Patent Publication Number: US-9423105-B2

Title: Lighting device having electrically switchable optical member

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
     This application is the U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/IB13/056847, filed on Aug. 23, 2013, which claims the benefit of U.S. Provisional Patent Application No. 61/692,731, filed on Aug. 24, 2012. These applications are hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lighting device having multiple light sources mounted on a carrier, the light sources emitting light of a first wavelength range, and a wavelength converting member arranged at a distance from the light sources and converting light of the first wavelength range into light of a second wavelength range. 
     BACKGROUND OF THE INVENTION 
     A lighting device of the above-mentioned kind is a kind of luminaire generally referred to as a large area lighting device, since the light output of the several light sources is distributed across a common output area of the lighting device. In various perception tests it has been shown that users would like to have a control over the light intensity distribution in large area lighting devices. For example, one can use point light sources and by varying the density/distribution of the point sources together with their individual intensity maintain the total intensity coming from the light source constant while changing the appearance of the light source. However, these solutions are relatively complex, and/or rigid. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a lighting device that alleviates the above-mentioned problems of the prior art and provides a straightforward adjustability of the appearance of the lighting device. 
     The object is achieved by a lighting device according to the present invention as defined in claim  1 . 
     Thus, in accordance with an aspect of the present invention, there is provided a lighting device comprising:
     multiple light sources mounted on a carrier, the light sources emitting light of a first wavelength range, wherein each light source has a light output opening;   a wavelength converting member arranged at a distance from the light sources, and comprising a first wavelength converting material arranged to convert light of the first wavelength range into light of a second wavelength range, and   a switchable optical member, arranged between the light sources and the wavelength converting member, wherein the optical member is switchable to adjust a light pattern made by the light sources on the wavelength converting member. By means of the switchable optical member, which is arranged before the light reaches the wavelength converting member, an optimum control of the light distribution is obtained. The control can be performed in different ways as regards the total light output, such as changing the light pattern with constant light intensity or with varying light intensity, etc. In accordance with an advantageous embodiment of the lighting device, the switchable optical member comprises multiple individual switchable optical elements, each one thereof arranged between a respective light source and the wavelength converting member. Still the optical elements can be adjusted in common.   

     In accordance with an advantageous embodiment of the lighting device, the switchable optical member is arranged to adjust the light pattern by means of one of scattering, refraction, reflection, and diffraction. 
     In accordance with an advantageous embodiment of the lighting device, the optical elements comprise first optical elements arranged to adjust the area of the light pattern. Thereby the appearance of the lighting device is simple to control to a desired appearance. 
     In accordance with an advantageous embodiment of the lighting device, the switchable optical member is an electro-optical member, which is controllable between different beam-shaping states. 
     In accordance with an advantageous embodiment of the lighting device, the switchable optical member is a mechanical member, which has moving structural parts. 
     In accordance with an embodiment of the lighting device, each light source generates at least one spot, wherein the switchable optical member comprises second switchable optical elements, which are switchable to adjust the number of spots generated by each light source. 
     Thereby the appearance of the lighting device is simple to control to a desired appearance. 
     In accordance with an embodiment of the lighting device, each light source generates at least a central spot appearing as a first color after light passage of the wavelength converting member, and a surrounding zone appearing as a second color, wherein the switchable optical member comprises third switchable optical elements, which are switchable to adjust the color of the surrounding zone. 
     Typically the surrounding zone is either not illuminated by the light source, and then it has the first color, or more or less illuminated, and then it has the second color. 
     In accordance with an embodiment of the lighting device, it further comprises a diffuser arranged downstream of the wavelength converting member, the diffuser being arranged to provide a white appearance of all of a light output surface of the lighting device. Thereby, there is no disturbance from parts of the wavelength conversion member that are not subject to light from the light sources and thereby has another color than the parts where the light from the light sources passes. The diffuser may be positioned at a distance from the wavelength conversion member or in optical contact with the wavelength conversion member. As used herein, “optical contact” is intended to mean that a path of light extends from a first object to a second object without having to pass through an intermediate medium such as air or an optical element. 
     In accordance with an embodiment of the lighting device, each light source comprises a collimator arranged to collimate the light output of the light source. Thereby, the light output of the light sources is well controlled. 
     In accordance with an embodiment of the lighting device, the wavelength converting member comprises a second wavelength converting material arranged to convert light of the first wavelength range into light of a third wavelength range. Thereby a more complex appearance of the lighting device is obtainable. 
     These and other aspects, and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail and with reference to the appended drawings in which: 
         FIG. 1 a    schematically, in a cross-sectional view, shows a first embodiment of a lighting device according to the present invention; 
         FIG. 1 b    schematically shows a perspective view of the lighting device of  FIG. 1   a;    
         FIGS. 2 a  and 2 b    schematically, in cross-sectional views, show an embodiment of the lighting device according to the present invention; 
         FIGS. 2 c  and 2 d    schematically, in cross-sectional views, show different states of an implementation example of a part comprised in the lighting device according to  FIGS. 2 a    and  2   b;    
         FIG. 3  illustrates spot adjustment according to another embodiment of the lighting device; 
         FIGS. 4 a  and 4 b    schematically, in cross-sectional views, show a further embodiment of the lighting device; 
         FIG. 4 c    schematically, in a cross-sectional view, shows an implementation example of a part of the lighting device of  FIGS. 4 a    and  4   b.    
         FIGS. 5 a  and 5 b    schematically, in cross-sectional views, show a further embodiment of the lighting device; 
         FIG. 6  schematically, in a cross-sectional view, shows a further embodiment of the lighting device. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present lighting device typically is a large area light source lamp or luminaire. According to a first embodiment of the lighting device  100  it comprises multiple light sources  102 , which are arranged in a housing  104 . Each light source  102  includes at least one light emitting element  106 . Preferably, the light emitting elements  106  are solid state light elements, such as LEDs (Light Emitting Diodes). The light sources emit light of a first wavelength range. There are many ways of arranging the light sources  102  in the housing, being general knowledge within this technical field. For instance, the light emitting elements can be mounted on a common carrier, or substrate, such as a PCB (Printed Circuit Board). The other parts of the light sources are attached to the carrier as well. The carrier is attached to the housing  102 . Alternatively, each light source is a separate unit. Since this is general knowledge there are no detailed figures in this respect. The light sources  102  are mounted in a, for instance, rectangular or square array having plural rows and plural columns of light sources  102 . 
     A wavelength converting member  108  is arranged at a distance, for instance a few centimeters, from the light sources  102  in front of them, i.e. downstream of the light sources  102 , and it comprises a first wavelength converting material configured to convert light of the first wavelength range into light of a second wavelength range. The wavelength converting member  108  is plate shaped and it is attached to the housing  104 . For example, the wavelength converting member  108  constitutes a front lid of the housing  104 , which is box shaped. The wavelength converting material is phosphor, i.e. the wavelength converting member  108  is a phosphor element. The wavelength converting material is preferably an organic phosphor, inorganic phosphor or quantum dots. Other materials are however feasible as well. As a further alternative, the wavelength converting member  108  comprises multiple phosphor layers. 
     Each light source  102  comprises a collimator  110  surrounding the light emitting element or elements  106 . For instance, the collimator  110  has the shape of a truncated cone, where the light is output at the wider end. The collimator  110  is made from e.g. a light reflective sheet material or an optical element of the TIR (Total Internal reflection) type. 
     Furthermore, the lighting device  100  comprises a switchable optical member  111 , arranged between the light sources  102  and the wavelength converting member  108 . The switchable optical member  111  is switchable to adjust a light pattern  114  made by the light sources  102  on the wavelength converting member  108 . In this embodiment the switchable optical member  111  comprises multiple individual switchable optical elements  112 . Each switchable optical element  112  is arranged between a respective light source  102  and the wavelength converting member  108 , wherein each switchable optical element  112  is switchable to adjust the light pattern  116  made by the light source  102  on the wavelength converting member  108 , which results in a different appearance of the lighting device  100  as seen from the outside of it. The switchable optical element  112  is arranged at the light output end of the collimator  110 , and covers that end. Thus, the switchable optical element  112  is positioned at a distance from the wavelength converting member  108 , upstream thereof. The switchable optical element  112  controls the shape of the light beam emitted from the light source  102 , and thus it controls the area of the wavelength converting member  108  that receives the light beam. As will be described below many different kinds of light pattern adjustments are possible. It should be noted that the collimators  110  are not essential, the general adjustability of the lighting device provided by the switchable optical elements will be obtained anyhow, but the operation is enhanced by collimating the light emitted from the light emitting elements  106 . 
     The switchable optical member can be either mechanically, or electrically switchable. In case of a mechanically switchable optical member movable diffractive or refractive elements, such as lens arrays, can be used. The mechanically switchable optical member, and each switchable optical element, respectively, can be moved by means of a motor or a piezo electric element. In case of an electrically switchable optical member electro-optical elements can be used, such as liquid crystal optics, e.g. PDLC (Polymer Dispersed Liquid Crystal) or liquid crystal cells comprising diffractive or refractive structures. 
     When switching the switchable optical member, the resulting adjustment of the light pattern can be made such that the total amount of light, i.e. the luminous flux (lm), emitted from the lighting device is kept constant, or at least approximately constant. Alternatively, the brightness of the lighting device, i.e. the luminance (lm/m 2 ), is kept constant, and options between these alternatives are possible as well. 
     According to a second embodiment of the lighting device  200 , as shown in  FIGS. 2 a  and 2 b   , it comprises the same parts as the first embodiment, i.e. multiple light sources  202  arranged in a housing  204 , a wavelength converting member  208 , and switchable optical elements  212 , etc. The specific property of this second embodiment is the effect obtained by switching the switchable optical elements  212 . The switchable optical elements  212  are arranged to adjust the area of the light pattern  214  made by the light sources  202  on the wavelength converting member  208 . More particularly, as shown in  FIG. 2 a   , when the switchable optical element  212  is switched to a minimum area state, its contribution to the pattern  214  on the wavelength converting member  208  is a circular spot  216  of a first diameter, and when the switchable optical element  212  is switched to a maximum area state its contribution to the pattern  214  on the wavelength converting member  208  is a circular spot  218  of a second, considerably larger, diameter. The switchable optical element  212  can be continuously switchable, two-position switchable or multistep switchable between the minimum area state and the maximum area state. In order to obtain this switching function the switchable optical member  211 , and consequently each switchable optical element  212 , can be, for instance, an electro-optical element providing different scattering of light. Electrically controlled scattering of light can be accomplished in many different ways. A common approach for accomplishing electrically controlled light scattering is to utilize polymer dispersed liquid crystals (PDLCs) or liquid crystal gels. PDLCs are created by means of dispersing liquid crystal molecules in an isotropic polymer. Typically, as shown in  FIG. 2 c   , liquid crystal material  220  is arranged between two glass plates  222  with transparent electrodes  224 , whereby a cell is formed. When no electric field is applied between the glass plates  222 , the liquid crystals  220  are randomly oriented which creates a scattering mode, wherein light is scattered in many directions, thereby generating the larger area spot  218 . By applying an electric field  226 , the scattering gradually decreases, and when the liquid crystals align parallel to the electric field, the crystal molecule refractive index match the polymer refractive index, wherein a transparent mode is created and light passes through the cell, thereby generating the smaller area spot  216 . 
     As an alternative, LC gels are used. They are created by dispersing liquid crystals in an oriented anisotropic polymer matrix. For LC gels with a negative dielectric anisotropy, the transparent mode is present when no electric field is applied. In the absence of an electric field, liquid crystal molecules are oriented in a direction perpendicular to the cell surfaces and consequently, there are no large-scale refractive index fluctuations within the LC cell. When an electric field is applied, the liquid crystals tend to become oriented perpendicular to the electric field and refractive index fluctuations are induced within the LC cell, and thus the scattering mode is activated. 
     According to a third embodiment of the lighting device, it is similar to the second embodiment. The only difference is that the light generated on the wavelength converting member by a light source, i.e. the shape of the light beam, is adjusted between different shapes. Of course here as well the area will typically change when changing the shape. As shown in  FIG. 3 , in a minimum area state the shape is a circular spot  302 , while in a maximum area state the shape is an elliptical spot  304  of a larger area than the circular spot  302  at the minimum area state. A change in spot shape can be obtained by using e.g. LC-filled switchable lenses, or LC-gradient index lens arrays, which per se are disclosed in the publication of patent application EP2208111. 
     According to a fourth embodiment of the lighting device  400 , as shown in  FIGS. 4 a  and 4 b   , it is similar to the first embodiment in that it comprises multiple light sources  402  arranged in a housing  404 , a wavelength converting member  408 , and switchable optical elements  412 , etc. The specific property of this forth embodiment is the effect obtained by switching the switchable optical elements  412 . The switchable optical elements  402  comprise second switchable optical elements, which are switchable to adjust the number of spots comprised in the light pattern generated by the light sources on the wavelength converting member  408 . More particularly, typically in a first state each light source  402  generates a single spot  414  on the wavelength converting member  408 . The switchable optical element  412  is switchable to a second state, in which the light source  402  generates two spots  416  on the wavelength converting member  408 . Many other relations are feasible as well, such as switching between a first state of two light spots and a second state of four light spots  418 , between one and three light spots, etc. 
     In order to obtain this switching function the switchable optical element, like in the third embodiment, can be obtained with electro-optical elements such as LC-filled switchable lenses or LC-gradient index lens arrays. However, a high degree of collimation is needed. In other words the TIR optics or reflectors should be added to provide good collimated light which can be diffracted in multiple spots. 
     An example of a mechanically switched optical member, as shown in  FIG. 4 c   , comprises a plate with different diffractive patterns  422 ,  424  in front of the LED light sources  402 . The plate is movable back and forth such that the different patterns  422 ,  424  are positioned in front of the light source  402 . 
     According to a fifth embodiment of the lighting device  500 , as shown in  FIGS. 5 a  and 5 b   , it is similar to the first embodiment in that it comprises multiple light sources  502  arranged in a housing  504 , a wavelength converting member  508 , and switchable optical elements  512 , etc. The specific property of this fifth embodiment is the effect obtained by switching the switchable optical elements  512 . In a minimum area state the switchable optical elements  512  cause the light sources  502  to generate a light pattern comprising separate spots  514 . In a maximum area state the switchable optical elements  512  cause the light sources  502  to illuminate a continuous surface of the wavelength converting member  508 . Thereby the luminance ratio is adjusted. Typically, in the minimum area state for a person viewing the lighting device  500 , the spot  514  appears as a first color, and a surrounding zone  516  appears as a second color. Typically, the wavelength converting member  508  has a color, such as yellow, and converts blue light emitted by the light emitting elements  506  of the light sources  502  to white light. In the maximum area state the surrounding zone  516  has the same color as the spot  514 . In order to obtain the widening of the light beams the switchable optical elements  512  comprise third switchable optical elements  512 , which are switchable to spread the light output of the light sources  502  from a basic rather narrow light beam, which passes the switchable optical elements  512  substantially unaffected in the minimum area state. 
     According to a sixth embodiment of the lighting device  600 , it has the same parts as anyone of the preceding embodiments. Thus, as a general description of this embodiment it has multiple light sources  602 , arranged in a housing  604 , a wavelength converting member  608  arranged at a distance from the light sources  602  in the direction of the light beams output of the light sources  602 , and a switchable optical member comprising multiple switchable optical elements  612  arranged between the light sources  602  and the wavelength converting member  608 . The lighting device  600  further comprises a diffuser  620  arranged downstream of the wavelength converting member  608 . The diffuser  620  is arranged to provide a white appearance of all of the light output surface of the lighting device irrespective of whether it is illuminated by the light sources  602  or not. 
     The wavelength converting material used in the present invention may be an inorganic wavelength converting material or an organic wavelength converting material. Examples of inorganic wavelength converting materials may include, but are not limited to, cerium (Ce) doped yttrium aluminum garnet (Y3A15O12:Ce3+, also referred to as YAG:Ce or Ce doped YAG) or lutetium aluminum garnet (LuAG, Lu3A15O12), α-SiAlON:Eu2+ (yellow), and M2Si5N8:Eu2+ (red) wherein M is at least one element selected from calcium Ca, Sr and Ba. Furthermore, a part of the aluminum of YAG:Ce may be substituted with gadolinium (Gd) or gallium (Ga), wherein more Gd results in a red shift of the yellow emission. Other suitable materials may include (Sr1-x-yBaxCay)2-zSi5-aAlaN8-aOa:Euz 2+ wherein 0≦a&lt;5, 0≦x≦1, 0≦y≦1 and 0&lt;z≦1, and (x+y)≦1, such as Sr2Si5N8:Eu2+ which emits light in the red range. 
     Examples of suitable organic wavelength converting materials are organic luminescent materials based on perylene derivatives, for example compounds sold under the name Lumogen® by BASF. Examples of suitable compounds that are commercially available include, but are not limited to, Lumogen® Red F305, Lumogen® Orange F240, Lumogen® Yellow F083, and Lumogen® F170, and combinations thereof. Advantageously, an organic 25 luminescent material may be transparent and non-scattering. 
     Furthermore, in some embodiments, the wavelength converting material maybe quantum dots or quantum rods. Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphide (InP), and copper indium sulfide (CuInS2) and/or silver indium sulfide (AgInS2) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore the emission color can easily be tuned by adapting the size of the quantum dots. Any type of quantum dot known in the art may be used in the present invention. However, it may be preferred for reasons of environmental safety and concern to use cadmium-free quantum dots or at least quantum dots having a very low cadmium content. 
     An “electro-optical element” should, in the context of the present application, be understood as an optical element, at least one optical property of which is controllable through the application of a voltage to the optical element. An electro-optical element is non-mechanical and has no moving structural parts. Examples of electro-optical elements include but are not limited to Polymer Dispersed Liquid Crystal (PDLC) elements, Liquid Crystal Gel (LC Gel) elements, Liquid Crystal Gradient Index (GRIN) lens array elements, electro-phoretic elements, electro-wetting elements. 
     A mechanically switchable optical member should, in the context of the present application, be understood as an optical member, at least one optical property of which is controllable through moving structural parts. Examples of a mechanically switchable optical member include but are not limited to diffractive, refractive, reflective or scattering elements which can be moved with respect to the light source such that it adjusts the light pattern made by the light source on the wavelength converting member. 
     As will be clear to those skilled in the art, the switchable optical member may comprise more than one type of switchable optical elements described herein. Furthermore, the switchable optical member may in addition contain other optical elements such as, for example, mirrors, lenses, etc. 
     Furthermore, the switchable optical member may in addition be connected to a controller, but also to detectors or sensors for controlling the beam properties of the beams generated by the light sources, which detectors or sensors may send a signal to the controller such that the beams can be adjusted or controlled. For instance, the detector is a presence detector detecting the presence of a person in a room. In another example the sensor is a time or temperature sensor. 
     Furthermore, the lighting device is connected to a user interface such as a remote control or switch. 
     Above, embodiments of the lighting device according to the present invention as defined in the appended claims have been described. These should only be seen as merely non-limiting examples. As understood by the person skilled in the art, many modifications and alternative embodiments are possible within the scope of the invention as defined by the appended claims. 
     It is to be noted that for the purposes of his application, and in particular with regard to the appended claims, the word “comprising” does not exclude other elements or steps, and the word “a” or “an” does not exclude a plurality, which per se will be evident to a person skilled in the art.