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Quizzes > Electronics & Gadgets

LED Basics Quiz: Test Core Concepts and Troubleshooting

Quick, free LED knowledge test: 15 questions, instant results.

Editorial: Review CompletedCreated By: Anthony EnmanUpdated Aug 28, 2025
Difficulty: Moderate
Questions: 20
Learning OutcomesStudy Material
Colorful paper art depicting a quiz for LED Basics Knowledge Test

This LED basics quiz helps you check how LEDs work, including efficiency, color, and simple fixes, in 15 quick multiple-choice questions. After you finish, deepen your practice with the led lighting quiz, try an electronics knowledge test, or explore a digital electronics quiz to reinforce key ideas.

What does the abbreviation LED stand for?
Luminous Electric Diode
Light Energy Detector
Low Emission Device
Light Emitting Diode
LED stands for Light Emitting Diode because it emits light when current passes through the semiconductor junction. The other options are not standard definitions.
What is the basic operating principle of an LED?
Magnetic flux inducing light emission
Thermal excitation of a filament
Chemical reaction producing light
Recombination of electrons and holes emitting photons
LEDs produce light via electron - hole recombination in a semiconductor, releasing photons. Filament heating and other mechanisms do not apply to LEDs.
Approximately what is the forward voltage drop of a typical red LED?
2 V
5 V
0.7 V
12 V
A typical red LED has a forward voltage around 1.8 - 2.2 V. Values like 5 V or 12 V are far too high for direct LED operation.
Which semiconductor material is commonly used in blue LEDs?
Silicon (Si)
Gallium Arsenide (GaAs)
Germanium (Ge)
Gallium Nitride (GaN)
Gallium Nitride is the primary material for blue LEDs due to its wide bandgap, which corresponds to shorter-wavelength emission. Silicon and germanium are indirect bandgap materials and not used for visible LEDs.
Which component is typically used in series with an LED to limit current?
Capacitor
Inductor
Transformer
Resistor
A resistor in series with an LED limits the current to a safe value based on Ohm's law. Capacitors and inductors do not directly limit DC current in the same way.
What is the definition of luminous efficacy for an LED?
Illuminance per electrical power (lux/W)
Luminous flux per luminous intensity (lm/cd)
Candela per watt (cd/W)
Luminous flux per electrical power (lm/W)
Luminous efficacy is defined as the ratio of luminous flux (in lumens) to electrical power input (in watts). Other ratios describe different optical metrics.
In which unit is color temperature of an LED specified?
Celsius (°C)
Nanometer (nm)
Lumen (lm)
Kelvin (K)
Color temperature is measured in kelvins, reflecting the spectral properties of a blackbody radiator at that temperature. Lumens measure luminous flux, not temperature.
Which instrument is best for measuring an LED's emission spectrum?
Oscilloscope
Lux meter
Spectrometer
Multimeter
A spectrometer measures light intensity as a function of wavelength, revealing the LED's emission peaks. Multimeters and oscilloscopes are used for electrical readings.
What is the primary purpose of a heat sink in an LED assembly?
Filter spectral emissions
Dissipate thermal energy to maintain junction temperature
Store electrical energy
Focus light output into a beam
A heat sink removes heat away from the LED junction to prevent overheating and efficiency loss. Optical functions and energy storage are not heat sink functions.
What is the typical forward current rating for a standard indicator LED?
200 mA
2 mA
20 mA
2 A
Standard indicator LEDs are usually rated around 20 mA. Currents like 2 A would damage a small LED, while 2 mA is too low for typical brightness.
For a 5 V supply, an LED forward voltage of 2 V, and desired current of 20 mA, what series resistor value is required?
200 Ω
300 Ω
150 Ω
100 Ω
Using R = (V supply - V forward) / I = (5 V - 2 V) / 0.02 A = 150 Ω. Other values will not set the correct current.
What does the term 'efficiency droop' refer to in LED performance?
Increase in luminous flux with temperature
Constant efficiency regardless of current
Increase in efficiency at low currents
Decrease in efficiency at high current densities
Efficiency droop describes the drop in light output per watt when current density is increased. It is not about low-current behavior or temperature-induced increases.
In a series circuit of multiple LEDs, how does the current behave through each LED?
Current is the same through each LED
Current splits equally among LEDs
Current increases with each LED added
Current decreases with each LED added
In a series circuit the same current flows through all components. Adding LEDs in series does not change the current but increases the total forward voltage.
If one LED in a parallel LED array fails open, what happens to the others?
The remaining LEDs continue to operate normally
Brightness of remaining LEDs doubles
Brightness of remaining LEDs decreases slightly
All LEDs turn off
In a parallel circuit each branch is independent. An open failure in one branch only affects that branch, leaving others unaffected.
Which instrument is best for measuring the forward voltage drop of an LED during troubleshooting?
Spectrometer
Oscilloscope
Digital multimeter
Ammeter
A digital multimeter set to a DC voltage range measures the forward voltage drop directly. Oscilloscopes and spectrometers are less convenient for simple DC voltage readings.
What is the approximate bandgap energy in electron volts for an LED emitting at 620 nm?
2.0 eV
2.5 eV
1.5 eV
3.0 eV
Bandgap energy E (eV) ≈ 1240/λ(nm), so for 620 nm E ≈ 1240/620 ≈ 2.0 eV. Other values do not match this relation.
Which correlated color temperature (CCT) appears as a ''warm white'' LED to the human eye?
6000 K
4500 K
3000 K
7500 K
Lower CCT values (around 2700 - 3500 K) appear warmer (yellowish) to the eye, whereas higher CCTs look cooler and more bluish.
What driver configuration is most appropriate for maintaining constant current in a high-power LED array?
PWM-based voltage driver
Charge pump driver
Constant current driver
Constant voltage driver
A constant current driver regulates current to the LED array, ensuring stable brightness. Constant voltage drivers do not protect against current variation.
Which physical mechanism is primarily responsible for efficiency droop at high LED current densities?
Auger recombination
Radiative recombination
Surface recombination
Quantum tunneling
Auger recombination is a non-radiative process that dominates at high carrier densities, causing efficiency droop. Radiative recombination is the desired light-emitting process.
Given a 12 V supply and LEDs with forward voltage 3 V each, what is the maximum number of LEDs you can place in series?
3
6
5
4
Total forward voltage must not exceed supply: 12 V/3 V = 4 LEDs in series. Adding more would exceed the supply voltage.
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Learning Outcomes

  1. Analyse the key operating principles of LEDs
  2. Identify common LED components and materials
  3. Apply voltage and current requirements for optimal LED function
  4. Evaluate efficiency factors such as luminous efficacy and thermal management
  5. Compare color temperature and emission spectra in LEDs
  6. Demonstrate troubleshooting steps for LED circuit issues

Cheat Sheet

  1. Understand the basic operation of LEDs - Imagine a tiny semiconductor dancing under electrical pressure - when electrons and holes meet, they release photons and voilà, you've got light! The exact hue depends on the material's energy band gap, so GaAs glows infrared while GaP shines green. Mastering this electroluminescence is your first step to LED wizardry. LED Basics at HyperPhysics
  2. Identify common LED materials - Different semiconductors create different colors: GaAsP serves up reds and oranges, whereas InGaN pumps out brilliant blues and greens. Knowing which alloy makes which glow helps you pick the perfect LED for mood lighting or high”tech displays. It's like choosing the right paint for your canvas! Common LED Materials at HyperPhysics
  3. Calculate the appropriate series resistor - To keep your LED shining safely, you need a current”limiting resistor. Use Ohm's Law: R = (Vsource - Vf)/If. For example, a 9 V battery, a 1.8 V red LED, and 10 mA current yields a 720 Ω resistor. Simple math keeps your LEDs alive! LED Circuit Design Guide
  4. Understand luminous efficacy - Luminous efficacy (lm/W) tells you how much visible light you get for each watt of power. Modern white LEDs can hit up to 150 lm/W, leaving incandescent bulbs in the dust. Higher efficacy means brighter rooms and lower energy bills - a win for you and the planet! Study on LED Efficacy
  5. Manage thermal performance - LEDs may look cool, but they generate heat under the hood. Use heat sinks and proper airflow to whisk that warmth away, preventing efficiency drops and extending lifespan. Think of it as giving your LEDs a spa day - they'll thank you with years of glow! LED Thermal Management Basics
  6. Compare color temperatures - Measured in Kelvins (K), color temperature sets the mood: 2700 K feels cozy and warm, while 6500 K is crisp and daylight”like. Choose wisely to match your project - from snug reading nooks to vibrant studio spaces. It's like picking the perfect filter for real life! LED Color Temperature Guide
  7. Analyze emission spectra - An LED's emission spectrum reveals its ability to render colors accurately. Full-spectrum LEDs give life”like color, crucial for photography, art galleries, and medical tools. Understanding these spectra helps you pick LEDs that show true hues and vivid details. Emission Spectra Insights
  8. Implement proper circuit design - Avoid overcurrent disasters by pairing LEDs with the right resistors or constant-current drivers. Factor in supply voltage and total forward voltage to keep each LED singing in harmony. Good design means fewer blown diodes and more reliable projects! LED Circuit Design
  9. Recognize common LED failures - Watch out for thermal runaway - excess heat boosts current, which creates more heat - and ESD shocks that can instantly turn your LED into a lifeless chip. Implement heat”management and ESD protection to dodge these pitfalls and keep your diodes shining bright. LED Failure Modes
  10. Practice troubleshooting techniques - When an LED circuit goes dark, check polarity, measure voltage drops, and ensure you've got the correct resistor values. A trusty multimeter and methodical checks will turn you into an LED detective in no time. Troubleshooting is half the fun and all the learning! LED Troubleshooting Tips
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