National Electric Light Source Quality Supervision and Inspection Center (Shanghai) National Lighting Quality Supervision and Inspection Center Shanghai Times Light Lighting Electrical Testing Co., Ltd.
Abstract: LED as a novel solid illumination source, with production process and almost no pollution, no vibration, easy to achieve 0~100% continuous dimming, can work under safe extra low voltage, can work continuously in switch The flashing working state and its light output are directional and many other unique advantages. In recent years, its remarkable improvement in light efficiency and light color has enabled it to enter commercial applications. However, due to the influence of China's planned economic industry layout and the lack of expertise in LED and the comprehensive knowledge of lighting appliances in the practitioners, there has been no application for the design and application of LEDs. Unreasonable and unqualified application products. This paper analyzes the current problems existing in the application of LEDs in road lamps, and also gives ideas and examples for solving problems, for the reference of the majority of peers.
Keywords: multiple light sources, directional illumination, cubic light distribution, over illumination, system efficiency, LPD
Introduction <br> <br> LED lighting used in the field, is currently China and the world lighting industry hot topics through the continuous efforts of employees, the current white LED lighting system efficiency under normal lighting conditions of work (including the drive circuit ), which has reached 40 lm/w, and the manufacturing cost of LEDs for lighting has dropped drastically. Therefore, white LEDs for lighting have commercial conditions that are applied to some lighting fields.
However, due to the situation caused by the industrial structure distribution of China for many years since the planned economy era, the current industrial groups that manufacture LEDs often lack understanding of the basic knowledge and requirements of lighting appliances, and the traditional lighting production groups are often lacking. In-depth understanding of the LED characteristics of lighting, in the design and application of the characteristics of the LED is not fully utilized, to promote the use of long and short, so that when the lighting LED is applied to the lighting device, there are many unreasonable misdesigns. This paper presents the following insights on some of the major issues in the application of LEDs for lighting applications in road lighting.
one. Features of lighting LEDs used in road lighting
1. Current status and defects of ordinary road lighting
At present, the light source commonly used in road lamps is a high-pressure sodium lamp or a metal toothed lamp. The most characteristic of these two kinds of light sources is that the size of the arc tube that emits light is small, and a large light output is generated by a small-sized arc tube, and has a very high High light efficiency, the former includes supporting electrical appliances, up to 110 lm / w, the latter including supporting electrical appliances up to 80 lm / w. However, when such a light source is applied to a road lamp, only about 40% of the light directly passes through the glass cover to reach the road surface, and other light is projected through the lamp reflector to project the lamp. Conventional lamps that generally use such a light source are currently widely used. There are basically two shortcomings. One is that the illumination in the direction of direct illumination of the luminaire is very high, and it can reach more than 50 lx on the secondary road. This area is obviously over-illuminated, and the illuminance at the intersection of the two lamps is only 40% to 20% of the illumination under the lamp. Second, the efficiency of reflectors of such lamps is generally only 50% to 60%, so about 60% of the light output is in the lamps, and is projected onto the road after losing 40% to 30%.
The overall efficiency of such lamps is generally around 70% (only such road lamps of internationally renowned brands can achieve 80% efficiency), and excessive illumination in the above-mentioned over-illuminated areas is also wasteful. Comprehensive analysis of the above-mentioned traditional road lamps has a comprehensive effective lighting efficiency (excluding excessive lighting) of only 50%. For the above reasons, the lighting effects (uniformity of road illumination and illumination) of the secondary trunk roads in China are currently not up to the requirements of CJJ45-2006 and CIE31 and CIE115 standards.
2. Current status of light distribution of road lamps using LED light sources
At present, there are two main types of LEDs used in road lamps. One is to use a traditional road lamp housing, but in the luminaire, a matrix is mounted on an almost flat mounting surface (also a reflective surface). LED, this design is impossible to get a good light distribution. The other is to integrate multiple LEDs in a circular area (area diameter is about 30mm~40mm), so that the light output density of this small area is close to that of high-intensity gas discharge lamps, and then use the luminaire reflector for light distribution. However, the luminosity of this design is not superior to that of traditional road lamps, and because of the integration of high-density LEDs in a small area, the heat dissipation of LEDs is obviously poor, which not only affects the illumination of LEDs. Efficiency, but also often affects the life of the LED.
3. The characteristics and application of LED for lighting
At present, the most important feature of LEDs for illumination is the function of directional emission of light, because currently power-type LEDs are almost equipped with reflectors, and the efficiency of such reflectors is significantly higher than the reflector efficiency of the lamps. In addition, the efficiency of the self-reflector has been included in the LED efficacy detection. Road luminaires using LEDs should utilize the characteristics of directional emitted light of LEDs as much as possible, so that each LED in the road luminaire directly directs the light to each area of the road surface to be illuminated, and then uses the auxiliary light distribution of the luminaire reflector to realize Very reasonable light distribution for road lamps. It should be said that the road lamps should meet the requirements of illumination and illumination uniformity of CJJ45-2006 and CIE31 and CIE115 standards. The function of three light distributions in the lamps should be better. The LED with reflector and having a reasonable beam output angle has a good primary light distribution function. In the luminaire, a good secondary light distribution function can be realized by designing the mounting position of each LED and the direction of the emitted light according to the height of the road lamp and the width of the road surface. Reflectors in such luminaires are only used as an auxiliary three-time light distribution to ensure better uniformity of road illumination.
In late September of this year, the author participated in the acceptance of the test road section of the Weihai secondary road using LED light source road lamps organized by the Shanghai Lighting Society. The lighting and layout of this test road were designed using the above principles. According to the measured results, this test section makes full use of the appropriate directional illuminating function of the LED, and adopts the three-time light distribution mode, which not only makes the illuminance of the secondary road and the illuminance uniformity of the road surface meet the requirements of national standards. Moreover, local over-illumination of this area is also prevented in the main illumination direction of the luminaire. Due to the full use of the characteristics of the LED, and the use of a reasonable light distribution method to fully utilize the light output of the LED, thereby making up for the LED light itself is not as good as the HID light source, so that the entire road unit area meets the standard requirements, The energy consumption is only about 70% of the energy consumption of the original lighting design using high-pressure sodium lamp road lamps, and has achieved significant energy-saving effects.
At present, governments at all levels have vigorously promoted energy conservation and emission reduction. In indoor lighting, the limits of lighting power density (LPD) have been enforced. China's road lighting energy-saving certification technical standard "road lighting energy-saving certification technical requirements" will be completed early next year, the technical requirements put forward the road lighting power density (LPD) assessment requirements, the core part is to meet the road surface illumination The illumination power density (unit: W/m 2 ) is reduced as much as possible under the premise of uniformity of illumination, thereby achieving the purpose of energy saving.
The design idea of the above-mentioned road lamps using LEDs is to meet the requirements of the "Technical Requirements for Energy-saving Certification of Road Lighting Fixtures". At present, the Canadian government has implemented its road lighting energy-saving work according to the requirements of road lighting power density (LPD). It is estimated that more countries will implement their road lighting energy-saving work in accordance with LPD requirements in the near future.
In the design of the actual road lighting fixtures, each LED can be fixed on the luminaire with the spherical universal joint under the premise of basically setting the direction of each LED, when the luminaire is used at different heights and illumination widths. At the same time, the spherical gimbal can be adjusted to achieve satisfactory results for each LED. When determining the power and beam output angle of each LED, the LEDs can be calculated according to E(lx)=I(cd)/D(m) 2 (the inverse law of the intensity and illuminance distance). The power that the beam should have when outputting the angle, and the light output of each LED can be predicted by adjusting the power of each LED and the different power output from the LED driver circuit to each LED. These adjustment methods are unique to road lamps that use LED light sources. By fully utilizing these features, it is possible to reduce the illumination power density and achieve energy saving while satisfying the illumination and uniformity of road surface.
one. Other problems and solutions for LED design with LED
1. LED heat dissipation and IP protection
The working condition and heat dissipation of the LED are not only directly related to the luminous efficiency of the LED when it is actually working, but also related to the service life of the LED. Also, because road lamps used outdoors should have a certain level of dustproof and waterproof function (IP), good IP protection often hinders the heat dissipation of the LEDs. Solving this contradictory problem that has to be solved is an important aspect that should be paid attention to when designing road lamps. In this respect, it is also the most unqualified and unreasonable situation in the domestic application of LEDs in road lamps. There are basically unqualified and unreasonable situations in the current domestic use:
(1) The radiator is used for the LED, but the design of the terminal and the heat sink of the LED connection cannot reach the IP45 and above, and cannot meet the requirements of the GB7000.5/IEC6598-2-3 standard.
(2) Using ordinary road lamp housings, matrix LEDs are used in the illuminating surface of the luminaire. Although this design can meet the IP test, the temperature inside the luminaire will rise due to the non-ventilation in the luminaire. At 50 ° C ~ 80 ° C, under such high conditions, the luminous efficiency of LED is impossible, and the service life of LED will be greatly reduced.
(3) The instrument fan is used to dissipate the LED and the heat sink in the lamp. The air inlet is designed below the lamp to avoid the entry of rainwater. The air outlet is designed to be around the LED light source. This can also effectively prevent the entry of rainwater. In addition, the heat sink and the LED (light source cavity) are not in the same cavity. This design is good, and it can pass smoothly according to the IP test requirements of the luminaire. (One enterprise has adopted the above design ideas, and its products have also passed the V65 IP65 test). This solution not only solves the heat dissipation problem of LEDs, but also meets the requirements of IP level. But this seemingly good design actually has obvious unreasonable circumstances. Because in the use of most road lamps in China, the amount of flying dust in the air is large, sometimes it will reach a large extent (such as sandstorms). After using this type of lamp for a period of time under normal conditions (about three months to In the half year), the gap inside the internal radiator will be filled with dust, which will greatly reduce the effect of the radiator. Finally, the LED will have a significantly shortened service life due to the high operating temperature. The shortcoming of this program is that it cannot be used well and well.
To balance the heat dissipation and IP protection of LEDs in road lamps, a more reasonable design guideline is (1) using heat-conducting plates at critical heat dissipation locations. The heat conducting plate is inside the metal plate, and is uniformly provided with a thin pipe for the refrigerant to flow, and the small pipe is filled with the refrigerant. When a certain part of the heat conducting plate is heated, the refrigerant in the thin pipe flows quickly to make the heat quickly. Ground conduction. The heat transfer coefficient of a good heat-conducting plate can reach 8 to 12 times that of a copper plate of the same thickness. Although the price is high, if it is used in a key part, the heat dissipation of the LED will have a multiplier effect. (2) Design the outer casing of the luminaire into a radiator. At present, most of the road lamp housings are made of aluminum. Directly using the outside of the lamp housing as a heat sink can not only ensure the IP protection level, but also obtain a large heat dissipation area. In addition, the radiator of the lamp housing is in the presence of dust. It can be flushed by natural wind and rain to ensure the continuous effectiveness of the radiator work.
2 . LED drive circuit efficiency and output characteristics
The requirement of the LED for the driving circuit is to ensure the characteristics of the constant current output. Because the relative change region of the junction voltage is small when the LED is working in the forward direction, the constant driving current of the LED ensures that the output power of the LED is constant. For the current situation of unstable supply voltage supply in China, it is necessary to have a constant current output characteristic of the driving circuit of the road lamp LED, which can ensure the light output is constant and prevent the super power operation of the LED.
In order to make the LED drive circuit exhibit constant current characteristics, the output internal impedance must be high when viewed from the output end of the drive circuit. During operation, the load current also passes through the output internal impedance. If the drive circuit consists of buck, rectification and filtering, plus DC constant current source circuit or general-purpose switching power supply plus resistance circuit, it must consume a lot of active power. Power, so the two types of drive circuits under the premise of basically meeting the constant current output, the efficiency is impossible. The correct design scheme is to use active electronic switching circuit or use high-frequency current to drive the LED. The above two schemes can make the driving circuit still have high conversion efficiency under the premise of maintaining good constant current output characteristics. For an introduction to improving the efficiency of LED driver circuits, please refer to "China Lighting Appliances", Issue 6, 2007).
3 . Lightning protection of electronic drive circuit in field lighting
At present, road lamps in China basically adopt the mode of HID light source with trigger and magnetic ballast. Although this mode has the problems of low energy efficiency and stroboscopic, its reliability is very high. While LED lamps using electronic drive circuits are used in field lighting applications, an important aspect that threatens their reliability is the lightning induction problem.
It is well known that lightning in the air emits a broad spectrum of radio waves, while overhead road lighting power lines are well accepted for wireless. The radio waves emitted by the same lightning output received by the two power lines belong to the common mode interference signal for the driving circuit. The common mode interference can reach several volts to several thousand volts, which easily breaks through the driving circuit. The EMC grounding capacitor or a small clearance to the ground (to the outer casing) causes damage to the drive circuit.
In addition, since the power supply line in China is a three-phase four-wire neutral line grounded polar power supply, in the segments of the two overhead power supply lines, at the moment when the radio waves of the lightning are sensed, the two power supply lines are grounded. The instantaneous impedance is different, which causes a differential mode interference voltage between the two power supply lines. The instantaneous differential mode interference voltage can also reach hundreds of volts to more than 3,000 volts. This voltage often breaks down the power supply rectifier diode and the printed circuit of the driver circuit. The electrical gap between the electrodes of different polarity on the circuit board also causes damage to the drive circuit.
To solve this problem, it is necessary to connect the fast-responding varistor to the input terminal of the LED driving circuit to ensure the leakage of differential mode interference. Since the inductive interference of lightning is repeated many times, when the interference voltage is high, the current of the varistor transient conduction bleed may be large, so the varistor should not only have a fast response capability, but also have a transient guide. The venting capacity of ten amps is not damaged. In addition to the use of varistor, the input of the LED driver circuit should also be combined with conducted interference (EMI) protection, designed with a composite LC network, so that these LC networks can not only hinder internal EMI leakage to the grid, but also The interference signal of lightning has a significant inhibitory effect.
In addition, the electrical clearance of each point-to-ground of the LED driver circuit should be kept above 7mm. The grounding capacitance of the EMI protection and the insulation strength of the grounding circuit of the driving circuit should meet the requirements of reinforced insulation (4V+2750V), which can make the LED The drive circuit has good resistance to differential mode and common mode lightning induction.
Concluding remark
As a novel solid light source, LED has almost no pollution in the production process and products. It is not afraid of vibration. It can realize continuous dimming from 0 to 100%. It can work under extremely low voltage and can work continuously in switching and flashing. The state and its output light have many unique advantages. In recent years, its significant improvement in light efficiency and light color has enabled it to enter commercial applications. However, in design and use, it is necessary to pay full attention to the characteristics of LEDs. The application can achieve the desired good results.
The current LED application in road luminaires should give full play to its function of directional light output, using three specific LED output angles and different light output and reasonable design of the installation direction and the function of the luminaire reflector. The light distribution maximizes the direct light and directivity of the LED to maintain the full utilization of the LED emission light, and maintain the uniformity of the road illumination, thereby preventing excessive illumination of the local area, making up for the lack of self-illumination efficiency, and making the system efficient. Obtaining considerable improvement, on the premise that the illuminance meets the standard requirements, the lighting energy consumption per unit area is about 30% higher than that of the lamps using high-pressure sodium lamps. However, LEDs are now at the level of energy efficiency and output light intensity. As a commercial application in the main road as the main lighting, there are still many gaps.
In addition, road lamps using LEDs as light sources should be designed to ensure reliable and continuous heat dissipation under the premise of IP protection. LED drive circuits should have high efficiency and perfect EMI and EMS protection characteristics. LED road lamps with these characteristics not only have good illumination power density (LPD) indicators, but also have the advantage of output light without stroboscopic, which is very beneficial for the illumination of moving objects.
references:
1. CJJ45-2006 Urban Road Lighting Design Standard
2. CIE31:1978 glare and uniformity of road lighting equipment
3. CIE115:1995 Road lighting design for motor vehicles and pedestrian traffic
This article was published in the first issue of the Journal of Lighting Engineering in 2008.
Personal profile of this author:
Yu Anqi , professor-level senior engineer, is dedicated to the field of lighting appliances, electric light sources and lamps for 28 years.
Member of the Electric Light Source Professional Committee of China Illumination Society Director of Shanghai Lighting Society Director of National Electric Light Source Quality Supervision and Inspection Center (Shanghai) Deputy General Manager and Technical Leader of Shanghai Times Light Lighting Electrical Testing Co., Ltd. CCC Certification TC05 Lighting Electrical Technology Member of the National Quality System (ISO9000) Registered Senior Auditor Member of the National Lighting Appliance Standardization Technical Committee
CCC Senior Inspector | |
First, work experience:
From September 1968 to January 1979, the Heilongjiang Production and Construction Corps, the Sixth Division, the 24th Regiment, and the Thirty-seventh Company served as the Deputy Instructors. From January 1979 to March 1996, the Shanghai Guorong Enameled Wire Factory Military Workshop served as the Chief Commissioner - → Technology Director of Equipment Department March 1996 ~ Present National Electric Light Source Quality Supervision and Inspection Center (Shanghai) Electric Light Source Room Lighting Appliance Main Inspection -→
National Electric Light Source Quality Supervision and Inspection Center (Shanghai) Deputy Director; National Lighting Quality Supervision and Inspection Center,
Deputy General Manager and Technical Leader of Shanghai Times Light Lighting Appliance Testing Co., Ltd.
Second, the awards:
1. In 1995, won the third prize of scientific and technological progress awarded by Shanghai Municipal Engineering Administration Bureau (project name: 36V, 30W fast start fluorescent lamp ballast)
2. Received the third prize of Science and Technology Progress Award of the State Bureau of Technical Supervision in 1996 (project name: tubular fluorescent lamp ballast performance requirements, general requirements and safety requirements)
3. In March 2004, the company was awarded the title of Outstanding Scientific and Technological Worker of Shanghai Quality and Technical Supervision Bureau. 4. In 2006, it was awarded the title of “Advanced Scientific and Technological Inspection by the State Administration of Quality Supervision, Inspection and Quarantine” (National Quality Inspection Department [2006] No. 348)
5. In December 2006, he was awarded the “Second Prize for Scientific and Technological Achievements” by Shanghai Quality and Technical Supervision Bureau.
6. In October 2006, the first prize of China Standard Innovation Contribution was jointly awarded by the General Administration of Quality Supervision, Inspection and Quarantine and the China Standardization Administration ( 2006-357-1-07-E-R06 )
Third, the formulation of national standards and the preparation of a unified textbook for the national standards of the State Administration of Quality Supervision:
A total of 19 textbooks on the development of national standards and the preparation of national standards and unified textbooks have been fruitful. As the editor-in-chief and the first author, the National Standard for Lamp Control Devices and the National Standards for Energy Efficiency of Metal Halide Lamps have been prepared. More than 430,000 words, independently writing more than 410,000 words.
Fourth, special lectures and published papers:
From 1987 to the present, at the invitation of the China Lighting Society, the China Lighting Society Electric Light Source Professional Committee, the China Lighting Society Lighting Professional Committee, the Shanghai Lighting Society, the Zhejiang Lighting Association, the Jiangsu Lighting Society, and the China Lighting Appliance Standardization Technical Committee, At the professional meetings organized by the above-mentioned units, more than 30 special lectures have been held. At the invitation of Fudan University's electric light source department, a special lecture was given to the electric light source professional training class organized by Fudan University's electric light source department (4 class hours). In addition, it should also be Philips Lighting Electronics (Shanghai) Co., Ltd., Osram (Foshan) Lighting Co., Ltd., Philips Yaming Lighting Co., Ltd., Philips Yaming Lighting Co., Ltd., General Electric (China) Technology Center, Shanghai Yaming Bulb Factory Co., Ltd. Shanghai Lighting City, Shanghai Haojiajia Lighting City, and more than 30 enterprises and institutions invited to give lectures on various topics.
From 1984 to the present, more than 40 papers have been published in various lighting electrical magazines and papers nationwide.
V. Hosting patent applications and obtaining patents
(1) In 2002, obtained the patent certificate for “Multi-band Reference Ballast for Gas Discharge Lamps”. Patent No.: ZL 02 2 15795.6 (Designer, Patentee).
(2) In 2007, he obtained the patent certificate of “a three-terminal tandem trigger”. Patent No.: ZL 2007 2 0067205.7 (Designer,).
(3) October 2006 invention patent application “a full-scale adjustable high-frequency fluorescent lamp reference ballast” Application No. 4. (Design, inventor,). The preliminary review was passed (publication phase).
Editor: China Lighting Network Liu Li
