This document provides an overview of light emitting diodes (LEDs). It discusses the history and development of LEDs from early experiments in the 20th century to recent breakthroughs enabling high-brightness white light. The working principle of LEDs is that they emit light through electroluminescence when electrons recombine with holes in a semiconductor, releasing photons. The document also describes different types of LEDs including miniature indicator LEDs, high-power LEDs used for lighting, and application-specific LED displays.

1. • Omar Hussein Mohamed
• Group:B Section:4 No.111Presented By
• Dr.Tarek Abdelshahid
Supervision
• Optics
Subject
Light Emitted
Diode

2. Contents List
 Introduction
 History & Background
 Working Principle
 Types
 Applications

3. Introduction
•A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits
light when activated. When a suitable voltage is applied to the leads, electrons are able to combine with electron
holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and
the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the
semiconductor. LEDs are typically small (less than 1 mm2 ) and integrated optical components may be used to
shape the radiation pattern.

4. History & Background
•Early pioneers like H.J. Round, Oleg Losev, and Rubin Braunstein Put the
foundation in the first half of the 20th century, experimenting with crystals and
gallium arsenide to produce the first examples of electroluminescence .
•(is an optical phenomenon and electrical phenomenon in which a material emits light in response to
the passage of an electric current or to a strong electric field)
•In the fall of 1961 when a couple of Texas Instruments researchers discovered that gallium
arsenide emitted infrared light when exposed to an electrical current. James R. Biard and Gary
Pittman earned their place in history as the fathers of LED light when TI introduced the SNX-
100 the following year. The first example of an infrared LED bulb, the SNX-100 produced a
900 nanometer wavelength of invisible light and used a pure GaAs crystal as its sole source of
illumination.

5. History & Background
 In 1962, Nick Holonyak, Jr. developed the first visible-spectrum LED. Holonyak’s red LED
was later followed by yellow light in 1972, invented by M. George Craford, a former student of
Holonyak’s. Low light output from these LEDs limited their usefulness to anything more than
indicators. For LEDs to become a legitimate source of light, researchers would have to figure
out how to boost their output.
 In the 1990s, Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura did just that. With
breakthrough development that earned the trio the Nobel Prize in 2014, they invented the
first blue light beams, creating a revolutionary step forward in commercial lighting technology.
With the blue LED, bright white light was now a possibility. More energy efficient and
environmentally responsible than bulbs, the new LED lights could move worldwide power
consumption into Whole new age .

6. Working Principle
 How The LED Works ?
 As We Discussed Before LED gets their light Through the
electroluminescence Process .
 In The P-N Junction Diode as the electrons cross from the N-region and
recombine with the holes existing in the P-region We will have free
electrons exist in conduction band , and holes in valence band when the
electrons recombine with those holes the energy emits due to the
difference between energy level this energy will be in form of heat and
light .

7. Working Principle

8. Working Principle

9. Types
Miniature LED’s
These are the one’s you see almost everyday in
your life as indicators in mobile phones, television
sets and a range of digital devices. They are usually
available in market on a predefined, standard size &
shape.
High Power LED
These LED’s are the result of advancements in
semiconductor technology. these LED’s are known
for its high output. They are capable of producing
light output with higher luminous intensity. High
power LED’s come in different shapes & sizes. A
common example of high power LED in daily use is
“LED strips” that are used light walls & room
interiors. High power LED’s has very high heat
dissipation. These LED’s need to mounted along
with a cooling system .

10. Types
Application Specific
LED (AS-LED)
These are LED’s which are manufactured for a
particular application in mind. Some examples
are digital billboards, public displays, bi color &
tri color LED’s
LED based digital display RPG-SMD LED

11. Types
Miniature LED
High Power LED
Led Bulbs

12. The End