

The heart of this Automatic Street Light Circuit is the LDR.

When ambient light diminishes the LDRs resistance decreases allowing a bias to form at the base of transistor Q1.

This bias activates transistor Q1 while transistor Q2 remains in the off state due to the absence of bias at its base.

Thus, the relay coil remain unpowered and remains in a deactivated state.

And when the LDR is exposed to no light or low light levels its resistance increases significantly.

In this scenario there is no bias at the base of transistor Q1 causing it to switch off.

With bias applied to the base of transistor Q2 it is turned on supplying power to the relay coil thus activating it.

This action leads to the illumination of the output bulb.

Formulas:

The circuit control the activation of transistors Q1 and Q2 which in turn limits the relay coil, by using the behavior of the LDR.

The following equation describes how the LDRs (RLDR) resistance changes with light intensity:

RLDR = R0 (1+α * Illuminance)RL​DR = (1+α * Illuminance) R0​​

here:

• RLDR is the resistance of the LDR.
• R0​ is the resistance of the LDR in complete darkness.
• α is the sensitivity factor of the LDR.
• Illuminance represents the light intensity.

Application and Uses:

The Automatic Street Light Control System has become common as an energy efficient lighting system particularly for street lighting.

The system switches on the lights to provide a safe and well lit environment when there is a power outage or when it gets dark.

This technology is an affordable and environmentally friendly lighting option for a variety of outdoor situations since it not only saves energy but also reduces the need for human involvement.

Conclusion

The latest breakthrough in lighting automation and energy savings is the Automatic Street Light Circuit with LDR.

This circuits design offers a reliable and efficient street lighting solution encouraging a more environmentally friendly and greener future.

References:

Design, construction and calibration of automatic street light controller using Light Dependent Resistor (LDR)