An automatic street light circuit is used to switch a lamp ON when the surrounding light becomes low and switch it OFF when daylight comes back.
We can use these circuits for garden lights, pathways, driveways, outdoor lamps, solar lights and many other lighting projects. Different circuits can do this work using an LDR, transistors, IC 555, operational amplifiers or other electronic parts.
Some circuits are very simple, but other circuits need more parts and careful construction. Solar street lights also need a battery charging circuit and proper protection.
What Is an Automatic Street Light Systems
An automatic street light system detects the surrounding light and switches a lamp according to the light condition. The most common method is to use an LDR as the light sensor.
The LDR forms part of a sensing circuit. When the light changes, its resistance also changes. This produces a change in voltage, which is detected by the switching circuit.
The switching circuit may use a transistor, IC 555, operational amplifier or comparator. A relay can be used to switch a separate electrical load. Other circuits may use electronic switches or suitable LED drivers.
The main purpose is, the lamp should turn ON automatically when the surrounding light becomes low and turn OFF when sufficient daylight returns. But all automatic street light circuits are not the same. Some are very simple, while others provide more adjustment and additional functions.
So we must select the circuit according to the lamp power, supply voltage, required switching behaviour and other needs.
Comparison of Automatic Street Light Circuits
| Circuit Type | Main Use | Main Advantage | Main Limitation | Best For |
|---|---|---|---|---|
| Single Transistor Circuit | Automatic ON/OFF control | Simple and low cost | Basic light sensing and control | Small lights and simple projects |
| IC 555 Circuit | Automatic light control | Adjustable switching levels can be designed | Correct circuit design is needed to avoid unwanted switching | Adjustable street light projects |
| Solar Street Light Circuit | Solar-powered lighting | Uses solar energy and can work without mains supply | Needs a suitable solar panel and battery | Outdoor locations without easy mains access |
| Two Transistor Circuit | Automatic dusk-to-dawn switching | Simple components and easy construction | Performance depends on component values and sensor arrangement | Basic home and garden lights |
| IC 741 Circuit | Light sensing and switching | Can be used as a light-level comparator | Supply voltage and input limits must be checked | Projects needing adjustable light sensing |
| Four Transistor Circuit | Automatic light switching | Allows a different transistor-based control arrangement | More components do not always mean better performance | Projects needing a specific transistor design |
| 40 W Solar LED Controller | Solar LED lighting with battery control | Combines solar power and LED control | Must match the panel, battery, LED load and protection requirements | Suitable 40 W solar LED applications |
Note: The actual performance of each circuit depends on its schematic, component values, supply voltage and connected load. Before choosing a design, check the original circuit diagram and its stated ratings. For mains-powered circuits, proper electrical isolation and enclosure protection are essential.
Seven Automatic Street Light Circuit Designs
Now let us look at the seven circuit types and understand where each one may be useful.
Design 1: Single-Transistor Automatic Street Light
Circuit category: Basic transistor switching.
Main purpose: Automatic day and night switching using a simple circuit.
This circuit uses a small number of components to detect the surrounding light and control the switching stage.
It is a good starting point for beginners who want to make a simple automatic street light. The main advantage is that the circuit is simple and economical to build.
But the switching performance and load capacity depend on the actual circuit design, component values and relay driver. This circuit is suitable for basic low-voltage automatic lighting projects.
Design 2: IC 555 Automatic Street Light
Circuit category: IC-based light sensing.
Main purpose: Automatic switching using an IC 555 and an LDR sensing network.
The IC 555 can be used to make a light-sensitive switching circuit.
Depending on the circuit connections, we can adjust the switching threshold and use additional components to control the response to changing light conditions.
The main advantage is that the IC 555 provides a convenient way to build a light-sensitive control circuit.
But we should not assume that every IC 555 circuit provides perfect switching stability or prevents relay chatter. This depends on the actual design. This circuit is suitable for projects where we want to use an IC-based sensing arrangement.
Design 3: Solar-Powered Automatic Street Light
Circuit category: Solar-powered lighting control.
Main purpose: Automatic lighting where mains electricity is not available.
A solar street light stores energy in a battery during daytime and uses that energy to operate the lamp after dark.
The complete system needs a solar panel, suitable battery, charging controller, day and night sensing circuit and LED driver. The main advantage is that the lamp can operate without a continuous mains electricity supply.
But we must select the solar panel and battery according to the lamp power, operating hours and available sunlight. The battery must also have suitable charging and discharge protection.
This type of circuit is useful for gardens, pathways, farms and other places where we need off-grid lighting.
Design 4: Two-Transistor Automatic Street Light
Circuit category: Two-stage transistor switching.
Main purpose: Automatic light switching using two transistor stages.
This circuit uses two transistors to carry out the sensing and switching functions.
Depending on the design, one transistor may respond to the sensing network while the other transistor controls the output stage.
The main advantage is that we get more flexibility in the switching arrangement.
But adding another transistor does not automatically make the circuit more accurate or reliable. The complete circuit must be designed properly.
This type is suitable for projects where we want to use a two-transistor switching arrangement.
Design 5: IC 741 Automatic Street Light
Circuit category: Operational-amplifier-based light sensing.
Main purpose: Light detection using a sensing voltage and a reference voltage.
An operational amplifier can be used to compare the voltage produced by the LDR network with a reference voltage.
We can adjust the reference voltage to select the required switching threshold. The main advantage is that the sensing voltage and reference voltage can be adjusted according to the circuit requirements.
But the IC 741 has limitations in its input voltage range and output voltage swing. So it may not be suitable for every low-voltage circuit.
For a new design, a suitable comparator like LM393 may be a better choice.
This circuit can be useful for educational projects and light-sensing experiments when the limitations of the IC 741 are considered.
Design 6: Four-Transistor Automatic Street Light
Circuit category: Multi-stage transistor switching.
Main purpose: Automatic light control using several transistor stages.
This circuit uses four transistors to carry out the sensing and switching functions. Such a design gives the circuit designer more flexibility in arranging the different stages.
The main advantage is that we can divide the sensing and switching work between different transistor stages.
But using more transistors does not automatically provide better accuracy or switching stability. We must check the actual circuit and its operation.
This type of circuit is suitable for projects where we specifically need a multi-transistor switching arrangement.
Design 7: 40-Watt Solar LED Street Light Controller
Circuit category: Solar-powered LED lighting.
Main purpose: Automatic operation of a higher-power LED lamp using stored solar energy.
This type of circuit needs more than a simple LDR switching arrangement.
We must consider the battery charging circuit, low-battery protection, LED current control and heat dissipation.
The main advantage is that the system can combine automatic lighting with the requirements of a higher-power solar LED lamp.
But the solar panel, battery, charging controller and LED driver must be selected to work properly together.
The battery must receive the correct charging voltage and current. The LED driver must also supply the correct current to the LED array.
This type of circuit is suitable for solar lighting projects that need a higher-power LED lamp.
Comparison of the Seven Designs
Now let us compare the seven designs so that we can select a suitable circuit for our project.
Single-transistor circuit: This is suitable for simple lighting projects. The main advantage is its simple construction, but the actual performance depends on the circuit arrangement.
IC 555 circuit: This is useful when we want to use an IC-based sensing circuit. But the switching behaviour depends on the design.
Solar street light: This is suitable for places where mains electricity is not available. But we need a suitable solar panel, battery and charging controller.
Two-transistor circuit: This provides a two-stage switching arrangement. But we must select the correct transistor values and connections.
IC 741 circuit: This can be used for light sensing with a reference voltage. But we must consider the supply voltage and IC limitations.
Four-transistor circuit: This uses several transistor stages to control the lamp. But more components do not automatically mean better performance.
40-watt solar LED controller: This is intended for a higher-power solar lighting system. But the battery, charging circuit and LED driver must be properly matched.
We should use this comparison as a general guide. The best circuit depends on our actual requirements and not simply on the number of components used.
How to Select the Right Circuit
Before we choose a circuit, let us consider a few important points.
Required Lamp Power
First, we must know how much power the lamp needs.
A small transistor circuit may be enough to control a relay, but we should not assume that the transistor can drive a high-power lamp directly. The relay contacts and switching devices must be suitable for the required voltage and current.
For high-power LEDs, we should use a suitable LED driver.
Available Power Supply
We must decide whether the circuit will work from a DC power supply, battery or AC mains-connected system. The supply voltage and current must match the circuit requirements.
For solar lighting, we must also check whether the battery voltage is suitable for the control circuit and LED driver.
Switching Threshold
Some applications need the lamp to switch ON at a particular light level. In that case, we should select a circuit that provides a suitable adjustment range.
The actual adjustment range depends on the LDR network and switching circuit.
Switching Stability
The surrounding light may change slowly during dawn and dusk. Vehicle headlights and other artificial lights may also affect the LDR.
If the lamp switches repeatedly around the selected threshold, then we may need a circuit with suitable hysteresis or filtering. The correct method depends on the circuit and the place where it will be installed.
Solar Battery Requirements
For a solar street light, we must estimate how much energy the lamp will consume during the night.
Energy required in watt-hours = Lamp power in watts × Operating time in hours
For example, a 12 W lamp operating for 10 hours will consume approximately 120 Wh.
This is the energy used by the lamp itself. The actual battery requirement will be higher because we must also consider driver losses, battery limitations and other losses.
So, we must select the battery and solar panel according to the complete system requirements.
Construction Complexity
We should select a circuit according to our experience and available equipment.
A simple transistor circuit may be suitable for a beginner. But a solar LED controller needs more care because we must handle battery charging, LED current control and protection.
Important Design Points for Outdoor Lighting
Now let us look at some general points that apply to most automatic street light circuits.
LDR Position
The LDR must detect the surrounding light without receiving direct light from the lamp it controls.
Otherwise, the lamp may illuminate the LDR and cause the circuit to switch OFF. After this, the sensor may become dark again and switch the lamp ON.
This can cause repeated switching. We should also avoid placing the LDR where vehicle headlights or other artificial lights can cause unwanted operation.
Weather Protection
Outdoor circuits must be protected against rain, dust, insects and moisture. We should use a suitable enclosure and protect the cable entries.
But the LDR must still receive enough ambient light to detect the day and night conditions.
Relay Selection
If the circuit uses a relay, its coil voltage must match the control circuit. The relay contacts must also be suitable for the connected lamp and its starting current.
This is important because some LED lamps can draw a brief high current when they are first switched ON.
Power Supply Stability
The control circuit must receive the correct supply voltage. An unsuitable or unstable supply can cause improper switching, relay chatter or other problems.
We must also make sure that the supply can provide enough current for the complete circuit.
LED Current Control
High-power LEDs need proper current control. The LED driver must match the LED arrangement and supply voltage. We must also provide suitable heat dissipation.
PWM dimming can be used to control LED brightness, but it does not replace the current regulation required by the LEDs.
Battery Protection
Solar-powered street lights need suitable battery charging control. We must also protect the battery against excessive discharge when required by its specifications.
A simple voltage regulator should not be assumed to provide all the charging and protection functions.
General Troubleshooting Guide
Here are some common problems that may occur in automatic street light circuits.
The Lamp Switches ON During Daytime
This may happen due to incorrect LDR connections, a wrongly adjusted switching threshold or a problem in the output stage. We should check the circuit connections and compare the sensing voltage under bright and dark conditions.
The Lamp Does Not Switch ON at Night
We should check the supply voltage, LDR connections, switching stage and relay operation. If the circuit has a preset, then we should check whether its adjustment range is suitable for the required light level.
The Relay Keeps Switching ON and OFF
This may happen when the light level changes around the switching threshold. The controlled lamp may also be shining directly onto the LDR.
We should check the sensor position and see whether the circuit needs suitable hysteresis or filtering.
The Lamp Flickers
We should check the power supply, wiring, relay contacts and output switching arrangement. If an electronic LED driver is used, then we must check whether it is suitable for the switching method.
The Solar Lamp Turns OFF Too Early
This may happen when the battery is not receiving enough charge or when the lamp consumes more energy than expected. We should check the battery condition, solar panel output, charging controller and lamp power consumption.
The LED Array Becomes Too Hot
We should check the LED current, driver operation and heat sink.A suitable LED driver must be used so that the LEDs do not receive excessive current.
These are general checks. For problems related to a particular circuit, we should follow the detailed instructions given in its individual article.
Safety Requirements
Automatic street light circuits may operate from low-voltage DC supplies, batteries or AC mains. So, we must follow the correct safety precautions according to the circuit.
Low-Voltage Circuits
We should use the specified supply voltage and check the component polarity before applying power. Transistors, ICs and relays must operate within their permitted ratings.
Mains-Powered Lamps
A low-voltage sensing circuit does not make the mains-connected section safe to touch. The mains wiring, relay contacts, insulation, PCB spacing and enclosure must be suitable for the voltage and connected load.
We should use suitable overcurrent protection and disconnect the supply before making any wiring changes.
If we are not qualified to work with mains voltage, then the mains-connected section should be installed and checked by a qualified electrician.
Solar and Battery Systems
We must use a charging controller suitable for the selected battery chemistry. The battery should have the required charging and discharge protection.
We should also make sure that the wires, connectors and switching components can handle the expected current.
Frequently Asked Questions (FAQs)
Which circuit is best for a simple automatic street light?
A basic transistor circuit may be suitable for a small lighting project. But the final choice depends on the supply voltage, lamp power and required switching behaviour.
Which sensor is commonly used in an automatic street light?
An LDR is commonly used because its resistance changes according to the light falling on it. We can also use a photodiode or phototransistor in a suitable circuit.
Can an automatic street light work without a relay?
Yes, we can use a suitable electronic switching device or LED driver instead of a mechanical relay. But the selected device must handle the required voltage and current.
Can an automatic street light work using solar power?
Yes, a solar panel can charge a battery during daytime, and the battery can supply the lamp after dark. But we must use a suitable charging controller and provide the required battery protection.
Why does an automatic street light switch repeatedly at dusk?
This may happen when the ambient light changes around the switching threshold. It can also happen when the controlled lamp shines directly onto the LDR.
We can reduce this problem by using suitable sensor placement and an appropriate switching circuit.
Can an IC 555 be used for an automatic street light?
Yes, an IC 555 can be used in a light-sensitive switching circuit. But the actual operation depends on the circuit connections and component values.
Can a high-power LED be connected directly to an LDR circuit?
No, an LDR is only a sensing component. It cannot supply the current required by a high-power LED. We need a suitable switching stage and LED driver for that purpose.
Does every solar street light need a battery?
A conventional solar street light that must operate throughout the night normally needs a way to store energy, such as a battery. The complete system should be designed according to the required operating hours and available sunlight.
Conclusion
Automatic street light circuits can be built using simple transistors, IC 555, operational amplifiers and solar-powered LED controllers.
The correct choice depends on the lamp power, supply arrangement, switching requirements and other features we need.
For a simple project, a basic transistor circuit may be enough. But for a solar-powered system, we must also consider the battery, charging controller and LED driver.
So we should compare the available designs and select the circuit that matches our application.
After this, we can follow the detailed construction guide for the selected circuit and check all component ratings and safety requirements before installing it.
Questions & Answers
please recheck the diagram because it’s indicated switch not LDR, sorry to disturb
That switch is optional, you can remove it if you want, and replace it with short link.
I have included it for an optional manual ON/OFF operation.
If you don’t want the AUTOMATIC day/night detection, then you can remove the BC547 and its base resistor network, and use the ON/OFF switch for the manual toggling of the LEDs.
please try to rate the resistors going to the LED lights and you first create a circuit using LDR in case I may want the switch to be automatic turn on/off
Please provide the LED specifications, I will calculate the resistor…
please design 100w solar panel charge controller minus a relay that can charge 70ah battery please make it simple
The previous circuit (below) which I suggested can be modified for any solar panel and battery, just by changing the solar panel, LED and the transistors.
I want you to create a circuit for my project of making street light solar that doesn’t use a relay but I want the LED bulb watt to be 20w or 30w , solar panel 10w, battery 12ah , please design it in two ways, the first way without automatic switch and the second way with automatic switch, please make it very nice power saving so it can protect and keep the battery so it can stay for a longer period of time
Here’s the complete circuit diagram for your specified requirement:
Please let me know if you have any further questions…
Hi Swagatan, Thank you so much for your tireless assistance and patience with beginners electronic enthusiasts, – it’s really appreciated. In one of your ” 7 Automated Streetlight Circuits”, I am building the No 2 cct, using a Ne555. The only question I have, is where the 10k resistor (R3), mentioned in the parts list, fits in?
Kind Regards and keep up the awesome work!!
Thank you so much Pieter for your kind words,
I am sorry about the confusion, as far as remember the 10k is nowhere present in the 2) diagram using IC 555, so please ignore it.
I have removed the 10k from the parts list now.
Please let me know if you have any further issues with the circuit…
Hello, good afternoon. All the public lighting circuits are very good. But I’m looking for one that has the peculiarity of being able to turn it off with a button… I mean, it turns on only when night comes but when I want to turn it off I can do it with a button, it has to stay off until the next day when night comes again … From already thank you very much.
Hi, yes that’s possible.
You can implement it in the following manner.
Select any circuit which has a transistor relay driver for controlling the lamp.
Now connect an SCR between the base of the transistor and ground, in the following manner:
Anode to transistor base.
Cathode to ground line.
1k between gate and ground.
A push-to-ON momentary switch between gate and the positive through another series 1k resistor.
SCR can be a BT169.
I will try to do it soon
Good morning Sir, thanks for all you do.
Please Sir I need a circuit for 3v DC source to automatically power 3v 50watt DC light, that will not affect the illuminousity of the light. I have tried various transistor connection but they tend to reduce the brightness of the LED.
Thanks
Thank you Evangel,
You will need the input current to be at least 50 / 3 = 16 amps to ensure the LED illuminates brightly. Are you supplying this much amount of current?
Yes Sir,
I need the circuit to work fine with this specifications.
Thanks ????
To switch 16 amps you will need one of these transistors, as mentioned in the following datasheet:
https://www.onsemi.com/pdf/datasheet/mj11028-d.pdf
Thank you Sir.
I am very grateful.
I will give it a trial
No Problem, Evangel. all the best to you!
Thanks for your impact so far,
I am finding it hard getting the recommended transistor you suggested, can I try 2N3771 transistor?
2N3771 will not be suitable, because it is just 20 amp and the not a Darlington transistor.
You can try building a Darlington transistor by combining a TIP35 and 2N2222 transistor and see if it works or not.
I hope you know how to connect these two transistors in Darlington pair.
No I don’t Sir, please help me with the circuit.
Thanks ????
Here’s an example of how to create a Darlington pair transistor:
I’ve laid the IC555 circuit perfectly, except I used a white LED and a 1K ohm resistor in line with the relay. The circuit activates and the light turns on, but I cannot utilize the photo resistor. It is not activating properly. The circuit stays energized all the time. Is there anything I can do to fix this?
Thank you.
The 555 based circuit is a tested design, you can see the video proof for the IC 555 design.
As there are hardly any components used in the IC 555 design there’s nothing I can suggest to troubleshoot.
You can manually short circuit the LDR terminals and check whether the IC responds or not?
What is the pin configuration of ic324 as used in the circuit above .
Use any two op amps from the LM324 and join the Vdd and Vss pins to the supply lines. You can also use LM358 IC.
Dear Sir Swagatam
Hello. A few years ago, I bought a house light circuit consisting of four transistors. I put aside its printed circuit board and mounted all components except Relay, LDR, and power supply, on a bread-board so that I can easily substitute the components in case they became defected later. I also took a few pictures of it for a future like today. Since it has been working well till today; meaning it has switched on the lamp by sunset and has switched it off the next morning; I decided to draw its circuit diagram and send it to you. Perhaps it would possibly be interesting for you and your visitors.
He who never forgets you for a lot of things that he has learnt from you,
Ersa
Thank you so much Dear Ersa,
I greatly appreciate your contribution!
The images and the circuit diagram look very nice and perfect.
I have posted the images at the end of the above article, I hope the readers will like them very much.
Many thanks once again.
Dear Sir Swagatam
Hello. it is my pleasure you liked the circuit. Thank you so much for your kind words and publishing it.
Wish you all the best
sincerely yours
Ersa
It is my great pleasure Ersa, thank you so much for your kind contribution!
Thank you very much for your inovative ideas.
All your design are very well understood.
But I have one problem.
Please how can I purchase the various components needed to build the board?
Thank you for your kind feedback, appreciate it very much!
You can buy the parts from your nearest local spare part dealer, or you can visit any online electronic spare part store and order the parts online from those stores.
Thanks for this. I hope a TRANSFORMERLESS version of this is possible using a capacitive power supply
That’s a good idea, yes a transformerless version can be also created, if possible I will try to update it in the article.