【 Weak current College 】 LED light source of road lighting should focus 】

LED to the lighting area, is at present China and the world of lighting sector, through the efforts of employees, current lighting white LED lighting in general working conditions in system efficiency (including driver), has reached 40lm/w, plus lighting LED manufacturing costs dropped, so the illumination white led has applied to some lighting conditions in the field of business.

However, because since the times from a planned economy in China for many years the industrial structure of the situation created by the distribution, making current manufacturing lighting LED by industry groups often lack the basics of lighting appliances and required to understand, yet traditional lighting production groups often lack the characteristics of the lighting LED insight in the design and the application does not fully exploit the features of the LED, with the combined strengths of use, resulting in illumination LED to lighting, produce many unreasonable design of the error. This article is currently lighting LED to road lighting in a number of key issues, makes the following observations.

1. lighting LED in road lighting in use of expertise

1. ordinary road lighting situation and defects

Current road lighting in a common light source is high pressure sodium or metal gear of the lamp, the two biggest characteristics of light source is, luminous arc tube size small, size small arc tube produces very large light output, and has very high luminous efficiency, the former including ancillary equipment, up to 110lm/w, the latter including the necessary electrical appliances up to 80lm/w. But this kind of light source used in road lighting, only 40% of the light is directly through the glass reaches the surface, the other is through the lamp reflector then projected lighting, is currently widely used this type of light source of the basic traditional lamps are two, one is the direct rays of light in the direction of illumination is very high, at the time the traffic corridors can reach more than this 50lx region belongs to the obvious excessive lighting, while the two lamps Lighting crossing of illumination only light intensity of 40% to 20%. Second, this type of lamp reflector efficiency General only 50-60%, 60% of the light output in the lamp, is in a loss of 40% ~ 30% then projected onto the pavement.

This type of lamp and the overall efficiency is generally 70% (only the international famous brands of this type of road lighting efficiency can reach up to 80%), and the excessive lighting area of illumination is a waste. Comprehensive analysis of the traditional road luminaires of its integrated, effective lighting efficiency (less excessive lighting section) is only 50%. Because of the above reasons, my time trunk road lighting effects (pavement illuminance and luminance uniformity) are not reach CJJ45-2006 and CIE31 and CIE115 standards.

2. the current use of led light source of road lighting situation of light distribution

Current LED in road lighting in the most popular form used by mainly two kinds, one is using the traditional road lamp housing, just within the lamp, in a nearly flat plate mounting surfaces (also the reflective surface), fitted with a matrix of LED, this design approach is not possible to get good photometric lamps. The other type is multiple LED integrated in a circular zone (zone diameter approximately is 30 mm ~ 40mm), so that this small area of light output density close to high-intensity discharge lamps, and then use a lamp reflector with light, but this design pattern of distribution of photometric lamps will not be superior to traditional road lighting, and because in a very small area integrates high density of LED to LEDs marked adverse heat, not only affects the LED luminous efficiency, but also often affects the service life of LED.

3. lighting LED's expertise and application

Current lighting with LED's greatest features directional firinglight function, as the current power led almost always equipped with a reflector, and this reflector efficiency are clearly higher than the lamp's Reflector efficiency. In addition, led luminous efficiency detection already include the efficiency of their reflector. Use of led lighting of roads should be as much as possible to use LED transmit light of directional characteristics of the various road lighting LED directly to the rays respectively to be according to the various regional, pavement recycling lamps and reflectors auxiliary light distribution, for a very reasonable road lamps integrated light distribution. It should be said, road lighting to really meet CJJ45-2006 and CIE31 and CIE115 standard illuminance and luminance uniformity requirements, lamps should contain three times the functionality of light distribution in order to achieve better. But with reflectors with reasonable beam output angle LED itself has good photometric features at a time. In the lamp, in accordance with the road lamp height and width design various pavement LED transmit the installation location and direction of light will be able to achieve good two-time optic feature. In this type of reflector luminaire, only as a secondary means of three light distribution, to guarantee a better road illumination uniformity.

The author in late September of this year, attended by the Shanghai municipal lighting society organizations on the use of secondary road, Weihai, LED light source road test road luminaire of acceptance, this test road lighting and layout is designed with the above principles, the results from the field of view, this is a test sections making full use of the directional light emitting LED the appropriate function, and adopted the three light distribution patterns, not only to secondary road illumination of roads and road pavement Illumi met the requirements of national standards, but also in the light of the major lighting direction, or prevent this region local excessive lighting. Since takes full advantage of the features of the LED, and reasonable way of distributing the full use of LED light output, which make up the LED luminous efficiency than HID light itself, making the entire road unit area to meet the standard requirements of the energy consumption of only using high pressure sodium lamps of road lighting energy consumption by 70% and achieved significant energy savingEffect.

Currently, Governments are promoting energy conservation and emission reduction, indoor lighting, lighting power density of enforcement (LPD) limits. China road lighting certified technical standards the road lighting energy saving certification technical requirements will be completed early next year, the technical requirements of the proposed road lighting power density (LPD) examination requirements, the core part is to meet the road for illuminance and luminance uniformity of as much as possible to reduce lighting power density (W/m2), so as to achieve the purpose of energy saving.

The use of led lighting of roads is designed to meet the road lighting energy saving certification technical requirements assessment requirements. At present the Government of Canada has on-road lighting power density (LPD), pursuing its road lighting energy-saving work, it is estimated that in the near future will have more countries according to the LPD request its road lighting energy-saving work.

In the actual design of road lighting, can be used in the Basic setting of each LED set shot direction, each LED by fixation of spherical joint at the lamp, when the lamp is used to different heights and irradiation width, by adjusting the spherical joint allows each led light is achieved satisfactory results. In determining each LED power, beam output angle, according to E (lx) = I (cd)/D (m) 2 (irradiance and illuminance from the inverse square law), the LED is calculated separately in basic selected beam output angle should have the power, andyou can adjust the power LED and LED driver circuit output to each LED to different power to enable every LED light output reached the expected value. These adjustment tools are based on the led light source of unique road lighting, take full advantage of these features can be implemented to meet the road for illuminance and luminance uniformity reduce lighting power density, achieve energy-saving purposes.
? A. using led lighting design of other problems and solutions

The thermal conditions and 1.LED IP protection

LED work conditions and the heat not only directly related to the actual work of LED luminous efficiency, but also in relation to the service life of LED. Also because in the outdoor use of road lighting, should have a certain level of dust-proof waterproof function (IP), good IP protection tends to hinder the LED heat. Resolution of this conflict but also had to resolve two problems is the design of road lighting should be an important aspect of concern. In this context it is applied to the LED lamps when roads are not qualified and unreasonable conditions. Currently used in non-qualified and not reasonable basic are:

(1) on LED uses a heat sink, but the LED connection of terminals and heatsink design cannot reach the above grade, IP45 and cannot satisfy GB7000.5/IEC6598-2-3 standard.

(2) adopt common road lamp housing, smooth out the lamps within the matrix LED, this design while able to meet the IP test, but because the lighting in the ventilation will result in work lamps lumen's temperature rises to 50 ℃ ~ 80 ℃, in such a high operating mode, the LED light-emitting efficiency is not high, the service life of LED will also be greatly diminished.

(3) the adoption of the lamps and instrument fan on the heat sink thermal LED and the air intake below the luminaire design in order to avoid the rain water into the air outlet design in the following shot led light source. This can effectively prevent the entry of rain, heat sink and LED (light-cavity) is not in the same cavity, this design if done well, according to the lamps IP test requirements, successfully passed. (One company adopts the design idea, its products also adopted the VDE test of IP65) this programme, not only solved the problem LED thermal, but at the same time meet the requirements of the IP level. But this looks like a good design, in fact, there is obviously unreasonable. Because the vast majority of road lighting in China to use, the amount of dust in the air is relatively large, sometimes reach very large (such as dust) that this kind of lamps in the General conditions of use for a period of time (approximately three months to six years), its internal heat sink clog the slit in the dust, so that the heat sink effect greatly discounted, last may also make the LED for the operating temperature is too high and service life significantly shortened. Lack of such a programme is not sustainable good use.

To balance road lamps LED thermal and IP protection, a more reasonable design guidelines are (1) the location of the key, use of thermal heat. Thermal plate is a metal plate inside, uniform for refrigerant flow in a thin catheter and thin catheter is filled with refrigerant, when thermal plate of a site when heated, thin tubes of refrigerant flow quickly and make the conduction of heat quickly. Good thermal conductivity of the plate can be reached with the thickness of the copper plate 8 ~ 12 times, although more expensive, but if used in the key positions on the LED heat will play a more effective role. (2) the lighting design of shell into the radiator. At present most of the roads in the lamp housing is aluminum, direct use of lamp housing outside as a heatsink can ensure that the requirements of the IP protection class, or you can get very large radiation area, in addition, the lamp housing is comprised of the heatsink in erotica, can natural wind and rain while flushing, thereby ensuring the continued effectiveness of the work of the heat sink.

2.LED driver efficiency and output characteristics

LED to the driver circuit requirements is to ensure constant current output, because the work is LED forward voltage relative changes in regional ties are very small, so that the LED driving current constant that basic guarantees a constant output power LED. For our power voltage supply unstable situation, road lighting LED driver circuit with constant current output characteristics is necessary to guarantee a constant light output andAnd prevent the run super power LED.

If you want to render constant current LED driver circuit, from driving circuit output to look inwards, its output is high impedance inside. When the load current is also through this output impedance inside, if the driver circuit by buck, Rectifier filtering and DC current source circuit or universal switching power supply with a resistance circuit, it will also consume a lot of active power, so the two types of driver circuit in basic satisfy constant current output, efficiency is not high. Correct design is the use of active electronic switching circuit or high frequency currents to drive the LED, the adoption of the above two options can make the driver in maintaining good constant current output characteristics, still has a high conversion efficiencies (the LED driver circuit efficiency introduction see China lighting, 2007 No. 6).

3. outdoor lighting in electronic driver circuit of lightning induction

At present, China's road lamp, HID lights used Basic plus with triggers and ballasts model, this model though low in energy efficiency and exist stroboscopic, but its reliability is very high. While the use of electronic driving circuit LED lamps, outdoor lighting occasions, threaten its reliability is an important aspect is the lightning induced problem.

It is well known that the emission of air lightning is a broad-spectrum of radio waves, and the overhead of road lighting power supply line, is good for wireless. Two power received the same lightning of radio waves, is the driver circuit is a common mode interference signal, this common mode interference on up to a few number of 1500 volts to kilovolt, easy breakdown driver circuit within EMC Earth capacity or smaller ground (shell), the electrical space, causing damage to the driver circuit.

Because our power supply line is a three-phase four-wire system neutral grounding of polar power, so the two overhead lines in the line of each paragraph, in the sense that the moment of lightning waves, because of the two power lines on the ground of the instantaneous impedance different two power supply line between a differential mode interference voltage, this moment slack die interference voltage can reach several hundred volts to 30 volts, this voltage tends to breakdown of driver circuit power rectifier diodes and printed wiring board of different polarity clearance between electrodes, also makes the driver circuit is damaged.

To resolve this problem, you must have LED driver circuit input and receive rapid response of varistor, to ensure that the differential mode interference of relief. Because lightning induced interference is repeated many times, when the interference voltage high, varistor transient conduction current venting can be quite large, so the use of Varistors should not only have the ability to respond quickly, you should have instantaneous breakover dozens of amperes relief capacity without damage. In addition to the use of Varistors, LED driver circuit input also should be conducted interference (EMI) shielding, designed with composite of LC network so that they can hinder the LC network not only within the EMI on the grid of the disclosure, but also on the lightning of interference signals marked inhibition.

Also, LED driver circuit points on land clearance should be kept above, EMI protection 7mm grounded capacitor and a drive circuit of insulation strength, should achieve enhanced insulation (4V + 2750V) requirements, which can make the LED driver circuit has good resistance to differential mode and the ability of common-mode lightning induction.

Concluding words

LED as a novel solid light source, with the production process and product almost no pollution, not afraid to shake, you can achieve 0 ~ 100% continuous dimming, can work under extremely low voltage, can continuously work to switch, working status of the Flash off and its output has directivity and many other unique advantages, in recent years in its luminous efficiency and light color on the significant progress has been made it into commercial applications, but when used in the design to give full attention to the characteristics of LED to our weaknesses of the application, in order to achieve good results.

Current led application in road lighting, should give full play to its directional light output of the function, use of every single LED specific beam output angles and different light intensity output and rational design of installation direction and lighting reflectors, achieving third light distribution, maximum use of the LED's direct light and LED transmit orientated to retain full use of light, keep the uniformity of road lighting to prevent local area lighting, compensate for the excessive luminous efficiency of the system efficiency is impressive, at the time the traffic corridors can be achieved in illumination meet standard requirements, its lighting energy consumption per unit area than adopting energy-saving lamps of high pressure sodium lamps for about 30%. But LED to energy-efficiency standards now and output light intensity level, as business applications on the trunk road as the primary lighting, there are still many gaps.

In addition, the use of LED as the light source of road lighting, at design time should satisfy the premise of IP protection, reliable and guaranteed thermal, led driver with high efficiency and excellent EMI and EMS protection characteristics. Have these characteristics of road lighting not only LED lighting power density (LPD) indicators, and have the output light strobe advantages, this movement of lighting is very useful.