Automatic Night Lamp Circuit

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Automatic-night-lamp-circuit-using-LDR
Automatic Night Lamp Circuit

Night lamp circuits generally employ LDR to sense the light in the environment and turn on the light based on light intensity. Here is a similar circuit which uses LDR and transistors to switch the lamp during night time. Relay was used above in order to switch the lamp ON/OFF. Lamp was powered by 230v AC supply and Fuse was added to offer protection.

WORKING OF AUTOMATIC NIGHT LAMP CIRCUIT:

The LDR (Light Dependent Resistor) used to sense the light in the environment. LDR has the characterstics of giving high resistance in dark and low resistance during day time. The RV1 should be adjusted until the transistor Q1 is switched ON. When the transistor Q1 was in ON state it keeps the Q2 in OFF state. Therefore the relay is in OFF state and the lamp remains in OFF state.

When night falls, the resistance of the LDR increases and therefore the base voltage of Q1 decreases below 0.6v. This makes the transistor Q1 to switched off which in turn makes Q2 ON. Then the relay gets turned ON switching the lamp ON. The bulb of any wattage can be used provided the relay should have sufficient rating.

Related Designs and Schematics

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Frank Donald

Junior Network Engineer at Tata Communications
Frank Donald is an Electronics and Communication Engineer who is very passionate about his subject. Reading, Surfing and Blogging are the things he loves.

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9 Comments on "Automatic Night Lamp Circuit"

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Mohsen
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i build this circuit but when i test it in the dark the lamp is flash on/off on/off….
very Quickly !!!!

CBL
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make Sure ,LDR in dark place. Not near the Light bulb.

Anonymous
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Will not the relay chatter at dim ambient light level both at dawn and dusk?

Frank Donald
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Yes it will. Try to lower the sensitivity level of your ldr

Anonymous
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The relay will blow if you use a 9V relay directly inline with 230VAC and a simple light bulb and fuse combo. You need to place a high power resistor in series with the relay 1. to reduce the current and 2. to reduce the voltage across the relay. Better yet use a relay rated for 120VDC

Alan Tinsley
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Forget about it. 9v to activate relay. My Bad. just had a Homer Simpson moment.

2150dalek
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I like it.! I want one for my house Door…I see the names of the Transistors, values for the discrete components, but where do you buy an LDR?

Frank Donald
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LDR is widely available component so you dont need to worry about it…You can also purchase it online too

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