2013年03月06日

White LED Road Lighting 2

White LED operation up to 20% energy form of photon radiation, and the remaining 80% of the energy is transformed into heat can make chips and phosphor coating heating. For low-power LEDs, the 80% of the input power of the heating effect does not rise too much so that the chip temperature, little effect of the LED luminous efficiency, life and operational state. But 0.5W or more high-power white LED, more than 80% of its power concentrated in a very small pn junction area, and will make the chip and phosphor coating substantial warming, which affects not only the luminous efficiency, but will also cause rapid light failure and shortened life expectancy.

50000 or 10-hour long-life judge is estimated monochromatic LED small power LED early stage of development, the power LED, the white light LED chip and phosphor baked at a high temperature for a long time, will make the life of a substantial decline. This is the poor design of the LED lighting engineering operation in three to four months after the sharp decline of the light enables designers often had to replace the light source.

The Ⅲ LED road lighting the the white LED huge investment and excessive publicity, to make this area part of the personnel sent to the high expectations of the white LED, white LED eager to push conventional functional lighting, a lot of personnel in this area and the direct promotion of road lighting, over the years the country completed the LED road lighting and LED photovoltaic road lighting model works dozens (authors examine the excessive road lighting using LED as the light source) and has made enough experience and lessons to be summarized. I think that this test should be a temporary slowdown, the conditions are ripe and then restart.

Road lighting the main light source in China and developed countries is still high pressure sodium lamp, a small number of metal halide lamps, the former 100-120lm / W luminous efficiency, color rendering index of only 20 or less, the luminous efficiency of the latter 80 ~ 100lm / W, color rendering index of 80 or so, taking into account the energy consumption of electrical accessories, such light source system light efficiency 75lm / W ~ 90lm / W between. The road lighting the lighting device is not high optical reflectance, and is often below 60%. About 40% of the use of such lamps direct light to the ground, and the remaining 60% of the light is fired at the ground require the approval of the lamps reflected. Rough estimate to remove a variety of loss does not exceed 76% total light utilization of conventional road lighting, and thereby estimate the ultimate effect of light is about 60lm / W to 70lm / W. In addition, due to unreasonable as well as high-pressure sodium lamp lighting design a special slender columnar luminous body caused by the uneven distribution of light for the dark area between the road centerline and two lights meet lighting standards, the design had to use more power, more high luminous flux of the light source to meet the dark area of ​​the illumination requirements, and thus more caused a waste of energy.

Based on the above, LED road lighting designers that the use of the LED directional radiation performance road lighting design, can significantly reduce energy waste, they believe that the white LED is more energy efficient than high pressure sodium lamps. They designed a number of use of high power LED (1W, 3W) road lighting program and made a model project. However, most of these model projects has not been carefully tested and certified. One lighting design is 120 1W white LED matrix distribution 200 × 250mm rectangular planar circuit board, board wiring, then the overall installed in conventional street lamps. This design is very unscientific, the program selected LED single light-emitting no more than 40lm estimated to 40lm theory, taking into account the the supporting electrical loss (10%) and 90% light utilization, light use of the actual system rate of less than 32 lm / W, 120 LED's total luminous flux approximately 4300lm. If the LED light emission angle of 120 °, press this design 4300lm of light will be the emission angle of 120 ° toward the bottom. Conceivable that such a design will enable ground light is very unevenly distributed between the middle of the street and the light poles completely dark. Did not consider them these facilities to take effective measures to cool the LED substrate, so the LED is concentrated in such a small space, more than 80 watts of power consumption the continued accumulation will make the chip temperature is too high, blocking pressure drop decreased the fat Blu-ray to the long direction of the drift, which will inevitably lead to a serious decline of its light efficiency. Investigated the outskirts of Beijing in a photovoltaic lighting model road (the total power of the light source to 105W) lamp illumination of only 3.5 lux, It is said that the previous two and a half, the completion of the project, the lamp illumination of 7 lux. Lamp diameter of 15 meters away from the place, there is no lighting effects. Those engineering samples in Jiangsu, Zhejiang, Shandong, Guangdong, Guangdong Shunde somewhere, and somewhere in Shenzhen LED road lighting demonstration Street dimly lit, and the light source must be replaced every 3-5 months.

LED road lighting tests must be under the guidance of experts, after strict certification and design to implementation.

Guangdong enterprise specializing in LED road lighting engineering from access to the lessons, they take measures to make the 1W LED work in 0.5 ~ 0.6W or 3W LED design 1W use, so although the cost is high, light low efficiency, poor lighting effects, but basically solved the light fades and life issues.

Hot in view of China's white LED, developed specifically for the Chinese for road lighting white LED 1W LED front-end packaging materials designed for the specific structure of the convex lens, and the alleged use of such LED without a multinational twice, three times optical design can get a uniform illumination of the road, and easy to use. The company claims that such LED cold light efficiency 70lm / W, compared to 50lm / W in normal use.

Zhejiang, a company designed for road lighting, the integrated-type white LED, the plurality of blue LED chips assembled on the same substrate, using a specially designed larger convex lens for the output window, the coated phosphor in the inner wall of the output window, so that all the LED chips jointly excited the same phosphor coating. This modular LED light-emitting characteristics transformed similar with conventional spherical light source, is more convenient to use, but this structure LED substrate cooling problem persists.
Note that together the plurality of LED road lighting design, in addition to a sufficient luminous flux and a reasonable optical design in order to ensure reasonable light distribution and, more importantly, the heat problem. As mentioned above, approximately 80% of the energy consumption of the LED transformed into heat, high temperature semiconductor devices, if you can not heat generated instant guide to walk you will cause serious consequences.

Road with led lighting conditions are not yet mature, and both need to be LED light efficiency improvement and power increase, more remains to be effective LED cooling solution and measures to solve, of course, the more reasonable optical design is very important.

Of Ⅳ DOE's assessment of the effectiveness of commercial LED products (CALiPER)
LED luminous efficiency and life expectancy indicators, there is a big disagreement, one of the important reasons is that there is no uniform standards and test methods, such as the lighting industry has always been as parameters of the stable operation of the luminous flux output and optical efficiency, while LED industry in general to the initial (cold), the maximum luminous flux and luminous efficiency as the standard, there are many differences in the color rendering index measuring methods and standards of life standards and measurement methods are different, the data falls far short , the evaluation is also very different.

This problem is not only our country, in a foreign country is equally serious, the U.S. Department of Energy had discovered seven market product survey, they were carried out from December 2006 to September 2008, in 2008 alone on continuous January three spot checks were carried out in May and September, and was released in September of the assessment and reporting of the effectiveness of the "commercial LED products CALiPER (Commercially Available LED Product Evaluation & Reporting), they released the data and conclusions are negative in the detect 24 types of products, only two categories (ejection downlight) data and product specifications consistent few LED luminous efficiency of 62lm / W, an average of only 32lm / W the low lack 10lm / W, far from being able to achieve energy Star of the standard. Chaos and data exaggerated propaganda made a very harsh and negative conclusions, including the luminous efficiency, color temperature, color quality, light distribution, as well as the power factor of the lighting system. Optical efficiency, in particular, tend to exaggerate the propaganda they found 2 to 3 times higher than the general users do not understand this. The conclusion of the U.S. Department of Energy is required to establish uniform standards to regulate product quality and indicators, the above problems in our country is more prominent and important.

The Ⅴ conclusions LED is an excellent light source of the future, the specific luminescence mechanism to give it a range of features and characteristics. Because of its small luminous body, the density of the medium, the light emitting very concentrated, high brightness. Even if the power is very small, little luminous flux of LED also give the human eye in a clear, bright the correct optical signal, to indicate, show no superiority than with the theory, its application has an extremely broad in the display area, everywhere. Low-power color LED also decorative lighting and art lighting display unique features and charm, and the 2008 Beijing Olympics, give full play to the LED such functions.

The white LED is an outstanding member of the LED family has a lot of features and characteristics. One of the important purpose of the development of white LED is used to replace the conventional electric light sources such as incandescent, fluorescent, high intensity discharge lamps, etc., however it seems its development as expected rapid. Actual market white LED luminous efficiency of about 40lm / W, up more than 50lm / W for functional lighting, these parameters are to be increased. Even more important for the promotion of the white LED is a cheap and efficient development of the cooling system.

As is known, other than the addition to the LED, all the light emitting body of the light source are to work at high temperatures, a high temperature of several thousand degrees, is to ensure its efficient light-emitting conditions, but the temperature rise of the semiconductor light emitting device such as an LED, a light emitting center is extremely harmful, if this problem can not be solved, the LED light efficiency improvement, power increase is limited.

Small power white LED (1W and below) in a wide range of applications shows tremendous advantages, such as very widely in the small space for local lighting, garden lights, close small power flashlight, lamps and emergency lighting room for growth. White LED does not require, nor conditions and in high-power conventional lighting sources compete for road lighting market.

Not reflective objects, the wide open spaces around the road lighting indoor lighting, road lighting requirements of the luminous flux, which is most of the road lighting 250W 400W high luminous flux high pressure sodium reason, this lamp luminous flux 28000lm to 48000lm range terms 1W, 3W white LED replaces the requirement of the LEDs is too large, the high cost and difficulty of design, and the effect is difficult ideal. In recent years LED road lighting has made a lot of lessons to be white LED light efficiency is not high, life is not long, and I think that should be put off for road lighting with LED test, to be successfully developed higher efficiency, more power white LED and a cheap and efficient cooling system before advancing.

Road lighting consumption for huge energy has great potential to be tapped, the transformation imperative, Philips and Fudan University in cooperation recently, this a very useful study [5], they concluded that the ceramic metal halide lamps is a very good replacement products in the high-pressure sodium lamps.


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