WO2004088761A1

WO2004088761A1 - Light-emitting panel

Info

Publication number: WO2004088761A1
Application number: PCT/CH2004/000195
Authority: WO
Inventors: Gerhard Staufert
Original assignee: Lucea Ag
Priority date: 2003-04-02
Filing date: 2004-03-31
Publication date: 2004-10-14

Abstract

The invention relates to a light-emitting panel with an essentially sheet- or film-like support plate (31) and a number of illumination bodies, mounted on the support plate (31) and operated by electricity. The support plate has a heat extraction hole embodied as an opening in the support plate (34). Cooling fins (35a, 35b, 35c, 35d, 35e, 35f) can also be provided on a rear face and embodied and arranged such as to be optimised with relation to natural convection whereby a local heating of the support element (31) at any point at which the illumination bodies (32) are attached generates a convection along the cooling fins. The invention further relates to a module for active generation of a convection flow without moving parts, particularly by use of a heating element, a method for reduction of the heat emitted by a light-emitting panel with a pulsed operation and a light-emitting panel which may be operated such as to be switched off by sectors, on overheating of the illumination bodies.

Description

LIGHT-EMITTING PANEL

The invention relates to the heat management of light-emitting panels, for example with arrays of unhoused light-emitting diodes (LED chips). It also includes a process for reducing the heat loss emitted by light-emitting panels and an energy supply and control unit for light-emitting panels.

One possibility for generating a high luminous flux - as is necessary, for example, for street lighting or room lighting - is to combine a large number of unhoused LED chips on a suitable carrier plate, which are brought together to light up by means of appropriate electrical contacting. So that such arrangements do not become too large in terms of area, the LED chips must be arranged in a high spatial density, that is to say, for example, 10 LEDs / cm ² or higher.

A key problem with such arrangements is the fact that the summed power loss of the luminous LED chip can lead to such high temperatures with a large number of densely packed chips that the functionality of the luminous panel is questioned, or at least its service life is drastically reduced. The maximum temperature that must not be exceeded for a sufficient service life depends on the type of housing used. Conventional housing solutions that are essentially inexpensive When working with plastics, this temperature is approx. 60 ° C, the limit of permanent functionality is reached at approx. 80 ° C. Even with more advanced housing solutions, so-called high-temperature housings, the permitted maximum temperatures are not above approx. 150 ° C. It is therefore of great importance for LED light panels to ensure that any heat loss is dissipated as well as possible and / or less heat loss is generated.

Numerous approaches are described in the patent literature to solve this problem.

For example, Patent Publications EP1139439, US6428189, WO0212788, US6480389, WO02084750, US2002042156, US5113232, US6274924, US6501103, US6376902, US6481874, JP2002278480, at US200 when used by or under the heading of EP200394, US2002-07487807 or US2002-07488, which were published in 2002-2007, at the same time with an additional, highly heat-conducting, usually plate-like structure arranged on the back or on the front or on both sides of the LED carrier plate. This plate-like structure has the task of guiding the heat away from the LED as efficiently as possible and releasing it to the surroundings. In one of the arrangements mentioned (EP 1139439), the plate-like structure therefore has cooling fins. In another arrangement (US 2002/0167807), the LED carrier structure consists of individual metallic transverse walls and also metallic rails running perpendicularly to them and electrically insulated from them. This arrangement allows the LEDs to be attached directly to a metallic base, which promotes heat dissipation Nevertheless, the LEDs can be controlled “random access”. The arrangement is suitable for use on displays; in general, it is positioned so that the LEDs are in a vertical, ie vertical, plane. Another approach is described in US5278432. LED chips are arranged here on a carrier plate, which has a continuous, electrically conductive, and thus also good heat-conducting layer on the back. The heat generated by the chips is dissipated only via a ceramic insulation layer to the rear layer. Furthermore, the rear electrically conductive layer is designed as a metallic plate provided with cooling fins.

In addition to the approaches described for passive dissipation of heat via suitable heat sinks, the approach for actively dissipating heat is of course known, in that the LED light panel is flown by a cooling medium which is forced into it by means of a suitable auxiliary device, such as a fan or a pump Movement is set. An example of this is found in U.S. Patent 4,729,076 (Fig. 5 (c)).

Approaches to passively dissipating heat via suitable heat sinks have the significant advantage that no additional equipment is required. However, the approaches described all have the disadvantage that the heat release to the environment, i.e. usually in the air, is not optimized. On the one hand, this is expressed in sub-optimal heat transfer to the environment and sub-optimal heat radiation.

The approaches mentioned for heat dissipation by forced inflow with a suitable cooling medium, that is to say usually with air, have the disadvantage that the additional devices required have moving elements, which is useful for applications such as street lighting for reasons of maintainability and for applications such as room lighting for reasons of additional Noise is problematic. All in all, the approaches described have the disadvantage that they are not used as elements of a systematic approach for optimized heat management of an LED panel, which can be used in a modular manner.

The object of the invention, as defined in the patent claims, is to improve the thermal management of light panels with current-operated light bodies. In particular, the disadvantages of the individual approaches described should be remedied or decisive improvements brought about. The improved individual approaches are to be used, for example, as modules of a system for the heat management of LED light panels.

The invention leads to a solution to this problem.

In the following discussion, “LEDs” are used to refer to electroluminescent elements in a very general way, so the term includes newer approaches to electroluminescence, such as are used, for example, in organic OLEDs. Unhoused LEDs (ie LEDs without Individual housing) which can be applied directly to a carrier plate or another carrier element and which permit an essentially direct thermal contact between the LED chip and carrier element.

The invention makes use of the following approaches, individually or in combination:

The improvement of the passive dissipation of heat is first possible with an improvement in the heat transfer to the surrounding medium. Second is one

To strive to improve heat radiation. Both objectives are simple, namely with a simple adjustment of the surface structure of the to achieve the heat sink used. A better heat transfer occurs with greater roughness of the surface. Better heat radiation can be achieved by approximating the surface color to that of a black radiator, ie by using a matt black.

Both wishes can be fulfilled in a simple manner, for example, by the part serving as a heat sink consisting of a suitable metal, for example aluminum, which is etched in a first (electro-) chemical processing step and thus roughened and in a second - if necessary in one (same) bath taking place - (electro-) chemical processing step, for example by anodizing black with a matt-dark surface as possible.

Another idea on which the invention is based is that the cooling effect is used by convection of a fluid, typically air, surrounding the panel or elements of the panel. According to this aspect of the invention, the best possible development of a flow of the surrounding medium through natural convection is ensured. The panel is thus designed in such a way that a convection flow of the surrounding medium is triggered, for example increased compared to the marginal convection that occurs in conventional arrangements, and that this convection flow is directed in order to achieve a cooling effect. To a certain extent, the convection flow is channeled and optimized to produce a cooling effect. It takes place at least locally, i.e. it can essentially be assigned a clear, desired direction at any location.

The convection flow can be generated by heating the heat-generating components. According to a first approach, the best possible development of a flow of the surrounding medium by natural convection is achieved in that a disturbance of the surrounding medium is also possible when the panel is quasi-horizontal. A "quasi-horizontal" position is intended to include all panel layers in which free flow of the ambient medium heated by the panel through the panel itself is severely hindered. Typical applications of this type are the use of LED panels for lighting purposes, especially when high light densities are required, as is the case, for example, with street or room lighting. In all applications of an LED light panel, in which the panel has to be installed in a quasi-horizontal position, the cooling is severely disturbed by the fact that the outflow of the ambient medium heating up on the underside of the panel is made more difficult by the lateral expansion of the panel.

There is an amazingly simple solution to this problem that has not yet been described. As a rule, it is no problem to arrange the LED and the conductor tracks of an LED light panel so that there is space on the panel for heat exhaust holes that penetrate the panel in the direction of its smallest dimension. The term "hole" is also intended to include all conceivable forms of openings, for example, circular, straight slit-like or arbitrarily curved slit-like openings. If such a "perforated" panel is installed in a quasi-horizontal position, the hot surrounding medium that forms can be removed by the Drain holes vertically upwards. Experiments have shown that even with narrow, ie approx. 2 cm wide and approx. 20 cm long, panels with an LED temperature of approx. 60 ° C, temperature differences of up to 15 ° C between panels with or without heat exhaust holes occur. This temperature difference becomes clearer the greater the lateral expansion of the panel, the greater the number of heat exhaust holes and the higher the mean LED temperature. In addition, the relationship between hole diameter and hole length, which in turn in the Is essentially determined by the panel thickness, a crucial role. The thinner the entire panel can be designed, the greater this ratio can be. This also reduces the flow resistance of the heat exhaust holes and increases the cooling effect. In the experiments mentioned, the ratio of hole diameter to hole length was approximately 0.3, which can be assessed as rather unfavorable. A ratio of 1 and larger can easily be achieved for panels on which unenclosed LED chips are used.

One task that should not be neglected when building LED lighting panels with heat extraction holes in applications such as street lighting is the λ-der sealing of the LED chip, which is impervious to water vapor and resistant to salt water, and its electrical contacts. There are also simple solutions for these cases. For example, it is easily possible to subsequently provide an appropriate LED light panel with the desired heat extraction holes, for example by drilling or milling. So that the connection points between the layers exposed by the holes are provided with the required tightness, the entire panel can subsequently be provided with a thin transparent, water-repellent layer all around, ie also on the surfaces of the heat exhaust holes. A suitable method for this is, for example, the known plasma polymerization, with which, for example, Teflon-like thin plastic layers can be applied to complex surfaces in such a way that they are covered by the protective layer everywhere. The layer thicknesses can be set from a few 0.1 μm up to many μm. By adjusting the process parameters accordingly, the wetting properties of the plastic layers can be generated from almost completely hydrophilic to almost completely hydrophobic. Another approach is as follows: Regardless of the use of the heat exhaust holes described, cooling fins can be used to improve the heat dissipation to the environment. In terms of manufacturing technology, there is now the possibility of using very fine, relatively high cooling fins to enlarge the theoretically effective surface by a factor of the order of 10 and more. For example, with the well-known, inexpensive UV-LIGA process it is possible to produce 10 cooling fins with a height of approx. 0.5 mm and a width of 1 mm. However, calculations have shown that cooling fins with such a large height / distance ratio (approx. 5 in the example) - at least in the case of a quasi-horizontal installation position - do not improve the cooling effect compared to a flat plate. This is due to the fact that no flow of the surrounding medium through natural convection can form in the narrow, high channels between the ribs, but, due to the high flow resistance of the closely spaced walls, a thick layer of standing hot surrounding medium is formed. This phenomenon occurs - in a weakened form - even with a much smaller ratio of the fin height / spacing. For example, it can be observed that even with a ratio of approximately 1, the improvement in the cooling effect which is to be expected from the increase in surface area still does not occur.

This situation can be improved if the cooling fins are arranged in shape and position in such a way that, in their entirety, they support the formation of flowing surrounding medium. This can be achieved, for example, by using local temperature differences present on the LED panel, which are deliberately generated by appropriate arrangement of the LED chip, to locally increase the ambient medium by natural convection and to cool ambient medium from the sides appropriately arranged flow-optimized cooling fins over to make them flow. In other words, the cooling fins are designed and attached in such a way that they are flow-optimized. Heating the support element - often it is a support plate; the support element does not have to be plate-shaped - at certain points, convection creates along the cooling fins. In general, in contrast to the prior art, the cooling fins will therefore not be parallel but, for example, run in sections towards one another, for example to form venturi-like channels and generally to channel ambient medium flows.

A natural convection generated by the structure and arrangement of the cooling fins can also be generated if there are no or only slight local temperature differences, for example by heating the panel as a whole to produce convection. This can be the case, for example, in the embodiment described below:

The cooling effect of the described heat exhaust holes and the described flow-optimized cooling fins can be improved if they are combined with one another. For this purpose, the shape and the course of the cooling fins are advantageously chosen such that a flow is formed in the cooling fin spaces between the ambient medium flowing out of the heat extraction holes. This can be achieved, for example, in such a way that the cooling fins create a pattern of open, for example Venturi tube-like channels, the wide flow cross-sections of which are in the vicinity of the heat exhaust holes and the small opening of which is as hot as possible on the panel, preferably in a chimney-like manner upwards leading opening, ends. Calculations have shown that patterns of ribs with a height of 0.1 to 1 mm, a wall thickness of 0.01 to 0.5 mm and an average distance of at least 0.1 to 2 mm on the one hand result in the desired surface enlargement and on the other hand have a sufficiently small flow resistance. At first glance, the cost-effective production of such cooling fins appears difficult. However, this is not the case because, on the one hand, the cooling fins can be produced as an independent module that can subsequently be applied to the panel, for example by large-area soldering, and because, as mentioned above, they can have relatively large structures due to the flow resistance. This can be used as an example to describe a production sequence that allows the production of very cost-effective cooling fin modules whose cooling fin shape and pattern - often in the sense of 2 ^J / _2- D structures, but also in the sense of "real" 3-D structures - are almost arbitrarily complicated The following may be: First of all, by conventional milling, an embossing tool is produced that has the positive cooling fin shape with sufficient accuracy.This tool is used to emboss a suitable plastic layer as a lost shape, which in turn was previously applied to a metallic foil In a subsequent chemical etching step, the embossed grooves are opened down to the metal foil so that it is exposed at the bottom of the grooves, after which the grooves are filled with metal in a galvanic step serving plastic ski removed by means of a selective etching step. The described method can be carried out on areas of the size of one meter, which means that numerous cooling fin modules can be produced at the same time in an extremely cost-effective manner.

Another approach is based on active cooling, also by convection: A forced flow of an LED light panel through cool ambient medium can also be generated without devices with moving parts: If the ambient medium above the LED light panel is locally heated, it is heated flow this up. If it is additionally ensured that cool ambient medium flowing in from below has to flow past the LED light panel, the desired cooling effect has been achieved. This principle is advantageously implemented in such a way that the elements which are required for the local heating of the surrounding medium are arranged in such a way that they do not - or as little as possible - heat the LED light panel itself. In addition, there should be guiding elements that force the cool ambient medium to flow past the LED light panel.

In the following, a correspondingly constructed cooling element will be referred to as a "convection cooler".

In the case of the quasi-horizontal installation position of an LED light panel, a convection cooler can be implemented, for example, by providing a support plate with holes at a suitable distance above the LED light panel, which carries short, tubular heating elements and makes electrical contact, which , concentric to the holes, are fixed on the top of the carrier plate. If these heating elements are heated by their own electrical resistance, for example when electrical current is passed through, they force the surrounding medium to flow upward through their opening, so that cool surrounding medium has to flow in from below. The amount of the flowing ambient medium can obviously be regulated by the amount of active heating elements and a corresponding increase or decrease in the heat given off by the heating elements.

In the case of a quasi-horizontally installed LED light panel without heat exhaust holes, this afterflow must take place from the sides between the cooler plate and the LED light panel, which may be equipped with appropriate cooling fins. In the case of a quasi-horizontally installed LED light panel with heat extraction holes, the holes or the tubular heating elements are advantageously to be positioned such that they coincide with the solder on the geometric center of a few heat extraction holes in each case. In this way, the cool ambient medium flowing in first has to flow through the heat exhaust holes and then to flow a short distance between the cooler plate and the LED light panel, which may be equipped with appropriate cooling fins.

In the case of an almost vertical installation position of an LED light panel, the principle described can be implemented by providing a support plate without holes (but possibly also with holes) at a suitable distance from the back of the LED light panel, which has a closed row of tubular tubes at its upper end Bearing heating elements, which are electrically contacted, for example. If these heating elements are heated by their own electrical resistance, for example when electrical current is passed through, they force the surrounding medium to flow upward through their opening, as a result of which cool surrounding medium has to flow in. The amount of the flowing ambient medium can obviously be regulated by a corresponding increase or decrease in the heat given off by the heating elements.

A systematic, adaptable solution to the heat management of an LED lighting panel must be designed so that it can optionally combine all the existing elements in a modular manner. This can easily be done with the individual solutions described above:

First, the simplest case is to start with the carrier plate of the LED light panel being constructed in such a way that the individual LED chips are as narrow as possible Contact - that is, if necessary, only separated by a very thin electrically insulating layer - be applied to a metallic layer which is in direct contact with the surrounding medium to the rear. In addition, the surface in contact with the surrounding medium can be optimized with regard to heat transfer and radiation by being roughened and blackened. Even the simplest variant ensures optimal heat transfer from the LED chips to the surroundings.

Secondly, this support plate can be provided with the described heat exhaust holes and / or with the described flow-optimized cooling fin modules, optionally or in combination, from the outset or subsequently (modular element two).

Thirdly, a convection cooler can also be attached to the LED light panel (modular element three).

Each of these modular elements can be combined with any other modular element or with several other modular elements, each modular element can also be combined with the characteristic of the matt-dark, roughened surface of the carrier element (for example the carrier plate).

The third modular element (convection cooler) is advantageously combined either at least with the first and / or second modular element or at least with a carrier element with conventional cooling fins.

The modular element three can be controlled as an active element by a higher-level "intelligent unit". The modular elements of the heat management according to the invention for LED light panels are explained below with the aid of schematic figures of exemplary embodiments.

Fig. La, lb and lc show oblique layers from below on three different embodiments of an LED light panel with heat exhaust holes according to the invention.

2a and 2b each show an inclined layer from above onto an LED light panel with different designs of flow-optimized cooling fins according to the invention

3 shows an oblique view from above of an LED light panel with the combination of different embodiments of heat exhaust holes according to the invention and flow-optimized cooling fins.

4a, 4b and 4c show oblique layers from above onto three different embodiments of a “convection cooler” according to the invention.

5 shows an oblique view from above of an LED light panel according to the invention with heat exhaust holes and flow-optimized cooling fins, which is combined with a "convection cooler" according to the invention.

A large number of small LED chips 2 (area, for example 0.3 * 0.3 mm) are in direct contact on FIG Arranged at regular intervals and electrically contacted by means of electrical conductor tracks, not shown. A "as direct a contact as possible" means that the LED chips are either in direct contact with a surface of a surface of the carrier plate or are separated from it only by flat, for example as thin and as possible heat-conducting intermediate layers that they are So not individually housed and thus separated from the carrier plate by the housing and any housing contacts.

The carrier plate can be a conventional printed circuit board which is made of a ceramic or polymer material. But it can also be made of new materials. Alternatively, it can be a substantially metallic plate. In places where this is necessary - for example, to avoid short-circuiting of contact areas of adjacent LED chips - there is an electrical insulation layer, for example a sol gel, which is as thin as possible (not shown for reasons of clarity) between LED chips 2 and have carrier plate 1. As an example, the SiON sol gels are mentioned here, which are practically puncture-proof even at thicknesses of 0.5 micrometers and have a significantly higher thermal conductivity than conventional coating materials. The entire carrier plate 1, including the LED chips 2, is covered by one or more layers 3 of transparent material, which has the task of protecting the LED chips 2 and the electrical contacts mechanically and against environmental influences.

The LED light panel constructed in this way is intended for quasi-horizontal installation. For this reason, the entire structure is provided with a plurality of heat exhaust holes 4 arranged at regular intervals. In FIG. 1b, a large number of small LED chips 2 (area, for example, 0.3 * 0.3 mm) are arranged in as direct a contact as possible on a carrier plate 1 which is a good conductor of heat, that is to say, for example, made of thin copper sheet, in such a way that zones of dense assembly alternate with those without assembly , The LED chips 2 are electrically contacted by means of electrical conductor tracks (not shown) arranged on the carrier plate 1. In places where this is necessary, there is a thin electrical insulation layer (not shown for reasons of clarity) between LED chips 2 and carrier plate 1. The entire carrier plate 1, including the LED chips 2, is covered by one or more layers 3 made of transparent material, which has the task of protecting the LED chips 2 and the electrical contacts mechanically and against environmental influences.

The LED light panel constructed in this way is intended for quasi-horizontal installation. For this reason, the entire structure in the zones not equipped with LED chips 2 is provided with slot-like heat exhaust holes 4. Where possible, circular heat exhaust holes 4 are also available in areas with a dense LED chip 2.

In FIG. 1c, a large number of large LED chips 2 (surface area, for example, 2 * 2 mm, or larger) are arranged in regular contact on a heat-conducting carrier plate 1, that is to say, for example, made of thin copper sheet, at regular intervals and by means of electrical devices (not shown) Conductors electrically contacted. The distances between the LED chips 2 are so large that there is space for heat exhaust holes 4. In places where this is necessary, there is a thin electrical insulation layer (not shown for reasons of clarity) between the LED chips 2 and the carrier plate 1 The entire carrier plate 1, including the LED chips 2, is covered by one or more layers 3 of transparent material, which does the job has to protect the LED chips 2 and the electrical contacts mechanically and against environmental influences.

The LED light panel constructed in this way is intended for quasi-horizontal installation. For this reason, the entire structure in the zones not equipped with LED chips 2 is provided with slot-like heat exhaust holes 4.

To ensure that the structure is completely sealed against water or water vapor, the entire outer surface, including the perforated surfaces, is covered in FIGS. 1a, 1b, 1c by a very thin, not shown, water-repellent layer. A suitable method for producing such layers is, for example, the known plasma polymerization, with which, for example, Teflon-like thin plastic layers can be applied to complex surfaces in such a way that they are covered by the protective layer everywhere. The layer thicknesses can be set from a few 0.1 μm up to many μm. The wetting properties of the resulting plastic layers can be produced from almost completely hydrophilic to almost completely hydrophobic by appropriately setting the process parameters.

In FIG. 2a, different cooling fin structures 25 which are flow-optimized for a quasi-horizontal position are shown, all of which are attached to the top of a carrier plate 21 which is a good heat conductor, that is to say, for example, copper sheet. The LED chips 22, shown in broken lines in the figure, are fastened on the underside in as close a contact as possible to the carrier plate 21 and are electrically contacted by electrical lines not shown on the carrier plate 21. The entire structure is protected on the underside by a transparent layer 23. The LED chips 22 are either large in area or densely arranged as small chips in certain zones. There are wide intermediate zones without LED chip assignment between the large LED chips or the zones with a dense arrangement of small LED chips. As a result, there are local temperature differences on the back of the carrier plate, so that the temperatures above the LED chips 22 are higher than in the intermediate areas. Depending on the width of the unoccupied intermediate zones, these temperature differences range from a few ° C to well above 10 ° C.

The shape of the cooling fin structures 25 takes advantage of these temperature differences in that they are all arranged symmetrically to the respective center of a hot zone and have a channel-like structure which is open at the top, so that hot air can flow upwards without any noticeable flow resistance. Radially arranged cooling fins lead to this center, which is open at the top and, as a result of this arrangement, flow channels tapering from the cool zones to the center of the hot zone, through which cool ambient medium flows to the hot center.

First examples of cooling fin structures 25a, 25b, 25c and 25d have cooling fins of constant height. A first cooling fin structure 25a differs from all other cooling fin structures in that the ends of the cooling fins form a circular outline, which causes a somewhat poorer inflow of cool ambient medium.

A second cooling fin structure 25b differs from this in that the cooling fin ends form a non-round and, for example, roughly rectangular plan. A third and a fourth cooling fin structure 25c, 25d and all further cooling fin structures differ from the first two cooling fin structures 25a and 25b in that here the cooling fins are arranged in three different lengths in such a way that no too narrow flow channels arise towards the center, which improves an improvement Flow of the surrounding medium results. In other words, the distance from the end edges of the cooling fins to the center is not constant, and in that at least some cooling fins are not drawn too close to the center, as a result of which the flow channels towards the center are slightly widened in deviation from a continuously tapering course.

The fourth and a fifth and a sixth cooling fin structure 25d, 25e, 25f have cooling fins which become higher towards the center, which results in a further improved flow of ambient medium from the cool zones to the center of the hot zones.

FIG. 2b shows different cooling fin structures 25 which are flow-optimized for a quasi-vertical position. The other structure of the LED light panel corresponds, for example (here without the heat exhaust holes) to the structure of the LED light plate in FIG. 2a.

All of the cooling fin structures shown are arranged and shaped in such a way that the resulting flow channels towards the cool zones are significantly wider than above the center of the hot zones, which leads to an increase in the cooling surface (due to an increased fin density) over the hot zones Outflow of hot ambient medium upwards away from the center, as well as an afterflow of cool ambient medium from below. The cooling fins of the seventh cooling fin structure 25h have a constant height.

The cooling fins of the eighth and ninth structures 25i and 25j become continuously higher upwards, which results in an even better flow.

The ninth structure 25j is partially covered on its surface by a thin film 25k, which brings about a further improvement in the flow and additionally ensures that the surrounding medium, which flows out from the structure 25i underneath, largely flows outside via the film 25k and cool ambient medium thus flows into the covered structure 25j from below.

At first glance, the production of overlaps of the cooling fin structures with film-like layers 25k appears complex, but this is not the case.

It is sufficient for this to form a stretchable film, for example a plastic film, with a corresponding forming tool on the cooling fins and to connect them to them by heating. With the same tool can then, by

Appropriate cutting edges, the film is cut so that the film parts that are not above the cooling fins can be removed,

The material of the film must be selected so that it can first be stretched in moderate heat or at room temperature, secondly that it can be "glued" to the cooling fins by being mentioned, and thirdly that it can be

Withstands the operating temperatures of the LED light panel. Suitable plastic films can be found in large numbers on the market. A PE film is an example.

In FIG. 3, the LED light panel described in FIG. 2a for quasi-horizontal position is provided with cooling fin structures 35 with heat exhaust holes 34. The designations 31-35 correspond to 21-25 in Figure 2a. The heat exhaust holes 34 are arranged and shaped in such a way that slot-like holes are located in the cool intermediate zones between the LED chips 32, which allow the flow from the underside of the panel to the top to be as free as possible. In this way, the natural convection, which is improved by the cooling fin structures 35, acts as a pump for ambient medium from the underside of the panel and not only prevents heat build-up on the underside but also sucks up relatively cool ambient medium.

The sixth cooling fin structure 35f, which becomes higher towards the center of the hot zone, is provided in FIG. 3 as in FIG. 2a with a film-like cover 35g, 25g, which can extend over the entire LED panel in a corresponding structure. This film-like cover 35g is opened around the central open zone of the cooling fin structure 35f, so that hot ambient medium can escape unhindered here. With such a cover film 35g it is achieved that almost everything by natural convection flowing upward ambient medium with cool ambient medium flowing through from below through the heat exhaust holes and through the flow channels formed by the cooling fins has to be replaced. This embodiment of the invention therefore also works when there are no local temperature differences on the top of the panel which would in themselves produce a convection flow, that is to say, for example, with a high lateral thermal conductivity of the carrier plate.

Such a cover film can be produced in accordance with the production procedure outlined for FIG. 2b.

Different exemplary embodiments of a convection cooler are shown in FIGS. 4a to 4c. In the simplest case, shown in FIG. 4a, the convection cooler consists of a convection cooler support plate 41 which has convection holes 42 at suitable intervals. Arranged concentrically around these convection holes 42, there are heating elements 43 on the upper side of the convection cooler support plate 41, which are electrically contacted by electrical lines 44. In the example, it is a serial electrical connection of the heating elements 43. If this is expedient, the heating elements can of course also be electrically contacted in parallel or in serial groups by means of correspondingly arranged electrical lines 44.

The heating elements 43 are applied to the carrier plate using either thick film or thin film technology. The electrical connections 44 usually with thick film technology. Corresponding structures are generally known, for example, from the art of inkjet printers with thermal print heads in which the ink is ejected by means of pulse-like heating. In the area of thin-film technology, heating elements made of platinum, polycrystalline silicon, metal-silicon-nitride composites or metal-silicon-oxy-nitride composites have proven their worth. Titanium, tantalum, chromium, molybdenum or tungsten are used as metals in the case of the composites mentioned. In the field of thick film technology, there are numerous resistance pastes available on the market that are suitable for building heating elements.

Heating elements 43 and electrical lines 44 - or the entire structure described - are covered by a thin passivation layer, not shown, which protects the elements mentioned against chemical or electrical influences from the environment, so that the entire structure, for example, directly in the water or can be used in the air under the direct influence of rain and snow. Suitable such layers are, for example, thin film layers such as Silicon oxide or silicon (oxide) nitride. However, it is also possible to use a PTFE-like thin layer produced by means of plasma polymerisation.

The operation of this simple convection cooler is obvious. By heating the heating elements 43, ambient medium rises above them. As a result, ambient medium has to flow in from below through the convection holes 42 - and in the case of FIG. 4a also from the side - which results in a cooling flow below the cooler.

The efficiency of the convection cooler sketched in FIG. 4a can be increased even further by additional measures, this becomes clear in the explanations below. A corresponding improvement is shown in Figure 4b. A thick auxiliary layer 45 is arranged here above the carrier plate 41 with the convection holes 42, the heating elements 43 and the electrical connections 44, said auxiliary layer 45 having auxiliary layer convection holes 46 above the holes 42. These auxiliary layer convection holes 46 have at least on the side with which they touch the convection cooler support plate 41 a diameter which corresponds to the outer diameter of the heating elements 43. The diameter of the auxiliary layer convection holes 46 can at most decrease 46c or enlarge 46b. This auxiliary layer can consist, for example, of a plastic plate which is injection-molded or stamped and stamped with the corresponding heat extraction holes and which is subsequently connected to the convection cooler support plate 41 with the convection holes 42, the heating elements 43 and the electrical connections 44, for example by gluing. But it can also consist of one of the insulation materials mentioned below. Or it can be sprayed from a photo-structurable plastic such as polyimide or SU8 over the entire surface onto the convection cooler carrier plate 41 with the convection holes 42, the heating elements 43 and the electrical connections 44 or was laminated or doctored and then provided with the appropriate convection holes 46 by means of deep photolithography.

The improvement achieved by this auxiliary layer 45 is obviously that in such an arrangement no ambient medium can flow in from the side to the heating elements 43 and so the entire surrounding medium flowing away by natural convection is sucked in from below through the convection holes 46, 42 got to.

Another optional improvement is outlined in FIG. 4b. The efficiency of the convection cooler becomes higher the less the heat generated by the heating elements 43 reaches the underside of the cooler. For this reason, a heat insulation plate 47 with corresponding convection holes 48 is located below the convection cooler support plate 41.

The material of this heat insulation plate 47 is of course selected so that it has the lowest possible thermal conductivity λ. Glass (λ approx. 1 [W / m K]) or a plastic such as e.g. PVC (λ approx. 0.15). However, a special heat insulation material is preferably selected, such as, for example, pressed and, if necessary, sintered, precipitated silica (λ approx. 0.018) or PU foam (λ approx. 0.025). In extreme cases, the heat insulation plate 47 can of course also be constructed as a vacuum insulation panel, with which the thermal conductivity coefficient λ can be reduced down to approximately 0.001 [W / m ° K].

Of course, it is also possible to construct the convection cooler support plate 41 directly from, for example, one of the insulation materials mentioned. FIG. 4c shows a further possibility for improvement of the convection cooler: The structure explained in FIG. 4b can, in theory as often as desired, be repeated in the sense of a sandwich structure. In this sense, an insulation layer 47, a carrier plate 41 with the convection holes, the heating elements and the electrical connections, an insulation layer 47, another convection cooler carrier plate 41 with the convection holes, the heating elements and the electrical connections follow from bottom to top. This can be repeated as often as desired; a sandwich with convection cooler carrier plates 41 containing up to 5 heating elements is sensible. Finally, an auxiliary layer 45 follows as the upper end of the sandwich.

In order for such a sandwich-like structure to achieve the best possible efficiency, the heating elements present on the convection cooler carrier plates 41 have to be operated at ever higher temperatures, viewed from the bottom up. This ensures that the hot ambient medium, which is already rising due to natural convection, receives additional lift from layer to layer, which increases the flow.

FIG. 5 shows an overall structure of an LED light panel that is optimized with regard to heat dissipation. This structure consists of the actual LED light panel 51, which has corresponding heat exhaust holes 52 and cooling fin structures. In direct connection with the cooling fins 53, a convection cooler 54 with the convection holes 55 is attached in this example, in accordance with FIG. Of course, a multi-layer convection cooler could also be selected. The arrangement of the heat extraction holes 52, the arrangement and alignment of the cooling fin structures 52 and the arrangement of the convection holes 55 is selected such that everything surrounding medium flowing in from the bottom through the heat extraction holes 52 or from the sides past the cooling fin structures 53 through the Convection holes 55 is drawn up. In this arrangement, the convection cooler also serves as a cover, which ensures that the ambient medium has to flow past the cooling fins.

The structure of FIG. 5 represents in itself one possibility of how, for example, a street lamp with LED as a light source can look. The actual LED light panel 51 described permits a very dense arrangement of LED chips (for example approximately 20 chips / cm ² ) and therefore permits the generation of very high light densities. The described optimal heat dissipation ensures that the maximum permissible temperature for a long service life is not exceeded. The fact that both the actual light panel 51 and the convection cooler 54 are constructed in such a way that they can be exposed to the direct influence of wind and weather ultimately allows the entire structure to be placed in suitable locations, for example at the upper end of one, without additional housing Mast or attached to appropriate mounting cables.

Claims

1. Light-emitting panel with a carrier element (1, 31, 51) and a plurality of luminous elements (2, 32) that can be operated by electricity and are applied to the carrier plate (1), characterized in that it is designed in such a way that a convection flow can be generated, which is supported by the geometrical structure of the panel and that means are available to steer it in such a way that a cooling effect occurs.

2. Light-emitting panel according to claim 1, characterized in that the luminous bodies (2, 32) are unhoused LEDs which are attached to the carrier plate (1).

3. Light-emitting panel according to claim 1 or 2, characterized in that the production of heat loss by the component triggers a convection flow of the surrounding medium.

4. Light-emitting panel according to one of the preceding claims, characterized in that the carrier element is designed in the form of a film or plate and has at least one heat extraction hole (4, 34, 52) formed as an opening in the carrier element.

5. Light-emitting panel according to one of the preceding claims, characterized in that at least one surface of the carrier element or with a surface of the carrier element by thermal contact connected element has a roughened and / or matt-dark surface.

Light-emitting panel according to one of the preceding claims, wherein the luminous elements are attached to a front side of the carrier element, characterized by cooling fins (25a-25k, 35a-35f, 53), which are attached to a rear side and are flow-optimized according to natural convention, in such a way that heating of the Carrier element (21, 31, 51) generates convection along the cooling fins at those points at which the luminous elements (22, 32) are applied.

7. Light-emitting panel according to claim 6, characterized in that the cooling fins (25a-25k, 35a-35f, 53) are arranged so that the distance between adjacent cooling fins is at least partially reduced to where the luminous elements are attached.

8. Light-emitting panel according to claim 6 or 7, characterized by a partial or complete coverage (25g, 35g, 54) of the cooling fins

Guiding the flow of the surrounding medium.

9. Light-emitting panel according to claim 4 and one of claims 6 to 8, characterized in that the position and orientation of the heat exhaust holes (34, 52) and the cooling fins (35a-35f, 53) are matched to one another, such that through the heat exhaust hole nachströmendes

Ambient medium must flow at least partially by convection along the cooling fins.

10. Light-emitting panel according to one of claims 1 to 9, characterized by a from the carrier element (1) thermally insulated heating element (43) which is attached so that when the heating element (43) is heated

Convection flow is generated so that it has a cooling effect on the carrier element (1) and / or the luminous element.

11. Light-emitting panel according to claim 10, characterized by a heat insulation layer (47) with at least one heat insulation layer through hole (48), the heating element on a side facing away from the carrier element (1) of the heat insulation layer (47) and on the heat insulation layer through hole (48) or is attached adjacent to this.

12. Light-emitting panel according to claim 10 or 11, characterized by a

Auxiliary layer (45) with an auxiliary layer through hole (46a, 46b, 46c), the heating element (43) being attached to a side of the auxiliary layer (45) facing the carrier element (1) and to the auxiliary layer through hole or adjacent thereto.

13. Light-emitting panel according to one of claims 3 to 5 and one of claims 6 to 9 and one of claims 10 to 12, characterized in that the position and orientation of the heat exhaust hole (s) (52), the cooling fins (53) and the Heating element / the heating elements are matched to each other so that all surrounding medium flowing through the heat exhaust holes must flow past the cooling fins.

4. Light-emitting panel according to one of claims 1 to 13, characterized in that the control and energy supply unit has a "Powerline" communication module for communication with a superordinate control system, which communication module is designed such that communication signals can be transmitted via a power supply line of the light-emitting panel are.