This article teaches us how to use an LDR and relay to construct an automatic street light circuit.
Due to the need of energy conservation many places are using LED street lights that activate on their own!
In order to save energy these lights use a light sensor known as an LDR to detect darkness.
This article describes how to use an LDR sensor to create a circuit that will automatically turn on a standard 230V street light at night without the need for a switch.
Circuit Working:
Parts List:
| Component | Value | Qty |
| LDR | Standard Value | 1 |
| Transistors | BC547 and 2N2222 | 1 each |
| Resistor | 1.2k | 2 |
| Relay | 9V SPDT | 1 |
| Fuse | 1A | 1 |
| Lamp | 220V | 1 |
| Potentiometer | 120k | 1 |
The LDR is the main component of our Automatic Street Light Circuit.
A bias can develop at the base of transistor Q1 when the LDRs resistance drops due to a decrease in the surrounding light.
Because there is no bias at its base transistor Q2 stays in the off state whereas transistor Q1 is activated by this bias.
As a result the relay coil stays disabled and unpowered.
Also the LDRs resistance significantly rises when it is exposed to either no light or very little light.
Here the transistor Q1 switches off since there is no bias at its base.
Transistor Q2 is activated when bias is provided to its base turning it ON and powering the relay coil.
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)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 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.