Photoresistors (LDR)

A photoresistor, also known as a light-dependent resistor (LDR) or photocell, is a type of resistor whose resistance changes with the intensity of light falling on it. This property allows photoresistors to be used in various applications where light detection is required.

Definition:
A photoresistor is an electronic component that functions as a variable resistor. It is made from a semiconductor material, often cadmium sulfide (CdS), cadmium selenide (CdSe), or organic photoconductors. The resistance of a photoresistor decreases as the light intensity increases, and vice versa.

Function:
The primary function of a photoresistor is to detect light. When light shines on the photoresistor, the photons excite the electrons in the semiconductor material, creating a flow of current. This change in resistance can be measured and used to control electronic circuits. The sensitivity to light makes photoresistors useful in light-sensitive applications.

Applications:
1. Light Sensors: Used in devices like light meters, camera exposure controls, and automatic light switches.
2. Proximity Sensors: Detect the presence of an object by measuring the change in light reflected back to the sensor.
3. Ambient Light Sensors: In smartphones and other devices to adjust screen brightness based on the surrounding light conditions.
4. Security Systems: To detect movement or changes in light patterns.
5. Robotics: For line following and obstacle detection in autonomous robots.

Selection Criteria:
When choosing a photoresistor, consider the following factors:
1. Spectral Response: The range of light wavelengths the photoresistor is sensitive to.
2. Resistance Range: The resistance value in the dark and under light conditions.
3. Sensitivity: How quickly the resistance changes with light intensity.
4. Linearity: The degree to which the resistance change is proportional to the light intensity.
5. Temperature Coefficient: How the resistance changes with temperature, which can affect performance.
6. Size and Shape: Depending on the application, the physical dimensions of the photoresistor may be important.
7. Cost: The budget for the project may influence the choice of photoresistor.

In summary, photoresistors are versatile components that can be found in a wide array of electronic devices and systems, providing a simple and effective means of detecting and responding to light changes.
Please refer to the product rule book for details.