automatic night lamp description

1. - 1 -
AIM
LIGHT ACTIVATED SWITCH WORKS
AS A AUTOMATIC NIGHT LAMP
INTRODUCTION
Of all the sources of energy, electricity is a major source of
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, “electricity saved is 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 proof system 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 sensor can be preset depending
upon the requirement.

2. - 2 -
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 base of
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 oppose the
current to the base of T1. If there is no current at transistor
T1, then T1 is off and T2 is switch on automatically.

3. - 3 -
COMPONENTS USED:
ONE L.D.R.
3 LED’S
RESISTANCES (R1- 1K, R2- 470 OHMS)
TWO TRANSISTORS BC-548
D.C. POWER SUPPLY