26-07-2012, 12:25 PM
The Transition to Solid State Lighting
The Transition to Solid State Lighting.doc (Size: 4.09 MB / Downloads: 35)
Abstract
In 1879, Thomas Edison made the first public demonstration of his incandescent light bulb and the invention was so perfect, nothing rivaled it for more than 100 years. For the longest time, incandescent bulbs, which replaced lanterns, reigned as the solution for lighting the world over. Compact fluorescent lamps (CFLs) that consume less power to get as much lighting are slowly and steadily gaining acceptance in the market. As a result incandescent bulbs will soon be shelved for good. However, even as CFLs are gaining momentum, they already have an emerging threat in the form of an even lesser power consuming and higher-efficiency technology—light-emitting diodes (LEDs).
LED lighting is on the edge of becoming the lighting method of choice and surpassing the market dominance Edison’s invention has held for so long. And as the world is speaking about LED as the next big thing we already have Organic LED as the predicted future of lighting. It is by far the best invention yet and the day is not far when we can see mass practical uses of OLED.
This report begins with a brief account of the evolution of electric lighting technologies over the past century. It then discusses key lighting systems’ characteristics, before going on to discuss the likely future evolution of the performance of light-emitting diodes (LEDs) that produce white light either by combining monochromatic LEDs or by using a down converting phosphor layer Then, it presents engineering-economic estimates of the future cost of light from the perspective of both commercial and residential customers. Other factors, such as total energy use and greenhouse gas emissions, are also important from a social perspective. Thus, the report explores the social cost-effectiveness of white LEDs. It further estimates the potential energy savings and greenhouse gas reductions that could be achieved under different types of policies. The report is concluded with recommendations on policy implementation for a rapid and widespread adoption of more efficient lighting in the near future.
BRIEF HISTORY OF LIGHTING TECHNOLOGIES
Incandescent Lamps
While Edison is credited with the development of the first commercially practical incandescent lamp in 1879, many others had worked on the idea over the preceding century [20]. Early bulbs used carbon filaments, which had limited lifetime and could not be operated at a high enough temperature to produce fully satisfactory light. General Electric patented the first tungsten filament for commercial use in 1906. Further improvements followed, including the use of inert gas in the bulb and the use of coiled tungsten filaments. While manufacturing costs continued
to fall, the efficacy (the ratio of light output to the input electric power) with which incandescent bulbs convert electricity into light has reached an asymptote at just under 18 lm/W .
Fluorescent Lamps
General Electric developed low-voltage fluorescent lamps in the 1930s. These were first marketed as tint lighting for decorative purposes. However, it soon became apparent that fluorescent lamps also held great potential for general lighting. The electric power industry became seriously concerned that the rapid proliferation of more efficient fluorescent lighting might reduce demand and thus negatively impact power sales. They were also concerned that the need for reactive power imposed by ballasts would increase current flows on their lines without resulting in marketable real power. As Bijker has detailed, a series of negotiations followed between the power industry and GE and the GE licensees (the Mazda companies) in which it was agreed not to market fluorescents aggressively until much brighter intensity lights, that required more power, could be developed. Today, with power companies and lighting firms experiencing much reduced market power, with much stricter antitrust law and enforcement, and with power companies struggling to meet load, such collusion between lamp manufactures and power companies is not a serious issue. Indeed, given the challenge of building new power plants, and growing concerns about CO2 emissions, many U.S. power companies are actively promoting more efficient lighting. However, while fluorescents, and
especially compact fluorescents, are now being actively promoted, their conversion efficacy is unlikely to grow much above 100 lm/W .
Light Emitting Diode’s
The first known report of a light-emitting solid-state diode was made in 1907 by the British experimenter H. J. Round. However, no practical use was made of the discovery for several decades. The first practical LED was invented by Nick Holonyak, Jr. in 1962 while he was at General Electric Company. The first LEDs became commercially available in late 1960s, and were red. They were commonly used as replacements for incandescent indicators, 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, and even watches. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, and LEDs became bright enough to be used for illumination.
LED Light Bulb Basics :- How Light Emitting Diodes Work
An LED is what's called a "solid-state lighting" technology, or SSL. Basically, instead of emitting light from a vacuum (as in an incandescent bulb) or a gas (as in a CFL), an SSL emits light from a piece of solid matter. In the case of a traditional LED, that piece of matter is a semiconductor.
Stated very simply, an LED produces light when electrons move around within its semiconductor structure.
What is a Diode?
A diode is the simplest sort of semiconductordevice. Broadly speaking, a semiconductor is a material with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that has had impurities (atoms of another material) added to it. The process of adding impurities is called doping.
In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms change the balance, either adding free electrons or creating holes where electrons can go. Either of these alterations make the material more conductive.
A semiconductor with extra electrons is called N-type material, since it has extra negatively charged particles. In N-type material, free electrons move from a negatively charged area to a positively charged area.
A semiconductor with extra holes is called P-type material, since it effectively has extra positively charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a positively charged area. As a result, the holes themselves appear to move from a positively charged area to a negatively charged area.
A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the diode, electrons from the N-type material fill holes from the P-type material along the junction between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow.