The controlling of lights and home
appliances are generally operated and maintained manually in several
occasions. But the process of appliances controlling may cause wastage
of power due to carelessness of human beings or unusual circumstances.
To overcome this problem we can use the light dependent resistor circuit
for controlling the loads based on the intensity of light. An LDR or a
photo resistor is a device which is made up of high resistance
semiconductor material. This article gives an overview of what is LDR, light dependent resistor circuit and its working.
Light Dependent Resistor
Construction of a LDR
The construction of a LDR includes a
light sensitive material which is placed on an insulating substrate like
as ceramic. The material is placed in a zigzag shape in order to get
the required power rating and resistance. The area of zigzag separates
the metal placed areas into two regions.
Construction of a LDR
Where the Ohmic contacts are made either
on the sides of the area. The resistances of the contacts must be as
less as possible to make sure that the resistance, mainly varies due to
the light effect only. The use of lead & cadmium materials are
avoided as they are injurious to the environment.
Working Principle of Light Dependent Resistor
The working principle of an LDR is photo
conductivity, that is nothing but an optical phenomenon.When the light
is absorbed by the material then the conductivity of the material
reduces. 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 than the band
gap of the material to make the electrons jump from one band to another
band (valance to conduction).
LDR Working Principle
Hence, when light having ample energy,
more electrons are excited to the conduction band which grades in a
large number of charge carriers. When the effect of this process and the
flow of current starts flowing more, the resistance of the device
decreases.
Light Dependent Resistor Circuit
The circuit of LDR is an electronic circuit built with LDR, relay, Darlington pair, diode, & resistors shown in the below circuit diagram. A voltage supply is given to the load
The required DC voltage of the LDR circuit is supplied from a bridge rectifier circuit or a battery. This circuit changes the AC supply into a DC. The bridge rectifier circuit uses a step-down transformer to step-down the voltage from 230v into 12v. The diodes are connected in the form of a bridge used to alter the AC voltage into DC. The voltage regulator
is used to change the 12v DC-6v DC, and then, this DC voltage is
supplied to the entire circuit. A 230v AC supply for both the bridge
rectifier and the load is to be kept continuously for continuous
operation of the light sensor circuit.
Light Dependent Resistor Circuit Diagram
In the morning time, this sensor has a
low resistance around 100Ω. Thus, the power supply flows through the LDR
& ground through the variable resistor and resistor as shown in the
above light sensor circuit. This is due to the resistance offered by
the light dependent resistor in the daytime or when the light falls on
the LDR, then it is less compared to the resistance of the remaining
part of the sensor circuit . We are alert of the principle of current,
that the flow of current always flow in the path of low resistance.
Therefore, the relay coil does not get
sufficient supplies to get strengthened. Hence, the light is switched
off in the daylight. In the same way, during the night time, the
resistance of the LDR increases to a high value (20MΩ). Thus, due to the
high resistance of the resistor,
the flow of current is low or almost zero.Now, the flow of current
through the low-resistance lane such that it increases the base voltage
of Darlington pair to reach more than 1.4v. As the Darlington pair
transistor is triggered, the relay coil acquires enough supply to get
energized, and hence, the light switches in the night time.
Applications of LDR
Light dependent resistors are simple and
low cost devices. These devices are used where there is a need to sense
the presence and absence of light is necessary. These resistors are
used as light sensors and the applications of LDR mainly include alarm
locks, street lights, light intensity meters, burglar alarm circuits.
For better understanding of this concept, here we have explained one
project namely; power conserving of intensity controlled street lights
using LDR.
Power Conserving of Intensity Controlled Street Lights using LDR
Nowadays, lightening-up of highways is
done through HID lamps but, the energy consumption of these lights is
high as well as there is no particular mechanism to turn on/off the
lights from sunrise to sunset. To overcome this problem, here is an
alternative method using LEDs i.e. power conserving of intensity
controlled street lights using LDR.
Intensity Controlled Street Light using LDR
The proposed system is built to overcome
the drawback of the present day of HID lamps.The proposed system
determines the usage of light emitting diodes as a light source and its
adjustable intensity control according to the requirement. These lights
consume less power as well as the life span of these lights is more
compared to conventional HID lamps.
The most important feature of this
project is, the light intensity can be controlled according to the
necessity during night time, which is not possible in HID lamps. An LDR
is used to detect the light and the resistance of the LDR drastically
reduces according to the light in the day time, that forms as an i/p
signal to the controller.
A bunch of LEDs is used to make a street light and the microcontroller using in the project is preprogrammed
with instructions which controls the light intensity based on the Pulse
width modulation signals generated. The light intensity is kept high
during the night time, and as the traffic on the roads tend to fall in
peak hours;the intensity also falls gradually till morning. Finally the
LED lights get turned off at morning 6 am, and continues again at 6pm in
the evening. This process will continue.
Furthermore, this project can be
developed by mixing it with a solar panel, which changes the intensity
of the solar to the equivalent voltage and solar energy is used to feed
the lights on highways.
Thus, this is all about the working
principle of light dependent resistor and LDR circuit diagram and its
applications. We hope that you have got a better concept through this
article. Furthermore, any queries regarding this article or electrical and electronic projects, please give your feedback in the comment section below. Here is a question for you, what is the function of a LDR?
Photo Credits:
- LED Construction sarutech
- LDR Working Principle technologystudent
- LDR wordpress
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