This document describes an intelligent automatic street light control system using a light dependent resistor (LDR). The system uses an LDR to sense light levels and automatically control street lights. When it gets dark, the high resistance of the LDR causes a relay to energize, which switches on the street lights. When it gets bright, the low resistance of the LDR prevents the relay from energizing, keeping the lights off. This automatic system eliminates the need for manual monitoring of street lights and saves energy by only powering them when it is dark. Applications include street lights, outdoor security lighting, and more.

1. Intelligent Automatic Street Light
Control system using high sensitive LDR

2. Introduction
Nowadays, it became essential for people work during nights and returning back to homes late nights, so safety parameter to be implemented to a great extent on Streets.
This can be best achieved by implementing proper lighting system on Streets.
The efficient monitoring of this lighting system must be taken into account.

3. The existing system is like, the Street lights will be monitored manually which in turns is a waste of huge human power as well as precious time in addition with power wastage at the instant when proper monitoring is failed.

4. This drawback can be overcome by implementing a sophisticated automatic monitoring system through which Street lighting can be monitored automatically before the sun sets and they are switched off the next day morning after there is sufficient light on the roads.
 But the actual timings for these high way lights to be switched on are when there is absolute darkness.

5. Block Diagram

6. Power Supply
This project uses regulated 5V, 750mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer.

7. LDR(LIGHT DEPENDENT RESISTOR)
An LDR is an input transducer (sensor) which converts brightness (light) to resistance.
When the light level is low the resistance of the LDR is high.
Thus in this project, LDR plays an important role in controlling the electrical appliances based on the intensity of light i.e., if the intensity of light is more (during daytime) the loads will be in off condition.

8. RELAY:
 A relay is an electrically controllable switch widely used in industrial controls, automobiles and appliances.
In choosing a relay, the following characteristics need to be considered
The contacts can be normally open (NO) or normally closed (NC). In the NC type, the contacts are closed when the coil is not energized. In the NO type, the contacts are closed when the coil is energized.

9. There can be one or more contacts. i.e., different types like SPST (single pole single throw), SPDT (single pole double throw) and DPDT (double pole double throw) relays.
The voltage and current required to energize the coil. The voltage can vary from a few volts to 50 volts, while the current can be from a few milliamps to 20milliamps.
The relay has a minimum voltage, below which the coil will not be energized. This minimum voltage is called the “pull-in” voltage.
The minimum DC/AC voltage and current that can be handled by the contacts. This is in the range of a few volts to hundreds of volts, while the current can be from a few amps to 40A or more, depending on the relay.

10. WORKING PROCEDURE
LDR offers Very high Resistance in darkness. In this case the voltage drop across the LDR is more than 0.7V.This voltage is more sufficient to drive the transistor into saturation region.
In saturation region, Ic (Collector current) is very high. Because of this Ic, The relay gets energized, and switches on the lamp.
LDR offers Very low Resistance in brightness. In this case the voltage drop across the LDR is less than 0.7V.

11. This voltage is not sufficient to drive the transistor into saturation region. Hence, the transistor will be in cut-off region.
In cut-off region, Ic (Collector current) is zero. Because of this Ic, The relay will not be energized, and the lamp will be in ON state only.
Diode is connected across the relay to neutralize the reverse EMF generated.

12. Advantages
Highly sensitive
Works according to the sun direction
Fit and Forget system
Night – Day mode sensing
Low cost and reliable circuit
Complete elimination of manpower

13. Applications
Street lights
Garden Lights
Hotels, hostels and house hold applications
Offices
Industries

14. CONCLUSION
This project presents “Intelligent Automatically street Light control system using high sensitive LDR”. The light sensitivity resistors (LDR’s) are used to determine the night – day vision.