13-03-2015, 10:46 PM
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seminar topic for white led ppt download
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21-02-2017, 11:41 AM
Abstract
Until recently, however, the price of an LED lighting system was too high for most residential use. With rising sales and falling prices, it has been said that whoever makes the best white LED will open a gold mine.
White LED lighting has been used for years by the RV and boating crowd, running off direct current (DC) battery systems. It was then popularized in out-of-network homes, powered by photovoltaic cells. It used to be that white LED was only possible by "rainbow" groups of three LEDs - red, green and blue - and control the current to each to give a white light overall. Now a phosphor lining blue indium gallium chip is used to create the wave shift needed to emit white light from a single diode. This process is much less expensive for the amount of light generated.
Each diode is about 1/4 of an inch and consumes about ten milliamps (one tenth of a watt). The lamps come in different diode arrangements on a circuit board. Standard matrices are three, six, 12 or 18 diodes, or custom sizes - factories can incorporate these into custom lights, fixtures and surface mounted fixtures. With a low-cost transformer, they operate with standard AC power of 120 volts, although with a slight loss of power (about 15% to 20%). They are also available as screw lamps to replace incandescent lamps. A 1.2-watt white LED light beam is as bright as a 20-watt incandescent lamp.
A GENERAL VISION
The LED stands for light emitting diode. An LED is a semiconductor chip that converts electrical energy into light. The conversion of energy into light occurs at the quantum level within the molecular composition of the semiconductor chip. The process begins with the chip acting as a two-terminal diode, a P (Positive hole carrier) and N (Electron negative) in its basic structure, which allow the chip to drive in one direction for its operation. In addition, chemical layers are added called layers of epitaxy that improve the device's ability to emit light (photons).
As electrical energy passes through the P and N regions of the LED, the electrons move to higher energy levels called band gap potentials. To fulfill the law of energy conservation, the excess energy of the electron, obtained while moving energy levels, will produce a photon that our eye will perceive as light. At this point, band potentials are equal to the photon energy created when the electron that was moving the energy levels returns to ground state. The color of the emitted light is directly related to the size of the band gap potentials or the amount of energy produced by the photons. Since different colors occur at different bandwidth potentials, or energy levels, this explains why different color LEDs show different forward voltages to operate.
Recent advances in LED technology have led to brighter LEDs due to higher quantum efficiencies and higher chip extraction efficiencies.
Another recent development of a blue LED has led to white RGB (Red Green Blue) lighting as well as Phosphor on Blue to form white LEDs. The Blue Phosphor Coating technique has shown that in the near future, white light from solid-state sources is a possibility, which has given rise to much excitement
Until recently, however, the price of an LED lighting system was too high for most residential use. With rising sales and falling prices, it has been said that whoever makes the best white LED will open a gold mine.
White LED lighting has been used for years by the RV and boating crowd, running off direct current (DC) battery systems. It was then popularized in out-of-network homes, powered by photovoltaic cells. It used to be that white LED was only possible by "rainbow" groups of three LEDs - red, green and blue - and control the current to each to give a white light overall. Now a phosphor lining blue indium gallium chip is used to create the wave shift needed to emit white light from a single diode. This process is much less expensive for the amount of light generated.
Each diode is about 1/4 of an inch and consumes about ten milliamps (one tenth of a watt). The lamps come in different diode arrangements on a circuit board. Standard matrices are three, six, 12 or 18 diodes, or custom sizes - factories can incorporate these into custom lights, fixtures and surface mounted fixtures. With a low-cost transformer, they operate with standard AC power of 120 volts, although with a slight loss of power (about 15% to 20%). They are also available as screw lamps to replace incandescent lamps. A 1.2-watt white LED light beam is as bright as a 20-watt incandescent lamp.
A GENERAL VISION
The LED stands for light emitting diode. An LED is a semiconductor chip that converts electrical energy into light. The conversion of energy into light occurs at the quantum level within the molecular composition of the semiconductor chip. The process begins with the chip acting as a two-terminal diode, a P (Positive hole carrier) and N (Electron negative) in its basic structure, which allow the chip to drive in one direction for its operation. In addition, chemical layers are added called layers of epitaxy that improve the device's ability to emit light (photons).
As electrical energy passes through the P and N regions of the LED, the electrons move to higher energy levels called band gap potentials. To fulfill the law of energy conservation, the excess energy of the electron, obtained while moving energy levels, will produce a photon that our eye will perceive as light. At this point, band potentials are equal to the photon energy created when the electron that was moving the energy levels returns to ground state. The color of the emitted light is directly related to the size of the band gap potentials or the amount of energy produced by the photons. Since different colors occur at different bandwidth potentials, or energy levels, this explains why different color LEDs show different forward voltages to operate.
Recent advances in LED technology have led to brighter LEDs due to higher quantum efficiencies and higher chip extraction efficiencies.
Another recent development of a blue LED has led to white RGB (Red Green Blue) lighting as well as Phosphor on Blue to form white LEDs. The Blue Phosphor Coating technique has shown that in the near future, white light from solid-state sources is a possibility, which has given rise to much excitement
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