Lights and Display Board Circuits

Auto Intensity Control of Street Lights

In the past, street lights were manually operated, but nowadays, there is a trend towards automating their control. However, it’s noticeable that during peak hours, when there is no traffic and in the early morning, there is no need for high-intensity lighting. By reducing the light intensity during these periods, some energy can be conserved.

Various energy-saving methods are available, including activating street lights when a vehicle is detected and utilizing light-dependent resistors (LDR) and relays for control. The proposed circuits calculate peak hours to effectively manage the intensity of street lighting. This article presents two circuit designs: one utilizes an ATmega8 microcontroller for street light control, and the other employs a PIC microcontroller for the same purpose. Traditional street lights typically use High-Intensity Discharge (HID) lamps, which consume significant energy. Instead, these circuits are designed to use high-intensity LEDs, which are more energy-efficient, as a replacement for HID lamps to help conserve electricity.


  • Auto Intensity Control of Street Lights using ATmega8
    • Circuit Principle
    • Auto Intensity Control of Street Lights Circuit Diagram
    • Circuit Components
    • Circuit Design
    • I2C Protocol
    • Simulation Video
    • How Auto Intensity Control of Street Lights Circuit Works?
    • Limitations of this Circuit
  • Auto Intensity Control of Street Lights using a PIC Microcontroller
    • Circuit Diagram
    • Components
    • Component Description
    • Working
  • Alternative Circuit
  • Auto Intensity Control of Street Lights Circuit Advantages

Auto Intensity Control of Street Lights using ATmega8

Circuit Principle

The fundamental concept behind this project is to manage the brightness of street lights through Pulse Width Modulation (PWM) technology. It involves the calculation of peak hours specific to a given location. The microcontroller is responsible for dynamically adjusting the PWM signal, thus regulating the street light intensity by either increasing or decreasing it.

To determine these peak hours, various factors are taken into account, including traffic density, time of day, and the ambient light intensity in the environment.

Auto Intensity Control of Street Lights Circuit Diagram

Street Lights

Circuit Components

  • ATmega8 micro controller
  • DS1307 IC
  • Light Dependent Resistor
  • LED array.
  • LCD display

Circuit Design

The auto intensity control of street lights circuit is simple but it requires more coding part. This circuit consists of Atmega8 controller, DS1307, LDR, Relay and LEDs.

LDR:LDR is used for calculating the light intensity of the environment .The light dependent resistor is connected to ADC1 (PC1) pin of the micro controller. The analog light value is converted to digital value using ADC.

RTC:Current time is calculated using RTC. Real time clock has 8 pins out of which SCL and SDA are connected to PC5 andPC4  pins respectively. SCL is serial clock while SDA is serial data RTC is I2C compatible, where I2C means inter integrated circuit. One bit of data is transmitted on data bus for each clock cycle.

Data can be transferred between devices, using only two bi-directional buses. Each device can act as a slave or master. The slave devices will have one address and these devices can be accessed using this address.

LCD:LCD is the display used for displaying time which is read from RTC IC. Interfacing of LCD in 4-bit mode is shown in circuit diagram. D4-D7 pins of LCD are connected to PD0-PD3 pins of microcontroller.

RS pin of LCD is connected to PD4 pin of micro controller. RW and Enable pins are connected to PD5 and PD6 pins of controller.

LED array is number of high power LEDs connected in series. It is connected to PWM pin of the microcontroller.

I2C Protocol

I2c is a communication protocol invented by Philips Company. This is well suited for communication between integrated circuits and peripherals. This uses two lines to transfer data.

  • Serial Data – SDA
  • Serial Clock – SCL.
  1. This can connect up to 128 devices using two wires. Each device connected will have an address. The device which initiates the data transfer is called Master.
  2. Every device will have 7 bit address.
  3.  Master initially sends the START bit on the data line.
  4. Then it sends the address of the device with which wants to communicate and the mode of operation i.e. read or write.
  5. The slave devices listen to the incoming data and checks if its address matches to the received data. The device whose address matches send an acknowledgement signal.
  6. Then master starts transmitting or receiving the data from the slave.
  7. After completion of the transmission, Master sends a STOP bit.
  8. Data on SDA can be changed only if SCL pin is low.

Simulation Video

How Auto Intensity Control of Street Lights Circuit Works?

  1. Initially power the circuit.
  2. Time is displayed on the LCD display.
  3. Place the LDR in darkness as the street lights switches on only when there is no light on LDR.
  4. Now check the time if the time is between 9 pm to 2 am street light glows with full intensity.
  5. From 2 pm intensity of the lights slowly starts decreasing and finally in early morning it glows with least intensity. When the light is sensed by the LDR lights are switched off automatically.

Code is written in such a way that up to 2 am lights will glow with full intensity. From then it slowly starts decreasing and finally it drops to zero in the morning.

Limitations of this Circuit

  • Even though energy is saved if there are any vehicles after fixed time, intensity of the light is low.
  • Maximum energy cannot be saved.

Auto Intensity Control of Street Lights using a PIC Microcontroller

Circuit Diagram


  • IC1 PIC 16F877A
  • IC2 DS 1307
  • LCD1 16X2 Alphanumeric LCD display
  • R1, R2 10 KΩ
  • R3, R4 1 KΩ
  • R5 10 KΩ
  • R6 1 KΩ
  • R7 10 KΩ
  • R8, R9, R10 and R11 330 Ω
  • R12 10 KΩ
  • R13 10 KΩ POT

Component Description


In the circuit, the microcontroller of choice is the PIC16F877A, which is an 8-bit microcontroller. This PIC16F877A performs two key functions: it reads the voltage across the Light Dependent Resistor (LDR) and keeps track of time using a Real Time Clock IC. It then utilizes these readings to control the activation or deactivation of the LEDs accordingly.


It is a Real Time Clock IC. The communication between microcontroller and DS1307 is via I2C protocol. It provides clock and calendar with details like seconds, minutes, hours, day, date, month and year. Time can be set in either 12 hour mode or 24 hour mode and there is an indication of AM/PM.


We incorporate both the Light Dependent Resistor (LDR) and the Real Time Clock (RTC) in the circuit because relying solely on the LDR would result in inefficient energy usage. With only the LDR, the street lights would switch on as soon as the ambient light intensity decreases on the LDR, and conversely, they would turn off when the intensity increases.

On the other hand, if we solely rely on the RTC, the street lights would follow a fixed schedule, irrespective of the external lighting conditions. The RTC operates based on a predefined time set in the code when the device is powered on.

In this system, the microcontroller patiently awaits a signal from the LDR. When the LDR registers a drop in light intensity, the microcontroller’s output is triggered, causing the street lights to illuminate. This action occurs only when it is dark outside.

The street lights remain at full brightness until 3 AM. At that point, the circuit gradually reduces the light intensity, and they will turn off either at 6 AM or when the LDR detects increasing light, whichever happens first.

Therefore, this circuit achieves automatic intensity control of street lights by combining the capabilities of an LDR, an RTC, a PIC microcontroller, and an LED array.

Alternative Circuit

The circuits depicted earlier employ an array of LEDs as a power-saving alternative for street lighting. However, it’s worth noting that the same circuit can also be adapted to control a standard High-Intensity Discharge (HID) street lamp. Below, we present the circuit for automatically controlling the intensity of an HID street light.

The circuit depicted above illustrates only the connection to the street light, while the remainder of the circuit remains unchanged. It includes a relay, a high-intensity discharge street light connected to the mains power supply, and a diode.

The relay’s contact is closed exclusively when the Light Dependent Resistor (LDR) detects low light intensity and the street light is illuminated.

Auto Intensity Control of Street Lights Circuit Advantages

  • Power wastage can be reduced.
  • Using LED array reduces the cost.
  • Using of RTC and LDR produces accurate results.

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