Dark Sensor ( Light Sensor / Automatic Street Light )


Introduction: Dark Sensor ( Light Sensor / Automatic Street Light )

Here is my new simple Electronics project about  Automatic Street Light Control System or Dark Sensor.

it is a simple and powerful concept , which uses transistor ( BC 547 NPN) as a switch to switch ON and OFF the street light system automatically .
It automatically switches ON lights when the sunlight goes below the visible region of our eyes. ( e.g in evening after Sunset ).

it automatically switches OFF lights when Sunlight fall on it ( e.g in morning ) , by using a sensor called LDR (Light Dependent Resistor) which senses the light just like our eyes.

Needs no manual operation for switching ON and OFF...

Step 1: Things You Need...


* 1    BC547 transistor
* 1   220 k resistor
* 1   330 ohms resistor
* 1   LED (any colour )
* 1   9v battery
* 1   battery clip
* 1   LDR ( light dependent resistor  )

Step 2: AND...

*  Connecting wires
*  soldering rod and wire
*  wire stripper
*   Cutter

Step 3: Circuit Diagram

solder the transistor on the board and solder one wire of the LDR to the emitter and other to the base  , solder the negative wire of the LED to the base of the transistor with a 330 ohms resistor and also solder 220k resistor with the one side of the 330 ohmsresistor .

Step 4: Finsih... Uuuhuuuu... :p

The simple circuit is ready for testing now . Connect 9v battery terminals to the circuit as show in fig and see the output . As you block light falling on Light dependent resistor (LDR), the LED glows .

2 People Made This Project!


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56 Discussions

The Circuit works as Light sensor not Darkness. In dark, the LED dims, in pitch dark it turns off and in sunlight, LED glows bright

1 reply

Sounds like you need to exchange the position of the LDR and the 220K resistor.

how can i make darkness sensor using only 9v battery,LDR,BC547 transistor

1 more answer

If instead of using 220 k resistance i use 22k only will there be any problem...actually my ckt is not wrkng??

1 more answer

Why do you change the design and act surprised when it fails ?

Changing the delicate current balance by a factor of ten may permanently turn the LED on...

Can we use light bulb instead of LED lights? I am asking for our research and this inspired me. Thank you for the idea. Please answer ASAP.Thank you

1 more answer

This circuit is only controlling 20ma using a peak 100ma collector BC547 NPN transistor.

If you have an incandescent light bulb that draws less then 20ma it might work.

The reason I say might is because any incandescent bulb is is a lot less resistance when cold and will draw ten times the current until it gets hot enough to produce light off of the filament glow..

What response say you ??

hi ! please help me , i want to connect 10 or more LED, asap thanks

Plz send the pic for wiring as it may clear all the doubt, I'm very New to electronics and the diagram is very Confusing.


11 months ago

Is it ok to use 6 volts


11 months ago

is that okey if i will use 6v insted of 9volts

Could the circuit be modified to work the other way round, so that it switches ON in sunlight and OFF in dark? I suspect its v. simple, but so am I!

1 reply

Which type of resistors I need to use

I want to connect 10 white LEDs with 9 volt.. suggestion please guys

Hey can someone help me plz?

can someone tell me what the 2 resistors specifically

How may bulbs can be connected in this circuit. Can you explain me ways to connect about 6 bulbs (total Approx 9 volts- 1.5 Volt Each). Also upto how much volt led i can connect in this circuit

How do you make sure that when the light turns itself on, it doesn't then sense the light and turn itself back off?