Lighting principle
LED (LightingEmittingDiode) lighting is lighting emitting diode, is a solid semiconductor light emitting device. It is used as light emitting materials by solid semiconductor chip, semiconductor carrier occurs through the release of excess energy complex caused by photon emission, directly emit red, yellow, blue, green light, on this basis, the use of the principle of three basic colors, adding fluorescent powder, can emit red, yellow, blue, green, green, orange, purple, white and other arbitrary color of light. Lighting LED lamp is made using LED as light source.
LED light source is from LED III - IV compounds, such as GaAs (Shen Huajia), GaP (Lin Huajia), GaAsP (P Shen Huajia) as its core is made of a semiconductor, p-n junction. So it has the characteristics of general I-V P-N node, namely the forward conduction, stop, reverse breakdown characteristics. In addition, under certain conditions, it also has the light emitting characteristics. In the forward voltage, electron injection P zone by N, the hole injection N zone by P. Minority carrier into the other area (Shao Zi) and a part of the majority carrier (sub) compound and light emitting. Assuming the luminescence is occurred in the P zone, then injected electrons and holes in the valence band direct composite and the light, or is first luminescence center after capture, again with the hole recombination luminescence. In addition to this light emitting compound, but also some of the electrons are non luminescent center (the center between the conduction and dielectric band near the middle) capture, and then recombine with holes, each release of energy is not, can not form a visible light. Compound amount relative to non luminous luminous compound quantity ratio increases, the higher quantum efficiency. Because of the composite is in the minority carrier diffusion area light, so only within a few mu m generated near the PN junction.
Theory and practice prove that the semiconductor material peak wavelength lambda light and light emitting region of the band gap of Eg related, i.e. lambda = 1240/Eg (mm)
Type Eg units as electron volts (eV). If you can produce visible light (wavelength 380nm in purple to red 780nm), semiconductor materials Eg should be between 3.26 ~ 1.63eV. Red light than long for infrared light. The existing infrared, red, yellow, green and blue light emitting diodes, but the blue diode cost, the price is high, the use is not universal.
The illumination characteristics
Limit parameter
(1) the maximum allowed power consumption on both ends of Pm: allows LED positive DC voltage and the current flowing through it product. More than this value, the LED heating, damage.
(2) the largest positive DC current IFm: the greatest positive DC current allows plus. More than this value may damage the diode.
(3) the maximum reverse voltage VRm: maximum reverse voltage are allowed to add. More than this value, the light emitting diode may be breakdown.
(4) the ambient temperature range of working environment of topm: light emitting diode working. Below or above this temperature range, the light emitting diode will not work properly, the efficiency is greatly reduced.
Without changing the material premise, in the limit in the range of LED, improve the brightness means is to improve the current, with the current increase, LED heat will increase. The use of LED light source portable projector, or the cast of friends, must have a deep understanding, projector, LED light source is very hot, but generally there will be obvious noise. These products, small body is on the one hand, the key still its own higher heat caused by.
With the increase in power, the heat of LED become more and more prominent, a lot of practical application show that, LED can not increase the input power is the basic reason, because LED will release a lot of heat in the working process, the tube core junction temperature rise rapidly, thermal resistance becomes large. The input power is higher, the greater the heating effect. The increase of temperature will cause the device performance change and decay, non radiative recombination increases, leakage current of the device is increased, the semiconductor material growth of defect, metal electrode migration, using epoxy resin yellow and so on package, seriously affect the photoelectric parameters of LED. Even the LED power failure. Therefore, for LED devices, reducing the thermal resistance and junction temperature and thermal properties of light emitting diode research becomes more and more important.
Reliability
LED drive an important reason for low power days is aluminum electrolytic capacitor drive power required life lack, is the primary reason for long time operation, when the LED lamp inside the ambient temperature is high, resulting in the electrolyte of aluminum electrolytic capacitor was quickly drained, life is much shorter, usually can only work 5000 hours. And LED light source life is 50000 hours, so the aluminum electrolytic capacitor working life becomes short rib LED drive power of life.
Now some suppliers in order to deal with this problem, create no aluminum electrolytic capacitor LED driver program. But not all of the LED drive power supplier to support this approach. Chen Rong pointed out: "the current production of the LED driving power supply without a plan is selected for driving without electrolytic capacitor, because without it, many test specification pass, such as the EMI test and no flicker test."
And the choice of aluminum electrolytic capacitor LED driver power supply plan is simple usually above tests, PCB copy board if change into a thin film capacitors and ceramic capacitors and tantalum capacitors, situation how? Film capacitor to reach the capacitance of the same (usually 100-220uF), the volume will be great, and the cost is too high, the ceramic capacitor is usually too small capacity, as such a large capacity with the completion of a plurality of ceramic capacitors, board area and cost are too big, tantalum capacitor should have so much capacity, one is too expensive the pressure is too low, but not up to the requirements, so the capacitor replaced any other breed, basically not too big in size, it is too expensive, as for these defects capacitor replaced a smaller capacity, not so good to eliminate the ripple effect, many export products required strict certification test target can not pass current, so the high quality LED driving power supply is still all over the selection of aluminum electrolytic capacitor.
No electrolytic capacitor LED many suppliers claim driving power supply plan, it may simply remove the aluminum electrolytic capacitor AC input terminal of the constant flow of aluminum electrolytic capacitor output should be difficult to remove or replace.
NXP pushed a TRIAC dimming embedded drive power 13WLED lighting, the driving power supply plan according to the selection of SSL2102 aluminum electrolytic capacitor. When I asked about the lighting work life, work life problem of aluminum electrolytic capacitor will affect the entire LED bulb life, but can take some of the physical methods to mitigate this problem, such as aluminum electrolytic capacitor in the PCB range near the lamp tail, generally speaking, the highest temperature near LED light some. Can arrive at 100-200 DEG C, cooling the metal shell of some second, usually around 100 degrees, a lamp tail some minimum, usually about 70 DEG C, which only focus on the aluminum electrolytic capacitor range close to the lamp tail, its life will not decay too fierce. Our experiments indicate that it can also reach his 10000 hours, the equivalent of 10 years of time of use, this regarding usually home users, for the first ten years of LED lighting is basically able to withstand.
Green environmental protection
No mercury, lead to heavy environmental pollution of heavy metals, light will produce ultraviolet light, so the LED lighting does not like the lamps have many mosquitoes around the light source side make the environment more clean and sanitary and clean; the metal shell of constant current drive to make the product innovation design of electrical energy converted into light efficiency is very high.
The unique advantage
(a) energy conservation: the LED spectra of almost all concentrated in the visible light spectrum, the luminous efficiency can reach 80 - 90%. The author also LED lamp with a common incandescent lamp, spiral energy-saving lamps and T5 three band fluorescent lamp made a comparison, the results showed: the optical efficiency of ordinary incandescent lamps is 12lm/w, the service life of less than 2000 hours, the light effect of spiral energy-saving lamp life is 60lm/w, less than 8000 hours, T5 fluorescent lamp is 96Alm/w, life for approximately 10000 hours, white LED and 5 mm in diameter is 20 to 28lm/w, life can be more than 100000 hours. It was also predicted, LED upper limit of the future will be infinite.
Ordinary people think, energy-saving lamp energy saving 4/5 is a great pioneering work, but LED than the energy-saving lamp energy saving 1/4 even, this is reform of solid light source more great. In addition, LED also has other advantages, high quality light, basically no radiation, typical of the green lighting; reliable and durable, very low maintenance costs and so on. Because of the characteristics of LED with the above other solid light source is unmatched, 10 years after LED will be the mainstream lighting industry.
(two) safety and environmental protection: the working voltage of LED is low, many 1.4 - 3V; common LED working current is only 10mA, but also 1A ultra high brightness. LED not in the production process to add "Mercury", also do not need to be inflated, does not need the glass shell, good impact resistance, good shock resistance, not easy to break, easy to transport, very environmentally friendly, known as "green energy".
(three) long service life: LED has the advantages of small volume, light weight, shell for epoxy resin package, not only can protect the internal chip, also has the capability of light spot. The service life of the LED is generally between 50000 to 100000 hours, because the LED is a semiconductor device, even frequent switches, it will not affect the service life. The main use of the domestic lighting is incandescent lamp, fluorescent lamp and energy-saving fluorescent lamp.
(four) fast response: LED frequency response of F tau and tau injected minority carrier lifetime is related to MC, such as GaAs material made of LED, the tau MC is generally in the range of 1 - 10ns, then the response frequency is about 16 160MHz, such a high response frequency for the display of the video signal to said to have 6.5MHz enough, this process is one of the key factors of LED large screen video.
LED minimum response time has reached 1 microseconds, generally for more than a few milliseconds, is about an ordinary light source response time of 1/100. So it can be used in many high frequency environment, such as automobile brake lamp or status lights, brake time can shorten the car after the vehicle, thereby improving safety.
(five) high luminous efficiency, light efficiency of incandescent lamp, halogen tungsten lamp as 12-24lm/w (LM / W), the optical efficiency of the fluorescent lamp is 50 to 70lm/w, efficiency of light lamp is 90 to 140lm/w, most of the energy into heat. But the light effect of the improved LED can reach 50 - 200lm/w, and the light of the good monochromaticity, narrow spectrum, without filtering can directly emit colored visible light.
(six) the LED element has the advantages of small size, layout and design more convenient for various equipment, and can achieve better landscape lighting "saw the light does not see the light" effect.
(seven) the LED light to high energy concentration: focused on smaller wavelength window, high purity.
(eight) LED light emitting strong point: brightness decay is much lower than the traditional light source.
(nine) LED low voltage DC power can be driven with advantages of small interference: load, weak, low requirement to use environment.
(ten) can be better controlled composition luminescent spectra: which can be well used for local lighting or major museums and galleries in the.
(eleven) can control the semiconductor light emitting layer, semiconductor materials prohibited web size: to emit different colors of light, and chroma higher.
(twelve) high color: will not damage the eyes of people.
Lighting specifications
As LED gradually into the indoor, outdoor lighting LED lighting market, prices also fell sharply, but quality is uneven also causes problems, it is pointed out, one after another around the set LED lighting standard, lighting a number of mandatory standards will hit the road from 2012 onwards, will be expected to accelerate the malignant competition out of inferior goods, and then drive LED lighting market shuffle effect.
Because LED lighting applications become more widespread and diverse, Taiwan Ministry of Economic Affairs Bureau of standards formulated many LED lighting standards, following the LED street lamp specification steps announced by the end of 2010 leading countries in the world, and issued 3 common LED indoor lamp standards, including LED T8 straight tube, LED light projector and light steel frame light (including flat lamp) industry pointed out, though, related standards have been set, but LED street after years of promotion, to 2012 is expected to be expanded to install, because the government into slow plus budget work, is estimated to be 2013~2014 years is expected to release the purchasing bid.
Although the mainland LED industry development like a raging fire, but due to climate difference of each area is too large, so the industry standard has not yet entered the national standards project, by their respective provinces leading and promoting regional LED lighting standards established, but it was pointed out, the NDRC will, through the technical specifications of LED lighting, indoor LED lamp as to priority projects, expected in technology specification may, 2012, the 12th Five Year Plan in promotion, the central fiscal package announced grants LED interior lighting will be expected to expand the implementation.
As for the LED lighting products enter the EU must through the CE certification, and consideration of electromagnetic radiation on the human body may cause harm, the EU also announced on 2013, to enforce radiation safety standard human body electromagnetic standard.
With the U. S. Environmental Protection Agency announced the new version of solid state lighting lamps and light source products listed standard, in 2011 October the industry pointed out that the attenuation test concern LM-80, is expected to be from 2012 April onwards enforcement, in the new standard setting out on the road, the North America market lamps manufacturers will give priority to purchase through the LM-80 verification LED products, for without verification Taiwan LED packaging and grain mill, later to enter the American market will suffer hinder fear.
Because the LM-80 attenuation of verification required after 6000 hours of testing, time-consuming up to 6~8 months, part of the LED industry that is changing with each passing day LED product specification and technology, after a few months later, the standard verification LED lighting may be changed, so this certification still hold doubts, but Gongyan = said, LM-80 is regarded as the admission ticket to enter the American market, manufacturers must provide LM-80 (LED lumen maintenance rate) test certificate, in order to obtain the Energy Star label, Illuminating Engineering Society of North America (IES) has set a LM-80 optical attenuation testing standards, not only provides the measurement standard for LED application products, also provides quality assurance for the consumer that will become the global common testing standards.
