WO2011058387A1

WO2011058387A1 - Led based public lighting lamp

Info

Publication number: WO2011058387A1
Application number: PCT/HU2010/000122
Authority: WO
Inventors: László DOMJÁN; Gábor SZARVAS; Attila SÁGHY; Szablocs Kautny; András MOLNÁR; Iván HOFFMAN; Péter HOFFMAN
Original assignee: Eka Elektromos Keszuelekek Es Anyagok Gyara Kft; OPTIMAL OPTIK KFT
Current assignee: Eka Elektromos Keszuelekek Es Anyagok Gyara Kft; OPTIMAL OPTIK KFT
Priority date: 2009-11-11
Filing date: 2010-11-11
Publication date: 2011-05-19
Anticipated expiration: 2012-05-11
Also published as: HUP0900709A2

Abstract

The invention is a LED based public lighting lamp, which comprises a heat absorbing support unit (10) and the LEDs (13) fixed thereto. The support unit (10) comprises side surfaces of a planar shape arranged along a surface of a truncated pyramid having a polygon base, facing down in an inclined way. The lamp further comprises LED units (12) arranged along the side surfaces, said LED units (12) comprise a carrier element having a flat bottom surface and at least one LED fixed thereon, as well as an upper mirror (20) limiting the light distribution of the lamp from above.

Description

LED BASED PUBLIC LIGHTING LAMP

TECHNICAL FIELD

The present invention relates to a LED based public lighting lamp. The invention especially relates to the internal structure and optical layout of a public (e.g. park-, promenade-lighting or street) luminaire which is realized with LEDs, simply built up and efficient.

BACKGROUND ART

In park and promenade lighting applications, a predetermined, average illumination level is to be provided in a specified area, while ensuring the appropriate homogeneity of illumination. For such applications, it is mostly needed to create light, distribution of circular symmetry, contrary to the common street lighting tasks, where usually the creation of asymmetric light distribution is justified.

Modern street lighting luminaires are energy-efficient and have long lifetime. Homogeneous lighting is possible by configuring a light density distribution generally called 'bat wing' configuration, which means that the light source emits light more intensively to the side than forward, i.e. the larger the angle measured from the vertical, the higher is the light intensity. Additionally, for the sake of avoiding light pollution, the luminaires may not emit light at all above 90° measured from the vertical, and even above 80° they may only do so to a heavily limited extent.

In park and promenade lighting applications, mostly the creation of a bat wing distribution of circular symmetry seems to be suitable for illumination tasks. A further important aspect is the color of the light source, because if this largely deviates from the ideal one, then the colors of the objects will not be seen truly, which could be confusing in certain traffic and public safety situations. All of the above strict set of requirements are not possibly or just cumbersomely to be satisfied with most of the luminaires comprising traditional light sources - like sodium lamp, mercury vapor lamp, metal halogen bulb and compact fluorescent lamp. A plausible solution is the application of LEDs by which the requirements can be met easily.

The luminous flux of currently available LEDs (Light Emitting Diodes) is substantially lower than the luminous flux of high power lamps. Therefore, it is necessary to build several high power LEDs into a luminaire to reach the light power of modern high power public lighting lamps. Due to cooling problems, the LEDs have to be placed at appropriate distance relative to each other, because the heat generated in the LEDs can only be dissipated by thermal conduction. For this purpose, fixing elements and heat sinks of appropriate thickness and good thermal conductance have to be configured. In the case of conventional lamps, most of the thermal loss escapes in the form of infrared radiation through the window or cap. The LEDs practically do not radiate in the infrared range, and therefore the thermal loss which is identical in order of magnitude with the thermal loss generated in more widely used modern lamps, have to be conducted from the LED chip to the surface of the luminaire, whence it escapes to the environment by heat transfer, heat conduction, or heat radiation.

Street luminaires with LEDs are disclosed in US 2009/0237930 A1 and US 2009/0034257 A1. These Prior art solutions comprise luminaires realized with large number of LEDs.

In US 6 250 774 B1 a luminaire is disclosed which comprises LEDs directed into several directions and an optics mounted thereon. The light distribution appropriate for tackling a street lighting task is altered by directing the LEDs and the collimation angles of the optics.

Prior art approaches do not care about the light distribution and its homogeneity or the range of issues related to light pollution. There is no such luminaire among the prior art solutions that provides low light pollution while catering for appropriate light intensity and homogeneity. In addition, LEDs with lenses are used in the prior art as a light source, which have an efficiency of approx. 85 % only of the LEDs' without a lens - the losses arise because of the Fresnel reflection on lens surfaces. It is a further disadvantage of prior art solutions that the support unit holding the LEDs and serving also for thermal conduction purposes do not offer identical and uniform heat conduction for all LEDs. According to the approach described in US 2009/0034257 A1 for example, the LEDs located at the edges and corners of the LED arrangement get a different type of cooling than the LEDs being inside of the arrangement, and hence the unbalanced loading of the LEDs results in a position dependent, more intensive wear-out of the light sources and therefore in a distortion of long-term light distribution.

DESCRIPTION OF THE INVENTION

It is an object of the invention to create a public lighting lamp containing such a LED light source, which is exempt from the disadvantages of prior art solutions and serves a solution for the problems mentioned. A further object is to create a lamp which can be configured with a simple structure and a low cost, which realizes the expected bat wing light distribution of circular symmetry efficiently and without light pollution, while enabling efficient and uniform cooling.

The objects according to the invention are achieved by a LED-based public lighting lamp according to claim 1. Preferred embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary preferred embodiments of the invention will be described hereunder with reference to drawings, where

Fig. 1 is a diagram depicting the light distribution of a conventional luminaire,

Fig. 2 is a schematic side view of an exemplary polygon base truncated pyramid shaped support unit,

Fig. 3 is a schematic top view of the support unit shown in Fig. 2,

Fig. 4 is a schematic view of a lamp used for street lighting purposes, showing the limit angles of the angle ranges causing light pollution,

Fig. 5 is a schematic side view of the inner part of a preferred public lighting lamp according to the invention containing an upper mirror only,

Fig. 6 is a three-dimensional drawing of a possible implementation of the schematic arrangement according to Fig. 5, Fig. 7 is a schematic side view of the inner part of a preferred public lighting lamp according to the invention containing lower and upper mirrors,

Fig. 8 is a three-dimensional drawing of a possible realization of the schematic arrangement according to Fig. 7,

Fig. 9 is a schematic view of a lower mirror made with cut-outs,

Fig. 10 is a three-dimensional drawing of a conic lower mirror made with cut-outs at the edges,

Fig. 11 is a three-dimensional drawing of the inner part of a lamp containing a lower mirror according to Fig. 10,

Fig. 12 is a schematic drawing of the inner part of a preferred lamp according to the invention and also comprising horizontally arranged LEDs,

Fig. 13 is a three-dimensional view of a possible realization of the schematic arrangement according to Fig. 12,

Figs. 14A to 14D are schematic side views of preferred embodiments comprising deflecting mirrors located in several rows,

Fig. 15 is a schematic view of a preferred luminaire arrangement according to the invention, which also comprises cover elements of the lamp,

Fig. 16 is a sectional view of a further preferred embodiment having a truncated cone shaped support unit, and

Fig. 17 is a three-dimensional view of the embodiment according to Fig. 16. MODES OF IMPLEMENTATION OF THE INVENTION

In Fig. 1 an exemplary predetermined light distribution, the diagram of the so- called bat wing distribution is shown in the case of a conventional luminaire. It can be clearly seen that the conventional lamp radiates also above 80° and 90° , causing light pollution and other disturbing effects.

We have recognized according to the invention that mirror type reflective systems fixed on the luminaire can be used with a better efficiency than the currently used lens type refractive optics, as their reflection losses are much lower than the Fresnel losses of refractive optics. Accordingly, the deflecting of light beams is carried out by means of a mirror system.

It was also recognized that in order to establish the desired circularly symmetric distribution, e.g. the circularly symmetric bat wing distribution, most of the LEDs are preferably to be fixed in one or more rows to a polygon base truncated pyramid or truncated cone shaped block or support unit, and in order to minimise the size of the luminaire, mirrors have to be located as close as possible to the LEDs. The material of the support block is preferably a good heat-conveying metal, thus it is also able to ensure heat conducting. Preferably, the direction of LEDs is roughly identical with that of the direction of the maximum of the circularly symmetric distribution to be realized, and this can be adjusted by the inclination angle of the lateral sides of the truncated pyramid or by that of the lateral surface of the truncated cone. It was also recognized that by means of a mirror or mirrors located above the row of LEDs or the rows of LEDs, the light otherwise causing light pollution and including a large angle with the vertical can be directed to the target area, thereby the light intensity can be increased, and by appropriately choosing the angle of the mirror or mirrors, the homogeneity of illumination can be increased. By means of lower mirrors located below the LED row, some of the light illuminated downwards vertically or deviating from this direction by a small angle can be directed to underexposed areas, hence the homogeneity can be improved by reducing the maximum illumination below the luminaire or in an optimal case by increasing the illumination of the underexposed areas.

The surfaces of the mirrors according to the invention may be simple or complex (multi-component) conic surfaces, but other spherical, aspherical or so-called free- form surfaces are also conceivable. In a given case it is advisable to eliminate the continuity of the lower mirror, hence the illumination of the areas below the lamp is not reduced significantly. By appropriately selecting the shape, size and location of the break-through points, cut-outs or openings that eliminate material continuity, the homogeneity of the light distribution to the illuminated surface can be improved. It has been recognized that eliminating the continuity of the lower mirror can be substituted or the effect improved by means of LEDs located horizontally on the bottom of the heat sink. The LEDs lighting vertically downwards ensure the appropriate illumination of the area below the lamp, thereby increasing homogeneity. It is preferred to determine the accurate angle, shape and location of the mirrors as known from prior art, by means of computer optimization. Figs. 2 and 3 show side and top views of a support unit 10 configured as a heat sink, which has a fixing and heat conducting function, and has a polygon base truncated pyramid shape and is of a metal of good heat conduction. The preferably disc-shaped block of the support unit 10 can also be of a hollow or profiled design; according to the invention the term 'block' covers all structures/forms in which the support unit 10 comprises an appropriate volume of material required for supporting and heat conducting. The practically circularly symmetric support unit 10 according to the invention ensures that the LEDs of the lamp get uniform and balanced cooling. To this end, the block is preferably of a truncated pyramid shape having a regular polygon base.

On the side surfaces 11 representing the outer surface of the polygon base truncated pyramid surface of the block, LED units 12 are arranged, which LED units 12 consist of a carrier element 14 having a flat bottom surface and of at least one LED 13 fixed thereon. The LED units 12 are preferably fixed by a screw joint, and the carrier elements 14 of the LED units 12 are preferably configured as a printed circuit board with an aluminium carrier. Preferably, a heat conducting lubricant, e.g. a heat conductive grease is applied between the bottom surfaces of the carrier elements 14 and the side surfaces 11 of the block.

The side view of Fig. 2 also shows fixing points of the LED units 12 in addition to the demonstration of the heat conducting function. The dotted arrows in support unit 10 in the figure show the direction of heat conduction. It is advisable to choose the tilting angle of the planar heat sink side surfaces 11 looking downwards in an inclined way so that the LEDs 13 light approximately to the direction of the maximum of the circularly symmetric distribution intended to be achieved. The normal of the side surfaces 11 preferably includes an angle of between 40° and 70° with the vertical, depending on the geometry defined by the area to be illuminated and by the street lighting pole. The LED units 12 are arranged on the side surfaces 11 preferably in a uniform distribution, so that they create a circularly symmetric light distribution.

Fig. 4 is a schematic view of a lamp according to the invention and used for street lighting purposes, showing the limit angles of the angle ranges that cause light pollution. To avoid light pollution and to improve light distribution/homogeneity, the lamp according to the invention also comprises an upper mirror 20 that limits from above the light distribution of the lamp as shown in Fig. 5 (for simplicity, the upper mirror 20 is not shown in the Figs. 2 to 4).

A possible embodiment of the inner part of the lamp according to the invention and only comprising an upper mirror or upper mirrors is shown in Fig. 5. This preferred embodiment comprises LED units 12 located in several rows and fixed to the polygon base truncated pyramid shape heat sink, as well as conic, spherical, aspherical or free-form upper mirror or mirrors 20. The lighting direction of the LEDs 12 is such that approximately they emit most of the light in the direction of the maximum of ideal circularly symmetric bat wing light distribution. Certain beams reach the target area without reflection. The beams directed to the sky and problematic from the aspect of light pollution are deflected to the target area after changing direction at the upper mirror 20, and thereby this mirror not only reduces light pollution, but also improves the illumination and homogeneity of the illuminated area.

Fig. 6 shows a three-dimensional view of a possible embodiment of the arrangement comprising the upper mirror 20 only. The upper mirror 20, which is conic in this case, is located very close to the row consisting of the LED units 12 fixed to the polygon base truncated pyramid shaped heat sink, i.e. to the support unit 10 in the appropriate direction to minimize the size of the lamp and the losses.

Another possible embodiment of the inner part of the lamp according to the invention, with a modified upper mirror 20 and downwards light distribution, also comprising a lower circular mirror 21 located below the LEDs 13 on the side surfaces 11 is shown in Fig. 7. These mirrors can also be conic, spherical, aspheric or free-form circular ring shaped. Also in this case the direction of the LEDs 13 in the LED units 12 is such that they emit most of the light in the direction of the maximum of an ideal bat wing light distribution. The beams starting towards the sky and responsible for light pollution are directed to the target area after changing direction on the upper mirror 20, and thereby this mirror does not only reduce light pollution, but also improves the illumination and homogeneity of the illuminated area. On the lower mirror 21, the light beams directed below the lamp change their directions and are reflected to larger angle directions. Thereby the illumination of the area below the lamp is reduced, but the lighting of certain underexposed areas can be increased, and therefore the homogeneity of illuminating the target area can be improved.

Fig. 8 is a three-dimensional view of a possible embodiment of the arrangement which comprises the upper mirror 20 and the lower mirror 21. The lower mirror 21 , which is conic in this case, and the upper mirror 20 are located very close to the row of the LED units 12 fixed to the polygon base truncated pyramid shaped heat sink, i.e. to the support unit 10 to light to the appropriate direction and to minimize the size of the lamp and the losses.

In a given case, it is advisable to apply a lower mirror 21' according to Fig. 9, which comprises cut-outs 22 of the appropriate shape and size at certain places, i.e. the width dimension of the lower mirror 21' varies along the periphery. The role of the cut-outs 22 is to make the mirror to pass the light through at certain places. By increasing the size of the lower mirror 21 , the illumination of underexposed areas can be increased, but the illumination of the areas below the luminaire is reduced. If the surface of the mirror is not continuous, i.e. it comprises breakthrough points at certain places, the illumination of the areas below the luminaire can also be ensured. By means of a mirror of such configuration, higher homogeneity can be provided in the circularly symmetric lighting of the target area.

Fig. 10 is a three-dimensional view of another exemplary lower mirror 21'. This mirror has cut-outs and break-through points 22 at its edges in appropriate shapes and sizes. By means of a mirror of such a configuration, higher homogeneity can be ensured in the circularly symmetric illumination of the target area.

In Fig. 11 a three-dimensional view of a system comprising a lower mirror 21' according to Fig. 10 is shown. It is clearly shown in the figure that the not continuous lower mirror 21' reflects the light of certain LEDs 13, thereby increasing the illumination of underexposed areas, but it passes through the light of certain LEDs 13, and thereby the illumination of the areas below the luminaire is not totally reduced either. The shape of cut-outs and break-through points 22 of the mirror can be chosen according to the given application. By changing the size of the cut-outs 22, the ratio of lights passed through as well as reflected to the underexposed areas can be altered. By choosing the positions and sizes of breakthrough points, the homogeneity of the circularly symmetric illumination of the target area can be increased. The operating principle is also shown in the figure in the case of two LEDs 13: it can be clearly seen that the light of some LEDs 13 is reflected by the non-continuous lower mirror, while the light of other LEDs 13, in the region of which the mirror comprises a break-through, is passed through.

In the case of the exemplary preferred construction shown in Fig. 12, the lamp comprises LED units 12 facing downwards horizontally on the bottom surface of the support unit 10. In order to limit the light beams proceeding at an angle larger than 80°, the LED units 12 facing downwards are sunk into the heat sink. The horizontally located LEDs lighting downwards provide larger homogeneity by illuminating the area below the luminaire. In this case the lower mirror 21 does not limit the illumination of the areas below the luminaire, hence the homogeneity. The horizontally located LED units 12 are preferably sunk into the support unit 10, i.e. into the heat sink, in order to limit the light pollution causing large angle beams.

Fig. 13 is a three-dimensional view of the inner part of an exemplary luminaire having a construction according to Fig. 12.

Figs. 14A-D show examples of locating of conic, spherical, aspherical or free-form mirrors in the constructions comprising LED units 12 in several rows. In Fig. 14A, the conic, spheric, aspheric or free-form mirrors are located above all of the rows arranged one below the other and consisting of the LED units 12; consequently the embodiment comprises an upper mirror 20 and an intermediate mirror 24 arranged circularly between the rows. In Fig. 14B, the conic, spherical, aspheric or free-form mirrors are located above the upper row and below the lower LED row, and an intermediate mirror 24 of conic, spherical, aspheric or free-form type is also located between the two LED rows. In Fig. 14C, the mirrors are arranged above the upper row or below the lower row. In Fig. 14D, below and above both LED rows, appropriate conic, spherical, aspheric or free-form mirrors are arranged.

Fig. 15 is an exploded three-dimensional view of an exemplary LED lamp comprising cover elements as well. For the sake of protecting against the impact of the environment, it is required to provide a kind of cover in all cases on the inner part of the luminaire, preferably a cover providing IP66 protection has to isolate the luminaire from the environment. The lamp is provided with a lamp cap 30, and the luminaire is surrounded by a cap 31 made of translucent plastic or hardened glass. A lower cap seal 32 is adjoined to this cap 31, which provides protection from the impacts of the environment together with the lamp cap 30.

In another preferred embodiment shown in Figs 16 and 17, the LED units 12 are not fixed directly to the heat sink, but to flat support plates 35, located along the lateral surfaces of a truncated pyramid. The truncated pyramid surface can be provided by a heat sink constructed with such a shape, but it may also be an imaginary surface. The support plates 35 are secured to the heat sink by a good heat-conveying metal joint, for example by a screw joint comprising screws 33. In the depicted preferred embodiment the block has a truncated cone shape. In the block, around each bore of the screws 33 fixing the LED units 12, a planar circular surface is etched. The circular surfaces etched around each two bores located on the same surface are parallel with each other. A flat bottom plate 34 made of a good heat conducting material is placed on each dented planar circular surface, the external surface of which protrudes from the surface of the block. Hence, the upper plane of each two bottom plates 34 creates a common planar base, which is matching to the lateral surface of a theoretic truncated cone. Support plates 35 holding the LED units 12 can be fixed to this planar base, which is also made of a good heat-conveying material. The flat support plates 35 holding the LED units 12 are located along an external surface of a theoretic polygon based truncated pyramid, and represent the lateral surfaces 11 with their external surfaces.

For the sake of low cost production, the heat sink is an aluminium casting. Theoretically, the LED units 12 could be fixed directly to the side faces of the truncated pyramid shaped block. However, the surface of the castings is not sufficiently planar without machining; hence the LED units do not abut to the 'flat' faces of the raw casting. Therefore, a casting of truncated pyramid shape is preferably machined, or the planar circular surfaces are to be dented according to the embodiment shown in Figs. 16 and 17. The latter process is more simple and cheaper, because in a single step together with constructing the bores for screws 33, the planar circular surfaces can be constructed by a bolt drill. As shown also in the embodiments presented above, the invention may also have the following advantageous characteristics:

- The LEDs are arranged in the lamp in one or more rows, practically in a circularly symmetric fashion.

- Most of the LEDs located in a circularly symmetric fashion in one or more rows light in the direction of the maximum of bat wing distribution or in a slightly different direction.

- The lamp may comprise horizontally located LEDs to illuminate the area below the luminaire to increase homogeneity.

- The light of LEDs located in one or more rows in a circularly symmetric way is directed by conic, spherical, aspheric or free-form mirror/mirrors to the target area. In addition to directing the light to the target area and increasing homogeneity, the upper conic, spherical, aspheric or free-form mirror/mirrors play(s) a role in preventing light pollution. The role of lower conic, spherical, aspheric or free-form mirror/mirrors is to increase the homogeneity further. Preferred mirrors may have a flange-like shape, but other shapes are also conceivable.

- The lower conic, spherical, aspheric or free-form mirror/mirrors may have cutouts and break-throughs at certain places to increase homogeneity. The shape and size of break-throughs in the mirrors can be selected for the given application.

The invention, of course, is not limited to the above detailed preferred embodiments, but further variations, modifications and developments are possible within the scope defined by the claims. The street lighting module may comprise additional elements and mirrors, and the predetermined light distribution may not only be a circularly symmetric bat wing distribution, but also any required, specified light distribution. The side surfaces arranged along the external surface of the polygon base truncated pyramid may not only be carried by a support unit designed as a truncated pyramid or truncated cone block, but any other suitable support unit providing appropriate thermal conduction may also be constructed.

Claims

1. A LED based public lighting lamp, comprising a heat conducting support unit (10) and LEDs (13) fixed thereon, c h a r a c t e r i z e d in that the support unit (10) comprises planar side surfaces (11) being arranged along lateral faces of a truncated pyramid shape having a polygon base, the side surfaces (11) facing down in an inclined way, and the lamp comprises

- LED units (12) arranged along the side surfaces (11), said LED units (12) comprising a carrier element (14) having a flat bottom surface and at least one LED (13) fixed thereon, and

- an upper mirror (20) limiting light distribution of the lamp from above.

2. The lamp according to claim 1 , characterized in that the side surfaces ( 1) face to a direction of a desired maximum range of light distribution.

3. The lamp according to claim 2, characterized in that the normal of the side surfaces (11) includes an angle of between 40° and 70° with a vertical direction, and on the side surfaces (11) the LED units (12) are arranged in a uniform distribution for creating a circularly symmetric light distribution.

4. The lamp according to any of claims 1 to 3, characterized by also comprising a circular lower mirror (21) arranged below the LEDs (13) on the side surfaces (11), the lower mirror (21) modifying the distribution of the light radiated downwards.

5. The lamp according to claim 4, characterized in that a dimension of the lower mirror (21') changes along the periphery, preferably there are equally spaced cutouts (22) on the lower mirror (21').

6. The lamp according to any of claims 1 to 3, characterized in that the LEDs (13) on the side surfaces (11) are arranged in several rows one below the other, and that the lamp comprises one or more intermediate mirrors (24) arranged circularly between the rows.

7. The lamp according to any of claims 1 to 6, characterized in that on the bottom surface of the support unit - preferably in a sunk manner for directing the light - one or more further LED units (12) are arranged.

8. The lamp according to any of claims 1 to 7, characterized in that the support unit (10) is formed as a block having a truncated pyramid shape with a regular polygon base, and the side surfaces (11) are formed by the lateral surfaces of the block.

9. The lamp according to any of claims 1 to 7, characterized in that the support unit (10) is formed as a truncated cone shaped block, and the side surfaces (11) are formed by external surfaces of support plates (35) fixed to the lateral surface of the block.

10. The lamp according to claim 8 or 9, characterized in that the block is made of metal, the LED units (12) are fixed thereto by screw joints, the carrier elements (14) of the LED units (12) are formed as aluminium carrier type printed circuit boards, and a thermal conductive lubricant is applied between the lower surfaces of the carrier elements (14) and the side surfaces (11).