Optoelectronics: LEDs and Photodiodes

Optoelectronics and Light Emitters/Detectors

• Diodes can generate or detect light.
• Light-Emitting Diodes (LEDs) are light emitters.
• Photodiodes are light detectors.

Light Emitting Diodes (LEDs)

• LEDs were introduced in 1962.
• Early LEDs emitted low-intensity red light.
• Modern LEDs emit across the visible, ultraviolet, and infrared spectra.
• LEDs are highly bright.
• Forward biasing causes electrons to cross the p-n junction.
• Recombination releases energy as photons.
• Electrons in the conduction band have higher energy than holes in the valence band.
• The energy difference corresponds to visible light energy.
• This effect is electroluminescence.
• The light color depends on the semiconductor's energy gap.
• Emitted light is typically monochromatic.
• LED size is often less than 1 mm.
• Integrated optical components can shape radiation patterns.

Advantages of LEDs Over Incandescent Lights

• Lower energy consumption
• Longer lifespan
• Improved robustness
• Smaller size
• Faster switching
• Greater durability/reliability

LED Variations

• LEDs vary greatly in size and brightness.
• Small indicators, displays, traffic signals, outdoor signs, and general illumination use them.

Lens Application in LEDs

• Lenses concentrate emitted light.
• This optimizes visibility.

LED Symbol

• [Diagram of LED symbol is shown].

LED Operation

• LED output power directly correlates to the forward current.
• Reverse breakdown voltage in LEDs is lower than silicon rectifiers (3V to 10V).

LED Material Selection

• Material composition determines wavelength.
• Wavelength is specified in the datasheet.
• LEDs are available for visible and infrared frequencies.

LED Spectral Output Curves

• Specific wavelength ranges depend on construction/dye materials.
• Peak wavelength graphs for different LED types are shown.

V-I Characteristics

• Radiation pattern (how light spreads) is shown in the datasheet.
• Pattern is controlled by lenses.
• Concentrated light patterns are narrower.

Forward Voltage Drop

• Forward voltage drop varies (1.5V to over 3V).
• Variation depends on the diode type, color, and forward current.

Resistor Selection for LEDs

• Limiting resistors are crucial.
• Resistors should be chosen to prevent excessive current.
• Resistor calculation example is provided.
• Calculations are based on maximum current and forward voltage drop.

LED Power Dissipation

• Maximum power dissipation is listed in the datasheet.
• Calculation example is shown for power.
• Power calculation involves forward voltage times current.

LED Applications

• Transistors switch LEDs on and off.
• Seven-segment LEDs are commonly used for displays.
• Various applications use indicator lights, readouts, etc.

Infrared LED Applications

• Infrared (IR) LEDs are often used in remote controls.
• Emit beams of invisible light.
• Electrical code is converted to a light code and transmitted.
• Receiver converts the light code.
• Receiver determines and executes the action.

Explore the fascinating world of optoelectronics, focusing on light-emitting diodes (LEDs) and photodiodes. Learn about how LEDs work, their advantages over traditional incandescent lights, and how they efficiently emit light across various spectra. This quiz will test your knowledge on the principles of electroluminescence and the applications of these essential components.