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If we see today's century then the world is totally filled with new inventions and among them, artificial light is a great invention that provides us the sensation of looking at things at night or dark places.
Almost all the vehicles are provided with light for night vision and driving. Among them, the bike is one. The bike uses a 12 Volt power supply to glow its headlight. Due to maximum road accidents and thieving, today's bike comes with automatic light that is even turned on in day time when the key is on. This brings loss in electrical energy.

Let's design a circuit that will conserve energy. In this tutorial, we have made a circuit that will make headlight automatically on when it is evening or night i.e. at low intensity of light. Also, we have provided a manual switch to turn on the light if the sensor sometimes fails to automatically turn on.

In the above circuit, the components needed are:
1.) LDR (Light Dependent Resistor)
2.) BC547 Transistor
3.) 100k Resistor
4.) 12 Volt battery, headlight, and Handel switch are already provided in bikes

Let's know about components:

A.) LDR (Light Dependent Resistor)
These are known as a photoresistor. There resistance changes with the intensity of light. When the intensity of light is high that is during the day then the LDR resistance decreases and allows current to flow. When the intensity of light is low that is during the night then the resistance of LDR increases and blocks the current flow.

B.) BC547 Transistor
Transistors are components that either act as current and voltage amplifiers or as a switch. In this tutorial, we have used transistor as a switch.

There a three output pins in a transistor: Collector(C), Base(B), Emitter(E).

For Transistor to flow current it should be in active region i.e.,

Voltage of;


In the above circuit, we are varying base voltage. During day time resistance of LDR will be high and base will have high voltage than the emitter. So transistor goes to cutoff region i.e. transistor will not operate and will make our headlight turned off.

During night time LDR will have very low resistance and the base of the transistor will get low voltage. So the transistor now will operate in active region and the headlight of the bike will glow.

Also, the circuit is connected to the manual turn on and off switch of bike headlight so that if sometimes the LDR fails to operate then the user can manually ON and OFF the headlight.

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