- Physics
- Class 1 to 9
Automatic Night LAMP Educational Circuit Board
Code B07P1XVJFX
- 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 automatic night lamp circuit board switches a light on by itself when it gets dark and off again when there is enough light. It shows how a light sensor and a simple switching circuit can automate an everyday task and save electricity.
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 usual sensor in this circuit is a light dependent resistor (LDR), whose resistance is low in bright light and very high in the dark. It is placed in a voltage divider with another resistor, and the voltage at their junction feeds the base of a transistor. In daylight the LDR's low resistance keeps the base voltage below about 0.7 V, so the transistor stays off and so does the lamp. As darkness falls, the LDR's resistance rises, the base voltage climbs past the switching point, and the transistor turns on, sending current through the lamp or LED. Many boards add a variable resistor to the divider to set how dark it must get before the lamp comes on. This is a simple automatic control system, with a sensor, a deciding part and an output. Street lights that switch on by themselves at dusk work on the same idea and save electricity.
Make it yourself
Make an automatic night lamp circuit 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 10
Step by step 8 steps
- Make a voltage divider
The 10 kΩ resistor and the 100 kΩ preset in series from the positive line to a junction point, and the LDR from that junction to the negative line.
Hold the BC547 with its flat face towards you: the legs are collector, base and emitter from left to right. Connect the junction to the base through the 1 kΩ resistor.
Join the emitter to the negative line.
Connect each white LED with its 470 Ω resistor between the positive line and the collector, with the LED's long leg facing the positive line.
Switch on in a bright room: the LEDs should stay off. Cover the LDR with your fingers and they should light.
Turn the preset slowly with a small screwdriver until the LEDs come on at the darkness you want, for example when the room lights are dimmed.
Build a small house and street lamp from card and a straw, put the LEDs in the lamp head, and fix the LDR on the roof facing the sky inside its short tube, so the lamp's own light cannot reach it.
Test the finished model in a dim corner and with a torch, and label each part of the circuit on the base.
Read this first
Safety first
Go through these points before you build or switch anything on. Younger students should do this with an adult.
- Always keep the 470 Ω resistor in series with each LED; an LED joined straight to 9 V burns out at once.
- Use scissors or a craft knife for the card only with an adult nearby, cutting away from your fingers.
- Disconnect the battery when you are not showing the model, and never let its terminals touch a coin or key.
- Keep the small parts away from very young children.
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 LEDs stay on even in bright light
The preset is set to too low a resistance, or the LDR and the resistors have been swapped round. Turn the preset towards higher resistance, and check that the LDR goes from the junction to the negative line.
The LEDs never come on, even in the dark
An LED may be the wrong way round, the transistor legs may be mixed up, or the battery may be weak. Check each LED's long leg faces positive, check the transistor's flat face, and try a fresh battery.
The lamp keeps flickering on and off at dusk
The lamp's own light is reaching the LDR, so it switches itself off, gets dark, and switches on again. Point the LDR away from the lamp and shade it with its tube.
The LEDs glow dimly instead of switching fully on
The light level is close to the switching point, which is normal for a single-transistor circuit. Make the test area darker or turn the preset a little further.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Cover the sensor with your hand to show the lamp turning on, then uncover it.
Explain the three parts of the system: sensor, transistor switch and lamp.
If the board has a sensitivity control, show how it changes the switching point.
Mention how automatic street lights save electricity in towns and cities.
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 as the light falling on it increases.
What is the role of the transistor in a typical night lamp circuit?
It acts as a switch that turns the lamp on when the voltage from the LDR divider rises high enough.
Why is a variable resistor often used with the LDR?
To adjust the light level at which the lamp switches on.
Give one real-life use of this circuit.
Automatic street lights or garden lights that switch on at dusk and off at dawn.
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 a lamp that switches on by itself when it gets dark
- Introduction: how automatic street lights save electricity
- What an LDR is and how its resistance changes with light
- How the voltage divider and the transistor work as a switch
- Circuit diagram and list of parts
- Steps of construction
- Observations: LDR resistance in sunlight, room light and darkness
- Uses: street lights, garden lights and night lamps
- Precautions and 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 that light sensors or simple circuits are part of what your class is studying, and that a circuit board model suits your teacher's brief.
- Read the listing to see what the board runs on and whether a battery is mentioned, and keep a fresh one ready.
- Practise showing the change by covering the sensor with your hand, as exhibition halls are often brightly lit.
- Keep the box to carry the board safely to school.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
2When it arrives
- Try it in a dark room and in daylight as soon as it arrives, so there is time to sort out any problem.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Measure the LDR's resistance with a multimeter at different distances from a lamp and draw a graph.
Add a second transistor so the lamp switches on sharply instead of fading in.
Use the transistor to drive a relay that switches a separate 6 V lamp, and explain how real street lights switch large loads.
Work out how many hours of electricity an automatic lamp saves compared with one left on all day.
Audience
Who it suits
Class 8 to 12 students looking for a practical automation project, and beginners learning about sensors and transistors.
- 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.
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Physics Working Models Explained
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Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
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Writing a Science Project File
How to write the report, from the cover page to the bibliography
