In this post we learn how to build an automatic street light circuit using LDR and relay.
Introduction:
Saving energy is important, so lots of 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.
Parts List:
| S.no | Component | Value | Qty |
| 1 | LDR | Standard Value | 1 |
| 2 | Transistor | BC547 and 2N2222 | 1 each |
| 3 | Resistor | 1.2k | 2 |
| 4 | Relay | 9V SPDT | 1 |
| 5 | Fuse | 1A | 1 |
| 6 | Lamp | 220V | 1 |
| 7 | Potentiometer | 120k | 1 |
Working Principle:
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.
Consequently, the relay coil remain unpowered and remains in a deactivated state.
Conversely, 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 utilizes the behavior of the LDR to control the activation of transistors Q1 and Q2 which, in turn controls the relay coil.
The resistance of the LDR (RLDR) varies with light intensity and can be described by the following equation:
RLDR = R0 (1+α * Illuminance)RLDR = (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 finds extensive application as an energy efficient lighting solution particularly for street illumination.
When power failures or dusk sets in, the system autonomously activates the lights ensuring safe and well lit surrounding.
This technology not only conserves energy but also reduces the need for manual intervention, making it a cost effective and sustainable lighting solution for various outdoor settings.
Conclusion
In conclusion, the utilization of LDRs and transistor based control circuits in automatic street lighting systems represents a significant advancement in energy conservation and lighting automation.
The designed circuit provides an efficient and reliable solution for street lighting contributing to a greener and more sustainable future.