Principle of led street lamp technology

- May 22, 2019-

1.Technical :

Traditional LED street lamp design mainly focuses on the lumen number of LED, but pays less attention to the heat dissipation. In fact, LED lumens are increasing rapidly. In 2009, the number of lumens per watt of LED in mass production has reached 100 lumens, and this number is still growing rapidly. The corresponding theoretical system of heat transfer has been mature, and the means of heat transfer we can use 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 the heat conduction plate, is a 5mm thick copper plate, in fact, is a temperature plate, the heat source temperature off; There are also heat sink to heat, but the weight is too large. 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 fin developed for high-power LED lamps also has good thermal conductivity and heat dissipation performance.

The main ways of heat dissipation are: natural convection heat dissipation, installation of fans forced heat dissipation, heat pipe and loop heat pipe heat dissipation. The installation of fan forced heat dissipation system is complex, low reliability and high cost of heat pipe and loop heat pipe heat dissipation. However, street lamps have the advantages of outdoor use at night, the heat dissipation surface is located on the side and the size is limited, which is conducive to natural convection heat dissipation of air. Therefore, LED street lamps are suggested to choose natural convection heat dissipation 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.

Radiating high-power LED street lamp. 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 stiffened heat conducting plate and the arched cylindrical shell form 5 ~ 11 heat dissipation channels for hot air flow in the heat dissipation body assembly of the lamps. The utility model has the advantages that there are multiple heat dissipation channels for hot air flow in the heat dissipation body cavity, and the vertical rib heat conduction plate also ACTS as the 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 that need to be solved. It is not only directly related to the luminous efficiency of LED in actual work, but also because of the high brightness requirement, high heat dissipation and harsh outdoor environment of LED street lamps, poor heat dissipation will directly lead to the rapid aging of LED and reduced stability. Because road lamps used outdoors should have a certain level of dustproof and waterproof function (IP), good IP protection will often hinder the heat dissipation of LED. To solve these two contradictory problems is an important aspect of road lighting design. In this aspect, LED is also the most unqualified and unreasonable when applied to road lamps in China. The unqualified and unreasonable situations in domestic use are basically as follows:

(1) radiator is adopted for LED, 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) the instrument fan is used to dissipate the LED and radiator in the lamp. The air inlet is designed below the lamp to avoid the rain. 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 the lamps. This solution not only solves the problem of LED heat dissipation, but also meets the requirements of IP level. However, 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 well and sustainably.

To take into account the heat dissipation and IP protection of LED in road lamps, a more reasonable design guiding principle is:

A. Heat conducting plate shall be used in the key heat dissipation position. The heat conducting plate is in the inner part of the metal plate, which is distributed with a thin tube for refrigerant flow and filled with refrigerant. When a part of the heat conducting plate is heated, the refrigerant in the thin tube will flow rapidly and conduct heat rapidly. Good thermal conductivity plate can reach the same thickness of copper plate 8~12 times, although the price is higher, but if used in key parts, the heat dissipation of the LED will play a multiplier effect.

B. design the lamp housing in the shape of 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.