INDEX
LIST OF CONTENTS PAGE
NO.
➢ AIM 2
➢ INTRODUCTION 2
➢ MATERIALS REQUIRED 3
➢ PRINCIPLES 4
➢ CHARACTERISTICS 5
➢ WORKING 8
➢ CIRCUIT DIAGRAM 9
➢ APPLICATIONS 10
➢ BIBLIOGRAPHY 11
1
AIM OF THE PROJECT
TO UNDERSTAND LDR AND THE APPLICATION OF
LIGHT DEPENDENT RESISTANCE(LDR).
Introduction to Light
Dependent Resistors (LDRs)
Light Dependent Resistors (LDRs), also known as
photoresistors or photocells, are electronic
components whose resistance varies depending on
the amount of light incident upon them.
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These versatile devices have found numerous
applications in various fields, from lighting control
systems to security systems and beyond.
This comprehensive project report will delve into the
principles, characteristics, and applications of LDRs
with a special focus on their use in street
lighting systems
MATERIALS REQUIRED
1. 1K Ω resistor
2. 50K Ω resistor
3. 9 V battery
4. BC547
5. CdS LDR
6. 3 V LED
7. Simple wire.
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Principles of Light
Dependent Resistance
LDRs operate on the principle of photoconductivity,
where the electrical resistance of a material decreases
when exposed to light.
This change in resistance is due to the creation of
electron-hole pairs within the semiconductor material,
which increases the number of charge carriers available
for conduction
The higher the light intensity, the lower the resistance of
the LDR. This fundamental property is what allows LDRs
to be used in a wide range of applications where light
detection and control are required.
The specific materials used in the construction of LDRs,
such as cadmium sulfide (CdS) or cadmium selenide
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(CdSe), have a significant impact on their performance
characteristics and sensitivity to different wavelengths of
light. Understanding the underlying principles of LDR
operation is crucial for designing efficient and reliable
light-based systems.
Characteristics and
Properties of LDRs
LDRs exhibit several key characteristics and properties
that make them unique and versatile components. Some
of the notable features of LDRs include:
Resistance Range: LDRs can have a resistance range that
spans several orders of magnitude, typically from a few
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hundred ohms in bright light to several megohms in
complete darkness.
Response Time: LDRs can respond to changes in light
intensity relatively quickly, with response times ranging
from milliseconds to several seconds, depending on the
specific design and construction.
Spectral Sensitivity: LDRs can be sensitive to different
wavelengths of light, with some being more responsive
to visible light, while others may be more sensitive to
infrared or ultraviolet radiation.
Power Handling: LDRs can typically handle low to
moderate power levels, making them suitable for a
variety of control and sensing applications.
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Understanding these characteristics is crucial when
selecting and implementing LDRs in various applications,
such as street lighting systems, where specific
performance requirements must be met
LDR DIAGRAM
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WORKING
The working principle of an LDR-based light sensing
system involves the variation in resistance of the LDR
based on the intensity of light.
The working principle of an LDR is photoconductivity,
which is nothing but an optical phenomenon. When the
light is absorbed by the material then the conductivity
of the material enhances.
When the light falls on the LDR, then the electrons in
the valence band of the material are eager to the
conduction band. But, the photons in the incident light
must have energy superior to the bandgap of the
material to make the electrons jump from one band to
another band (valance to conduction).
Hence, when light having ample energy, more electrons
are excited to the conduction band which grades in a
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large number of charge carriers. When the effect of this
process and the flow of the current starts flowing more,
the resistance of the device decreases.
CIRCUIT DIAGRAM
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APPLICATIONS
Applications of LDRs in Street Lighting
One of the most common applications of LDRs is in the
control and automation of street lighting systems.
LDRs can be used to detect the amount of ambient light
and automatically turn on or off street lights as needed,
providing energy-efficient and cost-effective lighting
solutions.
In a typical LDR-based street lighting system, the LDR is
placed in a strategic location, such as on the top of a
street lamp, where it can accurately measure the
available light.
When the ambient light levels drop below a
predetermined threshold, typically at dusk, the LDR will
detect the decrease and trigger the street lights to turn
on.
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Conversely, when the ambient light levels rise above the
threshold, typically at dawn, the LDR will detect the
increase and signal the street lights to turn off.
Some other applications of LDR
These resistors are mainly used when there is a need to
sense the absence and presence of the light such as
burglar alarm circuits, alarm clock, light intensity meters,
etc.
BIBLIOGRAPHY
NCERT Physics Textbook Class XII
Gamma.app
Watelectronics.com
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