Description
ABSTRACT
A light-emitting diode (LED) is a two-lead semiconductor light source. It is a basic pn-junction diode, which emits light when activated. When a fitting voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.
Light emitting diode offers well-described benefits, compared with conventional light microscopy. However, its use in resource-limited settings has been limited by the high cost of the excitatory light source, using light-emitting diode (LED) technology as an alternative to the conventional mercury vapor lamp (MVP) because of its efficiency.
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
A light-emitting diode (LED) is a two-lead semiconductor light source. It is a basic pn-junction diode, which emits light when activated. When a fitting voltage is applied to the leads, electrons are able to recombine 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.
An LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern.
Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity, and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays, and were commonly seen in digital clocks.
Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. However, LEDs powerful enough for room lighting are still relatively expensive, and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.
1.2 OBJECTIVE OF THE STUDY
This work focuses on the effective way light emitting diode can be useful both home and industries
1.3 SIGNIFICANCE OF THE STUDY
A significant difference from other light sources is that the light is more directional, i.e., emitted as a narrower beam. LED lamps are used for both general and special-purpose lighting. Where colored light is needed, LEDs that inherently emit light of a single color require no energy-absorbing filters.
White-light LED lamps have longer life expectancy and higher efficiency (more light for the same electricity) than most other lighting when used at the proper temperature. LED sources are compact, which gives flexibility in designing lighting fixtures and good control over the distribution of light with small reflectors or lenses. Because of the small size of LEDs, control of the spatial distribution of illumination is extremely flexible and the light output and spatial distribution of an LED array can be controlled with no efficiency loss.
LEDs using the color-mixing principle can emit a wide range of colors by changing the proportions of light generated in each primary color. This allows full color mixing in lamps with LEDs of different colors. Unlike other lighting technologies, LED emission tends to be directional which can be either advantageous or disadvantageous, depending on requirements. For applications where non-directional light is required, either a diffuser is used, or multiple individual LED emitters are used to emit in different directions.
LIMITATION OF THE STUDY
An LED efficiency and life span drop at higher temperatures, which limit the power that can be used in lamps that physically replace existing filament and compact fluorescent types. Thermal management of high-power LEDs is a significant factor in design of solid state lighting equipment.
LED lamps are sensitive to excessive heat, like most solid state electronic components. LED lamps should be checked for compatibility for use in totally or partially enclosed fixtures before installation since heat build-up could cause lamp failure and/or fire.
LED lamps may flicker. The extent of flicker is based on the quality of the DC power supply built into the lamp structure, usually located in the lamp base.
Depending on the design of the lamp, the LED lamp may be sensitive to electrical surges this is generally not an issue with incandescent, but can be an issue with LED and compact fluorescent bulbs. Power circuits that supply LED lamps can be protected from electrical surges through the use of surge protection devices.
The long life of LEDs, expected to be about 50 times that of the most common incandescent bulbs and significantly longer than fluorescent types, is advantageous for users but will affect manufacturers as it reduces the market for replacements in the distant future.
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 HISTORICAL BACKGROUND OF LIGHT EMITTING DIODE
Discoveries and Early Devices
Green electroluminescence from a point contact on a crystal of SiC recreates H. J. Round’s original experiment from 1907.
Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat’s-whisker detector.[11][12] Russian inventor Oleg Losev reported creation of the first LED in 1927. His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using gallium antimonide (GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature and at 77 kelvins.
In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein” had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier, and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup.” This setup presaged the use of LEDs for optical communication applications.
Diagram of the tunnel diode constructed on a zinc diffused area of gallium arsenide semi-insulating substrate
In the fall of 1961, while working at Texas Instruments Inc. in Dallas, TX, James R. Biard and Gary Pittman found that gallium arsenide (GaAs) emitted infrared light when electric current was applied. On August 8, 1962, Biard and Pittman filed a patent titled “Semiconductor Radiant Diode” based on their findings, which described a zinc diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias.
After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs, and Lincoln Lab at MIT, the U.S. patent office issued the two inventors the first patent for the infrared (IR) light-emitting diode (U.S. Patent US3293513), the first modern LED. Immediately after filing the patent, Texas Instruments began a project to manufacture infrared diodes. In October 1962 they announced the first LED commercial product (the SNX-100), which employed a pure GaAs crystal to emit a 900 nm output.
The first visible-spectrum (red) LED was developed in 1962 by Nick Holonyak, Jr., while working at General Electric Company. Holonyak first reported this breakthrough in the journal Applied Physics Letters on the December 1, 1962. M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
2.2 REVIEW OF COMMERCIAL DEVELOPMENT OF AN LED
The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, as well as watches (see list of signal uses). Until 1968, visible and infrared LEDs were extremely costly, in the order of US$200 per unit, and so had little practical use. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide (GaAsP) in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. In the 1970s commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor. The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. These methods continue to be used by LED producers.
LED display of a TI-30 scientific calculator (ca. 1978), which uses plastic lenses to increase the visible digit size
As LED materials technology grew more advanced, light output rose, while maintaining efficiency and reliability at acceptable levels. The invention and development of the high-power white-light LED to use for illumination, and is slowly replacing incandescent and fluorescent lighting (see list of illumination applications).
Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with rising power output, it has grown increasingly necessary to shed excess heat to maintain reliability, so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high-power LEDs bear little resemblance to early LEDs.
Reviews
There are no reviews yet.