Principle Of LED Street Lamp Technology

- Jun 10, 2019-

1.The traditional LED street lamp design mainly focuses on the LED lumen number, and pays less attention to the heat dissipation. In fact, LED lumens are increasing rapidly. The number of lumens per watt of mass-produced leds reached 100 in 2009 and is growing fast. The corresponding theoretical system of heat transfer is mature, and the means of heat transfer available to us are basically clear: conduction, convection, radiation and phase change heat transfer. Therefore, in terms of heat transfer or heat dissipation, the measures we can take are visible and limited.

LED street lamp heat dissipation technology, generally used for heat conduction plate, is a piece of 5mm thick copper plate, in fact, it is an even temperature plate, the heat source temperature off; There are also heat sinks, but they are too heavy. Weight on the street lamp system is very important, because of the high street light is 9 meters, if too much risk increases, especially in typhoon, earthquake can cause accidents. There are domestic manufacturers adopt the world's first acicular heat dissipation technology, acicular radiator cooling efficiency than conventional flake radiator has a great range, can make the LED junction temperature is lower than ordinary radiator more than 15 ℃, and the waterproof performance is better than ordinary aluminum radiator, also improved on the weight and volume. In addition, the graphite heat sink developed for high-power LED lamps also has good thermal conductivity and heat dissipation performance.

Heat dissipation modes mainly include: natural convection heat dissipation, forced heat dissipation by fan, heat pipe and loop heat pipe heat dissipation, etc. The system of forced heat dissipation by fan is complex and has low reliability. However, street lamps have the advantages of outdoor use at night, heat dissipation surface on the side and small size restrictions, which are conducive to natural convection heat dissipation. Therefore, LED street lamps are recommended to choose the natural convection heat dissipation mode as far as possible.

LED street light heat dissipation problems existing in the design are: heat dissipation fin area is set at random, unreasonable cooling fin arrangement, lamps and lanterns of the heat dissipation fin failed to consider the use of lamps and lanterns decorate way, affect the effect of fin, emphasis on heat exchange links, ignore the convection part, although many manufacturers to consider a variety of measures: loop heat pipe and heat pipe, thermal conductivity silicone grease, etc., but don't realize ultimately depends on the surface area of lamps and lanterns, heat dispersion,. Ignore the balance of heat transfer, if the fin uneven temperature distribution in the serious, will cause part of fin did not play a role or function is limited.

Heat dissipation type high power LED street lamps. Its purpose is to solve the problem of high power LED lamps and lanterns of heat dissipation, put forward a kind of air convection type high-power LED street lamps and lanterns, it includes a lamp holder components, lamps and lanterns of the cooling body and tail lamp components, lamps and lanterns of the cooling body components for chord, cylindrical shell openings on both ends, the two side arc cylinder for facade facade also have open hole array, the chord cylindrical shell lumen with 4 ~ 10 axial line and arc cylindrical chord cylindrical solid tud thermal conductive plate, stud the heat conducting plate and the chord two facade on either side of the cylindrical shell are also opened a hole array, The two facades on both sides of the vertical rib heat conducting plate and the arc-stringed column shell form 5 ~ 11 heat dissipation channels for hot air flow in the radiator assembly of the lamp. The advantages of the utility model are that the heat dissipation internal cavity has a plurality of heat dissipation channels for hot air flow, and the vertical rib heat conduction plate also serves as heat dissipation surface, the heat exchange surface is increased, and the heat emission efficiency is high.

The heat dissipation of LED street lamps is one of the key problems to be solved, which is not only directly related to the actual working efficiency of LED, but also due to the high brightness requirement of LED street lamps, high heat emission, and the harsh outdoor use environment, if the heat dissipation is not good, it will directly lead to the rapid aging of LED and decrease its stability. Because road lamps used outdoors should have a certain level of dustproof and waterproof function (IP), good IP protection will often hinder LED heat dissipation. Solving the two problems which contradict each other but both have to be solved is an important aspect that should be paid attention to when designing road lamps and lanterns. In this aspect, the application of LED in road lamps in China is the most unqualified and unreasonable situation. The main unqualified and unreasonable situations in domestic use include:

(1) LED radiator is adopted, but the design of LED wiring terminal and radiator cannot reach IP45 or above, and cannot meet the requirements of GB7000.5/ iec6598-2-3 standard.

(2) using common road lamps shell, using matrix LED inside the lamps and lanterns is a smooth surface, although this kind of design can meet the IP test, but not because of lamps and lanterns ventilation can cause at work, the temperature of the inner cavity of lamps and lanterns will rise to 50 ℃ ~ 80 ℃, under the working condition of the high, LED luminous efficiency is impossible high, the service life of the LED will also be discounted at the same time, in fact there is an obvious unreasonable situation.

(3) instrument fans are used in the lamps to dissipate heat to LED and radiator. The air inlet is designed at the bottom of the lamps to avoid rain water. The air outlet is designed around the LED light source. In addition, the radiator and LED (light source cavity) are not in the same cavity. If this design is well done, it can pass smoothly according to the IP test requirements of lamps. This solution not only solves the cooling problem of LED, but also meets the requirements of IP level. But this seemingly good design actually has obvious unreasonable situation. Because most of the roads in our country the use of lamps and lanterns, the dust in the air volume is larger, sometimes will achieve a lot (such as dust), under the condition of this kind of lamps and lanterns is in general use after a period of time (about three months to half a year), its internal dust will fill the gaps in the radiator, the radiator effect, finally still can make the LED because of working temperature is too high and obviously shorten the service life. The drawback of this scheme is that it cannot be used consistently and well.

To take into account LED heat dissipation and IP protection in road lamps, a reasonable design guideline is:

A. Heat conducting plate is adopted at key heat dissipation positions. The heat conducting plate is in the inner part of the metal plate, and it is uniformly distributed with a small conduit for refrigerant flow and filled with a refrigerant. When a part of the heat conducting plate is heated, the refrigerant in the fine conduit will flow rapidly and heat will be transferred rapidly. A good thermal conductivity plate can achieve the thermal conductivity of the same thickness of copper plate 8 to 12 times, although the price is high, but if used in key parts, the LED heat dissipation will play a double effect.

B. Design the shell of the lamp as a radiator. Most of the road lamps and lanterns is aluminum shell, direct use of lamps and lanterns outside shell as a radiator can meet the requirements of IP protection class and also be able to get great heat dissipation area, in addition, the shell of lamps and lanterns of the radiator in dust fall, can wash by natural wind and rain, which can ensure the continued effectiveness of the radiator.