Concept / Principle:
This project works on the principle of photoconductivity — using an LDR (Light Dependent Resistor).
The LDR’s resistance decreases when light falls on it and increases in darkness.
This change controls a transistor or relay circuit, which automatically turns ON the LED (street light) at night and OFF during the day.
Main Concept:
LDR senses light intensity → Circuit decides → LEDs automatically switch ON/OFF.
Scientific Principle:
- Daytime: Light intensity is high → LDR resistance is low → circuit keeps LEDs OFF.
- Nighttime: Light intensity drops → LDR resistance increases → circuit allows current → LEDs glow.
Materials Required:
- LDR (Light Dependent Resistor)
- Transistor (BC547 or 2N2222) or relay module
- Resistor (220Ω–1kΩ)
- LED lights (3–5 pcs for street lights)
- Battery (9V)
- Switch
- Wires & breadboard / cardboard base
- Small poles (straws, sticks, pens) for LED street lights
- Thermocol / cardboard base for setup
- Glue gun, tape, Fevicol
- Toy cars, road, and trees for decoration
Step-by-Step Model Making:
Step 1 – Prepare the Base
- Take a cardboard or thermocol base (1×1 ft).
- Draw or paste a road in the center using black paper.
- Add small poles on both sides to represent streetlights.
- Attach LEDs on top of each pole.
Step 2 – Connect the LEDs
- Connect all LED positive legs (anodes) together → to the transistor’s collector.
- Connect all LED negative legs (cathodes) to battery negative (–).
Step 3 – Connect the LDR Circuit
- Connect LDR and resistor in series.
- Connect their junction point to the base of transistor (BC547).
- Connect transistor emitter to GND (–).
- Connect transistor collector to LED positive wire.
- Power the circuit with 9V battery and add a switch for control.
Step 4 – Test the Circuit
- Turn ON the switch.
- Cover the LDR with your hand or a small cap — the LED streetlights will glow.
- When you uncover it (simulate daylight), the LEDs turn OFF.
✅ This shows how real streetlights work automatically using sensors.
Step 5 – Decoration & Finishing
- Add mini toy vehicles, houses, and trees.
- Label components:
- “LDR Sensor”
- “Street Light LED”
- “Battery (Power Supply)”
- “Automatic ON in Dark”
- Paint or cover the base attractively.
- Write your project title clearly:
“Automatic Street Light – Energy Saving Model”
Explanation (For Presentation):
“This is a working model of an automatic street light.
It works on the principle of photoconductivity using an LDR sensor.
In daylight, the LDR detects light and keeps the circuit OFF, so the streetlights remain off.
At night or in darkness, the LDR resistance increases and the circuit switches ON the LEDs automatically.
This project saves energy and is used in smart cities for efficient street lighting.”
Applications:
- Smart city street lighting
- Garden or campus lighting
- Automatic home lighting systems
- Power saving systems