This project presents the construction and operation of a light dependents switch using a light dependent resistor a relay used in the circuits energized when darkness falls on the light- dependents resistor, LDR which turns on a 12V bulb. The relay is de-energized when light falls on the LDR, as a results of which the 12V bulb goes off. The switching on is achieved when the intensity of light falling on the LDR is low and the switching off is achieved when the intensity of light falling on the LDR is high and at 100k value of the variable resistor.
A light dependent resistor (LRD) is a device whose resistivity is a function of the incident electromagnetic radiation. Hence, they are light sensitive device. They are also called conductors, photo conductive cells or simply photocells are made up of semi- conductor material having a high resistance.
The use of solar energy to control electronic circuits has become a reality. The radiant energy can be detected by a alight- dependent resistor in which the resistance changes with variation of the intensity of light falling on it. This phenomenon has been found useful in the operation of electronic circuit through transistor and semi conductors thereby reducing human effort in switching electrical appliances.
Many electronic circuit, relay on the availability of sources of d.c power for their operation. To ensure continous and regular supply of D.C power. It is necessary to devices a d.c power from an a.c main source. Hence a 12v d.c power supply will be used in this project as a supply for the light- operated switch.
Light dependent resistor changes its resistivity according to the amount of light falling on it. If light energy falls on it. If produce holes/ electronic pairs and the resistance falls on a bright day, the light emiting diode has a resistance of about 100 0hms. In total darkness its resistance is more than 120hilo ohms. The common example is the ORP12.
Light activated switch is an electrical project circuit by which we can switch ON and OFF the electrical load appliances like fans, coolers, air- conditioners, street- lights, e.t.c authomatically based on the day- light intensity instead of manually operating the switches.
In case of the street/ lamp erected on high ways it s not an easy task to manually control them, but, if uncontrolled the chances of power wastage would increase. To get rid of this situation, the implementation of authomatic light switch by using a light sensor that switches light authomatically ON and OFF is the best option.
The aim and objective of this project is to construct a light operated switching system using a light- dependent resistor.
The system is expected to turn a light bulb “ON: whenever there is darkness.
Some of the practical applications of the light operated switching are:
i. It is used for authomatic switching “ON” of street lights as soon as it gets dark.
ii. It can be used as security light switch in homes
iii.Useful as a light detector circuit
iv. Useful as a dark activated switch
v. It is also used in the industries for instance, to count products on production lines or an conveyor belts.
This can be achieved by making the product to continually abstract the lines falling on the LDR (light dependent resistor) fixed on the opposite side of the products. The energizing and de- energizing of the relay can them be registered by an electronic counter.
Therefore this project is significantly useful in that it distinguishes daylight and dark hours. This device eliminates the need of switching the porch lamp or backyard lamp daily and also helps to switch ON or OFF the premises of the house when the occupants are out of station.