WO2010010494A1

WO2010010494A1 - Luminaire device with several lighting units

Info

Publication number: WO2010010494A1
Application number: PCT/IB2009/053096
Authority: WO
Inventors: Sébastien MOURLHOU
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-07-24
Filing date: 2009-07-16
Publication date: 2010-01-28
Also published as: TW201018828A

Abstract

A luminaire device comprises at least two lighting units, and a first optical element (22) for moving an area illuminated by one of said lighting units (2). The first optical element deflects light rays emitted by the corresponding lighting unit according to an asymmetric distribution about an axis (X-X) of the lighting unit. Said illuminated area may be moved parallel or perpendicular to a reference direction, with variable moving distance, by changing the first optical element only. A second optical element (23) may also be added, for widening the illuminated area parallel to the reference direction. The first optical element (22) may be a prism array and the second optical element (23) may be an array of cylindrical lenses.

Description

LUMINAIRE DEVICE WITH SEVERAL LIGHTING UNITS

BACKGROUND OF THE INVENTION

The invention relates to a luminaire device with several lighting units.

When designing a luminaire device, it is necessary to know features of the area to illuminate, such as size and shape of this area. Indeed, these features of the illuminated area may vary in a great extent depending on the use intended for the luminaire device.

One particular case is that of luminaire devices intended for outdoor lighting, such as street lighting. Indeed, a street portion is preferably lit according to an illuminated strip which is oriented parallel to the street portion. Then, the following issues are to be addressed:

- the position of the illuminated strip between both side borders of the street, so that the light is distributed appropriately across the street. In particular, when the luminaire device is located near one of the side borders, the light is preferably directed obliquely towards a center longitudinal line of the street, with an angle in a vertical plane across the street which depends on the width of the street;

- the length of the illuminated strip, parallel to the street, should be adapted to the separating distance between successive luminaire devices installed along the street. Thus, a dim gap between successive strips illuminated by two neighbouring luminaire devices may be avoided; and

- the illuminated strip should be adapted in shape and orientation differently depending on the layout of the street, i.e. differently for a straight street and for a curved street for example. Although these issues have been recited in the case of a luminaire device suitable for outdoor lighting, one will consider that they are to be taken into consideration for designing any luminaire device, whatever its application indoors or outdoors. Then, for one and same type of luminaire devices, several designs are to be proposed so that one of these designs can be selected, which produces an illuminated area adapted to the special features of the application intended.

But such plurality of designs leads to a unit cost which is increased for each luminaire device.

Another possibility is to design a luminaire device that includes adjustable light-directing means. Thus, the user can orientate appropriately the light produced. But such adjustable light-directing means are not suitable for several applications. In particular, they are not suitable for street lighting, because street lighting devices are usually installed high above the ground, and are exposed to soiling.

Then, an object of the present invention is to provide a luminaire device which produces an illuminated area that can be easily adapted.

Another object of the invention is that such luminaire device has a unit cost which is not increased significantly with respect to a luminaire device with fixed illuminated area.

SUMMARY OF THE INVENTION

To this end, the invention proposes a luminaire device which is adapted for being installed at a selected height above a surface to illuminate, and which comprises:

- a first lighting unit arranged for illuminating a first area of the surface, and

- at least one second lighting unit oriented towards a second area of the surface. The first and second areas form together a first strip on the surface, and the luminaire device further comprises a first optical element which is arranged and located with respect to the second lighting unit for deflecting at least part of the light rays emitted by the second lighting unit. The first optical element causes the second area to move along a selected distance in a selected direction, and thus modifies accordingly the first strip in shape, orientation or location, for forming a second strip which is actually illuminated on the surface. In addition, the first optical element is adapted for deflecting light rays emitted by the second lighting unit with an asymmetric distribution about an optical axis of this second lighting unit. Thus, according to the invention, a part of the illuminated strip is moved by the optical element which is arranged with respect of the second lighting unit. Then, the luminaire device may be adapted according to the use intended only by selecting an appropriate optical element to be coupled with the second lighting unit. Such adaptation is easy to implement, and does not impact the installation time of the luminaire device.

Hence, a major part of the luminaire device can be mass-produced, and only the optical element intended for the second lighting unit is to be produced with variable designs. So, the unit cost of one luminaire device is not increased significantly, because the optical element contributes only in a small extent to the whole device cost.

Additionally, the optical element that is to be selected may be a simple optical component such as a prism or an array of adjacent prisms.

In particular, the first optical element may be designed and/or selected so as to move the second area lit by the second lighting unit in various manners, and change the illuminated strip accordingly. For example, when the first strip is oriented perpendicular to a reference direction, with first strip length and width respectively across and along said reference direction, then the direction selected for moving the second area may be parallel or perpendicular to this reference direction. Because of the asymmetric distribution of the light about the optical axis of the second lighting unit, as produced by the first optical element, this light distribution exhibits at least one maximum in a direction distinct from the second lighting unit optical axis. This maximum direction can then be set for moving the second illuminated area in accordance with the application and use conditions of the luminaire device. Therefore, the light produced by the second lighting unit may be used more efficiently, leading to improved lighting in the area of interest. The asymmetry of the light distribution produced by the first optical element also results in energy savings. Indeed, the light amount which is emitted out of the area of interest is reduced.

According to a preferred embodiment of the invention, the luminaire device may be adapted for being installed outdoors. Indeed, it may not include any mobile element, so that it is easily compatible with outdoor use conditions.

In particular, the luminaire device of the invention may be a street lighting device.

According to a first improvement of the invention, the luminaire device may further comprise a second optical element, which is adapted for widening the second area, and thus widening the second illuminated strip with respect to the first strip. Then, the first and second optical elements may be located respectively on first and second surfaces of one and same transparent substrate. Alternatively, they may be both provided on an outlet face of a collimator comprised in the second lighting unit.

According to a second improvement of the invention, the first and second lighting units may be similar to each other, and arranged and oriented symmetrically with respect to a reference plane perpendicular to the surface to illuminate. The luminaire device may then further comprise another optical element which is similar to the first optical element, and arranged with respect to the first lighting unit in a manner similar to that of the first optical element with respect to the second lighting unit. Thus, the first and second areas are both moved symmetrically on respective sides of the reference plane. In this way, the illuminated second strip may be varied easily on either side of the reference plane.

BRIEF DESCRIPTION OF THE FIGURES

These and other aspects of the invention will become apparent from the non-limiting embodiments described hereafter in reference to the following drawings: Figures 1a and 1 b show two implementations of a luminaire device according to the invention; Figure 1 c is an enlarged view of a part the luminaire device of Figure 1 a;

Figure 2a is a cross-sectional view corresponding to a first embodiment of the invention; Figure 2b is an enlarged view of an optical element used in the first embodiment of Figure 2a;

Figure 2c is a diagram of a light distribution obtained with the first embodiment of Figures 2a and 2b;

Figure 3a and 3b illustrate respectively two variants of a second embodiment of the invention; and

Figure 3c is a diagram of a light distribution obtained with the second embodiment of Figure 3a.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is now described in detail for the application of street lighting. This application is only used as an example, and implementing the invention for any other application provides advantages similar to those explained hereafter.

Referring to Figures 1 a and 1 c, reference number 100 generally denotes a luminaire device designed for outdoor setting up, and more particularly for street lighting. It comprises a mast 101 and a housing 102 which is affixed on the superior end of the mast. The housing 102 contains several lighting units. Two of these lighting units are labelled 1 and 2.

Figure 1 a also shows geometrical elements for the setting up of the luminaire device 100 in a street. B1 and B2 denote the two side borders of the street, and w denotes the width of the street. The luminaire device 100 may be located near one of the street side borders, for example B1. It is preferably oriented so that the housing 102 extends perpendicular to the side border B1 , towards a median vertical plane of the street. The surface to illuminate is the ground between the borders B1 and B2. PR denotes a reference plane which is vertical, perpendicular to the street borders B1 and B2, and which comprises a middle point of the housing 102. The plane PR is thus perpendicular to the surface to illuminate, h denotes the height of the lighting units above the ground of the street.

The lighting units 1 and 2 may be similar to each other, and arranged and oriented symmetrically with respect to the reference plane PR. They may each comprise a high-power LED (Light Emitting Diode), for example a 3 watt white LED, labelled 10, 20. The LEDs 10, 20 are provided with respective collimators 1 1 , 21 within the lighting units 1 , 2. Each collimator 1 1 , 21 produces an emerging collimated light beam from the light emitted by the corresponding LED 10, 20. Such arrangement can be seen on Figure 2a for the lighting unit 2. Actually, the collimator 21 used in the present embodiment of the invention consists of a transparent body with a peripheral side mirror 21 a which operates as a total internal reflection surface, and a core part 21 b which operates as a lens. Such collimator is well known and not further described here. Advantageously, each lighting unit is thermally coupled within the housing 102 with respective means that are adapted for dissipating heat produced by this lighting unit. Such heat dissipating means are also well known and are not represented on the Figures for clarity matter. They avoid that long time operation of the lighting units causes damage to the luminaire device. The lighting units 1 and 2 illuminate respective areas on the ground which are denoted A1 and A2. These illuminated areas form together an elongated strip on the ground, which has a shape, orientation and location varying with respective orientations of the lighting units 1 and 2, and depending on optical elements that are coupled with these latter units. The housing 102 may further comprise a third lighting unit 3, which is optional for the invention. The lighting unit 3 illuminates a third area on the ground (not shown), and thus participates to the second illuminated strip. Advantageously, the third area illuminated by the lighting unit 3 is located between the areas A1 and A2, for improving the distribution of the light intensity within the illuminated strip.

The housing 102 may comprise a front face F3 which faces the ground, and which is provided with an opening for the light emitted by the lighting unit 3 to pass through this opening. The housing 102 also comprises two lateral faces, labelled F1 and F2, which are each provided with a respective opening for the light emitted by the corresponding lighting unit to pass through this lateral opening. Although the description will focus now on the lighting units 1 and 2, the luminaire device 100 may additionally comprise at least one pair of additional lighting units, labelled 1 a and 2a. These additional lighting units may be located and oriented symmetrically with respect to the plane PR. In particular, the lighting units 1 a and 2a may be oriented in a similar manner to that of the lighting units 1 and 2, respectively.

Everyone will understand that the detailed arrangement of the luminaire device which has just been described is only supplied as an example for the purpose of illustrating the invention. However, other arrangements may be proposed, provided that they comprise the elements necessary for implementing the invention.

A transparent sheet 24, for example a glass sheet, which is designed for being arranged in the opening of the lateral face F2, comprises two optical elements 22 and 23. Actually in the embodiment of the invention currently described, the first and second optical elements, respectively 22 and 23, are the opposed faces of the transparent sheet 24, corresponding to the light- refracting interfaces of the constituting material of the sheet with air. Thus, the lighting unit 2 is provided with the optical element 22, which is suitable for deflecting the light rays originating from this unit. The optical element 22 may have various asymmetric structures, based on mirrors or prisms for example. According to Figures 2a and 2b, the optical element 22 is comprised in a. Thus, the light produced by the lighting unit 2 passes trough the optical element 22. The element 22 may be an asymmetric prism, or an array of asymmetric prisms juxtaposed close to one another, and forms one of the faces of the sheet 24. The following values may be used for the parameters indicated on Figure 2b:

Thickness of the sheet 24, denoted t: 3 mm

Length of each prism in the array, denoted I: 2,5 mm TiIt angle of each main prism face, denoted α: 8° (degree)

Draft angle of each prism, denoted β: 10°.

Such prism-based optical element 22 deflects the light rays emitted by the lighting unit 2 with an asymmetric distribution around an optical axis of the lighting unit 2. The deflection produced by the element 22 results from the orientation of the main faces 22a of the prisms. In Figure 2a, the optical axis of the lighting unit 2 is denoted X-X, and the light rays are deflected by the prisms represented towards the left part of the Figure.

For the application of street lighting, two issues may be considered for selecting the first optical element, i.e. the prism array 22.

A first one of these issues relates to adapting the illuminated strip on the ground to the width w of the street. Indeed, it may be desired to move the illuminated area A2 across the street, so as to shift it away from the street side border B1 when the width w is large. Figure 1a illustrates such effect, where the area A2 lit by the lighting unit 2 is shifted parallel to the reference direction D1 , defined as the intersection of the reference plane PR with the ground.

The initial area lit by the lighting unit 2 is indicated in broken line. The area A2 corresponds to this initial area translated parallel to the direction D1 due to the optical element 22. To this end, the main surfaces 22a of the prisms are to be tilted about a vertical axis, with the rotation edge 22b of each prism main face away from the median vertical plane of the street. The distance between the initial and final locations of the area A2 depends on the tilt angle α of the prism main faces 22a. The Man skilled in optics will know how to select the value of α for obtaining a desired distance between the initial and final locations of the area A2. S1 and S2 respectively denote the illuminated strip on the ground without and with the optical element 22.

Thus, the invention makes it possible to adapt the luminaire device 100 as a function of the street width w, only by changing the optical element sheet

24. Hence, except this optical element, one and same luminaire design can be used for streets with variable widths. Changing the optical element sheet 24 thus makes it possible to obtain a lighting efficiency optimized as a function of the street width w.

The second issue relates to the spacing distance between luminaire devices that are set up along the street on one and same street side border. The spacing distance may be selected based on various parameters, such as the power consumption of the lighting system in operation, the setting up cost, and the average light level desired in the street, etc. Once this spacing distance has been selected, it is an issue to obtain a light distribution parallel to the street direction which is as uniform as possible. The location of the illuminated area A2 with respect to the mast 101 may be adjusted parallel to the street direction so as to form a continuous junction with the strip of the next luminaire device. To this end, the optical element 22 should be selected so as to shift the illuminated area A2 parallel to the street direction, i.e. perpendicular to the direction D1 . Figure 1 b corresponds to Figure 1 a for this second issue. Compared to the configuration of Figure 1 a, the rotation edge 22b of each prism main face 22a is now substantially horizontal.

The optical element 23 may be adapted for increasing the length of the illuminated area A2 parallel to the street longitudinal direction. Thus, according to such improvement of the invention, the lighting unit 2 may be further provided with a second optical element adapted for widening the area A2 perpendicular to the direction D1 . Then, combining a shift of the area A2 produced by the optical element 22, with a widening of this area produced by the optical element 23, that are both oriented perpendicular to the direction D1 leads to recover a uniform distribution of the light intensity along the longitudinal direction of the street. Alternatively or in combination with this improvement, the second optical element 23 may be adapted for widening the illuminated area A2 along the reference direction D1 . Thus, the illuminated strip S2 is made larger on the ground, compared to the strip that would be obtained without this second optical element. Such effect along the direction D1 may be combined with any orientation of the shift of the area A2 produced by the optical element 22.

In the embodiment of the invention corresponding to the Figures 2a and 2b, the second optical element is a lens array 23 which is combined with the transparent sheet 24. Preferably, the lens array 23 is provided on the face of the sheet 24 other than that face which is provided with the prism array 22. Advantageously, each individual lens of the array 23 is associated with a respective one of the prisms, so that these lens and prism are effective on a same beam of light rays. For example, the prism array 22 may be provided on the face of the transparent sheet 24 which is facing outwards from the housing 102, and the lens array 23 may be provided on the face of the sheet 24 which is internal to the housing 102. Each lens of the array 23 is cylindrical, so that it is effective in modifying the focussing of the light rays parallel to one plane only. Figure 2a also shows the light beams as modified by the optical elements 22 and 23. First, the light beams are made convergent by the lenses. When the focussing distance is much shorter than the height h of the housing 102 above the ground, each light beam further increases in cross-section beyond the focussing distance. This results in an increased width of the area A2, parallel to the direction D1. For obtaining such increase in the width of the area A2 perpendicular to the street, the cylindrical lenses have their geometrical axis oriented vertically. In addition, light beams that are generated by adjacent lenses overlap, resulting in an improved uniformity of the light intensity at ground. For example, the following parameters may be used for the lens array 23 of Figures 2a and 2b:

Radius of the lens profile, denoted r: 4 mm

In-plane diameter of each lens in the array: 2,5 mm

Alternately, for obtaining an increase in the length of the area A2 parallel to the street, the cylindrical lenses may have their geometrical axis oriented horizontally. Furthermore, combined increases in both the width and length of the area A2 may be obtained by orienting obliquely the geometrical axis of the cylindrical lenses. Combined increases may also be obtained by using spherical lenses instead of the cylindrical lenses.

According to another improvement of the invention, another optical element similar to the optical element 22 may be arranged with respect to the lighting unit 1 , in a manner similar to the arrangement of the optical element 22 with respect to the lighting unit 2. In such case, this other optical element may have a design symmetric to that of the element 22, so that the illuminated areas A1 and A2 are both moved symmetrically on respective sides of the reference plane PR.

The diagram of Figure 2c displays an illuminance profile of the light impinging on the ground, which is obtained for two luminaire devices spaced apart from each other. Each luminaire device is provided with lighting units 1 to 3 as described above and with a sheet 24 which corresponds to Figures 2a and 2b. The height h is equal to 5 m (meter) and the street width w is equal to 3,5 m. The spacing distance between the two luminaire devices is equal to six times the height h, i.e. 30 m (6 x h). The horizontal axis refers to the distance in meters on the ground, along the center line of the street, with the origin just below the first luminaire device 100. The vertical axis indicates the light illuminance in Lux, in linear scale. The Man skilled in the art will assess that this distribution is quite spread and uniform. The broken line corresponds to the light intensity produced by one luminaire device only.

Figures 3a-3c relate to an alternative embodiment of the invention. In this other embodiment, each lighting unit 1 -3 still comprises a LED and a collimator, but the optical element 22 comprising the array of asymmetric prisms is provided on an outlet face of the collimator. Figure 3a is a perspective view of such collimator 21 , with the total internal reflection surface 21 a and the prism-shaped outlet face 22. According to a first variant of the present embodiment, the prism-shaped outlet face 22 is integral with the body of the collimator 21 . In such case, one must change the whole collimator 21 for obtaining a different shift of the second area A2. According to a second variant of the same embodiment, the collimator may be provided with a transparent disk on a side opposite to the LED. Such disk may be affixed to the collimator with appropriate means, for example gripping or clipping means. Thus, the disk forms the outlet face of the lighting unit. One face of the disk is provided with the prisms, so that changing the disk with another one with different prisms makes the illuminated area A2 move differently. The piece to be changed is even cheaper in this second variant, compared to the first variant. Obviously, this second embodiment also makes it possible to move the second area A2 parallel to the direction D1 (Figure 1 a) or perpendicular to this direction (Figure 1 b). By rotating the collimator with prism-shaped outlet face or the prism-shaped disk about the optical axis X-X of the collimator, one can obtain a shift of the area A2 which is oblique with respect to the street direction and the direction D1.

In a manner similar to that of the first embodiment of the invention, the second embodiment may also be combined with a second optical element adapted for widening the illuminated area A2 parallel to the direction D1. The second optical element may comprise again an array 23 of cylindrical lenses. Such lens array 23 may be incorporated in a transparent sheet separate from the collimator, and arranged in front of the outlet face of the collimator. The transparent sheet may form again the side face F2 of the housing 102.

Alternatively, the lens array 23 may be integrated in the outlet face of the collimator 21 , together with the prism array 22. Figure 3b corresponds to

Figure 3a for such combination. The outlet surface of the collimator 21 is then composite, and may be calculated by adding first sag values corresponding to the prism array 22 with second sag values corresponding to the lens array 23.

For such design of the collimator, the sag values are measured parallel to the optical axis X-X, with respect to a base plane perpendicular to this axis.

One advantage of providing the lens array 23 on the outlet face of the collimator 21 , or on an additional disk to be affixed onto the collimator, results from the focussing distance for the light rays emitted by the lighting unit 2. Indeed, the lighting unit 2 may be positioned within the housing 102 so that the light beams produced by the lighting unit 2 provided with the lens array 23 have their waist located at the lateral face F2 of the housing. Thus, the opening in the face F2 may be reduced, leading to increased possibilities for designing the housing 102.

The diagram of Figure 3c corresponds to that of Figure 2c, for the second embodiment. The spacing distance between the luminaire devices is now more than 40 m, i.e. superior to eight times the height h (8 x h). The distribution of the illuminance is quite uniform again. One will understand that numerous variations may be introduced in the embodiments of the invention which have been described before. In particular, the arrangements of the first optical element and the second optical element on the collimator or at the lateral openings of the housing may be mixed. Although prism and lens arrays have been described and represented in the Figures, one could also use a single asymmetric prism and a single cylindrical lens. Respective sizes of these elements will then correspond to the area of the outlet face of the collimator or the cross-sectional area of the light beam produced by the lighting unit. Also the number of lighting units may be increased, by providing additional units similar to those concerned by the invention.

Finally, the shifts of the illuminated areas produced by the first and second lighting units may be different in length and/or orientation, for adapting to special layout of the street. Put another way, the shifts of the illuminated areas may not be symmetrical with respect to the reference plane PR. In such case, the lighting units 1 and 2 may be provided with optical elements that are different, for adjusting independently the respective locations, shapes, sizes and orientations of the areas A1 and A2.

Claims

C L A I M S

1. Luminaire device (100) adapted for being installed at a selected height above a surface to illuminate, comprising:

- a first lighting unit (1 ) arranged for illuminating a first area (A1 ) of the surface, and

- at least one second lighting unit (2) oriented towards a second area (A2) of the surface, said first and second areas forming a first strip (S1 ) on the surface, wherein the luminaire device further comprises a first optical element (22) arranged and located with respect to the second lighting unit (2) for deflecting at least part of the light rays emitted by said second lighting unit, so as to move the second area (A2) along a selected distance in a selected direction, and thus modifying accordingly the first strip (S1 ) in shape, orientation or location for forming a second strip (S2) which is illuminated on the surface, and wherein said first optical element (22) is adapted for deflecting light rays emitted by said second lighting unit (2) with an asymmetric distribution around an optical axis (X-X) of said second lighting unit.

2. Luminaire device according to claim 1 , further comprising a second optical element (23) adapted for widening the second area (A2), and thus widening the second illuminated strip (S2) with respect to the first strip (S1 ).

3. Luminaire device according to claim 1 , wherein the first strip (S1 ) is oriented perpendicular to a reference direction (D1 ), with first strip length and width respectively across and along said reference direction, and wherein the selected direction is parallel the reference direction.

4. Luminaire device according to claim 3, further comprising a second optical element (23) adapted for widening the second area (A2) along the reference direction (D1 ).

5. Luminaire device according to claim 4, wherein the first optical element

(22) comprises an array of asymmetric prisms, and the second optical element

(23) comprises an array of cylindrical lenses.

6. Luminaire device according to claim 5, wherein the first (22) and second (23) optical elements are located respectively on first and second surfaces of a transparent substrate.

7. Luminaire device according to claim 1 , wherein the first strip (S1 ) is oriented perpendicular to a reference direction (D1 ), with first strip length and width respectively across and along said reference direction, and wherein the selected direction is perpendicular the reference direction.

8. Luminaire device according to claim 7, wherein the second lighting unit (2) comprises a collimator (21 ), and said first optical element (22) comprises an array of asymmetric prisms provided on an outlet face of the collimator.

9. Luminaire device according to claim 7, further comprising a second optical element (23) adapted for widening the second area (A2) perpendicular to the reference direction (D1 ).

10. Luminaire device according to claim 9, wherein the second lighting unit (2) comprises a collimator (21 ), and said first (22) and second (23) optical elements are provided on an outlet face of the collimator.

11. Luminaire device according to claim 1 , wherein the first (1 ) and second (2) lighting units are similar to each other, and are arranged and oriented symmetrically with respect to a reference plane (PR) perpendicular to the surface to illuminate, said luminaire device further comprising another optical element similar to said first optical element (22) and arranged with respect to the first lighting unit (1 ) in a manner similar to the arrangement of said first optical element with respect to the second lighting unit (2), so that the first (A1 ) and second (A2) areas are both moved symmetrically on respective sides of the reference plane.

12. Luminaire device according to claim 11 , further comprising a third lighting unit (3) arranged for illuminating a third area located between first (A1 ) and second (A2) areas, and thus participating to the second illuminated strip (S2).

13. Luminaire device according to claim 11 or 12, further comprising at least a pair of additional lighting units (1 a, 2a) located and oriented symmetrically with respect to the reference plane (PR).

14. Luminaire device according to claim 12, further comprising a mast (101 ) and a housing (102) affixed on the mast and containing the lighting units (1 -3, 1 a, 2a), the housing comprising a front face (F3) facing the surface to illuminate and provided with an opening for the light emitted by the third lighting unit (3) to pass through said opening, and two lateral faces (F1 , F2) each provided with another opening for the light emitted by at least the first (1 ) and second (2) lighting units to pass through said other openings, respectively.

15. Luminaire device according to claim 14, wherein each lighting unit (1 -3, 1 a, 2a) is thermally coupled within the housing (102) with respective means adapted for dissipating heat produced by said lighting unit.