Optoelectronics: LEDs and Photodiodes

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Questions and Answers

What process describes how light is emitted from an LED?

Thermoluminescence

Electroluminescence (correct)

Photoelectric effect

Photoconductivity

What is the primary factor that determines the color of light emitted by an LED?

The amount of current applied

The temperature of the diode

The size of the LED

The energy gap of the semiconductor (correct)

Which of the following is NOT an advantage of LEDs over incandescent light sources?

Higher heat generation (correct)

Greater durability and reliability

Lower energy consumption

Longer lifetime

In which type of material are holes typically found in an LED?

P-type material Signup and view all the answers

What characterizes the wavelength of emitted light from an LED?

It depends on the construction and dye material used. Signup and view all the answers

What is typically true about the light emission of LEDs?

They emit light in a specific range of wavelengths. Signup and view all the answers

What is the approximate peak wavelength of a green LED?

540 nm Signup and view all the answers

How do LED brightness levels vary?

They can vary widely from small indicating lights to high-intensity applications. Signup and view all the answers

What is the relationship between forward current and power of light output in an LED?

Power output is directly proportional to forward current. Signup and view all the answers

What happens to the radiation pattern of an LED as the viewing angle narrows?

More light is concentrated in one direction Signup and view all the answers

If an LED has a forward voltage drop of 2.2 V and the supply voltage is 5.0 V, what series resistor is needed to limit the current to 20 mA?

140 ohms Signup and view all the answers

What is the power dissipated by an LED with a forward voltage drop of 2.2 V at 20 mA?

44 mW Signup and view all the answers

Which of the following is a common application of LEDs?

Seven-segment displays Signup and view all the answers

In a remote control, what type of LED is commonly used?

Infrared LED Signup and view all the answers

How is the power dissipated by an LED calculated?

By multiplying the forward voltage drop by the forward current Signup and view all the answers

What occurs when multiple LED segments are forward biased in a seven-segment display?

Only decimal digits can be formed Signup and view all the answers

Study Notes

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.

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Description

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.