Patent Publication Number: US-10788167-B2

Title: Retrofit lighting assembly

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/EP2018/060684, filed on Apr. 26, 2018, which claims the benefit of European Patent Application No. 17168897.1, filed on May 1, 2017. These applications are hereby incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of lighting assemblies adapted to be mounted in lighting fixtures. 
     BACKGROUND OF THE INVENTION 
     Fluorescent tube luminaries are widely used for illumination of e.g. commercial office spaces, schools, and lab facilities. Such luminaries are often arranged in a dropped ceiling, i.e. a secondary ceiling hung below the main, structural ceiling. A dropped ceiling may consist of a metal grid structure defining regularly spaced cells, e.g. having the dimensions of 2×4, 2×2 or 1×4 feet, (600×1200 mm, 600×600 mm or 300×1200 mm) which cells can be filled with tiles or panels so as to provide a flat surface hiding the space above the dropped ceiling. 
     A fluorescent tube luminaire may be accommodated in a cell of the dropped ceiling. In general, the luminaire may comprise a lighting fixture, or troffer, and optical elements enabling a desired optical performance. The luminaire may be recessed above the dropped ceiling grid and adapted to accommodate one or several fluorescent tubes. It is also common to provide light fixtures that fit the same space as a tile in order to facilitate installation. 
     Today, there is a growing demand for replacing fluorescent tubes with less energy consuming illumination devices, such as e.g. light emitting diode (LED) based illumination devices. Aspects of a kit for replacing fluorescent tubes in a fluorescent tube luminaire with a plate-like LED based lighting system are discussed in JP 2013/118063. That document describes a LED system that makes use of existing light fixtures, wherein the fluorescent tubes are replaced with two rods that are fixated to the sockets of the fixtures. A flat LED unit is then attached to the light fixture by means of L-shaped hooks that engage with the rods. 
     Although such LED-lighting systems can be used for replacing fluorescent tubes, there is still a need for improved kits that are easier to install in the lighting fixture. 
     WO2015136110 discloses a lighting assembly that can be retrofitted into an existing lighting fixture. 
     SUMMARY OF THE INVENTION 
     It would be advantageous to achieve a light engine that is easier to install or retrofit into an existing lighting fixture, particularly, a fluorescent lighting fixture located in a drop ceiling. 
     To better address this concern, a light engine, a lighting assembly and a method for mounting such assembly with the features of the independent claims is provided. The dependent claims define preferable embodiments. 
     Hence, according to a first aspect, a lighting assembly comprising a light engine is provided. The light engine is adapted to be mounted in the lighting assembly. The light engine having at least one LED and a reflector, the reflector being mechanically connected to a first reflector of the lighting assembly. The lighting assembly comprises a first reflector, a second reflector and at least two sidewall parts, a first fastening arrangement adapted to secure the first reflector to at least one sidewall part, and a second fastening arrangement adapted to secure the second reflector to at least one sidewall part. The first reflector, the second reflector and the at least two sidewall parts are adapted to be arranged in the lighting fixture and secured to each other such that they define sidewalls of a four-sided cavity. Further, junctions between the first reflector, the second reflector and the at least two sidewall parts are arranged to be at the corners of the four-sided cavity when the first reflector, the second reflector and the at least two sidewall parts are arranged in the lighting fixture. 
     According to a second aspect, a method for mounting a lighting assembly according to the second aspect is disclosed. The method comprises arranging the first reflector, the second reflector and the at least two sidewall parts in the lighting fixture and securing the first reflector, the second reflector and the at least two sidewall parts to each other by means of the first fastening arrangement and the second fastening arrangement such that junctions between the first reflector, the second reflector and the at least two sidewall parts are arranged at the corners of the four-sided cavity, securing the light engine to the first reflector, arranging the light engine to connect with the second reflector, and securing the light engine to the second reflector. 
     The lighting fixture (which also may be referred to as a troffer) may be originally intended for a fluorescent tube and may e.g. be installed above a grid in a dropped ceiling. The light engine and the lighting assembly according to the present aspects may be used for replacing the fluorescent tube and/or the optical elements that fit to the fluorescent tube in such a lighting fixture. The lighting fixture, the light engine and the lighting assembly may together form a luminaire. This may, in the context of this document, be understood as a retrofit lighting assembly. In particular, this may be considered as retrofit light engine if at a future time the first reflector, the second reflector and the at least two sidewall parts are to remain in-situ in the lighting fixture and a replacement light engine is installed. This enables a LED refurbishment kit to be supplied to allow the ongoing use of an already fitted retrofit lighting assembly. This bring sustainability advantages by producing less waste products if the light engine requires further replacement or simply when the user wishes to tailor the light emitted, for example by changing the light engine to one having a different color temperature or even full color changing. The light engine may also be fitted with sensors to allow an intelligent lighting assembly. 
     Furthermore, the light engine may be supplied to third party companies to allow them to market their own retrofit lighting assembly whilst still benefiting from a light engine that is accepted by the marketplace. It has been seen that the market appreciates the appearance of a voluminous luminaire. 
     By assembling the lighting assembly from a first reflector, a second reflector and at least two separate sidewall parts adapted to form junctions at the corners of the four-sided cavity and which may not necessarily be secured to each other until they are arranged in the lighting fixture, relatively large lighting assemblies can be arranged at lighting fixtures even though the available mounting space is relatively limited. Even though the mounted lighting assembly may be larger than e.g. the opening of the grid, i.e. have a length exceeding the length of the opening of the grid and a width exceeding the width of the opening of the grid, the lighting assembly may be inserted in the lighting fixture by arranging the first reflector, the second reflector and the at least two sidewall parts in the lighting fixture one by one and subsequently securing them to each other. In some embodiments the securing fixtures may be quarter-turn fixings. These are so called because only a quarter of a turn is required to open (or close) the fixing. This is much less than the amount of rotation required by a nut and bolt fixing or a screw fixing for example. This makes the quarter-turn fixings particularly suitable for use in areas where a fast assembly is advantagous. 
     The quarter-turn fastener may take the form of a central shank with pins protruding at the normal to the shank&#39;s central axis. If the fastening location comprises at least one slit the fastener may be inserted and then rotated by 90°. This rotation means that the pins will no longer be aligned with the slit and will prevent the fastener being pulled out of the slit. Therefore, the parts are joined together. It can be seen that such fasteners may also remove or reduce the required use of tools. This may mean that it is easier for the installer to quickly and safely join the individual parts of the lighting assembly to each other. Thereby, the use of individual and non assembled parts to construct a lighting assembly being slightly larger than the opening in the grid or the lighting fixture can be provided, and the installation of the lighting assembly may be facilitated. 
     In an embodiment, each one of at least two of the first reflector, the second reflector and the at least two sidewall parts comprises a support surface adapted to support the lighting assembly in the lighting fixture and to be arranged at different sides of the four-sided cavity when the first reflector, the second reflector and the at least two sidewall parts are arranged in the lighting fixture. Further, the light engine is arranged to emit light out of the four-sided cavity. The support surfaces of the first reflector, the second reflector and the at least two sidewall parts may engage with the lighting fixture or with the grid, such as the upper surface of a rim forming an opening of the grid, so as to support the lighting assembly in the lighting fixture. The support surfaces may be formed such that the total length and width of the lighting assembly may render it difficult to insert a mounted lighting assembly in the grid. Being able to mount such lighting assembly in pieces or modules further enables the lighting assembly to (at least almost) fully cover the opening in the cell of the grid. Thereby, the space above the grid of the dropped ceiling may be hidden for a viewer observing the ceiling. 
     The first reflector, the second reflector and the at least two sidewall parts being adapted to be secured to each other by the first fastening arrangement and the second fastening arrangement provide a modular lighting assembly comprising relatively few module components, whereby manufacturing, handling, packaging, transportation and mounting of the lighting assembly is facilitated. 
     A light engine may be arranged in the cavity between the first reflector, the second reflector and the at least two sidewall parts. When assembled, the first reflector, second reflector and the at least two sidewall parts may form a truncated pyramid, that is to say, a hollow gap may be formed at the dissection plane of the pyramid. The light engine preferably spans the gap at the top face of the truncated pyramid. The physical strength of the lighting assembly may be increased by securing the light engine across this gap. By adapting the shape and/or design of the first reflector, the second reflector and the at least two sidewall parts and hence the cavity, a desired illumination pattern in terms of spreading, direction, distribution angle etc. of light emitted out from the cavity may be achieved. This desired illumination pattern may be further tailored by the addition of a diffuser at a light exit window of the light engine. The desired illumination pattern may be yet furthered tailored by altering the shape and or depth of the light engine reflector. 
     The lighting assembly may e.g. be a retrofit lighting assembly. Such retrofit lighting assembly may e.g. be used for modification or conversion of a luminaire already in use. As an example, a luminaire may be converted from an incandescent, fluorescent, or high intensity discharge light source into a LED light source. 
     In the present specification, the term “junction” between the first reflector, the second reflector and the at least two sidewall parts may refer to an intersection or boundary between neighboring parts. The junction may e.g. extend from a position close to the rim of the cavity towards the top face, or gap, of the cavity. It will however be appreciated that neighboring first reflector, second reflector and at least two sidewall parts do not necessarily have to physically abut each other at the junction; the junction may just as well be defined as the point, line or area in which an imaginary extension of a first reflector and a second reflector and at least two sidewall parts meet, or intersect. Further, the term “corner” of the cavity may refer to the boundary or area where two neighboring sides of the four-sided cavity (at least almost) meet. Hence, the four-sided cavity comprises four corners. 
     According to an embodiment, the light engine may comprise a diffuser arranged to diffuse light emitted by the at least one LED. The diffuser may be adapted to spread the light that is output from the light engine so as to provide a soft, diffuse lighting. This may reduce the levels of glare to acceptable amounts as LEDs are well known to be extremely bright point light sources. Hence, by using a diffuser, the homogeneity and distribution of the illumination may be improved. Advantageously, the diffuser may be arranged to cover the light engine and/or the first reflector, the second reflector and the at least two sidewall parts so as improve the visual appearance of the lighting assembly. The diffuser may also be arranged to cover possible gaps between the lighting assembly and the grid or lighting fixture so as to achieve a ceiling having a relatively smooth and flat surface. 
     In an embodiment, the diffuser may be arranged to cover the light exit window of the light engine. The diffuser may directly abut the light engine or it may be spaced away from the light exit window of the light engine by a end caps. 
     According to an embodiment, installation of the light engine may facilitate the earthing of the parts of the lighting assembly. The driver that is part of the light engine is provided with an earthing wire which is connected to the relevant earthing location on the luminaire that was already in use. Therefore, this means that the light engine is earthed and as such, if the other parts of the assembly are electrically connected to the light engine, they will be earthed also. 
     According to an embodiment, the driver may be attached to the light engine at an angle from, and not directly attached to the light engine reflector. This may mean that an angled bracket, i.e., a bracket wherein the driver mounting face and the face that mounts to the light engine reflector are at an angle to each other, is used to attach the driver to the light engine. 
     According to an embodiment, the first fastening arrangement and/or the second fastening arrangement may comprise at least one protruding member being integrally formed with at least one of the first reflector, second reflector and the at least two sidewall parts and at least one receiving member being integrally formed with at least another of the aforementioned parts. The protruding member is adapted to engage with the receiving member in order to secure the first reflector, the second reflector and the at least two sidewall parts to each other. Thereby, facilitated fitting of the aforementioned parts may be achieved, as the number of required additional components or material such as screws, rivets etc. is reduced. The fastening arrangement according to the present embodiment allows the first reflector, second reflector and at least two sidewall parts to be secured to each other by simply inserting the protruding member into the receiving member upon/after the sidewall parts are arranged in the lighting fixture which may shorten the time required for installation. 
     The protruding member and the receiving member being integrally formed with the first reflector, the second reflector and the at least two sidewall parts also enables for a facilitated manufacturing process since they can be formed at the same time as the first reflector, the second reflector and the at least two sidewall parts are formed. Thereby, the number of steps and tools of the manufacturing process, as well as the bill of material, may be reduced. 
     It will however be appreciated that the first reflector, the second reflector and the at least two sidewall parts may be engaged to each other by means of other fastening arrangements which may be integrally formed with the aforementioned parts or form elements that are structurally distinct from these parts. Examples of other fastening arrangements may include clips, clamps, pins, magnets, screws, rivets, quarter-turn fasteners etc. 
     According to an embodiment, the protruding member of the fastening arrangement may comprise a tab and the receiving member may comprise a slit. The tab is adapted to be inserted in the slit and bent so as to secure the first reflector, the second reflector and the at least two sidewall parts to each other. By bending the tab, e.g. by hand or by means of pliers, a mechanical joint between the adjacent parts may be achieved. The bendable tab may also enable disassembling of the lighting fixture. By letting the tab assume its original shape, it may be removed from the slit and the first reflector, the second reflector and the at least two sidewall parts loosened from each other. The tab may be formed of a material and/or having a shape allowing the tab to be bent several times without being impaired by fatigue or wear, thereby allowing the lighting assembly to be repeatedly installed and removed. Being able to reuse or re-install a lighting assembly a plurality of times may advantageously facilitate e.g. repairing, service, and maintenance of the luminaire, the lighting assembly, the light engine, or the lighting fixture. The use of a bendable tab may also enable future adjustment of the illumination device, such as e.g. adjustment of the securing of the first reflector, the second reflector and the at least two sidewalls and the fitting tolerance in the lighting fixture. 
     The tab and the slit may also be adapted to allow for the dimensions of the cavity to be adjusted so as to improve the fitting in the lighting fixture and/or the grid. This may e.g. be achieved by varying the length of the tab that is inserted in the slit and bent. As an example, a cavity being formed of adjacent parts that are secured to each other by tabs being fully inserted in the slit may be smaller than a cavity whose adjacent parts are secured by tabs that are only partly inserted in the slits. Consequently, by varying the length of insertion of the tabs, there may be provided an adjustable gap between neighboring parts, which gap can be used for adjusting the dimensions of the cavity. In other words, being able to vary the length of the inserted (and bent) tab so as to adjust the distance between joined adjacent parts allows for a lighting assembly having increased dimensional tolerance range. 
     Thus, the present embodiment enables a more flexible and robust lighting assembly that can be used with lighting fixtures and/or grids of slightly various sizes. 
     According to an embodiment, at least one (and preferably all) of the first reflector, the second reflector and the at least two sidewall parts is formed by sheet material, such as a sheet metal. Sheet materials, and in particular sheet metals, are advantageous in that they may be cut and bent into a variety of shapes with relative ease. A further advantage is that they may be pre-painted during manufacture (before being coiled and sent to the lighting assembly manufacturer), this may bring cost reduction benefits. A sheet material may also allow for parts that are relatively stable and light weight, which may facilitate production and installation of a lighting assembly with an improved robustness and reliability. Further, a sheet material having relatively high heat conductivity may be used in order to provide a heat sink capable of dissipating heat energy generated by the light engine. 
     Alternatively the sheet material may be painted after manufacture. This may be more labour intensive and thus more expensive than using prepainted sheet material but it does ensure that the fixing locations remain paint-free. This may prove advantageous for electrically connecting the parts together to provide an earth connection. 
     According to an embodiment, the fixing may “bite&#39; through the paint in order to provide an electrical connection. This may be achieved, for example, by the use of a serrated washer inserted between two parts or under the head of a bolt or screw fixing. When the fixing is tightened down, the washer will rotate with the fixing and the serrations will bite through the paint until a direct metal to metal connection is achieved. Advantagously, the washer is located between two parts and will bite into the painted surface of both of the parts and will provide a direct metal to metal connection via the serrated washer. Alternatively, the paint may be mechanically or chemically removed from the desired locations. 
     According to an embodiment, the use of stamping or folding tools may remove the paint at the required locations such that the electrical connection is achieved. 
     According to an embodiment, at least one of the support surfaces may be integrally formed with the first reflector, the second reflector and or the at least two sidewall parts. Thereby, a facilitated manufacturing process can be obtained, in which the support surface may be formed at the same time as the aforementioned parts are formed. This allows for a reduced number of steps and tools of the manufacturing process, as well as a reduced bill of material. 
     According to an embodiment, the light engine reflector is also formed with a support surface, this support surface may be a peripheral rim and may be used to facilitate the assembly of the lighting assembly. The support surfaces may have slots to allow a tab from the first reflector and the second reflector to pass through and to fasten the first reflector and the second reflector to the light engine reflector. In a preferable embodiment the at least two sidewall parts have tabs which are arranged to pass through further slots in the light engine first reflector and enable an even more rigid lighting assembly. 
     According to an embodiment, the light engine has a sprung plate at either end, these resilent plates extend away from the ends of the light engine when at rest but may be resiliently biased towards the light engine. The sprung plates are prefably identical to facilitate the light engine being fitted either either way round (end to end rotation). 
     The sprung plates may be mounted to the end panel of the light engine using a rivet, a screw, a nut and bolt, a quarter-turn fastener or any other fixing. The use of sprung plates means that installation of the light engine is simplified and furthermore, the opposing forces, which are preferably equal, will centralise the light engine between the opposing sidewall parts. This also means that the light engine can accommodate manufacturing tolerances of the lighting assembly which may affect the size of the opening in which the light engine is located. 
     In a preferred embodiment, the sprung plates may further comprise hook portions that engage with features on the at least two sidewall parts to provide an earthing connection between the sidewall parts and the light engine. 
     In an embodiment, two endcaps are fitted to the light engine to support a diffuser. These end caps may further comprise at least one opening to facilitate the releasing of the spring plates and the subsequent removal of the light engine or disassembly of the light assembly. 
     According to an embodiment, at least one of the support surfaces may be adapted to engage with (such as rest on) a frame arranged at a rim of the lighting fixture so as to support the lighting assembly at the lighting fixture. During assembly, at least one sidewall part may be arranged in the lighting fixture such that the support surface, and hence the at least one sidewall part, is resting on an upper surface of the frame. Thereby, the lighting assembly relatively easily and quickly can be mounted and supported in the lighting fixture. The frame may e.g. be a part of a grid (such as a cell of a grid) used as a support structure in a dropped ceiling. 
     The support surface may e.g. be arranged to engage with the frame such that the lighting assembly (at least almost) covers an opening defined by the frame, whereby any space or gap between the frame and the lighting assembly is reduced or even eliminated. Thereby, the space above the lighting assembly and/or lighting fixture may be hidden from a viewer observing the ceiling. 
     According to an embodiment, the support surface may comprise a protruding flange of the first reflector, the second reflector and/or the at least two sidewall parts. For example, an edge of the part may be folded so as to form the support surface. Thereby, a relatively robust and stable assembly is enabled, having a reduced risk of coming loose from the lighting fixture. 
     By adapting the configuration of the first reflector, the second reflector and/or the at least two sidewall parts, the illumination output may be controlled, or at least modified, so as to achieve an illumination having a desired beam angle, distribution, pattern, intensity etc. Further, the reflective surface of the first reflector, the second reflector and/or the at least two sidewall parts may improve the efficiency of the emitted light and reduce losses due to e.g. absorption in the cavity. 
     The reflective surface may be formed of a bulk material (i.e. the material of which the part is formed, such as e.g. a sheet metal) having a relatively high coefficient of reflection. The surface may also be provided by e.g. polishing of the material prior to forming the sidewall portion, prior to mounting the portions, and/or after the lighting assembly is installed. The reflective surface portion may also be provided by an at least partially light reflecting coating which may be applied prior to or after the first reflector, the second reflector and/or the at least two sidewall portions are formed. Such coating may also be applied after the lighting assembly is installed. 
     According to an embodiment, the light emitting element may comprise a LED. However, the term “light emitting element” may refer to any device or element that is capable of emitting radiation in any region or combination of regions of the electromagnetic spectrum, for example the visible region, the infrared region, and/or the ultraviolet region, when activated e.g. by applying a potential difference across it or passing a current through it. Therefore, a light-emitting element can have monochromatic, quasi-monochromatic, polychromatic or broadband spectral emission characteristics. Each light-emitting element may have at least one light source. Examples of light sources include semiconductor, organic, or polymer/polymeric light-emitting diodes (LEDs), blue LEDs, optically pumped phosphor coated LEDs, optically pumped nano-crystal LEDs or any other similar devices as would be readily understood by a person skilled in the art. Furthermore, the term light-emitting element can be used to define a combination of the specific light source that emits the radiation in combination with a housing or package within which the specific light source or light sources are placed. For example, the term light emitting element may comprise a bare LED die arranged in a housing, which may be referred to as a LED package. 
     It is noted that embodiments of the invention relates to all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the lighting assembly are all combinable with embodiments of the method as defined in accordance with the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects will now be described in more detail with reference to the appended drawings showing embodiments, in which: 
         FIG. 1  is a bottom plan view of a light engine according to an embodiment; 
         FIG. 2  is a bottom plan view unassembled lighting assembly according to an embodiment; 
         FIG. 3  is a bottom plan view of an assembled lighting assembly according to another embodiment; 
         FIG. 4  is a cross sectional perspective view of a mounted lighting assembly; 
         FIG. 5  is a schematic outline of a method for mounting a lighting assembly according to an embodiment; 
         FIG. 6  is a close up view of a fixation between parts of the lighting assembly; and 
         FIG. 7  is a bottom plan view of a partially assembled lighting assembly according to an embodiment. 
     
    
    
     All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted or merely suggested. Like reference numerals refer to like elements throughout the description. 
     DETAILED DESCRIPTION 
     The present aspects will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present aspect to the skilled person. 
     With reference to  FIG. 1 , there is shown a bottom plan view of a light engine  100  according to an embodiment. The light engine  100  comprises a reflector  103 , two end caps  104   a ,  104   b  and three light emitting elements  130 . The reflector  103  is provided with a peripheral rim that is bent to form support surfaces, or protruding flanges  106 ,  107 . 
     With reference to  FIG. 2 , there is shown an exploded bottom plan view of a lighting assembly  105 . The lighting assembly  105  comprises a first reflector  110  and a second reflector  114 , the first reflector and the second reflector are shown in a longitudinal direction, a first sidewall part  112  and a second sidewall part  116 , the first sidewall part and the second sidewall part are shown in a lateral direction, fastening arrangements  122 ,  124 , and a light engine  100 . 
     The first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  are formed of a sheet metal that is cut and bent into the desired shape. As shown in  FIG. 2 , the first reflector  110  and the second reflector  114  are in a longitudinal direction and are secured to the two sidewall parts  112 ,  116  (located in a lateral direction) by means of the fastening arrangements  122 ,  124  so as to form a four-sided cavity. In this embodiment, each first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  represents a sidewall of the cavity, wherein the light engine  100  forms a top wall, or roof, of the cavity. The first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  are provided with a peripheral rim that is bent (the fold is indicated by dashed lines in the figure) to form support surfaces, or protruding flanges  111 ,  113 ,  115 ,  117 . In other words, each one of the first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  may be described as a flat sheet metal piece that has been bent into an essentially plain portion forming a side of the cavity and a protruding flange  111 ,  113 ,  115 ,  117  adapted to support the lighting assembly  105  in a lighting fixture (not shown). However, it will be appreciated that the first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  may be formed of other material, such as e.g. polymers, by other techniques, such as e.g. injection molding, and into other shapes, such as e.g. a curved profile. Further, the dimensions of the first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  may be adapted to fit into wide variety of lighting fixtures and grids  160  of various widths and lengths. 
     According to the embodiment as shown in  FIG. 2 , the three light emitting elements  130  (e.g. LEDs), are arranged on the light engine  100 . The LEDs  130  may e.g. be preassembled on the light engine  100  in order to facilitate and speed up the installation of the lighting assembly  105 . 
     The first reflector  110 , second reflector  114 , first sidewall part  112  and second sidewall part  116  are adapted to be assembled upon insertion of the lighting assembly  105  in the lighting fixture and secured to each other by means of the fastening arrangement  122 ,  124 . The fastening arrangement  112 ,  124  may comprise protruding members, such as tabs  122  that are integrally formed with e.g. the first sidewall part  112 , second sidewall part  116 , and receiving members, such as slits  124  that are cut out from the first reflector  110  and second reflector  114 . The tabs may e.g. be formed by cutting and bending as the first sidewall portion  112  and second sidewall portion  116  are formed. Similarly, the slits  124  may be cut out during manufacturing of the first reflector  110  and the second reflector  114 . The slits  124  may have a shape, or geometry, that corresponds to a cross section of the tabs  122  in order to allow the tabs  122  to be inserted through the corresponding slits  124 . Further, the tabs  122  may be adapted to be deformed after being inserted through the slits so as to fix the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  to each other. The tabs  122  may e.g. be plastically deformed by bending, folding or wrenching into a shape that prevents the tabs from being loosened from the slits. Alternatively or additionally, the protruding members may be secured to the receiving members by other means, such as e.g. clenching, gluing, screwing, etc. 
     When the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  are secured to each other, they are arranged such that a peripheral portion of a first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  meets a peripheral portion of another one of the aforementioned parts, thus forming a junction between the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  that is arranged at one of the four corners of the cavity. 
     As each of the four flanges  111 ,  113 ,  115 ,  117  may be arranged to engage with e.g. the lighting fixture or a grid of a dropped ceiling, all four sides of the lighting assembly  105  may be supported in the lighting fixture. However, the lighting assembly  105  may comprise only two or three support surfaces. In case only two support surfaces are provided, each support surface may be arranged at different sides of the four-sided cavity, such as at opposing sides, so as to make the fixation of the lighting assembly  105  more stable. As an example, the first reflector  110  and second reflector  114  may be provided with support surfaces whereas the first sidewall part  112  and second sidewall part  116  may not. 
       FIG. 3  shows a bottom plan view of an assembled lighting assembly  105  according to another embodiment. The lighting assembly  105  may be similarly configured as the lighting assembly  105  described with reference to  FIG. 2 , but according to this embodiment, each of the first sidewall  112  and second sidewall  116  are provided with a recess  118  for receiving a protrusion  119  of the light engine  100 , respectively. By arranging light emitting elements, such as LEDs  130 , on the protrusion, the LEDs  130  may be positioned closer to the lateral side of the cavity. Thereby, the light emitted out of the cavity may be better distributed along the longitudinal extension of the lighting assembly  105 . However, it will be appreciated that the placement of the light emitting elements  130  by no means is limited to the light engine  100 , further light emitting elements  130  may be arranged on any part of the first reflector  110 , first sidewall part  112 , second reflector  114  and second sidewall  116 . Consequently, any of the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  may be provided with a recess  118  adapted to receive a protrusion  119  from any other of the aforementioned parts or the light engine  100  in order to provide a desired distribution of the emitted light. 
     In  FIG. 3 , the outline of a grid  160  of a dropped ceiling is indicated to illustrate an example of a lighting assembly  105  being supported by four flanges  111 ,  113 ,  115 ,  117  on the grid  160 . The dimensions of the flanges  111 ,  113 ,  115 ,  117  may be adapted to (at least almost) fully cover the gaps between the lighting assembly  105  and the grid  160  or lighting fixture. The first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  are secured to each other by means of the tabs  122  of the first sidewall  112  and second sidewall  116  which engage with the slits  124  of the first reflector  110  and second reflector  114 . As shown in  FIG. 3 , the tabs  124  may be bent or folded, after being fit into the slits  122 , so as to prevent the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  from coming loose from each other. 
     The first reflector  110 , first sidewall  112 , second reflector  114 , second sidewall  116  and light engine  100  may be arranged in the lighting fixture one by one and subsequently secured to each other by the fastening arrangement  122 ,  124 . Even though the mounted lighting assembly  105  may be slightly larger than e.g. the opening of the grid  160 , the lighting fixture or the opening of a frame of the lighting fixture, the lighting assembly  105  may still be inserted in the lighting fixture by assembling the first reflector  110 , first sidewall  112 , second reflector  114 , second sidewall  116  and light engine  100  one by one in the lighting fixture. As an example, the lighting assembly  105  in  FIG. 3  is provided with circumferential flanges  111 ,  113 ,  115 ,  117 , which due to the length and width of the lighting assembly  105  may render it difficult to insert a pre-mounted lighting assembly  105  in the grid  160 . However, the lighting assembly  105  may be inserted in the lighting fixture in pieces or modules, such as first reflector  110 , then first sidewall  112 , then second reflector  114 , then second sidewall  116 , the light engine  100 , which then may be secured to each other once they are inserted. As a result, a lighting assembly  105  having a circumferential periphery slightly larger than the opening in the grid  160 , or a corresponding opening in the lighting fixture or in a frame arranged at the lighting fixture, can thereby be mounted in the lighting fixture. 
       FIG. 4  is a perspective, cross sectional view of a lighting assembly  105  similarly configured as the lighting assemblies  105  described with reference to  FIGS. 2 and 3  mounted in a lighting fixture  170 . The cross section of the lighting assembly  105  is taken across the first reflector  110  and second reflector  114  and shows a LED  130  arranged on reflector  103  of the light engine  100  to emit light within the four-sided cavity  140  defined by the first reflector  110 , first sidewall part  112 , second reflector  114  and second sidewall  116 . 
     Each of first reflector  110  and second reflector  114  comprises a protruding flange  111 ,  115  which is adapted for supporting the lighting assembly  105  in the lighting fixture. As shown in  FIG. 3 , the flanges  111 ,  115  rest on the upper surface of a grid  160  of a dropped ceiling, in which the luminaire, comprising the lighting assembly  105  and the lighting fixture  170 , is recessed. 
     Further, the embodiment of the lighting assembly  105  shown in  FIG. 4  comprises a diffuser  150  arranged to diffuse the light emitted by the LEDs  130 . The diffuser  150  may e.g. by secured to the reflector  103  of the light engine  100 , the first reflector  110 , the first sidewall  112 , the second reflector  114  and/or the second sidewall  116  of the lighting assembly  105 , the grid  160 , or the lighting fixture  170 . The fixation may e.g. be realized by means of protruding and receiving members similar to those previously discussed, or by fastening means such as clips, screws, etc, it may also be realized by the provision of snap fixing geometry. This geometry may be provided in an interupted manner or as a continuous feature around the periphery of the diffuser  150 . The present diffuser  150  may e.g. be formed of a rectangular plate, it may be formed of a rectangular plate that is curved in one direction so as to conform with the envelope surface of a cylinder, or it may be formed in any preferred geometry. Thereby the diffuser  150  may be arranged to (at least almost) cover the LEDs  130  of the light engine  100  and hence improve the visual appearance of the lighting assembly  105 . The diffuser  150  may also be slightly larger than the opening, or cell, defined by the grid  160  in order to partially or fully cover the opening of the cavity  140  such that neither the other parts of the lighting assembly  105  nor the lighting fixture  170  are visible to a viewer observing the ceiling. The diffuser  150  may be flat so as to provide a flat lower or inner surface of the ceiling. 
     A method  500  for mounting a lighting assembly in a lighting fixture according to an embodiment will be described with reference to  FIG. 5 . The lighting assembly  105  may be similarly configured as the lighting assembly  105  described with reference to  FIGS. 1 to 3 . 
     The method  500  comprises a step of arranging  510  the first reflector  110 , the first sidewall part  112 , the second reflector  114 , the second sidewall part  116  and the light engine  100  in the lighting fixture  170 , and a step of securing  520  the first reflector  110 , the first sidewall  112 , the second reflector  114 , the second sidewall  116  and the light engine  100  to each other by means of a fastening arrangement  122 ,  124 . When the first reflector  110 , first sidewall  112 , second reflector  114 , second sidewall  116  and light engine  100  are secured to each other, they define sidewalls of a four-sided cavity  140  and junctions between the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  are arranged at the corners of the cavity  140 . Each one of at least two of the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  comprises a support surface, such as e.g. a flange  111 ,  113 ,  115 ,  117 , adapted to support the lighting assembly  105  in the lighting fixture  170 . The support surfaces are arranged to be at different sides of the four-sided cavity  140  when the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116  are arranged in the lighting fixture, and may e.g. engage with a frame arranged at the lighting fixture  170  or a grid of a dropped ceiling. 
       FIG. 6  shows a close up view of a fixation between the second reflector  114  and the first sidewall  112 . The second reflector  114  comprises a slot through which a protruding member  122  (in this case exemplified as a tab) passes. The protruding member  122  protrudes from the first sidewall  122 . Once the protruding member has passed through the slot, it may be bent such that dissambly cannot be carried out until the protruding member  122  has been straightened such that it may pass through the slot in the second reflector  114 . 
       FIG. 7  shows a bottom plan view of a partially assembled lighting assembly  105  wherein the light engine  100  has been hung using two hinges within the assembly. The driver (not shown) may be located at an angle from, and not directly attached to the light engine reflector  103 . This angular location of the driver may ease the installation of the light engine  100  into the partially assembled lighting assembly. The angle of the mounting may be chosen such that when the light engine has been hung using at least one hinge within the assembly, the driver is arranged vertically. This may facilitate the easy connection of the driver to the existing wiring from the lighting fixture. The final stage is to rotate the light engine  100  such that it engages with the second reflector  114  and is affixed in position. The angular mounting may furthermore allow the easy rotation of the light engine around the at least one hinge as it reduces the instances wherein the driver impinges upon the back face of the first reflector  110 . 
     Of course, any angle can be chosen for the driver mounting, it may be fitted directly to the rear of the light engine reflector  103  or it may be orientated such that when the light engine is hung using the at least one hinge the driver is arranged horizontally. The affixing of the light engine  100  to the second reflector  114  may be achieved in any manner of mechanical fixing methods such as, for example, a sprung clip (not shown). 
     The lighting assembly  105  according to the described embodiments may e.g. be a retrofit lighting assembly. Such retrofit lighting assembly may e.g. be used for modification or conversion of a luminaire already in use. As an example, a luminaire may be converted from an incandescent, fluorescent, or high intensity discharge light source into a LED light source. 
     The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the cavity  140  may be formed of more than the first reflector  110 , first sidewall  112 , second reflector  114  and second sidewall  116 . The first reflector  110 , first sidewall  112 , second reflector  114 , second sidewall  116  and light engine  100  may also be secured to each other by other fastening arrangements than those comprising a protruding member  122  and a receiving member  124 . As an example, the first reflector  110 , first sidewall  112 , second reflector  114 , second sidewall  116  and light engine  100  may be attached to each other by hook-and-loop fasteners, clips, adhesive tape, etc. 
     Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.