WO2009122453A1

WO2009122453A1 - Led lighting apparatus

Info

Publication number: WO2009122453A1
Application number: PCT/IT2008/000219
Authority: WO
Inventors: Franco Venturini
Original assignee: Wissen Lux S.P.A.
Priority date: 2008-04-02
Filing date: 2008-04-02
Publication date: 2009-10-08

Abstract

A LED lighting apparatus comprises at least three sets of LEDs (lla-llc), each of which is disposed along a strip the extension of which substantially starts from the vertex (V) of a spherical cap (C) and reaches the base (B) of same, the three LED sets (lla-llc) being spaced apart the same distance from each other and being arranged in such a manner that main lighting directions (Da-Dc) of the LEDs (lOa-lOc) face the region (100) to be lit. Each LED (lOa-lOc) is provided with an optical conveyor means of its own.

Description

"LED LIGHTING APPARATUS"

D e s c r i p t i o n

The present invention relates to a LED lighting apparatus. In more detail, the invention relates to LED lighting apparatus that are used in the technical lighting sector, i.e. for indoor lighting (in houses, offices, shops, warehouses, etc.) and outdoor lighting (street lighting, for example) .

It is known that in the concerned sector lighting apparatus are presently made available that make use of quartz-iodine lamps or semiconductor devices, such as LEDs and that, due to the disadvantageous positioning of the light sources and/or the poor efficiency of the optical elements employed, they supply quite insufficient illumination in terms of width of the lighted area or intensity of the light beam generated.

To obviate this drawback it is sometimes possible to increase the intensity of the generated light beams by correspondingly increasing the related energy consumption; obviously, the last-mentioned case too is far away from an ideal situation or an acceptable situation in terms of energy efficiency.

In this context, the main technical task of the present invention is to make available a LED lighting apparatus that does not suffer for the abovementioned drawbacks.

In particular, the present invention aims at providing a LED lighting apparatus enabling an acceptable illumination of areas of predetermined width, while ensuring a reduced energy consumption. It is another aim of the invention to make available a LED lighting apparatus capable of obtaining a homogeneous and uniform lighting.

A further aim of the invention is to provide a LED lighting apparatus of simple and cheap structure and involving a reduced manufacturing complexity.

The foregoing and still further aims are substantially achieved by a LED lighting apparatus having the features as recited in one or more of the appended claims .

Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of the invention. This description is taken hereinafter with reference to ^' the accompanying drawings, given be way of non-limiting example, in which: - Fig. 1 diagrammaticalIy shows a perspective view of an apparatus in accordance with the invention, with some parts removed for a better view of others;

- Fig. 2 diagrammatically shows a plan view of the apparatus seen in Fig. 1; - Fig. 3 diagrammatically shows a perspective view of an element of the apparatus of the invention,-

- Fig. 4 diagrammatically shows a perspective view of a further element of the apparatus of the invention;

- Fig. 5 is a diagrammatic perspective view of an alternative embodiment of the element seen in Fig. 4;

- Figs . 6 and 6a diagrammatically show a plan view and an enlarged perspective view respectively of a detail in Fig . 4 ;

- Figs. 7 and 7a diagrammatically show a plan view and an enlarged perspective view respectively of an alternative embodiment of the detail seen in Figs. 6 and 6a.

With reference to the drawings, a LED lighting apparatus in accordance with the present invention has been generally identified by reference numeral 1.

As above said, apparatus 1 can be used, depending on requirements, for indoor lighting but also for illuminating areas in the open, such as for street lighting, for example.

Apparatus 1 comprises a plurality of LEDs lOa-lOc that, as better clarified in the following, are suitably arranged so as to obtain a satisfactory lighting of a predetermined area.

LEDs lOa-lOc are divided into at least three sets lla- llc of LEDs, each of them being disposed along a strip the extension of which substantially starts from the vertex V of a cap C and reaches the base B of said cap. In other words, LEDs 10a-10c are disposed in strips substantially belonging to the surface of cap C, starting from vertex V of same and reaching base B (see Fig. 1) .

The strips are at least partly contained in cap C and preferably are fully contained therein.

It is to be noted that the sets of LEDs can also be more than three in number; preferred embodiments of apparatus 1 may comprise six or nine sets of LEDs, for example.

It is to be pointed out that the term "substantially" referred to the geometric features of parts of apparatus 1 referring to the shape of the cap or parts thereof is to be intended as "approximately" or "about" and not with a Pythagorean meaning.

Note that LEDs 10a-10c are disposed in the above described configuration in an ideal manner, i.e. irrespective of the true presence of a real physical cap (as it will be more apparent in the following of the present specification) .

In this context and in the following claims by "cap" it is intended a rounded or concave open surface, preferably substantially fully concave and having an opening the profile of which is defined by a base line, the latter delimiting an ideal base surface merely referred to as base B.

Vertex V of cap C is the point belonging to said open surface that has the maximum distance from base B. The cap height is the distance between vertex V and base B.

Preferably the sections of cap C in planes parallel to the base delimit surfaces having non decreasing areas, and in particular increasing areas, on moving away from vertex V towards base B .

Preferably, at least one plane containing the cap height is a plane of symmetry of cap C itself.

Preferably, at least two planes passing through the height of cap C are planes of symmetry of the cap C itself.

Preferably, all planes passing through the cap height are planes of symmetry of cap C; in this case, the straight line on which the cap height lies is an axis of cylindrical symmetry of cap C.

Preferably, cap C is a spherical cap, i.e. one of the parts into which the sphere is divided by a secant plane. Reference will be made to a hemisphere when the secant plane passes through a diameter of said sphere. Reference will be made to the height of the spherical cap C to indicate the diameter portion included between base B and the spherical surface. Vertex V is the point where this diameter meets the spherical ^• surface.

As shown in Fig. 1, the three sets lla-lie of LEDs are spaced apart the same distance from each other and are such arranged that main lighting directions Da-Dc of the LEDs face the region to be lit.

In particular, the main lighting directions Da-Dc of

LEDs 10a-10c converge away from said LEDs towards the surface to be lit.

Note that in the present context and the following claims by main lighting direction of a LED it is intended the axis of symmetry of the light beam generated by the LED itself .

In fact, a LED typically generates a light beam in the form of a cone the vertex of which is defined by the

LED itself; the main lighting direction is therefore the straight line along which the geometric height of said cone is measured.

Preferably, the width of the light .beam of the LEDs, i.e. the opening width of the above mentioned cone, is included between 5° and 40°. In this way, the light beam produced by the LEDs impinges on the area to be lit without having components directed towards other regions. This enables the presence of diffused light in regions that are not to be lit, to be avoided; for instance, should the lighting apparatus be used for illuminating a street, the presence of diffused light directed upwards is avoided.

LEDs lOa-lOc are such arranged that, on the surface to- be lit, the area lit by each LED at least partly overlaps the area lit by the adjacent LED/LEDs .

For instance, if this lighted area has a shape with a geometric centre, the LEDs can preferably be disposed in such a manner that the line delimiting the area lit by a LED passes through the geometric centre of the are lit by one or more adjacent LEDs.

By way of example, shown in Fig. 1 is how the LEDs belonging to the three sets lla-lie have main lighting directions Da-Dc intersecting at the same point placed between the lighting apparatus 1 and surface 100 to be lit. Alternatively, the main lighting directions Da-Dc can intersect at regions rather than at a single point.

The intersection point or region is placed at different heights in the distance separating the lighting apparatus from the surface to be lit, depending on the starting orientation of the light beams emitted by the LEDs.

Preferably, the main lighting directions Da-Dc of each set of LEDs lie in the same plane. Preferably, LEDs lOa-lOc of each set lla-llc of LEDs have different lighting powers, as a function of the features and in particular the geometry of the surface to be lit.

Preferably, the lighting power of LEDs 10a-10c of each set lla-llc increases on increasing of the distance of the LEDs from vertex V of the spherical cap C. In other words, on increasing of the distance of LEDs lOa-lOc from vertex V of the spherical cap C, the LED power increases too.

In one embodiment in which the surface to be lit is a pavement (in this case the lighting apparatus is a street lamp, for example) , the lighting power emitted by LEDs 10a-10c is not symmetric relative to an axis X

(Fig. 4) coincident with the height of the spherical cap C. This means that the powers of LEDs 10a-10c of a set lla-llc are not the same as the powers of corresponding LEDs of another set.

For instance, this asymmetry ensures that the lighting apparatus illuminates both the pavement and the street portion placed in front of same and does not illuminate (or illuminates in a very reduced manner) the building wall placed behind it (for instance because there is a window of a flat) .

Apart from the described embodiment, the lighting power emitted by LEDs lOa-lOc can be non-symmetric relative to an axis X coincident with the height of the spherical cap C, or non-symmetric relative to any other axis, each time a non-symmetric -lighted surface is wished to be obtained. In other words, by suitably selecting the lighting power of each LED lOa-lOc it is possible to obtain lighted surfaces having substantially any shape.

Preferably, each LED 10a-10c is provided with an optical conveyor means 20 of its own that is adapted to interact with a light beam emitted by the LED.

Referring particularly to Fig. 3, each optical conveyor means 20 comprises an optical element 21 substantially extending perpendicular to the main lighting direction Da-Dc of LEDs 10a-10c and disposed in close proximity thereto, preferably to ^' a distance included between 1 and 2.5 cm from the LED .

The optical element 21 is maintained in place by a waveguide 22 for the light beam emitted by the LED. The function of this waveguide 22 is to direct the light beam emitted by the LED onto the optical element 21.

As shown in Fig. 3, the waveguide 22 has a substantially frustoconical extension and its minor base placed close to the LED.

The waveguide is made of a fireproof material, preferably polycarbonate.

Preferably, the optical elements 21 of the optical conveyor means 20 of the same set of LEDs lOa-lOc are different from each other, i.e. have different optical properties. For instance, the optical elements 21 of the LEDs disposed close to vertex V of the spherical cap C have a substantially flat first surface facing LEDs lOa-lOc and a second prism-like surface 24 opposite to the first surface. Therefore, the light beams generated by LEDs lOa-lOc initially strike on the first surface and are submitted in cascade to the action of the second surface 24.

Note that, in the present specification and the following claims, by prism-like surface it is intended any surface having one or more inclined portions relative to said first surface, so as to create phenomena of refraction and/or reflection and/or diffraction and/or polarisation of light beams incident on the first surface.

In an embodiment, as shown in Fig. 3, the prism-like surface 24 is defined by a plurality of prismatic elements 24a disposed close to each other, each of which is defined by at least three side surfaces 24b that are inclined to the first surface and converge at an ideal vertex placed on the opposite side from the first surface.

Practically, the prism-like surface 24 can be defined by a plurality of right pyramids or truncated right pyramids, disposed close to each other and the base of which is parallel to the first surface.

The base of said pyramids or truncated pyramids can be hexagonal for example, preferably in the form of a regular hexagon (as shown in Fig. 3) .

Preferably the height of each pyramid or truncated pyramid is included between 0.5 mm and 1 mm and is of 0.8 mm, for example.

Preferably, the angle formed by each edge of the pyramid or truncated pyramid (not belonging to the base of same) with the respective base surface is included between 40° and 50°, and is preferably of 45°.

The optical elements 21 of the LEDs disposed close to base B of the spherical cap C have a substantially flat first surface facing the LED lOa-lOc (as in the case of the optical elements of the LEDs disposed close to vertex V) , and a second surface 24 also substantially flat (unlike the optical elements of the LEDs disposed close ^'to vertex V) opposite to the first surface.

In this case the second surface 24 can be slightly curved or convex, due to the working effects ^• resulting from the manufacturing steps of the optical elements .

The choice between the two types of second surface 24 of the optical element 21, i.e. a flat or prismatic surface, depends on the type of lighting that is wished to be obtained. At all events, irrespective of the type of second surface 24 of the optical element 21, the latter is preferably at least partly transparent to the visible light, i.e. the light beams generated by LEDs lOa-lOc.

The optical element 21 is advantageously made of fireproof material; for instance, the optical element 21 is made of polycarbonate.

Each optical conveyor means 20 comprises at least three, preferably four, support props 25 to engage the optical element 21^' with the LED at a predetermined position (the one described above) . Each set lla-llc of LEDs 10a-10c is mounted on a respective supporting surface 40a-40c. This means that LEDs lOa-lOc belonging to different sets are mounted on dedicated supporting surfaces. In particular, through the suitable arrangement and shape of the supporting surfaces 40a- 4Oc₇ the inclination of the main lighting directions Da-Dc are determined. In fact, the main lighting direction of each LED is preferably perpendicular to the supporting surface portion on which the LED is mounted.

Each supporting surface 40a-40c extends along said strip of cap surface.

In the preferred embodiment, as shown in Fig. 2, each supporting surface 40a-40c is of a substantially plate- like conformation and has a respective curvilinear or broken major-extension direction Wa-Wc.

LEDs lOa-lOc are preferably aligned along the major- extension direction W of the respective supporting surface 40a-40c.

To enable engagement of the LEDs with the supporting surfaces 40a-40c, the latter have a plurality of holes 41, preferably of the through type (see Fig. 2) . Preferably, in engagement with said holes 41 also is the optical conveyor means of each LED. In addition the LEDs can be directly connected to said holes 41, if no optical conveyor means 20 is provided.

In addition the LEDs or the optical conveyor means 20 can engage all holes 41 or only some of holes 41, so as to make a configuration in which empty spaces are present between adjacent LEDs or optical conveyor means (possibly to be engaged by other LEDs. or optical conveyor means 20) . In the preferred embodiment, four holes 41 for each optical conveyor means 20 are provided for receiving the four support props 25 in engagement.

The supporting surfaces 40a-40c are connected to each other at respective portions 42 substantially coincident with vertex V of the spherical cap C (see Figs. 1 and 2) . This means that the supporting surfaces 40a-40c are linked to each other so as to form a single piece preferably obtained by blanking.

In addition, the supporting surfaces 4Oa-4Oc have such a thickness that they can become deformed and take the mentioned configuration.-

The lighting apparatus further comprises a mounting body 30 on which the supporting surfaces 4Oa-4Oc carrying LEDs 10a-10c are mounted. The mounting body 30

(Fig. 4) substantially has the shape of a preferably spherical cap and comprises an inner surface, i.e. the concave surface of the cap, and an outer surface 30a (see Fig. 5) . i.e. the convex surface of the cap.

The cap defined by the mounting body 30 can be a spherical cap and in particular a hemispherical cap.

The supporting surfaces 40a-40c are in engagement with the mounting body 30 on the inner surface of the latter. The -mounting body 30 is preferably part of a box-shaped body 50 and is engaged with an optical screen 60 to define a closed volume in which the sets of LEDs lla-lie are contained (Fig. 4) .

The optical screen 60 has a substantially planar extension; practically, the optical screen 60 can have a plate-like structure with a preferably circular configuration in plan view.

Preferably, the optical screen 60 is operatively associated with all LEDs 10a-10c of apparatus 'i; in other words, the optical screen 60 is employed for acting on the light beams generated by the different

LEDs 10a-10c and already intercepted by the optical conveyor means of each LED and illuminating a predetermined area.

The optical screen 60 has a substantially flat first surface facing LEDs lOa-lOc and a second surface 62 opposite to the first surface. Therefore, the light beams generated by LEDs lOa-lOc initially strike on the first surface of the optical element 21, are submitted to the action of the second surface 24 of the optical element 21, subsequently strike on the first surface 61 of the optical screen 60 and are submitted to^' the action of the second surface 62 of the optical screen

60 before reaching the area to be lit.

In a first embodiment, the second surface 62 is defined by a plurality of prismatic elements 62b disposed close to each other, each of which is defined by at least three side surfaces 62c inclined to the first surface

61 and converging at a vertex 62d away from the first surface 61.

Practically, in the embodiment in Figs. 6 and 6a, the prism-like surface 62 can be defined by a plurality of right or truncated right pyramids disposed close to each other and the base of which is parallel to the first surface 61. The base of these pyramids or truncated pyramids can for example be a square or hexagonal base (as shown in Figs . 6 and 6a) and preferably has the shape of a regular hexagon.

Preferably, the height of each pyramid or truncated pyramid is included between 1.5 and 2.5 mm, and is of 2 mm, for example.

Preferably, the distance between the base of the pyramids or truncated pyramids and the first surface 21 of the optical element 20 is included between 1.5 mm and 3 mm, and is of 2 mm, for example.

Preferably, the angle formed by each edge of said pyramid or said truncated pyramid (not belonging to the base of same) with the respective base surface is included between 40° and 50°, and is preferably of 45°.

In an alternative embodiment, the_*, prism-like surface portions consist of a succession of pairs of surfaces 62a inclined to the first surface 61, in which the inclined surfaces 62a of the same pair converge away from the first surface 61; more particularly, the inclined surfaces 62a have the same longitudinal major- extension direction (as shown in Figs. 7 and 7a) .

Preferably, the angle formed by each pair of converging inclined surfaces 62a is included between 60° and 120°, and preferably between 80° and 100°. For instance, this angle can be of 90°.

Preferably, the distance between the line on which the inclined surfaces 62a converge and the plane defined by the edges of said surfaces 62a opposite to the convergence lines is included between 1.5 mm and 3 mm and is of 2 mm, for example.

Preferably, the distance between the first surface 61 and the plane defined by the edges of surfaces 62a opposite to the convergence lines is included between 1.5 mm and 3 mm and is of 2 mm, for example.

Practically, in the embodiment in Pigs. 7 and 7a, the prism-like surface has a zigzag extension defined by said inclined surfaces 62a. ₍

In the preferred embodiment of the invention, the second surface 62 is substantially flat and smooth.

The choice of the second-surface type i.e. a flat or prism-like surface, is a function of the type of lighting that is wished to be obtained.

At all events, apart from the type of second surface 62 of the optical screen 60, the LEDs lOa-lOc of each set have main lighting directions Da-Dc forming decreasing angles with the first surface 61 of the optical screen 60 starting from vertex V of the spherical cap C towards base B of same.

The optical screen 60 is advantageously made of a fireproof material; for instance, the optical element 60 can be made of polycarbonate.

The mounting body 30 can be suitably arranged so as to fasten apparatus 1 to the ceiling of a closed volume or to a suitable supporting structure.

In an alternative embodiment, shown in Fig. 5, the mounting body 30 comprises a preferably spherical further cap 31 which is substantially concentric with the first cap 30.

The second cap 31 fully surrounds the first cap 30 and a hollow space 32 preferably filled with a thermally insulating material is provided between the two caps 30, 31. This hollow space 32 can be also filled with air, for example.

The function of the hollow space is to protect LEDs 10a-10c mounted on the first cap 30, from heat transmitted from the sunbeams, for example.

It is to be noted that the pair of caps 30, 31 can also be used for lighting apparatuses other than apparatus 1.

These apparatuses generally comprise the following features:

- one or more lighting elements, preferably in the form of a LED; a first cap 30, within which said one or more lighting elements are mounted; - a second cap 31, at least partly and preferably fully surrounding said first cap 30.

Also in the case of lighting apparatuses different from apparatus 1, the two caps 30, 31 are preferably substantially concentric; in particular, the two caps 30, 31 can be spherical caps.

Preferably, apparatus 1 further comprises an electric feeding unit to feed the LEDs 10a-10c with the necessary power supply for correct operation. The feeding unit 70 can be associated with a control circuit 80 for selective feeding of said LEDs lOa-lOc; in more detail, the control circuit 80 can allow one or more sets lla-lie of LEDs that have to be fed to be selected, while the LEDs belonging to other sets are, on the contrary, maintained switched off.

Advantageously feeding of LEDs 10a-10c is current- controlled.

In addition the different sets of LEDs are powered in parallel, so that a possible fault or malfunction to a LED or set of LEDs does not impair, correct feeding of the LEDs belonging to other sets.

Preferably, the feeding unit 70 and/or control circuit 80 are mounted on said mounting surface 30.

It will be appreciated that in Fig. 4 the electric feeding unit 70 and control circuit 80 are represented as blocks^ external to the box-shaped body 50 only for the sake of clarity; actually, as described above, both the feeding unit 70 and control circuit 80 can be housed in said closed volume or in the hollow space 32 between the two spherical caps 30, 31.

Preferably, the control circuit 80 is operable by a user, through one or more switches or similar command means, for determining which LED set/sets is/are to be fed.

The invention achieves important advantages .

First of all, the apparatus of the invention enables an acceptable lighting of areas of predetermined width to be obtained, with a reduced energy consumption.

In addition, said lighting obtained through the apparatus of the present invention is uniform and homogeneous .

Claims

C L A I M S

1. A LED lighting apparatus comprising:

- at least three sets (lla-llc) of LEDs, each of which is disposed along a strip the extension of which substantially starts from the vertex (V) of a cap (C) and reaches the base (B) of same,

- said at least three sets (lla-llc) of LEDs being arranged in such a manner that main lighting directions (Da-Dc) of the LEDs (lOa-lOc) face the region (100) to be lit.

2. An apparatus as claimed in claim 1, wherein said at least three LED sets (lla-llc) are spaced apart the same distance from each other.

3. An apparatus as claimed in claim 1 or 2 , wherein said cap (C) is a spherical cap.

4. An apparatus as claimed in anyone of the preceding claims, wherein main lighting directions (Da-Dc) of the LEDs (10a-10c) converge away from the LEDs towards the surface to be lit.

5. An apparatus as claimed in anyone of the preceding claims, wherein the LEDs belonging to the same LED set (lla-llc) have different lighting powers.

6. An apparatus as claimed in the preceding claim, wherein the lighting power of the LEDs of the same set

(lla-llc) increases on increasing of the distance of the LEDs (lOa-lOc) from the vertex (V) of the cap (C) .

7. An apparatus as claimed in claim 5 or 6, wherein the lighting power emitted by the LEDs (lOa-lOc) is not symmetric relative to an axis (X) defining the height of the spherical cap (C) .

8. An apparatus as claimed in anyone of the preceding ^' claims, wherein each LED (lOa-lOc) is provided with an optical conveyor means (20) of its own adapted to interact with a light beam emitted by the LED.

9. An apparatus as claimed in claim 8, wherein each optical conveyor means (20) comprises an optical element (21) substantially extending perpendicular to the main lighting direction (Da-Dc) of the LED (10a- 10c) and disposed close to the LED.

10. An apparatus as claimed in claim 9, wherein the optical elements (21) of the optical conveyor means (20) of the same LED set (lla-lie) are different from each other.

11. An apparatus as claimed in claim 10, wherein the optical elements (21) of the LEDs (lOa-lOc) disposed in the vicinity of the vertex (V) of the cap (C) have a substantially flat first surface facing the LEDs (10a- 10c) and a second prism-like surface (24) opposite to said first surface.

12. An apparatus as claimed in claim 10 or 11, wherein the optical elements (21) of the LEDs (lOa-lOc) disposed in the vicinity of the base (B) of the cap (C) have a substantially flat first surface facing the LEDs (lOa-lOc) and a substantially flat second surface (24) opposite to said first surface.

13. An apparatus as claimed in anyone of the preceding claims, wherein each LED set (lla-lie) is mounted on a respective supporting surface (40a-40c) extending along said strip.

14. An apparatus as claimed in claim 13 , wherein said supporting surfaces (40a-40c) are connected to each other at a portion substantially coincident with the vertex (V) of said spherical cap (C) .

15. An apparatus as claimed in claim 13, further comprising a mounting body (30) on which said LEDs

(lOa-lOc) and preferably said supporting surfaces (40a- 40c) are mounted.

16. An apparatus as claimed in the preceding claim, wherein said mounting body (30) substantially is a cap, preferably a spherical cap.

17. An apparatus as claimed in claim 15 or 16, wherein said mounting body (30) is part of a box-shaped body (50) in engagement with an optical screen (60) for defining a closed volume in which said LEDs (lOa-lOc) are contained.

18. An apparatus as claimed in claim 17, wherein said optical screen (60) substantially has a ^"planar extension and is provided with a substantially flat first surface (619 facing said LEDs (lOa-lOc) and a second surface (62) opposite to said first surface (61) .

19. An apparatus as claimed in claim 18, wherein the LEDs (lOa-lOc) of each set have main lighting directions (Da-Dc) forming decreasing angles with the first surface (61) of said optical screen (60) , starting from the vertex (V) of the cap (C) towards the base (B) of same .

20. An apparatus as claimed in claim 18 or 19, wherein said second surface (62) is defined by a plurality of prismatic elements (62b) disposed close to each other, each of said prismatic elements (62b) being defined by at least three side surfaces (62c) inclined with respect to said first surface (61) and converging, away from said first surface (61) , at a respective vertex (62d)^'.

21. An apparatus as claimed in anyone of claims 16 to 20, wherein said mounting body (30) comprises two preferably spherical caps (30, 31) that are substantially concentric and separated from each other by a hollow space (32) .

22. An apparatus as claimed in anyone of the preceding claims wherein each of said LED sets (lla-llc) is defined by a respective array of LEDs.

23. An apparatus as claimed in anyone of the preceding claims, wherein the main lighting directions (Da-Dc) of LEDs belonging to the same set lie in the same plane.

24. An apparatus as claimed in anyone of the preceding claims further comprising a feeding unit (70) to supply electric power to said LEDs (lOa-lOc) .

25. An apparatus as claimed in the preceding claim, further comprising a control circuit (80). associated with said feeding unit (70) for selectively powering said LEDs (lOa-lOc) .

26. An apparatus as claimed in claim 24 or 25, wherein power supply to said LEDs (10a-10c) is current- controlled.