This document describes an automatic night lamp circuit that uses a light dependent resistor (LDR) and two transistors to automatically turn a light on at night and off during the day. The LDR has high resistance in the dark and low resistance in light. When the LDR senses darkness, it allows current to flow through the first transistor, turning it on and activating the second transistor to power the light. During daylight hours, the LDR has low resistance and prevents current flow, turning the transistors off and switching the light off to conserve electricity without human intervention. The system is useful for automatically controlling street lights and other outdoor lights without wasting energy.

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AUTOMATIC NIGHT
LAMP
Of all the sources of energy, electricity is a major sourceof energy touching
almost every human activity to think life without electricity is a nightmare.
But the grim reality is that the consumption of the electricity is much more
than its production. Hence, the need to conserve electricity has become need
of the hour.
In other words, “electricitysavedis electricity produced”
The introduction of light activated switch for switching on or off the street
light system is a step in this direction. It not only avoids wastage of
electricity caused due to human negligence, but is a full proofsystem in
govt. departments. City street lights etc. Where no one bothers for the
callous wastage. With the installation of this system the gadget automatically
switches on the connected device with the onset of darkness and puts it off
with the sunrise or daylight besides the desired light at sensorcan be preset
depending upon the requirement.
CIRCUIT WORKING
Main part of this project is light sensor. Light sensor sense the change of
light and switch on the circuit as per the requirement. As a light sensor we
use one light sensitive resistor name a L.D.R. LDR is a light dependent
resistor. LDR offers a high resistance in dark and very low resistance in
light. In this project along with LDR we use two transistor’s both the
transistor are NPN transistor. Here we use transistor as a switch. Output
bulb/LED is connected to the collector point of transistor T2. base point is
forward bias through 470 resistor. Emitter of both transistor is connected to
the negative voltage. LDR is connected to the second transistor T1. When
LDR is in light the LDR shows a low resistance, due to this low resistance
base of T1 is forward bias and transistor T1 is on. When transistor T1 is on
the collector of T1 is more negative and due to this negative voltage
transistor T2 is off. Transistor T2 is off. Transistor T2 is off because
collector of T1 is directly connected to the baseof transistor T2. If T2 is off
then bulb is also off because bulb is switch on by only transistor T2. When
LDR is in dark, then due to high resistance of LDR, LDR opposethe current
to the base of T1. If there is no current at transistor T1, then T1 is off and T2
is switch on automatically.