A Light Dependent Resistor (LDR), also known as a photoresistor, is an electronic component that exhibits a change in its electrical resistance in response to changes in light intensity. The LDR sensor you mentioned is a specific type of photoresistor with a diameter of 5mm. Here’s a more detailed description of the LDR sensor:

Construction and Composition: The LDR sensor is typically composed of a semiconductor material, often cadmium sulfide (CdS), which exhibits photoconductivity. The 5mm LDR sensor has a circular shape with a diameter of 5mm, allowing it to capture light effectively.
Working Principle: The working principle of the LDR sensor is based on the conductive properties of the semiconductor material it is made of. When exposed to light, photons interact with the semiconductor, causing the electrons in the material to move and generate an electric current. The intensity of light affects the number of electrons excited and hence the conductivity of the semiconductor, resulting in a change in resistance.
Resistance Variation: In low-light conditions or darkness, the resistance of the LDR is high as it is less conductive. When light, particularly visible light, illuminates the LDR, its resistance decreases significantly due to increased conductivity.
Applications: LDR sensors are widely used in various applications, including light-sensitive switches, automatic outdoor lighting systems, twilight switches, streetlights, and light intensity meters. They play a crucial role in sensing ambient light levels and enabling automated actions or control based on the detected light intensity.
Usage: The 5mm LDR sensor can be easily integrated into electronic circuits. When used in a voltage divider circuit, the varying resistance of the LDR due to changes in light intensity leads to variations in the output voltage, allowing for light-level measurements or triggering of specific actions based on the amount of light detected.