Automatic night light control system needs no manual operation for switching ON and OFF when there is need of light. It detects itself whether there is need for light or not. When darkness rises to a certain value then automatically light is switched ON and when there is other source of light i.e. day time, the light gets OFF.
In the project we use light detecting resistor as a light sensor & a NAND gate for detection of high level or low level of voltage to energize the RELAY coil which is used to interface the control circuit with the external light source.
Wastage of power is not desirable in any system. So it is very much economic to have this arrangement so that power is not wasted during day time where manual operation is not possible. Though we can use it in our daily life also for the betterment of our system.
While dealing with this project we faced a problem that the light remained on or off depending upon the presence of any other light source. If we want to make the light off in night hours when there is no need of light, or after switching off the light if we want to make the light on again it was not possible with the circuit investigated earlier. As we don’t want any manual operation we have an arrangement of doing this by means of sound (like clapping sound).This mechanism makes the circuit is more flexible.
By means of this circuit we can control any other electrical appliances as we use the double pole double throw relay switch.
Again for economic operation it is very much helpful and it is very much easy and cheap to make the circuit for house hold purposes.
The operation and operating characteristics of the components which are used in the circuits are briefly outlined below-
LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits. Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but when they are illuminated with light resistance drops drastically.
The figure above shows that when the torch is turned on, the resistance of the LDR falls,allowing current to pass through it.
When a light level of 1000 lux (bright light) is directed towards it, the resistance is 400 (ohms).
When a light level of 10 lux (very low light level) is directed towards it, the resistance has
risen dramatically to 10.43M (10430000 ohms).