Patent Publication Number: US-2023141644-A1

Title: Lighting apparatus having a flexible planar lighting element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of PCT/EP2021/067465 filed on Jun. 25, 2021, which is based upon and claims the benefit to DE 10 2020 116 917.5 filed on Jun. 26, 2020, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to a lighting apparatus, having a flexible planar lighting element, which has a plurality of illuminants distributed over the surface of a planar carrier material, which carrier material can comprise a textile-based flexible planar circuit carrier, which circuit carrier can be fitted with the plurality of illuminants on a front side, the illuminants being interconnected by electrical lines formed in or on the circuit carrier. 
     Prior Art 
     Corresponding planar lighting elements are marketed, among others, by the applicant under the name Carpetlight and have been described, among others, in the German patent DE 10 2014 206 882 B4. They are designed for various applications, for example planar illumination in the field of photography, film and television shooting. Especially in the latter areas, continuous illumination with high luminous intensities is required, which in most cases is achieved by systems of spotlights, reflectors and diffusers. To illuminate changing scenes, the lighting system components used must be flexible to combine, place and align. To this end, DE 10 2014 206 882 B4 proposes to provide a flexible planar lighting element having a plurality of illuminants distributed over the surface of a planar carrier material, which carrier material has at least two layers, a first layer being formed as a textile-based flexible planar circuit carrier, which is fitted with the plurality of illuminants on a front side, the illuminants being interconnected by means of electrical lines formed in or on the circuit carrier, a second layer being formed as a flexible planar cooling layer and being connected to the circuit carrier on its rear side opposite the front side. 
     Such a planar lighting element represents, in simple terms, a self-luminous cloth that is bendable, rollable, foldable, rotatable, and crushable, and that has a luminosity distributed over the surface that is sufficient to illuminate, for example, a scene or part of a scene. Corresponding “cloths” or rather flexible planar lighting elements can be manufactured in any size and are therefore easy to make up. The fact that they correspond to known reflectors and diffusers in terms of their flexibility and planarity makes them suitable for replacing the known combinations of spotlights, reflectors and diffusers. They also manage with a lower luminous intensity, since their luminous intensity is fully available for illuminating a given scene and is not, as is the case with conventional spotlight systems, only incompletely deflected and diffused towards the scene. This also leads to a reduction in the waste heat generated. 
     US 2016/0091185 A1 discloses a lightweight, portable and flexible light bank having LED strips attached to a fabric and having a Velcro attachment system for attachment to various objects. The light bank can be rolled up and folded. Batteries can be removably attached to the back of the light bank. 
     SUMMARY 
     Accordingly, an object is to provide a lighting unit that allows more flexible use than before. 
     Such object can be solved by a lighting unit, comprising a flexible planar lighting element, such as a planar light source, which has a plurality of illuminants distributed over the surface of a planar carrier material, which carrier material comprises a flexible planar circuit carrier, which can be textile-based, the circuit carrier is fitted with the plurality of illuminants on a front side, the illuminants being interconnected by electrical lines formed in or on the circuit carrier, and a controller configured to supply power to and control the plurality of illuminants, the controller comprises a housing disposed on an edge of the planar lighting element and mechanically connected thereto, an edge of the planar lighting element being partly accommodated in the housing of the controller, the housing comprising electrical and electronic components and lines connected to the electrical lines of the planar lighting element, and a strain relief configured to absorb tensile stresses between the housing of the controller and the planar lighting element to keep the tensile stresses away (i.e., eliminate, reduce or minimize such tensile stresses) from the electrical connections between the controller and the planar lighting element. 
     Such lighting apparatus integrates the planar lighting element and the controller and configures the lighting apparatus to be robust and without external cables by a high-tensile connection of the planar lighting element to the housing of the controller. Such lighting apparatus can be used in a variety of situations. For example, the lighting apparatus can be transported in a rolled or wound up state and unrolled and hung, stuck, laid out, etc., where it is needed, depending on the circumstances of the situation and the attachment options that are available. An external power supply is not necessary if it is already integrated in the controller. However, the controller can also have a connection for an external power supply regardless of whether a power supply is integrated. 
     Cases of application for the use of the lighting apparatus would be, for example, the illumination of tents, also makeshift tents in the military field, in disaster control or in mobile medical facilities, in police use for the illumination of accident sites, as well as for private use, as well as for photographers who need a mobile planar illumination system outside their studios that can be set up quickly. This list is not exhaustive. 
     The circuit carrier can be textile-based, such as synthetic fiber-based, or alternatively configured as a flexible film, such as polymer-based, such as polyimide or polyurethane. These materials can offer, among other things, high flexibility and low weight with good resistance. 
     The strain relief can be configured to create a high-tensile connection between the material of the planar lighting element and the housing. This means that there can be a direct high-tensile connection between the planar lighting element and the housing. 
     In embodiments, the strain relief can be configured as a clamp, as a row of tension-absorbing pegs, which are guided through a row of eyelets in the planar lighting element configured to match the arrangement of the tension-absorbing pegs, or as spacers with internal threads and screws, which are screwed or can be screwed into the internal threads of the spacers, or as a cover, which is screwed or can be screwed or, alternatively, is clamped or can be clamped to or onto the housing and, can have a stop bar, which can be attached to the planar lighting element and configured to prevent the planar lighting element from being pulled out of the cover, the carrier material can be reinforced in the region of the eyelets or the spacers, such as by a double layer of the flexible planar circuit carrier. Such a clamp can grip the planar lighting element in sections from one side or from two sides and be equipped with a slip-preventing surface or profiling, for example with a rubber coating or a barbed or ribbed profile. A simpler but equally effective embodiment can be a series of pegs or pins extending transversely to the planar extent of the planar lighting element through eyelets along the edge of the planar lighting element. The tension-absorbing pegs or, alternatively, pins can be part of the housing of the controller, or at least can be permanently connected to it. 
     The electrical lines between the controller and the illuminants can be continuous, i.e. without interruption, and their respective ends can be directly connected, for example soldered, to the corresponding contacts of the controller and the illuminants. Alternatively, the electrical lines can have an interruption with a contacting, which can be disposed in the region of the strain relief, the contacting can be configured as a spring pin contacting with spring pins and opposing contact surfaces, which are contacted and secured by fastening of the strain relief, or as a pin strip with contact pins, which can be accommodated or are accommodated in corresponding contact pin receptacles. 
     Spring pin contacting can still provide secure electrical contacting even under mechanical stress, because the spring pins have some clearance for relative movement with respect to their respective opposing contact surfaces. Because the spring pins have a springy) biased tip, gaps between the parts to be contacted caused by excessive tension can also be tolerated to a limited extent without interrupting the electrical through-contacting. The spring pins can also be configured as spring pin strips, and the contact surfaces as contact pans. 
     The spring pin contacting can be configured in such a way that a textile planar lighting element can have a pre-board in the area of the transition to the controller, which pre-board provides the contact surfaces for the spring pins and, if necessary, the strain relief. The contact surfaces and spring pins can each be disposed between the strain relief, with the strain relief being configured to press the pre-board and a circuit board of the controller against one another. This ensures secure spring pin contact. A suitable strain relief in this case can be a combination of spacers with internal threads on one of the two circuit boards and throughholes or through-openings for screws that engage in the internal threads of the spacers. The corresponding openings may penetrate several or all layers of the planar lighting element. 
     Other strain relief may also be rivets, SMD spacers (i.e., a spacer designed as a “surface mounted device”) with or without threads, or bolts for connecting the circuit boards. Thus, in further embodiments, the contacting may be such that a pre-board includes SMD sockets applied to the textile on its upper surface, into which SMD pins are inserted from the main board. This can be done in a vertical arrangement of the circuit boards on top of each other or in a horizontal configuration next to each other. The mechanical strain relief can be the same as described previously. The strain relief may be implemented alone or in addition to the previously described examples of strain relief. 
     An embodiment of the contacting with a pin strip with contact pins, which can be received or are received in corresponding contact pin receptacles, can be a simple and inexpensive possibility for the contacting. Since contacting is involved in which the contact pins of the pin strip are parallel, the contacting can be loaded in the direction of the alignment of the contact pins. In an embodiment, this happens in that the pin strip is received in a cover that is screwed or clamped to or onto the housing of the lighting apparatus. For this purpose, the housing can have a corresponding contact strip with contact pin receptacles for the contact pins of the pin strip and for matching screw or clamping structures that interact with matching screw or clamping structures on the cover. 
     In further embodiments, the strain relief can be configured such that an enclosure of the planar lighting element carrying the illuminants or the planar lighting elements themselves can have stop bars, such as keder strips, metal strips or plastic strips, which can have round, square, triangular or elliptical cross-sections, at their end edges towards the housing, which stop bars can be fixed to the housing behind a pushed-on attachment or rather frame. The stop bars can be sewn, glued or laminated, for example, to the planar lighting element, such as to layers enclosing the inner textile circuit carrier. In this case, a seal against water and environmental influences can be made on the inner module, which can be laminated or coated, by a clamping seal on an edge of the actual housing in such a way that the housing can become a single-chamber system. 
     The planar lighting element can remain completely or mostly outside the then already waterproof housing in embodiments with a stop bar or stop bars, and the stop bars can be disposed parallel to the housing wall outside the housing. Subsequently, an attachment or rather frame, for example made of plastic, metal or other suitable materials with a central recess, which can be optically closed by an upper and a lower flexible rubber lip, can be pulled over the planar lighting element and connected to the housing. The attachment or rather frame can then be disposed in front of the stop bars so that they remain in the space between the housing and the attachment or rather frame and cannot protrude through the central recess of the frame even under tension. This attachment or, respectively, frame can be connected to the housing by clamps and/or screw connections. The attachment or, respectively, frame can also be formed by an upper and a lower half shell, which grip over the stop bars and fix them against being pulled out. 
     In embodiments, the planar lighting element can have, on a rear side of the circuit carrier, a flexible planar cooling layer which can be mechanically or materially connected to the circuit carrier, and/or a rain- and dirt-repellent layer, such as the cooling layer being shielded on the outside by the rain- and dirt-repellent layer or being formed as a rain- and dirt-repellent layer. A rip-stop fabric can function as a rain- and dirt-repellent layer. The cooling layer can have the property that the waste heat generated during operation of the illuminants is dissipated better than if the cooling layer is not present. Materials with increased thermal conductivity can be used, for example fabrics that have metallic fibers or metallic coatings, and either consist of them or have an admixture of them. The illuminants, for example LEDs, heat up less than in the case without a cooling layer. 
     In further embodiments, the planar lighting element can have a diffusion layer, such as a removable diffusion layer, and/or a directional grating on a front side of the circuit carrier. A diffusion layer, also called a diffuser, can be a fabric or other layer that provides for uniformity of illumination and distributes some of the intensity generated directly at the location of the illuminants into the area between the illuminants and, if necessary, shapes a certain directionality of the radiated illumination that may be different from the original directionality of the illuminants themselves. This can lead to wider distribution. A directional grating can again narrow this directional distribution, whereby a very uniform and at the same time directed illumination is achieved, especially in combination with the diffusion layer. In addition or alternatively, a layer of absorbent cotton can also be used, such as between the diffuser and the illuminants, which in addition to a diffusion effect can also provide mechanical protection. The diffusion layer itself, if provided with a wadding-like structure, can also perform a mechanical protective function. 
     Such a diffusion layer can be configured as a three-dimensional spacer fabric, as a diffusion foil or several diffusion foils or as a textile fabric, such as being made of transparent or semitransparent plastic fibers, for example as a fabric made of PMMA fibers (polymethyl methacrylate) with mechanical surface treatment and/or polymer optical fibers (POF). POF are polymer-based optical fibers, using, for example, PMMA, polycarbonates, polystyrenes, silicones, polyether sulfones, polysulfones or polyetherimides as core material. A mechanical surface treatment, such as an abrasive treatment or a targeted application of imperfections, can provide irregularities or rather imperfections in the surface into which and from which light can enter and exit. Such a diffusion layer disperses the illumination light even more than is possible with the planar arrangement of the illuminants on the circuit carrier, and can be used when the uniformity of illumination achieved without a diffusion layer is still insufficient, such as when the distance to the illuminated objects or scenes is small. 
     The efficiency of the illumination can be increased if the circuit carrier below the illuminants is provided with a reflective surface, such as an aluminum layer. This can be a layer of its own or a coating, for example a complete or partial metal vapor deposition. 
     In embodiments that are configured for weather resistance, the circuit carrier with the illuminants and the electrical lines can be coated with a waterproof coating, such as silicone. Such a coating can also protect against the ingress of dust and foreign bodies and provide mechanical relief for the electronic components and lines on the planar lighting element and can also protect against short circuits. Suitable coatings can include air-curing silicones, water-repellent paints, membranes, laminations, or other water-repellent coatings. 
     In embodiments, the housing of the controller can include a perimeter seal at one or more openings configured to prevent moisture or liquids from entering the housing. Such a seal may be a neoprene seal and/or a silicone seal that is sealed by pressing or screwing together housing halves. This applies to all housing openings of the housing of the controller. For example, a neoprene seal can be used for sealing the opening through which the planar lighting element is inserted into the housing, but other sealing materials such as silicone can also be used at this location. 
     Further possible applications are opened up if a stiffenable frame is included which is connected or connectable to the planar lighting element circumferentially or at two or more points, the frame stretching the planar lighting element in the stiffened state and allowing the planar lighting element to be folded and/or rolled up together with the stiffenable frame in the unstiffened state. Such a planar lighting element does not necessarily require an external support or a support surface, but can be used in an upright position, since the flexible planar lighting element is supported by the integrated frame in its stiffened state. This also allows the lighting unit to be placed on the floor without the need for additional aids. 
     Various configurations can be used to implement the stiffenable frame. In some embodiments, the stiffenable frame can comprise an air- or fluid-tight inflatable tube that can be filled with air or a fluid and deflated again by an external pump or a pump integrated in the housing of the controller. Such a hose can be attached either circumferentially or at several points to the circumference of the planar lighting element and in this way can obtain a limitation of its shape in the inflated state. It may also be integrated into the planar lighting element at the edge. 
     In other embodiments, the stiffenable frame can include one or more sections in which is disposed a coil spring or a series of aligned tubes having internal tension wires connected on one side to a tightening device and on the other side to one end of the coil or series of aligned tubes, which can be stiffenable by tensioning the tension wires and can be made flexible by relieving tension on the tension wires by a stiffening device disposed in the controller. 
     In various embodiments, the stiffenable frame can have an O-shape, an X-shape, or a U-shape. 
     Where the frame is disposed at the front side of the planar lighting element, the surface of the frame may be configured to be connected to further layers, for example to a removable diffusion layer and/or a directional grating. This may be implemented, for example, in the form of a hook and loop fastener. 
     In further embodiments, the frame connected to the illumination device can include a metallic material based on porous nanostructures interspersed with an ionic liquid responsive to voltage. By applying an external voltage from the controller of the illumination device, this material can be reversibly stiffened into arbitrary shapes. Such a material was disclosed, for example, in Hai-Jun Jin, Jörg Weissmüller, “A Material with Electrically Tunable Strength and Flow Stress,” Science, Vol. 332, Issue 6034, pp. 1179-1182. For example, the planar lighting element can be rolled out while the frame material is soft. Once the planar lighting element has been formed into the desired shape, the frame is stiffened by the application of the external voltage so that the planar lighting element maintains the shape once assumed. 
     For transportation purposes, it may be convenient for the lighting unit to be coiled and fixed in the coiled state. In embodiments, for this purpose, the planar lighting element can comprise fixing means for releasably fixing an end of the planar lighting element opposite the controller to another location of the housing or the planar lighting element, which fixing means can fix the lighting element in a state in which the planar lighting element is wound around the controller. Such a fixing means may be, for example, a push-button, a Velcro fastener or a magnet cooperating with a counterpart on the housing or on the underside of the planar lighting element. Alternatively, a technology that stiffens under voltage may also be used here. 
     For operation, waterproof operating elements, such as a membrane keypad, and/or a wireless communication interface via which the controller can be operated remotely by a remote controller or a mobile terminal can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features will become evident from the description of embodiments, together with the claims and the appended drawings. Embodiments can fulfill individual features or a combination of several features. 
       The embodiments are described below, without restricting the general idea of the invention, based on exemplary embodiments in reference to the drawings, whereby we expressly refer to the drawings with regard to the disclosure of all details that are not explained in greater detail in the text. In the drawings: 
         FIG.  1    illustrates a schematic perspective diagram of an embodiment with strain relief, 
         FIG.  2    illustrates a schematic perspective diagram of an embodiment from the outside, 
         FIG.  3    illustrates a schematic cross-sectional diagram of an embodiment in the wound-up state, 
         FIG.  4    illustrates a schematic diagram of a layer structure of an embodiment, 
         FIG.  5    illustrates a schematic detailed diagram of a further layer structure, 
         FIG.  6    illustrates a schematic diagram of the components of a controller of one embodiment, 
         FIGS.  7   a - 7   c    illustrate various configurations of integrated stiffenable frames, 
         FIGS.  8   a  and  8   b    illustrate schematic diagrams of a further embodiment with strain relief, 
         FIG.  9    illustrates schematic top view of the embodiment of  FIG.  8   , 
         FIG.  10    illustrates schematic diagrams of a further embodiment with strain relief, 
         FIG.  11    illustrates a schematic top view of the embodiment of  FIG.  10   , and 
         FIG.  12    illustrates a schematic cross-sectional diagram of the embodiment of  FIG.  10   . 
     
    
    
     In the drawings, the same or similar elements and/or parts are, in each case, provided with the same reference numerals such that they are not introduced again in each case. 
     DETAILED DESCRIPTION 
       FIG.  1    shows an embodiment of a lighting apparatus  10  schematically in perspective. The lighting apparatus  10  comprises a controller  20 , the housing  22  of which is shown in the open state, and without the electronic components disposed therein, such as circuit boards, batteries, circuits, control electronics, etc. The housing  22  has, on a transverse side, three tension-absorbing pegs  24  projecting from a lower surface of the housing  22 , and onto which a planar lighting element  50 , such as a planar light source, is fitted, the planar lighting element having for this purpose, on one of its edges, three eyelets  54 , i.e., reinforced openings, which provide a tension-relieved fit of the planar lighting element  50  on the tension-absorbing pegs  24  in the housing  22 . The planar lighting element  50  is flexible and planar in configuration, having a luminous area  56  surrounded by an edge  52 , which is non-luminous or, respectively, need not be luminous. 
     Instead of strain relief by the tension-absorbing pegs  24  and eyelets  54 , a clamping device not shown can also be used, which grips and clamps the planar lighting element  50  along one of its edges  52 , optionally with a rubberized surface or with a profiled surface. The clamping is then performed along the side that has the eyelets  54  in the exemplary embodiment of  FIG.  1   . 
     In the exemplary embodiment in  FIG.  2   , a perspective schematic external diagram of a lighting apparatus  10  is shown, in which the housing  22  of the controller  20  is closed. Exiting the housing  22  is the planar lighting element  50 , which has approximately the same width as the housing  22 , and may be wider or narrower if necessary. Exemplary electrical lines  60  and LED illuminants  58  are shown in the luminous area  56 , which actually fill the entire luminous area  56 . It is indicated that the LEDs are each disposed on circuit boards  59 , each of which is connected by two or more lines  60  that serve to supply power. Several different LEDs with different colors or color temperatures may also be used per circuit board, which LEDs are individually controlled to adjust the color temperature of the overall illumination. The embodiment is not limited to the selection of LEDs as illuminants. 
     The LED illuminants  58  and electrical lines  60  are applied to a circuit carrier  80 , which may have a textile base, for example a textile cloth. Details of this are described in DE 10 2014 206 882 B4. The electrical lines and the circuit boards  59  may be sewn to the textile cloth, so that there is a connection between the electrical components and the circuit carrier  80  that is both secure and low-stress. The nature of the connection from the electrical connections to the textile circuit carrier  80  results in a structure that can be easily and repeatedly rolled and folded. 
     The edge of the planar lighting element  50  includes a circumferential stiffenable frame  70  in an O-shape. It is an inflatable tube that is filled with compressed air or other pressurizable hydraulic fluid. Once the tube is filled with compressed air or hydraulic fluid and pressurized, it expands to its maximum dimensions, stabilizing the planar lighting element  50 . The tube can either be part of the planar lighting element  50  or circumferentially connected to it, for example with a Velcro fastener. Once the compressed air or hydraulic fluid is released, the planar lighting element  50  can be rolled up together with its stiffenable frame  70 . 
       FIG.  3    schematically shows an embodiment of a lighting apparatus  10  in a rolled-up state in cross-section. The planar lighting element  50  with the integrated frame  70  and the circuit carrier  80  is wound tightly around the housing  22  of the controller  20  and fixed at its end by a fixing means  65  in such a way that it does not unwind again on its own. In this initial example, the fixing means  65  is a push button. However, it can also be a Velcro fastener or a magnetic fastener. In this state, the rear side of the planar lighting element  50  is turned outward, which may be protected with a dirt- and rain-repellent material, so that the sensitive electrical and electronic components inside are protected against dirt and water. 
       FIG.  4    illustrates a layer structure of an exemplary embodiment of a planar lighting element  50 . LED illuminants  58  are disposed on the textile circuit carrier  80 , and a reflective layer  90  is applied to the surfaces between the LED illuminants  58 . Alternatively, instead of the reflective layer  90 , a mechanical protective layer can be used, for example in the form of a plastic film that has mask-like recesses at the locations of the LED illuminants  58  and thus covers and electrically insulates the spaces between the LED illuminants  58 . This film may itself also be metallized, thus providing a reflective layer  90 . 
     On the backside of the circuit carrier  80  is a cooling layer  82 , which is configured to absorb heat from the LED illuminants  58  and transfer it into the surface and to the backside, thereby lowering the temperature of the LED illuminants  58  themselves compared to a configuration that does not have a cooling layer  82 . A rain and dirt repellent layer  84  is disposed on the back side of the cooling layer  82 , for example made of a rip-stop fabric. The rain and dirt repellent layer  84  may be attached to the cooling layer  82 , but may also be only marginally connected to the other layers, so that an air cushion may be formed between the cooling layer  82  and the rain and dirt repellent layer  84 . 
     A diffusion layer  86  made of a diffusion fabric may be disposed on the front side, which is or will be connected to the circuit carrier  80  on the edge  52  of the planar lighting element  50 . 
       FIG.  5    shows a detail of another initial example in which the circuit carrier  80  is encased together with the LED illuminant  58  in a waterproof coating  88 , such as a silicone coating. The coating  88  need not have the same thickness over the entire surface as shown, but may be thinner than shown in the area between adjacent LED illuminants  58 . Also shown in this embodiment is a cross-sectional diagram of an LED illuminant  58  having circuit boards  59  and electrical lines  60 , with the cross-sectional direction being transverse to the longitudinal extent of the electrical lines  60 . The electrical lines  60  may be sewn onto the circuit carrier  80 , for example, if it is a textile carrier. The two LEDs may have different color temperatures or colors. For example, one LED may produce a warm white while the other produces a cool white. A third LED (not shown) may also be included to provide red light illumination, which does not interfere with the human eye&#39;s adaptation to dark environments. 
     In  FIG.  6   , an example of the electrical and electronic components in the controller  20  is shown schematically. A central component is control electronics  34 , such as a processor, CPU, control circuits and the like, which are connected to a rechargeable or non-rechargeable battery  30  and may include charging electronics for a rechargeable battery  30 . Further, the control electronics  34  are connected to and control the LED illuminants  58  via the electrical lines  60 . A membrane keypad  32  is provided as an example of a manual input interface for communicating to the control electronics  34  how to control the LED illuminants  58 . 
     Optionally, an electric pump  38  may be provided to inflate a U-shaped circumferential frame  72  in response to input and actuation by the control electronics  34  in order to stabilize the shape of the planar lighting element  50 . In addition, a wireless communication interface  36  may be provided to receive signals from a remote controller  40 , decode them, and transmit them to the control electronics  34 . In this way, the operation of the lighting apparatus  10  can be controlled remotely. 
     Other possible components include pushbuttons, display elements, such as LEDs or screens, which are also to be integrated into the housing surface in a waterproof and dirtproof manner. 
       FIGS.  7   a - 7   c    show three exemplary embodiments of different configurations of stiffenable frames. In  FIG.  7   a   , the frame is a circumferential O-shaped frame  70  that is connected to the planar lighting element  50  along its edge and stretches it when inflated.  FIG.  7   b    shows a very similar configuration with a U-shaped circumferential frame  72 , which is similarly connected to the planar lighting element  50  along its edge and stretches it when inflated. There may also be additional cross braces which exert outward pressure with respect to the long sides to additionally hold the planar lighting element  50  in shape. 
     A third embodiment is shown in  FIG.  7   c   , in which the frame  74  has an X-shape. In this case, the frame is connected at its ends at the attachment points  76  to the planar lighting element  50  at its corners opposite the controller  20 , and obtains its stability in the transverse direction from the X-shape. The X-shaped frame  74  is to be disposed at the rear side of the planar lighting element  50 , while the  0 - and U-shaped frames  70 ,  72  may be disposed either at the front side or the rear side of the planar lighting element  50 . 
     All three of the inflatable frames  70 ,  72 ,  74  can be put in a slack state by releasing the compressed air or hydraulic fluid, in which state the lighting unit  10  can be rolled up from the controller  20 . 
     As an alternative to the design of the frames  70 ,  72 ,  74  as tubes that can be filled with compressed air, other embodiments are possible. For example, the frames can also be filled with spirals, through each of which a pull wire is passed, which is connected at one side to the end of a spiral and is connected to a tensioning device within the housing  22  of the controller  20 . When the tensioning device is actuated, tensile stress is applied to the tension wire, forcing the spiral into a close-fitting, inflexible configuration, thereby stabilizing it. Instead of a spiral, a series of cylindrical sections can also be used, through which a tension wire is passed accordingly, and which center on each other and support and stabilize each other when tension is applied. 
       FIGS.  8   a ,  8   b    and  9  schematically show another embodiment of a lighting apparatus  10  with strain relief. In the upper diagram, the main board  26  of the controller  20  is not yet connected to the textile planar lighting element  50 . The main board  26  has on its edge a row of spring pins  25   a  disposed between two spacers  27   a  with an internal thread. The spring pins  25   a  can change their length because the tips are longitudinally axially movable and spring-biased. This can be seen in  FIGS.  8   a  and  8   b   , where in the unassembled state ( FIG.  8   a   ) the spring pins  25   a  are at their full length and in the assembled state ( FIG.  8   b   ) they are retracted under the clamp load. 
     The planar lighting element  50  has a pre-board  28  that rests in a planar manner on and is connected to the textile substrate. The pre-board  28  has through openings for screws  27   b , which are disposed such that the screws  27   b  engage in the internal threads of the spacers  27   a  when assembled. When the screws  27   b  are tightened, the pre-board  28  is pressed onto the main board  26 . The pre-board  28  has a series of contact surfaces  25   b  which face the spring pins  25   a  in the assembled state of the main and pre-boards  26 ,  28 . They establish the electrical through-contacting. The contact surfaces  25   b  are connected, for example soldered, on the opposite side of the pre-board  26  to the lines which lead to the illuminants  58  and supply them with power. 
     The arrangement of the rows of spring pins  25   a  and contact surfaces  25   b  between the spacers  27   a  and screws  27   b  creates a very effective strain relief and contacting  26 . The mechanical loads are carried by the screws  27   b  and spacers  27   a . The spring pin contacting is flexible and allows for some torsion of the contacting row without losing electrical contact. 
     In  FIG.  10   , another embodiment of a strain relief is shown schematically. Compared to the embodiment of  FIGS.  8   a ,  8   b    and  9 , mainly the type of contacting is changed. The planar lighting element  50  is again provided with a pre-board  28 , which is connected at its underside to the electrical lines on the planar lighting element  50 . It has a pin strip  29   a  with contact pins aligned parallel to each other. The main board  26  has corresponding contact receptacles for receiving the contact pins of the pin strip  29   a . This is shown in more detail in a schematic top view in  FIG.  11   . 
     This contacting  29 ′ is not mechanically stable on its own and would be immediately separated again under tension. Therefore, as shown in cross-section in  FIG.  12   , a cover  100  or, alternatively, a frame is provided, which receives the end of the flat body  50  in an opening and is or will be screwed to or onto the housing  22 . The main board  26  inside the housing  22  is not specifically shown in  FIG.  12    for clarity reasons. 
     Behind the pre-board  28 , the planar lighting element  50  is provided on at least one side, in the exemplary embodiment shown on both sides, with stop bars  104 , which may be sewn on, glued on or the like. These prevent the planar lighting element  50  from being pulled out of the cover  100  or, alternatively, the frame again. Together with the cover  100 , they act as a strain relief. The cover  100  may also be provided with sealing lips made of rubber, silicone or other suitable materials, against which the stop bars  104  are pulled or, alternatively, pressed and which reinforce the sealing effect exerted by the stop bars  104 , such as if these are configured as keder strips. 
     While there has been shown and described what is considered to be preferred embodiments, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims. 
     LIST OF REFERENCE SIGNS 
     
         
         
           
               10  Lighting unit 
               20  Controller 
               22  Housing 
               24  Tension-absorbing peg 
               25   a  Spring pin 
               25   b  Contact surface 
               26  Main board 
               27   a  Spacer with internal thread 
               27   b  Screw 
               28  Pre-board 
               29 ,  29 ′ Contacting 
               29   a  Pin strip 
               30  Battery 
               32  Membrane keypad 
               34  Control electronics 
               36  Wireless communication interface 
               38  Pump 
               40  Remote Controller 
               50  Planar lighting element 
               52  Edge 
               54  Eyelet 
               56  Luminous area 
               58  LED illuminant 
               59  Circuit board 
               60  Electrical lines 
               65  Fixing means 
               70  Stiffenable frame in O-shape 
               72  Stiffenable frame in U-shape 
               74  Stiffenable frame in X-shape 
               76  Attachment points 
               80  Circuit carrier 
               82  Cooling layer 
               84  Rain- and dirt-repellent layer 
               86  Diffusion layer 
               88  Waterproof coating 
               90  Reflective layer 
               100  Cover 
               102  Attachment of the cover to the housing 
               104  Stop bar