Skip to main content
ElectraCore
LearnCalculatorsCircuit DesignerReferences
Saved
Educational use: ElectraCore supports learning and preliminary checks. It does not replace a competent electrician or engineer. Verify results, equipment data, and current local regulations before installation or live work.
Courses/LED & Lighting Design/LED Technology

lesson · 8min · Lesson 1 of 24

How LEDs produce light: p-n junction

Course syllabusCourse overview
01LED Technology
  1. ReadHow LEDs produce light: p-n junction
  2. ReadEfficacy: lumens per watt explained
  3. ReadLED chip formats: COB, SMD, filament
  4. ReadThermal management: heatsinks and junction temperature
  5. quizLED technology quiz
02Driver Circuits
  1. ReadConstant current vs constant voltage drivers
  2. ReadDriver efficiency and power factor
  3. ReadDimming methods: PWM, 0-10V, DALI
  4. ReadDriver selection and compatibility
  5. quizDriver circuit quiz
03Emergency Lighting
  1. ReadBS 5266 categories: escape, standby, high-risk
  2. ReadSelf-contained vs central battery systems
  3. ReadMaintained vs non-maintained operation
  4. ReadTesting requirements and log books
  5. quizEmergency lighting quiz
04Lux Calculations
  1. ReadIlluminance, luminous flux, and efficacy
  2. ReadLumen method: average illuminance
  3. ReadRoom index, UF, and MF
  4. exerciseLux calculation worked example
05Lighting Control & Quality
  1. ReadColour temperature: warm, neutral, cool white
  2. ReadColour rendering index (Ra/CRI)
  3. ReadGlare: UGR and how to reduce it
  4. ReadSmart lighting systems: DALI 2 and IoT
  5. quizFinal assessment
Lesson · 8min
LUMEN METHOD · ILLUMINANCEluminaire · lmwork plane · area AEav = N·F·UF·MF÷ Alux (lm/m²)
Lesson contents 0%

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
0% read
ElectraCore lesson handout

How LEDs produce light: p-n junction

Led Lighting · Lesson 1 · Intermediate

IntermediateReview: professional review pending

Purpose

Explain electroluminescence at an LED p-n junction without implying voltage directly sets safe current.

Before you beginVoltage, current and power · Basic semiconductor and circuit concepts

Learning objectives

  • Trace electrical-to-light conversion
  • Use declared operating boundaries
  • Separate component and luminaire metrics
  • Check control and load compatibility

Forward bias injects electrons and holes across a semiconductor junction; radiative recombination releases photons whose energy depends on the band gap. The LED's steep I-V curve requires controlled current.

LED JUNCTION LIGHT AND HEAT PATHLED JUNCTION LIGHT AND HEAT PATHDRIVERLEDlight · heatinput · regulation · junction · optics · control · environment

Core theory

Photon energy relates to wavelength, so semiconductor composition influences color. White LEDs commonly combine blue/near-UV emission with phosphor conversion, introducing spectral and conversion losses.

Forward voltage varies with current, temperature and device. Small voltage change can cause large current change; series resistance or, more commonly, regulated controlgear limits current.

Optical output, droop, color shift and lifetime depend on junction temperature and drive current. Never infer eye safety or luminaire performance from chip physics alone.

Terms, symbols, and units
TermMeaningSymbolUnit
ElectroluminescenceLight emission from electrical carrier recombinationNot applicableNot applicable
Band gapEnergy separation influencing photon energyNot applicableNot applicable
Forward voltageVoltage across a forward-biased LED at stated current/temperatureNot applicableNot applicable
Ephoton = h c / λ

Shorter wavelength corresponds to higher photon energy.

joules when SI units are used
Worked exampleCompare photon energy at 450 nm with 600 nm without calculating constants.

Assumptions: Supplied photometric/electrical values share the stated measurement boundary; Manufacturer limits remain governing.

  1. Relation: E is inversely proportional to wavelength.
  2. Compare: 450 nm is shorter than 600 nm.
  3. Conclude: A 450 nm photon has greater energy than a 600 nm photon.

The 450 nm photon has higher energy.

Reasonableness check: The result identifies whether it describes LED package, module, driver or complete luminaire and avoids claiming field performance from one laboratory number.

Common mistakes
  • Dividing lumens by LED-chip watts while calling it luminaire efficacy
  • Connecting constant-current LEDs to a constant-voltage source without current control
  • Assuming every dimmable driver works with every dimmer

Where this appears in practice

A reliable LED installation coordinates light source, optics, thermal path, driver, supply/protection, controls, environment and maintainability.

SafetyLED outputs can create glare/photobiological hazards and drivers can contain mains voltage and stored charge after switch-off. Isolate, prove dead, observe discharge instructions and never defeat thermal interfaces or enclosure barriers.
Local code checkConfirm current luminaire/module/controlgear safety and performance standards, BS 7671, exact driver/module/luminaire data, photobiological risk, thermal/fire enclosure requirements, EMC/flicker/harmonic obligations and control-protocol certification. A CE/UKCA or DALI-2 mark does not prove two arbitrary components are electrically, thermally or functionally compatible.

Knowledge check

Can an LED be connected to an arbitrary stiff voltage source because its forward voltage is known?

No. Its steep I-V curve needs appropriate current control.

Answer: No. Its steep I-V curve needs appropriate current control.

Practical exercise

Draw the electrical, recombination, phosphor and optical-loss path of a white LED.

Summary

  • Metric boundary changes the answer
  • LED current and junction temperature govern life/output
  • Driver and dimmer must match electrically and functionally

Sources and review

  • IEC 62031:2026: LED modules safety requirements: IEC; 2026; International
  • IEC 61347-2-13:2024: LED controlgear safety: IEC; 2024; International
  • DALI-2 certification overview: DALI Alliance; Current certification database/status must be checked; International

Editorial review date: 2026-08-22. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

Personal study record

Lesson notes

Ready

Notes are stored on this device unless you export them.