EP2924334B1 - LED street light - Google Patents

Description

The invention relates to a LED street lamp made of plastic according to the preamble of claim 1 and the EP2 489 930 ,

A lamp according to this document is designed to cope with the waste heat as follows: On an LED plate, the LEDs are arranged in front of this plate, an optical disc is mounted, which is in contact only with the LED plate in its edge region. Behind the LED plate, in operation above, a metal plate is provided, which keeps a small distance to the LED plate. With this metal plate, the lamp is mounted on a heat conductor, which is provided with cooling fins and housed with electronics in an outer housing. This outer housing has openings for circulating the air, sensitive components are protected by a separate water protection cap. The structure of the entire lamp is complex and therefore expensive, the risk of penetration of dirt and moisture in sensitive areas is great.

Since the LED has entered the street lighting, efforts are underway to develop luminaires that meet the specific requirements of the LEDs. The most important requirement is good heat dissipation because, compared to previous lamp systems, the LEDs are particularly sensitive to temperature and efficiency. The quality of the heat dissipation determines the necessary size or performance of the luminaire and is therefore a significant factor of the luminaire costs. In particular, lamp housings and mounting surfaces are made of aluminum, as die-cast parts or extruded profiles, usually provided with many cooling fins. These lights are often heavier than before and therefore not optimal, both from the material costs, as well as the weight, which poses considerable handling problems during assembly and must be borne by the most existing masts.

In addition, the change to LED lights is taken as an opportunity to increase the quality of lighting by the latest findings of lighting technology are incorporated, such as glare reduction, reduction of light pollution, photobiological compatibility, more precise light control at low Anrainerbelästigung, color quality of the Light, brightness controls for energy saving, monitoring of brightness and failures, etc., which directly affects the connection and control of the lights, but also in the design and orientation of the light sources and optics.

The applicant has decades of experience in the use of plastics for outdoor technical lighting. It was therefore natural to consider how a street lamp could be built in plastic. Plastic is not only much lighter and cheaper than aluminum, but also available in many colors, but above all, electrically insulating, resulting in further simplifications in the internal structure. But the corrosion resistance of plastic parts is also superior to aluminum, which must be protected by additional coating or anodizing and also colored. In addition, optics for LEDs have long been made of transparent plastics. A disadvantage, however, is the low thermal conductivity and lower resistance to aluminum, which must be compensated by a suitable concept.

There have been attempts to make street lights in plastic so far. These assume that the heat of the LEDs is first distributed over metal parts and dissipated and only then dissipated via a heavily fissured plastic housing, such as in the US2009310381A1 (Chang ).

On the other hand, plastic housings often represent only a design panel of conventional technology EP 2487406A1 (Innotec) a lamp that proposes parts of the frame and the upper perforated cover also made of plastic. The US 2009 / 0310381A1 (Chang ) uses heat pipes and aluminum heatsinks for heat dissipation, but this fixture also has a split plastic housing, which is also not involved in heat dissipation. Both here as well as in the case of US 2010 / 0309664A1 (Fu Zhun ), the light sources sit on ribbed aluminum die castings or extruded aluminum profiles to quickly distribute the waste heat and dissipate it into the ambient air.

The US 2012 / 0281404A1 (Wilcox ) shows a housing that is also used as a heat sink, but actually protects the precise attachment of the light source and lens plate to a flat bearing surface of this housing, so that no closer disclosures on the heat balance are available. From the figures, however, it can be concluded that because of the massive cooling fins and the large wall thicknesses, it is an aluminum die-cast part which first distributes the waste heat of the very compact light source over the entire housing and then discharges it directly into the air.

There are also many small or fainter lights, such as in the form of table lamps or flashlights, which have a plastic housing. As an example, here is the Chinese application CN 201925823U cited, in which a metal-core circuit board with three LEDs, some components on it and a connecting cable and with three LEDs separately pre-lenses, as a whole with plastic overmolded to obtain a waterproof light. Here, the heat dissipation takes place directly from the metal core board, which distributes the LED heat internally, through the plastic layer to the outside.

Such designs and manufacturing methods for small lights are not transferable to street lights, which must be many times larger and brighter, permanently exposed to the weather and diverse loads outdoors, a wealth must comply with regulations and tests and components should be interchangeable. For example, overmolding a PC board with polycarbonate would damage the LEDs thermally and cause a large distortion of the luminaire, but also the design would suffer from the procedural constraints.

It was therefore an overall concept sought, which provides an encapsulation of the light source in plastic, with very good heat dissipation, good stability, economically viable in larger dimensions and with a precise and efficient lighting technology. This is inventively achieved in that a flat, arbitrarily large, good heat conducting circuit board is equipped with LEDs in a uniform distribution, that on the side of the LEDs, a lens plate made of transparent material is arranged, which at least at each LED position a recess for receiving the same and has an optical system for light distribution, with its flat rear side fully rests against the circuit board and borders with its front to the free, and that a plate-shaped housing rests with its flat inner surface over the entire surface of the circuit board and its outer side adjoins the free. The heat loss of the LEDs is evenly distributed over the printed circuit board and dissipated directly on the one hand by the rear side housing wall, on the other hand by the front side fitting lens plate to the outside. Housing and lens plate are made of plastic and close the circuit board for protection Environmental influences tight. Housing and lens plate can optionally be stabilized by ribs or gluing or welding and then form a receiving cavity for the electrical and mechanical connection means of the lamp to the circuit board, or at least have fastening means for a connection unit.

Previously known embodiments of such a construction have for the housing only extruded aluminum profiles with a plurality of cooling fins, such as in the CN 201715388U and CN 201443705U shown. However, such embodiments are now undesirable because mainly deposits dirt between the ribs, which reduces the heat transfer and cleaning is correspondingly complex. The cooling effect of such narrow fins on the top of a lamp is rather low, even in the absence of good air circulation.

However, leaving a large part of these cooling fins, the result for the remaining profile compared to a plastic part only a small thermal advantage, with higher costs and significantly higher weight, and the inevitable mechanical machining operations. It is then only a small step, the printed circuit board and thus the luminous area to increase a little to compensate for the poorer heat dissipation, and to replace the aluminum profile with a plastic part, which has all the necessary fasteners already integrated free of charge.

• die Fig. 1 eine Leuchte in erfindungsgemäßer Bauweise im Teilschnitt,
• die Fig. 2 bis Fig. 5 unterschiedliche Ausgestaltungen der Erfindung im Detailschnitt,
• die Fig. 6 eine vorteilhafte Verschaltung der LEDs und
• die Fig. 7 ein vorteilhaftes Layout der Leiterplatte.

The invention will now be explained in more detail with reference to drawings. It shows or show

• the Fig. 1 a luminaire according to the invention in partial section,
• the Fig. 2 to Fig. 5 different embodiments of the invention in detail section,
• the Fig. 6 an advantageous interconnection of the LEDs and
• the Fig. 7 a favorable layout of the circuit board.

In Fig. 1 is a street lamp shown in the inventive design. The light source area is drawn in section. The light source is formed by the printed circuit board 1 with LEDs soldered on one side 2, which are usually of the same design and arranged at some distance from each other in a regular grid. The underside equipped with the LEDs is provided with a so-called lens plate 3, which has depressions 4 with optically designed lens surfaces 5 at the positions of the LEDs and otherwise rests against the printed circuit board 1 over its entire surface. On the bottom are located at the LED positions convex lens surfaces 6, which in cooperation with the inner lens surfaces. 5 provide the desired light distribution. The lens plate 3 is directly adjacent to the outside and is therefore made of UV and weather-resistant plastic, in particular made of Plexiglas or polycarbonate, by injection molding.

The circuit board 1 is located with its back over the entire surface of a housing 7, which is also made of plastic and stiffened if necessary by ribs 8 and directly adjacent to the free. It protrudes on all sides beyond the printed circuit board 1 and forms an edge 9, which on the one hand shields scattered light 10 radiating beyond the horizon, on the other hand forms a drip edge, so that traces of dirt are largely kept away from the lens plate 3. The housing 7 but also protrudes on one side far beyond the lens plate 3 and forms a roof over a spacious container 11, which receives the electrical connections, the ballast, fuses, communication equipment and sensors and also the cable connections. Furthermore, it also has an adjustable mechanical mount 12 for mast or boom integrated. The container 11 is sealed to the housing 7 in a manner not shown, any manner, but releasably connected for maintenance purposes via connection means 13, indicated here by a labyrinth seal. As a material, covered polycarbonate has been proven for decades, which has an excellent combination of UV resistance, toughness and strength.

If the lamp is turned on, the printed circuit board 1 is also heated uniformly because of the uniform distribution of the LEDs and conducts the heat, on the one hand, directly via the adjacent lens plate 3, on the other hand directly to the outside via the adjacent housing 7. Because the heat transfer resistance into the environment is much higher than the thermal resistance through the wall of the lens plate 3 or the housing 7, enclosing the printed circuit board 1 in plastic parts scarcely represents a significant deterioration in heat dissipation. Even the use of thermally conductive modified plastics brings little improvement, in most cases even outweigh the disadvantages of higher costs or poor mechanical strength values, because such modifications are usually made by adding metal powder or ceramic or fibrous particles, which significantly change the property spectrum of the base material.

Because of the two-way heat dissipation directly to the outside, this system can even be superior to conventional luminaires, which have a thermally insulating cover glass or a thermally poorly connected housing. However, that is Ensuring the heat dissipation on both sides over the entire size of the LED-equipped printed circuit board is a design limitation that may only be deviated from after thermal investigations and with corrective measures.

The ribs 8 extend here in the longitudinal direction over the entire lamp and are designed only according to static requirements. Because they are mitgeformt from the housing plastic, they have no relevant cooling ability. Therefore, they may have such distances to each other that a possible cleaning shows no problems, if this is necessary at all. The longitudinal extent together with a flat, or as shown here slightly curved upwards housing wall in any case allows a permanent rainwater drain, even with tilted light. Likewise, ribs could also extend exclusively across the housing.

Studies have shown that very low plastic ribs can actually improve the heat dissipation, as they increase the surface area like cooling fins, but there is no adequate increase in heat input in the plastic.

If a large area to be stiffened with crossing ribs, so as longitudinal ribs on the housing 7 and transverse ribs can be mounted on the lens plate 3, or vice versa. Above all, ribs on the lens plate can have a disturbing effect on the light distribution and must be examined and designed accordingly. Thermally, they act like housing ribs 8. It is recommended instead especially a reinforced training of the housing edge. 9

Fig. 2 shows a possibility of light source design in detail section. The printed circuit board 1 with the LEDs 2 in the recesses 4 is located between the lens plate 3 and the housing 7. It is aligned by means of holes and pin 14 precisely with the optics 5 + 6 of the lens plate 3. The lens plate 3 has circumferentially a rib 15, which is welded together with the pin 14 with the housing 7. The air 16 around the weld areas serves to discharge the material from the melt. After heating the welding zones, the lens plate 3 is pressed together with the inserted printed circuit board 1 and the housing 7 until the printed circuit board abuts both sides, wherein the molten material connects to each other and excess material exits into the free spaces 16. For this purpose, the centering pins 14 and the rib 15 before welding a suitable oversize.

The heating of the welding zones can be carried out by means of different proven technologies, be it heating element welding, vibration welding, infrared welding, Ultrasonic welding or laser welding. In any case, the circuit board 1 must be protected with the LEDs 2 from excessive heating.

Furthermore, it is shown here that any components 17, such as a light or temperature sensor or cable plug, can be accommodated on the rear side of the printed circuit board or in the front side in clearances 18. If these are kept small enough, there is no deterioration of the heat dissipation.

Single ribs 8 serve to easily stiffen the housing in one direction or serve a design-oriented design and are only optional. They do not affect the heat dissipation, because the heat pulls up a little bit in the ribs and the ribs increase the outer surface.

In Fig. 3 a glued light source is shown in detail, namely upside down in Verklebungslage. The circuit board has here not only the pin hole centering 14 to the lens plate 3, but more holes 19 for bonding. The housing 7 is placed horizontally in the tub position and a defined amount of a low-viscosity adhesive, such as an epoxy resin 20, filled. Subsequently, the lens plate 3 is inserted with the circuit board 1, whereby the adhesive 20 is distributed over the entire housing, rises through the holes 19 and glued by capillary action also equal to the lens plate 3 with the circuit board 1. Also in the edge region of the adhesive over the circuit board 1 drüber and seals with the lens plate 3 from. The adhesive can not rise in the recesses 4, since an air cushion is formed. Thus, the optical and lighting effect remains unaffected. After hardening, a compact, very stiff composite element is obtained, so that no ribs are required even with larger luminaires, with the best thermal performance and heat dissipation because of the full-surface bonding. The relatively symmetrical construction made of the same materials prevents distortion. The manufacturing process results in an air-free light source unit, except for the sealed LED recesses 4, without problems in the event of air pressure fluctuations, tightness or ingress of moisture.

The previously presented versions are not dismantled, although without trapped hazardous substances. If, for example, you want to separate the components cleanly for reasons of recycling, it is advisable to use them as an alternative Fig. 4 , Here, a circumferential sealing cord or sprayed seal 21 is used. The lens plate 3 is tightened to the housing 7 by means of screws 22 until it comes again to bilateral investment of the circuit board. The countersunk screws themselves are sufficiently tight in the lens plate 3. Because it is not solid Connection of the lens plate 3 comes with the housing 7, more stable ribs 8a are required, which are made hollow. This doubles the stiffening effect compared to single-walled execution. The cavity can in this case be used to receive the screws 22, but also to guide connection cables for components over the entire lamp. Again, there is no noticeable impairment of heat dissipation given low rib width.

As well as the hollow ribs 8a, the recesses 4 and lens surfaces 6 of the lens plate 3 can be regarded as low ribs with small width and height. They also act in their entirety stiffening, without affecting the heat dissipation.

Of course, instead of the screws could also snap connections or latching fasteners or, as in Fig. 5 shown, also thermally riveted housing pin 26 are provided, which are canceled when recycling by force. The riveted heads can protrude as shown or be sunk.

A criterion for good heat dissipation is the even distribution of heat loss over the PCB. Because even a single hotspot can lead to premature failure of an LED and thus to the exchange of the lamp. The lighting concept allows either relatively few high-power LED with large distances to each other and thus greater heat distribution costs, which usually requires expensive metal core boards, or relatively many LEDs in the midrange with reduced distances and drastically lower local heat input at much lower distribution costs and thus more uniform temperature, for which a conventional cost FR4 printed circuit board material with thicker copper layer is sufficient. A good heat distribution also depends on the layout of the PCB and the footprint of the LED used.

Fig. 6 shows the well-known so-called matrix interconnection of the LED, here for example in 4x4 arrangement, which provides some compensation in case of LED failure and emergency operation to replacement and can be advantageously used for larger LED quantities. If LEDs 23 are used with only one anode pad and one cathode pad, mostly so-called midrange LEDs, the result is a very simple and efficient layout with regard to the heat distribution, which in Fig. 7 for the 4x4 circuit Fig. 6 is shown. It is a sequence of substantially rectangular copper surfaces 24 whose gap spacing 25 is bridged by the parallel-connected LEDs. The copper surfaces are optimally able to distribute the LED heat evenly, and at the same time the same formed correct interconnection. This design is therefore primarily suitable for FR4 printed circuit boards, both in single-sided and double-sided copper plating, connected by numerous vias as known in the art.

Other Footptrints of LEDs, especially those with potential-free thermal pads, as often occur in high-power LEDs, as well as other interconnections often have a more complicated PCB layout, because here tracks through copper surfaces can disturb and restrict the heat flow, which is why mostly expensive metal core boards must be provided.

Due to the all-round encapsulation in plastic no further insulation measures are necessary, whereby costs are avoided, also the different potentials of the individual copper surfaces are irrelevant.

In a further embodiment of the invention, a plurality of printed circuit boards and lens plates can be installed adjoining one another in order to design a modular system with different sized lights and different light distributions.

Instead of a flat circuit board and a so-called flexiprint can be used and the housing together with the lens plate are made more or less curved.

The LEDs can also be arranged in arbitrary arrangements, curves or symbol formations, as long as the specific surface load due to heat remains approximately the same. It is possible to use high-power LEDs with greater distances from one another or even higher-numbered midrange LEDs with small distances between them. Of course, LEDs with colored light can be used, also separately switchable.

The LED positions relative to the lens plate can be variable in order to be able to adjust the light distribution. Multiple LEDs can also be placed under one optic for more light output and enhanced, blurrier light distribution.

The brightness and thermal load of a luminaire can be set inexpensively by means of various operating currents, but also partial equipping of the printed circuit boards.

Claims (22)

1. LED lamp, mainly for street lighting, comprising a flat light unit that has a horizontal, downwards facing light outlet window, consisting of at least one LED-equipped printed circuit board (1), a lens plate (3) and a housing (7), and comprising an adjoining connection unit (11), a planar, highly thermally conductive printed circuit board (1) of any size being equipped with LEDs (2) in a uniform distribution, and a lens plate (3) made of transparent material being arranged on the side of the LEDs (2) and having, at least at each LED position, a recess (4) for receiving same and an optical system (5, 6) for light distribution, which lens plate has a planar rear face which abuts the entire surface of the printed circuit board (1), and a front face that faces the open air, and the planar inner face of the planar housing (7) abutting the entire surface of the printed circuit board (1), and the outer face thereof facing the open air, characterised in that the housing (7) is made from a plastics material, in particular polycarbonate, which is dyeable as desired, weather resistant, electrically insulating and load-bearing, and the heat loss from the LEDs is distributed evenly through the printed circuit board (1) and is discharged directly into the open air directly through the rear-side wall of the plastics housing (7) and directly through the wall of the front-side lens plate (3).
2. LED lamp according to claim 1, characterised in that the lens plate (3) is manufactured from a weather-resistant, electrically insulating, transparent plastics material, in particular Plexiglas or polycarbonate.
3. LED lamp according to either claim 1 or claim 2, characterised in that the thermally conductive printed circuit board (1) consists of standard material such as FR4 which has an increased copper thickness, or is designed as a metal core board.
4. LED lamp according to at least one of claims 1 to 3, characterised in that the LEDs (2) are what are known as mid-range or high-power LEDs of the SMD design, preferably having white light emission.
5. LED lamp according to at least one of claims 1 to 4, characterised in that the LED positions correspond to lens positions of the lens plate (3), and the printed circuit board (1) is positioned, at least towards the lens plate (3), by mechanical means such as holes and pins (14).
6. LED lamp according to at least one of claims 1 to 5, characterised in that the housing (7) and the lens plate (3) overhang the printed circuit board (1) on all sides and are mutually sealed in this position.
7. LED lamp according to at least one of claims 1 to 6, characterised in that the housing (7) and/or the lens plate (3) are continued on at least one side of the printed circuit board (1) and form a receptacle (11) for receiving a power supply, plug-in connections, sensors and communication, or at least have connection means (13) for a connection unit.
8. LED lamp according to at least one of claims 1 to 7, characterised in that the housing (7) extends beyond the lens plate (3) and comprises an edge (9) which upwardly blocks any light emission or scattered light (10) and forms a drip edge for rainwater.
9. LED lamp according to at least one of claims 1 to 8, characterised in that the outside of the housing (7) is smooth and planar and the stability arises from a rigid connection between the housing (7), the lens plate (3) and the printed circuit board (1).
10. LED lamp according to at least one of claims 1 to 8, characterised in that the outer face of the housing (7) comprises ribs (8) for mechanical stabilisation only in a preferred direction, such that rainwater and dirt can run off even when there is a slight slope or no slope.
11. LED lamp according to claim 10, characterised in that ribs (8a) on the housing (7) are hollow.
12. LED lamp according to at least one of claims 1 to 11, characterised in that the lens plate (3) has ribs for mechanical stabilisation, which preferably extend transversely to the ribs (8) on the housing (7).
13. LED lamp according to claim 12, characterised in that ribs on the lens plate (3) are hollow.
14. LED lamp according to at least one of claims 1 to 13, characterised in that the lens plate (3) or housing (7) comprise cavities (18) for receiving components (17) of the printed circuit board (1), such as sensors, protective circuits or cables and connector plugs.
15. LED lamp according to at least one of claims 1 to 14, characterised in that the housing (7), printed circuit board (1) and lens plate (3) are releasably interconnected by means of screws (22), clamps or snap connections using sealing elements (21).
16. LED lamp according to at least one of claims 1 to 14, characterised in that the housing (7), printed circuit board (1) and lens plate (3) are non-releasably and sealingly interconnected by means of gluing or welding.
17. LED lamp according to claim 16, characterised in that the gluing of the housing (7), printed circuit board (1) and lens plate (3) takes place over the entire surface thereof in a circumferentially sealing manner.
18. LED lamp according to claim 16, characterised in that the welding of the housing (7) and lens plate (3) takes place by means of hot plate welding, vibration welding, infrared welding, ultrasonic welding or laser welding, it being possible for welding points to also be arranged within the printed circuit board outline.
19. LED lamp according to claim 16, characterised in that the housing (7), printed circuit board (1) and lens plate (3) are held together by thermal riveting by means of housing pins (26) which are distributed at regular intervals over the light source.
20. LED lamp according to at least one of claims 1 to 19, characterised in that the housing (7) and the lens plate (3) have the same base material, in particular polycarbonate.
21. LED lamp according to at least one of claims 1 to 20, characterised in that the housing material is modified so as to be thermally conductive.
22. LED lamp according to at least one of claims 1 to 21, characterised in that LEDs (2) each having only one cathode and anode pad (23) are interconnected in a matrix arrangement (Fig. 6), each cross-connection of the parallel strands in the printed circuit board layout is designed as a continuous copper surface, and the LEDs (23) bridge the gaps between the copper surfaces.

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