- Physics
- Class 1 to 9
Automatic Street Light Educational Circuit Board
Code B07NYMVYGY
- Paid for and delivered by Amazon. The current price and the delivery date for your PIN code are shown there.
- Sold by Gurukul Technicals Institute, Delhi.
- Need a different topic, a custom version or a school order? Ask on WhatsApp.
In this project guide
Physics
About this model
This educational circuit board demonstrates an automatic street light that switches on when it gets dark and off when daylight returns. It shows how a light sensor can save electricity by removing the need for anyone to operate a switch. It is one of the most popular school projects because the idea is simple and the use is obvious.
How it works
The science behind it
The idea the model demonstrates, in words you can use in your report and when you explain it.
The sensor is usually a light dependent resistor (LDR), made of a semiconductor such as cadmium sulphide. In darkness, few electrons in the material are free to move, so its resistance is high, often around a megaohm. When light falls on it, photons give electrons enough energy to break free and carry current; this is photoconductivity, and the resistance can fall to a few kilo-ohms or less. The LDR forms a voltage divider with a fixed or variable resistor, and the voltage from this divider drives a transistor. At dusk, the LDR's rising resistance shifts the voltage enough to switch the transistor on, which lights the LED or energises a relay for a bigger lamp. At dawn the reverse happens. Because the lamp burns only when it is needed, energy is saved. Many Indian towns and highways use light-sensing controllers, as well as timers, to switch their street lights.
Make it yourself
Make an automatic street light model yourself
Build your own version from scratch, or use the steps to understand how the ready-made model is put together before you present it.
What you need 9
Step by step 8 steps
Connect the 10 kΩ resistor and the potentiometer in series from the positive rail to the first transistor's base, and the LDR from that base to the negative rail, so they form a voltage divider.
Connect the first transistor's collector to the positive rail and its emitter to the second transistor's base, with the second emitter to the negative rail; together they act as one very sensitive switch.
Connect each LED in series with its 470 Ω resistor between the positive rail and the second transistor's collector, longer leg towards positive.
Measure the LDR's resistance with the multimeter in room light and with your hand cupped over it, and note how much it changes.
Build the model road, fix the LEDs on top of the straw lamp posts, and mount the LDR facing up inside its black tube, away from the lamps.
Switch on in normal light and turn the potentiometer until the lamps are just off; then cover the LDR and check that they come on.
Dim the room slowly and adjust the potentiometer so the lamps come on at dusk and not just in a passing shadow.
Record the LDR's resistance and whether the lamps are on at several light levels.
Read this first
Safety first
Go through these points before you build or switch anything on. Younger students should do this with an adult.
- Use only the 9 V battery; a model street light must never be connected to mains lamps.
- Keep the 10 kΩ resistor in series with the potentiometer, so turning it fully cannot pass a large current into the transistor's base.
- Do not stare into bright white LEDs from close up.
- Use the glue gun, cutter and soldering iron only with an adult.
Troubleshooting
If something does not work
The usual problems with this model and how to fix them. Open a problem to see the fix.
The lamps are on all the time
The potentiometer's resistance is set too low for your room's light, or the LDR is shaded. In normal light, turn it towards higher resistance until the lamps just go off.
The lamps never come on
Check the transistors' pin order and the LEDs' direction, then cover the LDR completely and turn the potentiometer slowly. If nothing changes, the LDR may be disconnected.
The lamps flicker on and off at dusk
The LDR is seeing the lamps' own light, so they switch themselves off. Point the LDR away from the LEDs and keep it inside its black tube.
The lamps glow dimly instead of fully
The light level is right at the switching point, where the transistors are only half on. This is normal at the threshold; a Schmitt trigger gives a cleaner switch.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Cover the LDR with your hand or a cup to make it night and show the light coming on.
Measure the LDR's resistance in light and in shade with a multimeter to show photoconductivity.
Explain how switching lights only when needed saves energy across a whole town.
Shield the LDR from the lamp or LED so that its own light does not switch it off again.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
What is an LDR?
A light dependent resistor, whose resistance decreases when light falls on it and increases in darkness.
What is photoconductivity?
The increase in the electrical conductivity of a material when light falls on it, because the light frees more charge carriers.
Why must the LDR not face the street lamp itself?
The lamp's own light would lower the LDR's resistance and switch the lamp off, making it flicker on and off.
What is the advantage of an automatic street light?
It switches on and off by itself according to daylight, so no manual effort is needed and electricity is not wasted.
Project file
Project file outline
The headings of the project file, in order. Give each heading its own section and write it in your own words.
Free ebook: Writing a Science Project FileContents
- Aim: to make street lights that switch on automatically at dusk and off at dawn
- Why automatic street lights save electricity
- The LDR and photoconductivity
- The voltage divider and how it sets the switching level
- The transistor as a switch, and the two-transistor (Darlington) pair
- Circuit diagram and construction of the model road
- Observation table: light level, LDR resistance and lamp state
- Limitations and improvements
- Conclusion
Buying checklist
Before you buy
What to check before you order the model, and what to do when it arrives.
1Before you order
- Check with your teacher that an automatic street light suits your class and the chapter on electricity or semiconductors.
- Read the listing for the supply it needs and anything else it mentions; do not assume a battery is included.
- Exhibition halls are often brightly lit, so practise covering the sensor smoothly so visitors can see it switch.
- Keep the box so the board's components are not bent in transport.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
2When it arrives
- When it arrives, test it by covering the sensor with your hand and by dimming the room.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Add a small solar panel and rechargeable cells so the lamps run at night on energy stored during the day.
Estimate the electricity saved if a street of lamps switched off one hour earlier each morning, using lamp wattages from a reliable source.
Replace the transistor switch with a 555 Schmitt trigger and compare how cleanly the two versions switch.
Audience
Who it suits
Class 8 to 12 science exhibitions and physics projects on sensors, semiconductors and energy saving.
- ClassClass 1 to 9
- SubjectPhysics
Free to read
Free ebooks for this topic
Free PDF ebooks from Gurukul Technicals Institute on the science, the making and the presenting of projects like this one.
- Free PDF ebook
Electricity and Magnetism Experiments
Hands-on experiments with cells, wires, bulbs and magnets
- Free PDF ebook
Physics Working Models Explained
Twenty classic models, how each works and how to make it
- Free PDF ebook
Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
- Free PDF ebook
Writing a Science Project File
How to write the report, from the cover page to the bibliography
