Fixture design for flexible LED circuit boards

[0001] This disclosure relates to lighting fixtures, and more specifically to flexible LED circuit board fixtures.

[0002] In lighting systems luminaires and LED arrays may be mounted using various lighting fixtures. Once the lighting fixture is assembled, the light distribution pattern it provides is typically fixed.

[0013] Techniques are disclosed for designing light fixtures for flexible LED circuit boards. The flexible LED circuit boards include an array of LED packages or LED chips and the surface of the flexible circuit boards is highly reflective, in some embodiments. In one example, a flexible LED circuit board may be shaped to conform to a rigid preform and the preform may be concave, convex, corrugated, or have any other custom shape depending on the desired light distribution pattern. In such an example, the shape of the preform as well as the location of the LEDs within the flexible LED circuit will determine the light distribution of the light fixture. Alternatively, the lighting fixture may have multiple rods held in place with side plates and a flexible LED circuit board may be woven between the rods, in some embodiments. In such embodiments, a set of hole patterns in the side plates will determine the location of the rods and the rods will determine the shape of the flexible LED circuit. In some cases, the side plates may include multiple hole patterns and attaching the rods to different hole patterns will result in different light distributions. In other embodiments, the rods may be attached to the side plates using mechanical actuators, or other techniques that allow the rod positioning to be mechanically adjusted. In such embodiments, instead of removing the rods from one set of hole patterns and inserting them into another set of hole patterns, the rods may be mechanically repositioned with respect to the side plates within a range of position patterns, each pattern providing a unique light distribution. The position of the rods as well as how the flexible LED circuit is woven between the rods will determine the final shape of the LED circuit within the lighting fixture.

[0014] General Overview

[0015] Flexible substrates with screen printed circuit patterns are used to fabricate flexible circuit boards. However, flexible LED circuit boards with reflective substrates may be configured into multiple shapes and may provide various light distribution patterns with the same physical parts. Furthermore, different LED placements within a flexible circuit board may provide different light distributions even if the shape of the flexible circuit is held constant. A lighting fixture may be designed that takes advantage of these unique characteristics of a flexible LED circuit board.

[0016] Thus, in accordance with an embodiment of the present invention, a lighting fixture is disclosed for housing a flexible circuit board populated with an array of LED packages or LED chips. The flexible substrate of the LED array may be a reflective material (e.g., PET), and the circuit pattern may be screen printed onto the substrate, in some embodiments, which can reduce production cost as compared to standard circuit boards or metal substrate boards. The flexible board may be shaped prior to being used in a light fixture, in some cases, and the flexible board may conform to a non-flat shape, in some embodiments. Such a design has a low input power density such that heat may be dissipated by convection and radiation and no heat sink is required. In one embodiment, a flexible LED array with a reflective surface may provide customized light delivery with a fixed set of parts. For example, the same parts may be used to provide a highly directed light source or a dissipated light source depending on the contours of the flexible LED array and the spacing of the LEDs within the array.

[0017] In one example embodiment, a flexible LED array is placed against a curved preform and the LED linear arrangements may be either separate strips with appropriate electrical connections or printed circuit patterns on a large flexible sheet. The curved preform may be concave, convex, corrugated, or any other custom shape depending upon the intended light distribution. In some cases, the curved preform may be a section of PVC corrugated roofing material. In another embodiment, the flexible LED array may be laced between a number of rods and the placement of the rods may customize the shape of the LED array and therefore the light distribution. In one such example, the lighting fixture may include two side plates that hold the rods in place.

[0018] In some embodiments, custom screen printed circuits or LED arrays may be matched with the correct fixture configuration in order to achieve the desired light distribution. The variations in shape and LED placement would contribute to the final light distribution and could be customized for particular applications without major changes in parts.

[0019] Example Fixtures for Flexible LED Circuits

[0020] FIG. 1 shows a flexible laminated LED circuit. As can be seen, the LED circuit includes four copper ribbons and the upper laminate sheet has multiple perforations exposing portions of the copper ribbons for the placement of the LED packages. The upper laminate sheet in this particular embodiment is transparent and the entire copper ribbons are visible, while the lower laminate sheet has a reflective upper surface. In other embodiments, the upper laminate sheet may have a reflective upper surface. Although this particular example shows four copper ribbons laminated between two sheets, other embodiments may include fewer or more copper ribbons and the copper ribbons may be replaced with copper wires, or any other suitable conductive material. In some cases, the thin copper ribbon may be around 0.003 inches thick. The LED packages may be attached using a conductive epoxy or solder, in some embodiments. Because the LED packages are being attached to a metallic conductive wire (a copper ribbon in this example), solder may be used in order to avoid the difficulties associated with conductive epoxies.

[0021] FIGS. 2a-b illustrate examples of flexible LED circuit boards including multiple LED strings connected in parallel. As can be seen in the example of FIG. 2a, a flexible LED circuit may be fabricated with screen printed Ag ink on a flexible substrate, in some embodiments. The substrate could be, for example, PET or any other suitable flexible substrate material. LED packages may be connected in series along the conductive traces to form multiple LED strings and the surface of the flexible circuit board may be reflective. FIG. 2b illustrates the flexibility of the LED circuit board when it is rolled.

[0022] FIG. 3a shows a cross-sectional view of various LED package spacings that may provide different light distributions, according to an embodiment of the present invention. As can be seen in this example, the flexible LED array is arranged in a corrugated shape and the top LED package spacing has the LEDs near the crest of each corrugated wave, while the middle LED package spacing has the LEDs at the center of each corrugated wave, and the lower LED package spacing has the LEDs at the bottom of each corrugated wave. FIG. 3b shows a view from below of the flexible LED circuit fitted to a corrugated form, according to one embodiment of the present invention. The direct light path from the LED packages is shown. Such a corrugated shape could be readily used in various area lighting applications including, for example, a drop ceiling light fixtures with dimensions of 2 ft.×2 ft. or 2 ft.×4 ft. However, the lighting fixtures described herein could be designed for any area lighting application and the present invention is not intended to be limited to any particular size or set of dimensions.

[0023] FIGS. 4a-c collectively illustrate an example LED lighting fixture with a flexible LED circuit woven between rods, according to an embodiment of the present invention. In such an embodiment, the flexible circuit board may be mounted within a lighting fixture housing without being attached to the surface of a rigid preform. Such a fixture may provide a more versatile system whereby the “wavelength” and the “amplitude” of the shaped flexible LED circuit would be more customizable based on the location of the rods. The example LED circuit board in FIGS. 4a-c has the LED packages placed such that they are near the crest of the circuit board wave pattern. As can be seen in FIG. 4a, the rods in this example define the shape of the flexible LED circuit when the circuit is woven between the rods. As can be seen in the example of FIG. 4b, this design has two side plates, each having hole patterns through which the rods may be placed. FIG. 4c shows a view from below of the flexible LED circuit, and the direct light path from the LED packages is shown. The direction of the light from the LED packages may be changed, for example, by changing the spacing and location of the rods.

[0024] FIGS. 5a-f collectively illustrate three LED package spacings along with their corresponding light distribution patterns, according to various embodiments of the present invention. In these example embodiments, the light distribution is influenced by locating the LED strips at different points along the “curve” or “wave” of the corrugated LED circuit (whether the circuit is attached to a corrugated preform or shaped using rods and side plates). FIG. 5a shows the LED strips placed near the crest of the corrugated LED circuit and FIG. 5b is a graph of the corresponding polar light distribution. FIG. 5c shows the LED strips placed near the middle of the corrugated LED circuit shape and FIG. 5d is a graph of the corresponding polar light distribution. FIG. 5e shows the LED strips placed near the bottom of the corrugated LED circuit shape and FIG. 5f is a graph of the corresponding polar light distribution. The polar light distribution plots shown in FIGS. 5b, 5d, and 5f graph the light intensity in candelas (CD) and demonstrate that there is a significant difference in the light distribution pattern for each LED strip placement. As can be seen, therefore, the light distribution of a flexible LED circuit is customizable using the same basic parts, depending on the location of the LED strips within the shaped LED circuit.

[0025] FIGS. 6a-b show graphs of the light distribution coming from two points along a sinusoidal shaped flexible LED circuit, according to two embodiments of the present invention. In these example embodiments, non-diffused reflection is assumed for illustrative purposes. The example in FIG. 6a shows the light distribution coming from a point near the crest of the sinusoidal LED circuit, while the example in FIG. 6b shows the light distribution coming from a point near the middle of the sinusoidal LED circuit. In one specific example embodiment, a flat array of Lambertian LED packages may produce a Lambertian light distribution when used in a downward facing lighting application, as shown in these example embodiments. As can be seen when comparing the example of FIG. 6a with the example of FIG. 6b, minor changes in the LED package locations would produce different light distribution patterns other than a Lambertian distribution.

[0026] FIG. 7 shows an example flexible LED circuit including multiple LED packages woven between transparent rods, according to an embodiment of the present invention. In this particular example embodiment, the rods are glass tubes and the side plates are ¼ inch aluminum plates having a particular hole-pattern. In other embodiments, side plates may include multiple hole-patterns and the user may configure the rod placement as desired. In still other embodiments, a consumer may specify the type of light distribution desired and the rod placement may be determined and the circuit may be laced for the desired application. The rods could be made of reflective material and may be fastened with setscrews or held with lock nuts on the end of threaded rods, in some embodiments. The rods may also be replaced with cables laced through the hole pattern and held taught at the ends, in some embodiments. Such cables could be thin and coated with a reflective material. As discussed above, in other embodiments the rods may be attached to mechanical actuators within the side plates that allow the rod positioning to be dynamically adjusted. In such embodiments, instead of removing the rods from one set of hole patterns and inserting them into another set of hole patterns, the shape of the flexible circuit board may be adjusted by mechanically repositioning the rods within a range of user selectable position patterns, each pattern providing a unique light distribution. As will be appreciated, electromechanical, mechanical, hydraulic, and/or any other suitable linear actuator scheme may be used to adjust rod positioning in various dimensions and the present invention is not limited to any particular type of actuator.

[0027] FIGS. 8a-d illustrate various shapes and fixture designs for flexible LED circuits, according to various embodiments of the present invention. FIG. 8a shows a flexible LED array attached to a concave down rigid preform, while FIG. 8b shows a flexible LED array attached to a concave up rigid preform, and each LED circuit shape provides a specific light distribution pattern. FIGS. 8c-d show a concave down configuration for a flexible LED circuit utilizing a rod and side plate configuration. FIG. 8c is a cross-sectional view of the rod and side plate fixture with the flexible LED circuit woven between the rods while FIG. 8d shows the same configuration from below. Various shapes and heights may be used for the rigid forms, and in some cases the flexible LED circuit may be replaced with a new flexible LED board with the same or different pattern and the fixture itself could remain the same. The various preforms and rod arrangements may be incorporated within a light fixture housing, in some embodiments.

[0028] Methodology

[0029] FIG. 9 illustrates a method for fabricating a light fixture for a flexible LED lighting circuit, according to an embodiment of the present invention. The method may begin with determining 901 the desired light distribution. Once the desired light distribution is known, the method may continue with determining 902 the ideal circuit shape and LED placement in order to achieve the desired light distribution. As discussed above, the light distribution may be manipulated by altering the shape of the flexible LED circuit as well as the placement of the LED strings within the LED circuit. The method may continue with determining 903 whether the flexible LED circuit will be fastened to a rigid form. In some cases, the rigid preform may be concave, convex, corrugated, or any other suitable shape for achieving the desired light distribution. If the LED circuit will be fastened to a rigid form, the method may continue with fabricating 904 the flexible LED circuit and the rigid form. As discussed above, the shape of the preform as well as the placement of the LED strings within the flexible LED circuit depends on the desired light distribution. The method may then continue with assembling 906 the light fixture housing, which may include attaching the LED circuit to the rigid preform. If the flexible LED circuit is not to be attached to a rigid form, the method may continue with fabricating 905 the flexible LED circuit and light fixture side plates with the desired hole patterns or achieving the intended light distribution. As discussed above, the hole patterns in the side plates are used for inserting the rods which will determine the shape of the flexible LED circuit. The method may then continue with assembling 906 the light fixture housing, which in this particular case includes inserting transparent or reflective rods into the holes of the side plates and weaving the flexible LED circuit between the rods.

[0030] Numerous embodiments will be apparent, and features described herein can be combined in any number of configurations. One example embodiment of the present invention provides a lighting fixture. The lighting fixture includes a lighting fixture housing, and a plurality of rods mounted within the housing configured to define a non-flat shape for a flexible LED circuit, wherein the placement of the rods within the housing is determined by a desired light distribution pattern produced when a flexible LED circuit is woven between the rods. In some cases, the plurality of rods are configured to define a corrugated shape. In some cases, the housing includes at least two side plates having hole patterns for mounting and removing the rods. In some cases, the side plates have multiple sets of hole patterns for mounting the rods in different positions, and each position is configured to provide a unique light distribution pattern when a flexible LED circuit is woven between the rods. In some cases, the housing includes one or more actuators operatively coupled to at least one of the rods and configured to adjust rod positioning, each position configured to provide a unique light distribution pattern when a flexible LED circuit is woven between the rods. In some such cases, the one or more actuators are operatively coupled to the rods via side plates to which the rods are secured. In some cases, the fixture includes the flexible LED circuit configured to be woven between the rods. In some such cases, the flexible LED circuit has a reflective surface. In other such cases, the spacing of LEDs within the flexible LED circuit is determined by the light distribution pattern produced when the flexible LED circuit is woven between the rods. In some cases, the lighting fixture is configured to provide a customized the light distribution pattern by altering the placement of the rods. In some such cases, altering the placement of the rods is accomplished via an actuator. In some such cases, the actuator is controlled by a processor programmed to automatically adjust light distribution. In some cases, the rods are transparent. In some cases, the rods are reflective.

[0031] Another embodiment of the present invention provides a method of fabricating a lighting fixture. The method includes determining a desired light distribution pattern, and fabricating a flexible LED circuit housing configured to hold a flexible LED circuit in a desired non-flat shape, wherein the housing for the flexible LED circuit includes a plurality of rods, the placement of the rods within the housing determined by the light distribution pattern produced when the flexible LED circuit is woven between the rods. In some cases, the method includes fabricating a flexible LED circuit wherein the spacing of LEDs within the circuit is determined based on the desired light distribution pattern. In some cases, the flexible LED circuit housing is configured to hold the flexible LED circuit in at least one of a concave, convex, and/or corrugated shape. In some cases, determining the desired light distribution pattern includes receiving a desired light distribution pattern from a customer. In some cases, the method includes adjusting rod positioning within the housing using a plurality of linear actuators operatively coupled to the rods, wherein each rod positioning pattern provides a unique light distribution pattern when a flexible LED circuit is woven between the rods.

[0032] Another embodiment of the present invention provides a lighting fixture. The lighting fixture includes a lighting fixture housing. The lighting fixture also includes a plurality of rods mounted within the housing. The lighting fixture also includes a flexible LED circuit woven between the plurality of rods, wherein the placement of the rods within the housing is configured to define a non-flat shape for the flexible LED circuit. The lighting fixture also includes a plurality of linear actuators operatively coupled to the rods and configured to change the placement of the rods within the housing, each rod placement providing a unique light distribution pattern from the flexible LED circuit.

[0033] The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.