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Question-1. What is LED?
Answer-1: A light-emitting diode (LED) is a semiconductor light source.
Question-2. How LED is used?
Answer-2: LEDs are used as indicator lamps in many devices, and are increasingly used for lighting.
Question-3. What is electroluminescence in LED?
Answer-3: When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence.
Question-4. What are advantages of LED over incandescent light sources?
Answer-4: A4LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability.
Question-5. What are Practical use of LED?
Answer-5: The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches (see list of signal uses).
Question-6. What Technology is used in LED?
Answer-6: Like a normal diode, the LED consists of a chip of semi conducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers?electrons and holes?flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
Question-7. What are the applications of LED?
Answer-7: Applications of LED
1. Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning.
2. Illumination where light is reflected from objects to give visual response of these objects.
3. Measuring and interacting with processes involving no human vision.
4. Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light.
Question-8. what is Photosensor?
Answer-8: Photosensors or photodetectors are sensors of light or other electromagnetic energy.
Question-9. What should we do for converting LED to photodiode?
Answer-9: LEDs reverse-biased to act as photodiodes
Question-10. Give examples of photoconductors?
Answer-10: Vacuum-tube devices, semiconductor photodiodes, thermocouple semiconductor, photocondtive devices
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