Unit-2 Chapter- 7 I took this from the internet
A light-dependent resistor (LDR), a photoresistor, is an electronic component that changes its resistance based on the amount of light it detects. In simpler terms, the brighter the light shining on the LDR, the lower its resistance. Conversely, in darkness, the resistance of an LDR shoots up.
how they work:
Material: LDRs are typically made from light-sensitive semiconductor materials like cadmium sulfide (CdS) or lead sulfide (PbS).
Working Principle: When light hits the LDR, it excites electrons in the semiconductor material, allowing them to flow more easily. This increased flow of electrons translates to a decrease in resistance.
Resistance Range: In darkness, an LDR can have a resistance of several megaohms (MΩ). When exposed to bright light, this resistance can drop to a few hundred ohms.
Applications of LDRs:
Due to their light sensitivity, LDRs are used in various applications, including:
Automatic lighting systems: LDRs can be used to automatically turn on streetlights or security lights at dusk and turn them off at dawn.
Light intensity meters: LDRs can be incorporated into devices that measure light intensity, such as camera light meters.
Security alarms: LDRs can be part of security alarm systems to detect movement by sensing changes in light levels.
Touchless switches: LDRs can be used in touchless switches that activate when someone waves their hand in front of the sensor.
LDRs are a simple and inexpensive way to detect light or measure its intensity. They are a versatile component used in various electronic circuits where light sensitivity is needed.