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LED Question & Answers

June 5, 2021 By WatElectronics

This article lists 100+ LED MCQs for engineering students. All the LED Questions & Answers given below include a hint and wherever possible link to the relevant topic. This is helpful for the users who are preparing for their exams, interviews, or professionals who would like to brush up their fundamentals on the LED topic.

The optical semiconductor device purpose is to convert electrical energy to light energy. These are broadly classified into two different groups: Light receiving devices (Example: Solar cells) and Luminescent devices (Example: Light-emitting diodes and the LASER diodes).

In comparison to the LASER diodes, LEDs are low in cost and offer a longer service life. The very first commercially available LED was used to replace the indicator lamps made of neon and incandescent lamps.

Nick Holonyak, Jr. was the first to invent the LED that is capable of producing visible-spectrum red light. These LEDs are further classified as Surface emitting LEDs (SLEDs) and Edge emitting LEDs (ELEDs).

1). ____________ replaced neon indicator and incandescent lamps.

Hint
2). The compound material of semiconductors used in LEDs make use of ___________ elements of periodic table.

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3). LEDs operates at _________ bias.

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4). Which color LED was first available commercially?

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5). The p-n junction in a LED is made of ____________.

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6). The recombination process in the diodes made of silicon and germanium occur due to ________________.

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7). Recombination of electron-hole produces _________ in LEDs.

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8). The junction in LED is __________ doped.

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9). The spectral distribution of LED is _____________.

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10). The power in the LED reaches maximum at ____________.

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11). For the larger photon energy the power tends to ___________.

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12). The recombination in a semiconductor is of _______ types.

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13). The recombination in which the photon is emitted is termed as ________.

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14). The light emitted from the surface of the LED is known as ____________.

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15). The light in SLED is emitted through _________.

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16). The optical losses in LED are ___________.

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17). The efficiency in the SLED can be enhanced by _________.

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18). LED efficiency can be increased by __________ substrates.

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19). ________ increases the photon energy as the higher current is passed.

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20). The electrons collected directly by the electrode at another end and the photon is not generated is known as _________.

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21). Stimulated emission is considered as a loss in __________.

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22). The effect of recombination leading to the emission of light is known as _________.

Hint
23). ____________ is the example of Direct band gap or recombination material.

Hint
24). InGaN/GaN uses _________ substrate.

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25). Package material refractive index must ___________ to the semiconductor’s index.

Hint

LED Multiple Choice Question & Answers

26). In __________ recombination, the free electrons at the conduction band bottom can directly recombine with the free holes present at the valence band top.

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27). The probability of recombination of electron-hole directly is less in ___________.

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28). Donor states as the centers for recombination in ____________.

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29). ____________ is an example for Indirect recombination.

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30). In Gallium Arsenide Phosphorus __________ serve as the center for recombination.

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31). Band gap energy of the semiconductor materials decides ______________.

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32). ___________ should satisfy momentum and conservation energy both.

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33). The energy emitted by photon must be equal to ___________.

Hint
34). LEDs with two semiconductors doped differently but using the similar material is known as _____________.

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35). ____________ LEDs are realized with different materials of band gap.

Hint
36). Which LED is brighter?

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37). To ensure mostly the recombination to take place on the surface of the LED ____________ must be followed.

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38). To emit the light through surface, doping concentration of the substrate must be _______.

Hint
39). Increase in the length of diffusion beyond the critical length the photons in the device may get _________.

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40). LED must be _______ so that the photons must be emitted without getting reabsorbed.

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41). _____________ quantifies the efficiency of electrical energy conversion into the optical energy emitted.

Hint
42). The product of internal radiative efficiency and the extraction efficiency is defined as ____________.

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43). The external quantum efficiency for semiconductors with indirect band gap is generally lesser than ______.

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44). The internal efficiency is based on _____________.

Hint
45). The ratio of the rate of recombination of radiation to the total recombination is known as ______________.

Hint
46). __________ can be reduced by making use of dome-shape package along with a diode.

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47). Designing an LED to support both Reabsorption and reflection of emitted light known as __________.

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48). LEDs made with Aluminum Gallium Arsenide produces _______ colour.

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49). High brightness orange-red color is produced by ___________.

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50). Sapphire substrate produce ________ color in LED.

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51). Blue color can be produced by ____________ substrate LEDs.

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52). Diamond glow under ________.

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53). Blue LEDs have __________ band gap for semiconductors.

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54). Who invented first blue LED?

Hint
55). _________________ LEDs used in sterilization and disinfection devices.

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56). White light LED can be produced by mixing ______ color LEDs.

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57). The product obtained after mixing Red, Green and Blue LEDs is known as ____________.

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58). Multi-colored white LEDs with the mixing of Red, Green and Blue LEDs have ____________.

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59). What is the second method to produce white LEDs?

Hint
60). CRI in LEDs stands for ______________.

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61). The application of multiple layers of phosphor consisting different colors can increase ____________.

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62). White LEDs produce using Phosphor coatings are known as ______________.

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63). Quantum efficiency degrades in ___________.

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64). Type of Multicolored White LEDs is __________.

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65). What is the key factor to deal with energy efficiency in LEDs?

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66). Which type of white LEDs possess high luminous efficiency but low color rendering capability?

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67). ____________ white LEDs offer high color rendering capability but low luminous efficiency.

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68). ________ maintains fair capabilities of color rendering nad good amount of luminous efficiency.

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69). Although having an easiest way of manufacturing what is the basic limitation of phosphor based LEDs?

Hint
70). A loss occurred due to the conversion of short wavelength consisting photons to large wavelength photons is known as __________.

Hint
71). Phosphor coating based white LEDs technique offers __________.

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72). _______________ substrate is used in the new method to produce white LEDs.

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73). Homoepitaxially grown ZnSe on the substrate on ZnSe emits __________ color light from the active region.

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74). Who developed the technique to produce white LEDs by coating the blue light using quantum dots?

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75). ____________ are the nano crystals of semiconductors that have unique optical properties.

Hint

LED Interview Questions and Answers

76). Quantum dot LEDs offer ___________.

Hint
77). ______ LEDs offer Full-colour potential.

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78). ____________ LEDs possess high photoluminescence quantum efficiencies (QEs).

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79). ____________ are the advantages of quantum dots over organic fluorophers.

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80). _________ LEDs offer high external quantum efficiencies over Gallium Nitride.

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81). What are the advantages of Zinc oxide based LEDs over Gallium Nitride?

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82). OLED is an acronym of ______________.

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83). What are the two classes of OLEDs?

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84). How many organic layers are present in double-heterostructure of small-molecule OLED?

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85). __________________ is the layer adjacent to anode and the cathode in small molecule based LEDs.

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86). Light-emitting polymer layer is present in ___________.

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87). Organic material of emission possesses conjugated _________.

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88). _________ known as Flexible OLEDs.

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89). Light emissive layer made up of biological materials in _________.

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90). Electrostatic discharge leads to ____________.

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91). If the AC supply is provided to LED, but they only lights up for _______ voltage.

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92). The lead of anode in LED is ________.

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93). Bi-color LED consists of _______ diodes.

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94). ____________ have multivibrated integrated circuits in it.

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95). LED made using single die is known as ____________.

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96). LED emission is ________ on temperature.

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97). _________ LEDs are used in remote control systems.

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98).For acne LED phototherapy can be done by using _________ color LEDs.

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99). Organic LEDs in display applications have _________________.

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100). __________ semiconductor type emits light.

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101). ______________ have fastest times of transitions.

Hint

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