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JINLING Chen
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KIM Chen
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Subject: AUTOMOTIVE LED LIGHT
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2009-10-06 |
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To
provide an appropriate measure of useful life of an LED, a level of
acceptable lumen depreciation must be chosen. At what point is the
light level no longer meeting the needs of the application? The answer
may differ depending on the application of the product. For a common
application such as general lighting in an office environment, research
has shown that the majority of occupants in a space will accept light
level reductions of up to 30% with little notice, particularly if the
reduction is gradual. Therefore a level of 70% of initial light level
could be considered an appropriate threshold of useful life for general
lighting. Based on this research, the Alliance for Solid State
Illumination Systems and Technologies (ASSIST), a group led by the
Lighting Research Center (LRC), recommends defining useful life as the
point at which light output has declined to 70% of initial lumens
(abbreviated as L70) for general lighting and 50% (L50) for LEDs used
for decorative purposes. For some applications, a level higher than 70%
may be required.
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LEDs differ from traditional light sources
in the way they produce light. In an incandescent lamp, a tungsten
filament is heated by electric current until it glows or emits light.
In a fluorescent lamp, an electric arc excites mercury atoms, which
emit ultraviolet (UV) radiation. After striking the phosphor coating on
the inside of glass tubes, the UV radiation is converted and emitted as
visible light.
An LED, in contrast, is a semiconductor diode. It consists of a chip of
semiconducting material treated to create a structure called a p-n
(positive-negative) junction. When connected to a power source, current
flows from the p-side or anode to the n-side, or cathode, but not in
the reverse direction. Charge-carriers (electrons and electron holes)
flow into the junction from electrodes. When an electron meets a hole,
it falls into a lower energy level, and releases energy in the form of
a photon (light).
The specific wavelength or color emitted by the LED depends on the
materials used to make the diode. Red LEDs are based on aluminum
gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium
nitride (InGaN) and green from aluminum gallium phosphide (AlGaP).
"White" light is created by combining the light from red, green, and
blue (RGB) LEDs or by coating a blue LED with yellow phosphor. See
"Color Quality" section for more information.
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In
terms of voltage source for the light-emitting diode power supply, LED
voltage - current characteristics of the relationship between the
number of pairs will make a small change in voltage will cause a huge
current changes, combined with light-emitting diode discrete production
processes, using voltage source-driven, then not only difficult to
control brightness, but also very easy because the current is too large
LED burn out very quickly. * The application of the general will lead
to problems in parallel, as in parallel all of the LED are subject to
the same voltage, the same voltage because of the LED current in
discrete manufacturing processes are not the same, resulting in the LED
brightness varies. If the LED is the same model will have a relatively
similar luminosity, even so, fluctuations in the production process
also makes the parallel application unsatisfactory. On the contrary,
the LED in series, all have the same current, luminosity will be very
similar. |
Blue and white light-emitting diode Using
gallium nitride (GaN) to form a blue LED available from the LED, after
many years apart yet to be manufactured that produce blue light LED,
because blue is one of the three primary colors in order to then other
LED light wavelength can be derived from the more Blu-ray long, it is
not possible with other existing LED indirect produce Blu-ray, the lack
of a blue LED has also led to not make the same white light LED. Blue
LED In 1993, the then Nichia Chemical of Japan (Nichia Corporation) the
work of Shuji Nakamura (Shuji Nakamura) invented the wide-band gap
semiconductor materials based on gallium nitride (GaN) and indium
gallium nitride (InGaN) that has commercial applications in the blue
Light LED, this LED in the late 1990s to be widely used. White LED Red,
green and blue system (RGB system) With the blue LED, the combination
of the original red LED and green LED can produce white light, which
produces white LED has a very wide color gamut, but because costs are
high, most of the white LED seldom used this method, now only only in
the high-grade, there is high demand products to use.
LED Benefits Light (energy conversion)
efficiency - that is more energy-efficient. Higher than the bulbs, but
fluorescent Meet. And as time goes on, LED light effects will be higher
and higher. [2] Reaction (switching) time soon - can reach very high
frequency flicker. Long service life - in the appropriate cooling and
application environments of up to 35,000 ~ 50,000 hours, relative
fluorescent 10,000 ~ 15,000 hours, 1,000 ~ 2,000 hours of incandescent
lamps. Resistance to shocks and other mechanical impact - because it is
solid-state components, there is no filament, relative fluorescent,
incandescent and so can withstand greater shocks. Small size - its own
volume can be made very small (less than 2mm). Easy to focus on -
because of light is small and easy-to-order lenses, etc. to achieve the
required level of distribution, by changing its packaging shape, the
direction from the large-angle scattering as well as focus on the small
angles can be achieved. A variety of colors - can not filter under a
variety of different colors, and monochromatic strong. Gamut-rich - the
white LED cover the color gamut than other white light source widely.
[3] Cold beam - LED beam itself does not contain infrared or UV, to pay
attention to protect the object according to the occasion, such as
museum exhibits the most suitable for lighting applications.Light-emitting diodes
(Light-emitting diode, LED) [1] is a semiconductor device. At first,
many used as a light, display boards, etc.; as the white light-emitting
diode emergence has also been used for illumination. It is the 21st
century, a new light source, with high efficiency, long life, easy to
damage and other traditional light sources can not compare the merits.
Forward voltage increases when the physical issue of single-color
light-emitting diodes, non-continuous light, which is caused by energy
transfer of a light effect. Changes in semiconductor material used in
the chemical composition will enable the issue of light-emitting diodes
near ultraviolet, visible or infrared light. In 1955, RCA (Radio
Corporation of America) of the Lubinbulang Steiner (Rubin Braunstein)
health for the first time found a gallium arsenide (GaAs) and other
semiconductor alloys the role of infrared radiation. In 1962, General
Electric Company, Nick Ho Lun Yake (Nick Holonyak Jr.) Developed the
first practical application of visible light-emitting diodes. To reduce costs, due to indoor lighting for
high-power LED lamps, LED light source accounted for the cost of some
very large proportion of high-power LED light source thus reducing the
cost of the unit lumen is the key. 2 development of high color
rendering index and a wide spectrum of the LED light source, to meet
the lighting of the light source is an inner quality of high demand. 3
development of novel modeling lamps, if we adopt the traditional style
lamps, LED light is not novelty and newness, no one knows what one
source. At this stage, the limited energy-efficient LED light source
itself can not support high prices. Solid-state lighting as the next
generation lighting technology, has gradually become the mainstream of
the field lighting is an inevitable trend, high-power LED lighting in
the indoor and outdoor common areas of application is the ultimate goal
of its development. At this stage, LED can already replace the
traditional light sources in many places to use, in particular, the
emergence of high power and high luminous flux LED, LED has accelerated
the speed of light sources to replace traditional lighting. High price is hard to popularize the
largest LED lighting reasons, the market demand at this stage in order
to project demand-driven, Tomoaki launched a project to the quality of
priority and in order to promote a price to the customer. Thank you,
Chi-ming, the company's customer support and trust. To replace incandescent lamps with LED In
the past, only to be used only at the conceptual model in LED lighting.
Today, in many cars and trucks, instrument panel backlighting, interior
lighting and brake lights can be found in the LED. In addition, the
luxury car manufacturers are increasingly using the latest solid-state
LED lighting technology to enhance the beauty of the 2007-2008 models,
these lighter, smaller and more reliable components for internal and
external lighting. LED also has a lower cost and longer life, for
example, for internal lighting with incandescent lamps as well as a
pre-HID (High Intensity Discharge), and has obvious advantages compared
with halogen lamps. Car battery-powered LED needs of DC / DC converters
to accurately adjust LED current, in order to ensure a consistent light
intensity and color uniformity and to protect the LED. In addition,
according to the different LED applications, such as former lamps, rear
lights, turn signal indicator, the internal atmosphere of light or
reading lamp, DC / DC Regulators should also be based on specific power
requirements for optimization. There is also a larger challenge, and
may be lower than, equal to or higher than the load voltage of the
battery voltage supply one or several LED strings. Another concern is
based on a large dimming ratio of pairs of high-efficiency LED dimming
at the same time have maintained the level of LED brightness regardless
of the color characteristics of the same. DC / DC drive, high
efficiency is a key requirement, especially in the drive HB (High
Brightness) LED, when the more so because it is not converted into
light power is in the form of waste heat.
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led
lighting system After years of research and development in which Audi's
led out of the new lighting system, equipped with a start in 2004,
Audi-style A8W12, followed by 2006-style Audi S6, Audi R8 and Audi
A5/S5 are beginning to carry the technology. Audi was the first one
would be led lighting system for headlight parts, each lamp group
composed of 54 led lights, can provide the brightest light source, but
power consumption is the lowest. Although the brightness of HID xenon
headlights are not as effective in reducing the depot but because the
cost of this technology will be increased emphasis on new cars from the
factory and then to scrap the former can be said that do not have pulls
bulb. First of all Audi A8 equipped with the latest model of led
lighting systems, followed by Audi Q7V12TDI will also begin carrying
the latest technology, the technology costs come down in the future
high-power led, specifications popularity, it will gradually replace
the HID Xenon headlamps to be the next a generation of lighting the
mainstream.
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