What Is a Photodetector?
A Photodetector is a device that detects light and converts it into electrical signals, functioning as a light sensor or photosensitive element. It is used in various devices like TV remotes and automatic door systems, often utilizing infrared light.
Applications of Photodetectors
1. Photoresistor
Photoresistors are used in light meters, indoor thermometers, camera exposure meters, and for controlling street and car lights. They are sensitive to changes in electrical resistance based on light exposure.
2. Photodiode
Photodiodes are used in light intensity meters, CD players, smoke detectors, TV remote receivers, automatic faucets, solar cells, and image sensors.
3. Phototransistor
Phototransistors, known for high sensitivity, are used in infrared remotes, cameras, optical communication, and automatic doors.
Principles of Photodetectors
1. Thermal-type Elements
These convert light into heat, measuring changes in electromotive force, conductivity, and pyroelectric effects. Examples include thermopiles, bolometers, and pyroelectric elements.
2. Quantum-type Elements
Quantum-type elements measure changes in current, conductivity, and electromotive force due to carrier excitation. Examples include phototubes, photomultiplier tubes, photocells, photodiodes, phototransistors, and CCDs.
Features of Photodetectors
1. Non-contact Detection
Allows non-contact detection by illuminating the target and receiving reflected or transmitted light.
2. Wide Range of Targets
Can detect various materials including metals, non-metals, liquids, and glass.
3. High Speed, Responsiveness, and Resolution
Offers high-speed response and precise detection without mechanical motion.
4. Color Discrimination
Can distinguish colors based on the difference in light wavelengths.
Types of Photodetectors
1. Reflective-type Detectors
Measure reflected light from the target with combined emitter and receiver units.
2. Transmissive-type Detectors
Project light through the target to a receiver, measuring light obstruction. Suitable for long-distance stable detection.