Automatic Night Lamp Circuit Diagram using lm358
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Automatic Night Lamp Circuit Diagram by LDR & LM358 OPAMP

This article explains automatic night lamp circuit using a high power LEDs circuit which automatically turns the LEDs ON at night and OFF when it is daytime. The sensing part which is being used for detecting the light is Light Dependent Resistor (LDR). The resistance of LDR depends on the light incident on it. Greater the light, the lower will be the resistance. We are arranging here twenty LEDs in an array such that 5 LEDs are in series and four such series LEDs are in parallel.

Automatic Night Lamp Circuit Diagram:

Automatic Night Lamp Circuit Diagram using lm358
Automatic Night Lamp Circuit Diagram using LM358

Working of Automatic Night Lamp Circuit:

The working of the circuit is simple. The transistors are used as Switch. When there is no light (at night), light-emitting resistance will increase. The voltage across LDR will increase. When it reaches 0.6V, transistor Q1 will turn ON and turn Q2, Q3 ON too. Hence there will be a closed path and current will pass through Q2, Q3 glowing LEDs.
The LEDs used here are high powered white Lights whose light is almost equal to the ordinary fluorescent bulb. The whole circuit can be assembled on PCB.LEDs should be arranged correctly. Keep LEDs 1cm away to each other So that light will be well distributed.
You can set when LEDs should turn ON by adjusting the variable resistor RV1.

Automatic Night Lamp Circuit Diagram using LDR

The whole circuit is powered by a 12V DC supply. It should be stable enough for the better intensity of LEDs.


LDR (light dependent Resistor)
Rv1 1M potentiometer
R1 100k
R2 1k
R3, R4, R5, R6 330 ohm (1watt)
Q1 BC547 (NPN Transistor)
Q2, Q3 tn2905 (PNP Transistor)
C1 1uF (non-polar)
LEDs (high power white color)

For pin configurations of transistors, see the datasheet.

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