Abstract:
Proposed is a luminaire ( 1 ), comprising light sources ( 10 ) and optical elements ( 20 ). The light sources ( 10 ) are arranged in a first ( 11 ) and a second array ( 12 ), while the optical elements ( 20 ) are arranged in a first ( 21 ) and a second section ( 22 ). The first ‘light sources&#39; array ( 11 ) and the first Optical element’ section ( 21 ) form a first group ( 31 ), and the second array ( 12 ) and the section ( 22 ) form a second group ( 32 ). The luminaire ( 1 ) is characterized in that the optical elements ( 20 ) of each group are arranged to have different beam shaping characteristics, and the arrays ( 11,12 ) are arranged to be individually addressable. This is especially advantageous in illumination applications where the control of the beam shape is required or desired. Advantageously, the invention provides a luminaire ( 1 ) capable of adjusting the beam shape without using an adjustable optical system. Moreover, the control bandwidth of the light sources limits the speed with which the beam shape can be adjusted.

Description:
FIELD OF THE INVENTION 
     The invention relates to a luminaire according to the preamble of claim  1 . The invention also relates to a beam shaping method. Such luminaires and beam shaping methods are useful in illumination applications where the control of the beam shape is required or desired. 
     BACKGROUND OF THE INVENTION 
     Luminaires capable of adjusting the shape of the emitted light beam find their way in many applications. The beam shaping feature is highly interesting, both in static as well as in dynamic applications. Adjustable beam shapes in static application are normally implemented through a number of preset modes, for instance ‘spotlight’, ‘floodlight’, or ‘ambient light’. In applications using dynamic beam control, the beam shape can normally be adjusted over a continuous range. 
     In conventional luminaires, the emitted light beam is created through the use of a light source and an optical system. The optical system usually is a reflector system but may also be a refractive system, a diffractive system or a diffusive system. Adjusting the relative position of the light source and the optical system classically controls the beam shape. Taking a torch as an example, repositioning the light bulb relative to the parabolic reflector (or the lens relative to the light bulb) controls the shape—narrowly focused vs. wide flooding—of the light beam. Applying switchable refractive elements—e.g. liquid crystal lenses and electro wetting lenses—or switchable diffusers constitute alternative well known technologies to adjust the beam shape emitted by a luminaire. 
     A drawback of the prior art technology to adjust the beam shape of the light emitted by a luminaire is the use of adjustable optical systems, either through mechanical movement or electrical control. While moveable systems are prone to wear and tear, electrically controllable systems are usually highly complex and expensive. Furthermore, the bandwidth of the mechanical moveable and electrically controllable optical systems usually is limited to the frequencies with which the optical system can be adjusted. Typically the bandwidth is 10-100 Hz for mechanically moveable systems, up to 10 kHz for rotating systems, 100 kHz-1 MHZ for micromechanical systems (MEMS), and 50-1000 Hz for electrically controllable systems. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a luminaire of the kind set forth, capable of adjusting the light beam shape up to extremely high frequencies. According to a first aspect, the invention is characterized in that the optical elements of each group are arranged to have different beam shaping characteristics, and the first light source array and second light source array are arranged to be individually addressable. Advantageously, the invention provides a luminaire that is capable of adjusting the beam shape without the necessity of using an adjustable optical system. Moreover, the speed with which the beam shape of the emitted light can be adjusted is now limited to the control bandwidth of the light sources. 
     In an embodiment of the invention, the light sources are chosen from the group consisting of inorganic LEDs, organic LEDs, and semiconductor lasers. The control bandwidth of these light sources typically ranges from 1 MHz to 1 GHz. 
     In an embodiment the light sources of the first array are interdispersed among the light sources of the second array. This embodiment realizes advantageously different beam shapes having a common centre of symmetry. Moreover, the first and second group will consequently be interdispersed causing an observer not to recognize the physical origin of for instance two different beam shapes. 
     In another embodiment at least one ‘light source’ array is arranged in a first sub-array capable of emitting light of a first primary color and a second sub-array capable of emitting light of a second primary color. In an embodiment, the light sources of the first sub-array are interdispersed among the light sources of the second sub-array. Advantageously, the color and the beam shape can be controlled and adjusted independently from each other. In view of the fact that the luminaire makes use of additive color mixing, the term ‘primary color’ has to be understood to comprise any color (i.e. spectrum) of light emitted by the light sources in the luminaire. Thus ‘primary color’ both comprises a narrow bandwidth spectrum and consequently highly saturated color as well as a large bandwidth spectrum and consequently unsaturated color of light emitted. Hence, the scope of additively mixing ‘primary colors’ explicitly is not limited to f.i. highly saturated red, green &amp; blue light sources. On the contrary, the scope extends to mixing f.i. warm-white and cool-white light sources. 
     In yet another embodiment according to the invention the first light source array is arranged to emit light of a first primary color and the second light source array is arranged to emit light of a second primary color. Advantageously, both the color and the beam shape can be controlled and adjusted simultaneously. 
     In an embodiment the luminaire comprises a light guide comprising a first facet arranged to couple light emitted by the light sources into the light guide and a second facet arranged to couple light out of the light guide, advantageously enabling very thin luminaires. In an embodiment the beam shaping characteristic of the optical elements are arranged to collimate the light emitted by the light sources. Advantageously, the light guide mixes the light originating from the different light sources causing an observer not to recognize the different physical origins of the light. 
     In an embodiment the indentations comprise side facets adapted to reflect incident light rays. Advantageously, no light will be lost due to absorption or scattering at the light sources, ensuring good light efficiency. 
     In an embodiment the indentations are arranged in the plane of the light guide in a stacked distribution. Advantageously the distance between the stacked indentations controls the degree of light mixing (resulting in for instance a more homogeneous colored beam when applying multiple primary color light sources). 
     According to a second aspect, the invention provides a method for controlling the light beam shape emitted by a luminaire. The method is characterized by arranging the optical elements of each group to have different beam shaping characteristics, and arranging the first light source array and second light source array to be individually addressable. Advantageously, the invention provides a method for adjusting the beam shape of a luminaire without the necessity of using an adjustable optical system. Moreover, the speed with which the beam shape of the emitted light can be adjusted is limited to the control bandwidth of the light sources. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, features and advantages of the invention are disclosed in the following description of exemplary and preferred embodiments in connection with the drawings. 
         FIG. 1  shows a front view of a luminaire according to the invention including LEDs and lenses 
         FIG. 2  shows a light guide based luminaire according to the invention 
         FIG. 3  shows a cross section through the light guide based luminaire 
         FIG. 4  shows a different configuration of the light guide based luminaire 
         FIG. 5A  shows a top view of another embodiment of a light guide based luminaire, having a plurality of light sources arranged in a square grid array 
         FIG. 5B  shows a schematic cross-section view along a section parallel to the luminaire in  FIG. 5A  illustrating the beam-shaping properties of the rectangular in-coupling recesses 
         FIG. 5C  shows a schematic cross-section view along a section perpendicular to the luminaire in  FIG. 5A  illustrating an exemplary beam-shaping structures for collimating light in a direction perpendicular to the light-guide 
         FIG. 5D  shows a schematic cross-section view along a section perpendicular to the luminaire in  FIG. 5A  illustrating an exemplary beam-shaping structures for collimating light in a direction perpendicular to the light-guide 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows the front view of a luminaire  1  according to the invention comprising a plurality of light sources  10  and optical elements  20  arranged in optical relationship to each other. The light sources  10  are indicated by the squares, triangles, and diamonds, while the optical elements  20  are indicated by the full, dashed, and dotted circles. The light sources  10  are arranged in at least a first array  11  and a second array  12 . Furthermore, the optical elements are arranged in at least a first section  21  and a second section  22 . The first light source array  11  and the first optical element section  22  form a first group  31 . Similarly, the second array  12  and second section  22  form a second group  32 . To control the beam shape of the light emitted by the luminaire  1 , the optical elements  20  within the first group  31  (i.e. the first section  21 ) are arranged to have different beam shaping characteristics from those in the second group  32  (i.e. the second section  22 ). Furthermore, the light sources  10  in each group are arranged to be individually addressable. That is to say, the first ‘light source’ array  11  can be controlled independent from the second ‘light source’ array  12 . 
     The advantage of this approach lies in the fact that the beam shape of the light emitted by the luminaire  1  can now be adjusted by controlling the individual ‘light source’ arrays  11 , 12 . Light sources  10  generally have a large control bandwidth (on-off, dimming). This certainly holds for LEDs (inorganic and organic) and laser diodes, for which the control bandwidth typically ranges from 1 MHz to 1 GHz. 
     In an embodiment of the invention all the light sources  10  emit the same spectrum, which can range from a single saturated primary color (RED, GREEN, BLUE, etc) to a full white spectrum. The characteristics of the optical elements  20  in the different groups  31 ,  32  determine the beam shape of the light emitted. For instance, consider a LED based luminaire  1  capable of switching between a ‘spot mode’ and a ‘flood mode’. A highly concentrated and focused light beam characterizes the ‘spot mode’; while a wide spreading beam shape characterizes the ‘flood mode’. Assembling for instance collimators in front of LEDs in the first group  31  (enabling the ‘spot mode’) and diverging lenses in the second group  32  (enabling the ‘flood mode’) realizes the switching capability of the luminaire  1 . 
     Lenses, collimators, and diffusers may all function as optical elements  20 . As an example, the full circles in  FIG. 1  may represent positive lenses, the dashed circles negative lenses, and the dotted circles collimators. The choice and beam shaping characteristics (such as focal length, collimation angle, or scattering angle—influenced f.i. through the size or shape of a scattering particle in the diffuser) of the optical elements  20  may depend on the emission characteristics of the light sources  10  and the luminaire  1  beam pattern desired. While LEDs typically emit light with a large angular distribution (e.g. Lambertian), laser diodes typically emit collimated light beams. Hence, groups  31 , 32  comprising LEDs and collimators/lenses on the one hand and groups comprising of laser diodes and lenses/diffusers on the other hand yield good results in practice. 
     Interdispersing the light sources  10  of the first array  11  among the light sources  10  of the second array  12  will intrigue a layman observer of a luminaire  1  according to the invention. Consequently, the first  31  and second group  32  will be interdispersed so that the observer will not recognize the physical origin of the for instance the ‘spot and flood modes’. From a technical standpoint, this embodiment realizes advantageously different beam shapes having a common centre of symmetry. Many tilings exist interdispersing two or more of the arrays, sections, and groups. The choice of a particular tiling constitutes a design consideration. Therefore, the scope of the invention covers any possible tiling, whether symmetrical, asymmetrical, or quasi symmetrical. 
     In an embodiment, the light sources  10  emit light with different spectra. Several configurations can be distinguished. In an embodiment of the invention every light source  10  is capable of emitting a plurality of primary colors. As an example, a LED package comprising for instance three chips, where each chip (i) emits a primary color and (ii) is individually addressable, functions satisfactorily. In another embodiment, the light sources  10  emit only a single primary color. Several arrangements exist for assembling such single color light sources  10  in the luminaire  1 . 
     In one embodiment, the first ‘light source’ array  11  is arranged to emit light of a first primary color and the second ‘light source’ array  12  is arranged to emit light of a second primary color. Combining each array with optical elements  10  having different beam shaping characteristics, to form the first  31  and second  32  group, has the advantage of adjusting both the color and the beam shape simultaneously. Hence, the luminaire  1  may switch from for instance a white ‘spot mode’ to a blue ‘flood mode’. Alternatively, applying both modes at the same time may create desirable lighting effects in for instance a retail environment. The white ‘spot mode’ enables a customer to investigate the object for sale in detail, while the colored ‘flood mode’ creates an ambient lighting enhancing the atmosphere and/or setting of the retail environment (ranging from premium boutique to functional Do-It-Yourself). 
     In an embodiment of the invention the luminaire  1  comprises a light guide  50  as shown in  FIG. 2  (top view) and  FIG. 3  (cross section). The light guide  50  comprises at least one first facet  51  arranged to couple light emitted by the light sources  10  into the light guide and at least one second facet  52  arranged to couple light out of the light guide. The light guide  50  comprises a transparent material, typically glass or a plastic, guiding the light rays  15  and enabling the mixture of the light rays of different primary colors or originating from individual light sources  10 . Applying side emitting LEDs as light sources  10  and collimators as optical elements  20 , advantageously enables very thin luminaires  1  (typically with a thickness of 1-3 times the LED package height, i.e. 1-5 mm for luminaires with a degree of collimation of 2×45 degrees beam width or wider). Mounting the LEDs on a PCB (not shown) with two parallel layers of electrical connections allows for their individual or group wise control. In an embodiment, indentations in the light guide  50  allow for positioning the light sources  10  and the optical elements  20 . Advantageously, the optical elements  20  constitute collimators to control the beam shape of the light emitted by the luminaire  1 . Collimation accommodates the anti-glare requirements for luminaires  1 , as these requirements prescribe that the light out-coupled from the light guide  50  should not have too large angles of departure. The indentations have a first facet  51  allowing the light emitted by the LEDs to couple into the light guide  50 . Furthermore, the indentations have a second facet  52  for coupling the light out of the light guide. Moreover, the indentations have side facets  53  adapted to reflect incident light rays  15 , f.i. through TIR or a coating. 
       FIG. 2  depicts a very simple tiling of the light sources  10  and optical elements  20 . For clarity reasons the Figure depicts the groups  31 , 32  with reference to only a limited number of light sources  10  and optical elements  20 . In fact, in this tiling the first group  31  comprises the rows  201 ,  203 ,  205 , and  207 , while the second group  32  comprises the rows  202 ,  204 ,  206 . Many tilings exist, however, interdispersing two or more of the arrays, sections, and groups. The choice of a particular tiling constitutes only a design consideration. Hence, the scope of the invention covers any possible tiling, whether symmetrical, asymmetrical, or quasi symmetrical. 
     Advantageously, the light emitted by a first LED and entering the light guide  50  through the accompanying indentation&#39;s first facet  51  will not penetrate the indentation accommodating a second LED. Arranging the indentations in the plane of the light guide in a stacked distribution, with all first ‘incoupling’ facets  51  oriented in one direction and all second ‘outcoupling’ facets  52  oriented in the opposing direction, results in all the light rays  15  being reflected by either the side facets  53  (through TIR) or the second facets  52 . Advantageously, no light will be lost due to absorption or scattering at the light sources  10 , ensuring good light efficiency. Advantageously the distance between the stacked indentations controls the degree of light mixing (resulting in a more homogeneous beam when applying multiple primary color light sources  10 ). 
     In another embodiment, at least one ‘light source’ array  11 ,  12  is arranged in a first sub-array  101  capable of emitting light of a first primary color and a second sub-array  102  capable of emitting light of a second primary color ( FIGS. 1 &amp; 4 ). Consequently, addressing the individual sub-arrays  101 ,  102  in a single group  31 ,  32  enables adjusting the color of a light beam emitted by the luminaire  1  without changing its shape. Interdispersing the light sources  10  of the first sub-array  101  among the light sources  10  of the second sub-array  102 , advantageously enables a homogeneous color mixing in the light beam. Although  FIG. 4  depicts this configuration for a light guide based luminaire  1 , the scope of the invention covers non-light guide based luminaires with this configuration as well. 
     In  FIG. 5A  shows another embodiment of a luminaire  1 , comprising a light guide  50  and a plurality of light sources  10 , here in the form of omni-directional light emitting LEDs, located at corresponding indentations/recesses having a square cross-section in the plane of the light guide  50 . The faces of the rectangular/square indentation form the first ‘in-coupling’ facets  51   a - d  (see  FIG. 5B . Adjacent to each indentation associated second ‘out-coupling’ facets  52   a - d  are provided. Each of these out-coupling portions comprises four regions a-d having groove-shaped second ‘out-coupling’ facets  52  extending in the directions 45°, 135°, 225°, and 315° with respect to the centrally located indentation. The rectangular/square cross-section of the indentation in the plane of the light guide  50 , collimates the light emitted by an uncollimated light-source  10 , such as an omni-directional LED, in the plane of the light guide  50  and thus splits it into four separate light rays  15   a - d  along two orthogonal axes as schematically indicated in  FIG. 5A  (only one light ray  15  is shown). This collimating property of the indentation will be described in greater detail below in connection with  FIG. 5B . 
     As can be seen in  FIG. 5A , the indentations are oriented in such a way that the directions of the light rays  15  essentially coincide with the directions of the second ‘out-coupling’ facets  52  in the four regions directly adjacent the indentation. Thus, a light ray  15  in-coupled into the light guide  50  through the first ‘incoupling’ facet  51 , will encounter either parallel grooves, which do not out-couple the light, or perpendicularly oriented grooves, which do out-couple the light (illustrated in the Figure for one light ray  15  only). The out-coupling of light emitted by a particular light source  10  need not necessarily take place in an out-coupling portion of the light guide associated with another light-source, as is illustrated in  FIG. 5A . Instead, the light from a light source  10  can be out-coupled in the out-coupling portion associated with that light-source following reflection so that the light rays  15  emitted by the light-source change direction in the plane of the light guide. 
     Turning now to  FIG. 5B , the dimensioning of the rectangular indentation/recess in  FIG. 5A  for achieving an acceptable degree of collimation in the plane of the light guide  50  will be discussed. For a point source, each of the four light rays  15   a - d  entering the first ‘incoupling’ facets  51   a - d  is collimated (in air) within 2×45 degrees. For a finite source, however, the length D of the incoupling facets  51   a - d  (assuming a square cross-section) of the indentation should be about 2.5 times the light source  10  diameter d, in order to produce a cut-off angle Θ cut-off  of 60 degrees, as schematically illustrated in  FIG. 5B  (important to minimize glare by light leaving the luminaire  1  at angles &gt;60 degrees.) In order to achieve a collimation in the plane of the light guide  50  which is narrower than 2×45 degrees, additional optical elements  20 , such as conventional collimator funnels are required. 
     With reference to  FIGS. 5C&amp;D , two exemplary optical elements  20  for achieving collimation in a direction perpendicular to the light guide  50  will be briefly described. In  FIG. 5C , a side-emitting LED package  10  is shown, including a collimating TIR (total internal reflection) optical element  20  inserted in the in-coupling indentation in the light guide  50 . Light emitted by the LED is coupled into the TIR optical element  20  at an in-coupling face thereof and then, through the geometry of the TIR element internally reflected to be emitted as a light ray  15  (here only shown in one direction) which is collimated in a direction perpendicular to the light guide  50  and to enter the light guide  50  through the first ‘incoupling’ facet  51 .  FIG. 5D  schematically illustrates another exemplary collimator  20  in the form of a reflective funnel which redirects light emitted by the light source (LED)  10  as indicated by the light ray  15  drawn in  FIG. 5D  entering the light guide  50  through the first ‘incoupling’ facet  51 . 
     Although the invention has been elucidated with reference to the embodiments described above, it will be evident that alternative embodiments may be used to achieve the same objective. The scope of the invention is therefore not limited to the luminaire described above, but can also be applied to any other light emitting device where it is desired to control the beam shape of the light emitted such as, for example, automotive headlamps and theatre spotlights. Moreover, many possible modifications fall within the scope of the invention. For example, the collimation means in the light guide  50  described above may be combined in various ways. Furthermore not every indentation necessarily needs to accommodate a light source  10  and an optical element  20  combination. Some indentations may for example be used for outcoupling light only. Furthermore the indentations need not necessarily be arranged as individual isolated structures. For example, the scope of the invention covers arranging the indentation as a linear array of parallel grooves—thus creating a prism faced zig-zag surface where the ‘zig’ provides a first ‘incoupling’ facet  51  and the ‘zag’ a second ‘outcoupling’ facet  52 . Alternatively, the light sources  10  and optical elements  20  may all be located at one side edge of the light guide  50 .