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School-college Physics Notes: Electricity 4.5 Use of LED device

Electricity section 4: 4.5 An LED light emitting diode - how does electrical device work? and what is it used for?

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[KEY POINTS and learning objectives for this page, after initial notes]

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INDEX for physics notes on testing circuit devices and how they used

4.5 An LED light emitting diode - how does electrical device work? and what is it used for?

An LED emits light when a current flows through it in the forward direction.

Electrical energy is converted into visible light energy, and very efficiently.

Uses of an LED

You should know that there is an increasing use of LEDs for lighting, as they use a much smaller current than other forms of lighting.

They have a much greater efficiency in converting electrical energy into visible light.

LEDs are used in torches, which are far more efficient than filament bulb torches.

An LED is used as a visual indicator that current is flowing through a circuit. e.g. small red, green or blue lights that might indicate your computer power system is functioning.

Key points about electric circuits in physics courses - LED function and use

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE physics 9-1 level science examinations.

Here's a structured, exam-board-aligned summary on Light Emitting Diodes (LEDs), tailored for GCSE/IGCSE Physics students:

Light Emitting Diodes (LEDs) – Summary Revision Notes

What is an LED?

An LED (Light Emitting Diode) is a special type of diode that emits light when a current flows through it in the forward direction.

  • It is a non-ohmic component: it does not obey Ohm’s Law
  • It only works when forward biased (i.e. current flows in one direction)
  • It emits visible or infrared light depending on the material used

Circuit Symbol of an LED

A standard diode symbol with two arrows pointing away, indicating light emission

How an LED Works

Condition Behaviour Explanation
Forward Bias LED emits light when threshold voltage is reached (~1.8–3V) Electrons recombine with holes, releasing energy as photons (light)
Reverse Bias No current flows; LED does not emit light High resistance prevents conduction

Function and Uses of LEDs

LEDs are widely used due to their low energy consumption, long lifespan, and small size:

  • Indicator lights (e.g. on TVs, chargers, appliances)
  • Traffic lights and street lighting
  • Digital displays (e.g. calculators, clocks)
  • Remote controls (infrared LEDs)
  • Decorative lighting (e.g. fairy lights, LED strips)
  • Automotive lighting (e.g. brake lights, indicators)

I–V Graph Characteristics of an LED

  • Non-linear graph
  • Forward bias: No current until threshold voltage, then sharp rise
  • Reverse bias: No current flows

This confirms that LEDs are non-ohmic and directional.

Required Practical (All Boards)

Aim: Investigate the I–V characteristics of an LED

Method Overview:

  • Connect LED in series with a resistor, ammeter, and variable power supply
  • Use voltmeter in parallel across LED
  • Vary voltage and record current
  • Plot I–V graph

Expected Result:

Sharp rise in current after threshold voltage in forward direction; no current in reverse

Typical Exam Board Syllabus Contents regarding an LED

Key Focus
LEDs as non-ohmic components; practical applications in circuits
Emphasis on interpreting I–V graphs and LED efficiency
Includes LEDs in component behaviour and energy-efficient lighting
Focus on circuit diagrams and LED use in control systems
Investigates LED function and current flow direction
Strong emphasis on LED applications, I–V graphs, and energy transfer

Student Tips for an LED question

  • Memorise: LED = Light Emitting Diode; only works in forward bias
  • Sketch the I–V graph: Show threshold behaviour and no reverse current
  • Use correct terms: “Forward bias”, “threshold voltage”, “non-ohmic”
  • Explain energy transfer: Electrical energy → light energy
  • Revise practicals: Be confident describing method, apparatus, and expected results
  • Think real-world: LEDs are everywhere—from phone screens to traffic lights

Keywords, phrases and learning objectives for an LED device in an electrical circuit

Know how does an LED (light emitting diode) device works in an electrical circuit.

Know examples of what an LED device is used for e.g.  torches, indicator light of power systems.

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