Abstract:
In accordance with certain embodiments, lighting systems feature lightsheets including multiple illumination units or modules electrically interconnected such that unremoved illumination units or modules remain energized upon removal of at least a portion of one or more illumination units or modules.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/175,725, filed Jun. 15, 2015, and U.S. Provisional Patent Application No. 62/242,630, filed Oct. 16, 2015, the entire disclosure of each of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    In various embodiments, the present invention generally relates to electronic devices, and more specifically to array-based lighting devices. 
       BACKGROUND 
       [0003]    Broad-area illumination systems are used in a wide range of applications, e.g., backlighting of signs and graphic panels, as well as backlighting of decorative, non-information-carrying panels, such as translucent stone, luminous ceilings, luminous walls, and the like. Such applications may involve illumination of hundreds or thousands of square feet and thus require a large number of individual light sources. Typically, lighting solutions for these applications have a number of competing requirements, including uniform illumination (both intensity and color), thin system profile, the ability to customize both the size and shape of the illuminated structure, high efficiency, and low cost. Systems designed for outdoor, wet, or other challenging environments have additional requirements related to protection of the lighting system. 
         [0004]    These needs are often at odds with each other. For example, variations in light and/or color intensity may be mitigated by having a deep (i.e., thick) mixing chamber to homogenize the light among the illumination sources within the system, but this makes the overall system significantly thicker. Thin systems typically require a larger number of light sources in order to reduce the mixing chamber depth, which increases the cost. 
         [0005]    Uniform illumination across custom shapes and sizes is particularly difficult to achieve for a number of reasons. Incandescent and fluorescent light sources come in fixed sizes, limiting the granularity of the illumination sources—for example, fluorescent tubes come in fixed lengths and cannot be cut to length. Lighting systems based on light-emitting diodes (LEDs) typically are mounted on a circuit board having an electrical topology not amenable to being cut to length. For example, for large-area lighting applications, LEDs may be electrically laid out in groups of series-connected strings, e.g., on a square or rectangular tile, where each string contains multiple series-connected LEDs all operating at the same current. While in some topologies, one or more strings may be removed to permit dimensional customization, parts of a string typically cannot be removed without opening the circuit and causing de-energization of that string. The physical layout of the string therefore may limit the level of achievable granularity. Once installed in a lighting system, such fixed size illumination sources may visually result in regions having undesirably different light intensity levels or colors. A second issue with removing LED strings is that such systems are typically driven by a constant-current driver, so when one or more strings are removed, the current from the driver is divided among fewer strings, resulting in a local brightness increase. The lack of granularity in the sizing of the illumination sources and/or possible current variations between LEDs or groups of LEDs may result in visually distinguishable variations in light intensity level and/or color, for example correlated color temperature (CCT). From an application perspective, this is undesirable because the illumination level is desirably uniform over the entire illuminated area. 
         [0006]    Another electrical topology that may be utilized for LED-based illumination sources is the connection of all of the LEDs in parallel. This topology may permit removal of individual LEDs and thus may achieve relatively finer granularity, in some cases on the order of the LED spacing. However, such systems are prone to “current hogging,” in which the current preferentially flows through the LED(s) with the lowest forward voltage. This can result in increased heating of such LEDs, which further reduces the forward voltage, thus increasing the current—this process can continue until those LEDs fail. In some cases, this process may occur over and over, for example cascading from one LED to the LED having the next lowest forward voltage in the system. In some cases, this effect may be mitigated by carefully matching the forward voltage of all of the LEDs, but this typically adds significant expense. Another approach is to incorporate a ballast resistor or other current-limiting device with each LED; however, this may increase cost and significantly reduce efficiency because of the power loss in the ballast resistor. A further efficiency disadvantage of this electrical topology is that it typically is driven at about the forward voltage of one LED. Low-voltage systems typically have increased power losses in the lines (wires) as well as lower driver efficiency. 
         [0007]    A third electrical topology, using a constant-voltage supply in combination with an array, for example a parallel array, of small, low-cost LEDs configured in strings of series-connected LEDs, where each string also includes a current-regulating element, addresses a number of the deficiencies of the systems described above. Exemplary electrical and physical schematics of this approach are shown in  FIGS. 1A and 1B  respectively. This approach is described in detail in U.S. patent application Ser. No. 13/799,807, filed on Mar. 13, 2013, (the &#39;807 application) and U.S. patent application Ser. No. 13/970,027, filed on Aug. 19, 2013 (the &#39;027 application), the entirety of each of which is incorporated herein by reference. Such as lighting system may include power conductors  120  and  121 , which supply power to strings  150 . Each string  150  includes light-emitting elements (LEEs)  140  electrically connected in series by conductive elements  160  and energized by power from power conductors  120  and  121 . Each string  150  also includes a current control element  145 , which regulates the current in each string. In various embodiments strings  150  may be electrically connected in parallel with each other. One or more strings may be removed from the system without changing the brightness of the LEEs in the other strings. Strings may be straight, as shown in  FIG. 1A , or folded, as shown in  FIG. 1B  (a folded string has multiple segments (in  FIG. 1B  they are parallel) between power conductors  120  and  121 . (Here folded refers to the physical layout of the strings, rather than any particular geometric configuration of the system itself). In this example, power conductors  120 ,  121 , conductive elements  160 , control elements  145  and LEEs  140  are mounted on substrate or circuit board  165 . The system granularity is determined at the base level by the LEE pitch  125 . For a straight string, the size increment is on the order of pitch  125 . For a folded string, the size increment is on the order of an integer multiple of pitch  125 . The relatively small pitch permits a relatively thin system, for example including the light source and an overlying diffuser or optic, for example on the order of about 1.5 or 2 times the pitch distance. 
         [0008]    The system described in relation to  FIGS. 1A and 1B  permits customization in one direction. For example, this may be used to produce a linear illuminated region having the sheet width, with the length customized by cutting off one or more strings. However, many applications require area lighting, such as shown in  FIG. 1C , in which the desired illuminated area is not an integer multiple of the sheet width and/or length. In this case, fixed-size pieces or sheets of lighting system  110  may be tiled together to cover a desired portion  172  of a total area  170 . A cut-to-length system may be used to tile regions  174  and  176 , the dimensions of which are smaller in one direction than the tiles used in region  172 . However, region  178 , which requires cutting in two directions (in this case in substantially orthogonal directions), typically cannot be illuminated via this approach. That is, both dimensions of region  178  are smaller than those of available light-system sheets  110 , which will not function properly if cut along both dimensions to the desired size. Similar challenges arise for non-rectangular shapes, such as those shown in  FIGS. 1D and 1E . In these cases, square or rectangular tiles may be used to fill up most of the area, but undesirably non-illuminated regions remain. Furthermore, area lighting systems may be required to accommodate various penetrations or holes in the lighting plane, or regions without one or more illumination sources, for example for fire suppression systems such as sprinkler heads or the like, smoke or fire sensors, cameras, heating, ventilation and air conditioning ducts, supports or stand-offs for overlying material such as diffusers, optics, fabric or the like. 
         [0009]    In view of the foregoing, a need exists for systems and procedures for thin, low-cost lighting systems enabling uniform illumination of arbitrarily sized areas. 
       SUMMARY 
       [0010]    Embodiments of the present invention relate to illumination systems based on areal light sheets that incorporate functionality that enables the arbitrary removal of one or more light-emitting elements, and/or one or more strings of light-emitting elements, while maintaining functionality of the unremoved light-emitting elements and light-emitting strings. In various embodiments, after removal of a light-emitting element or string, the same operating voltage is maintained across the remaining, unremoved light-emitting elements or strings despite the removal of one or more light-emitting elements. Embodiments of the invention thus enable the shaping and/or size reduction of standard light sheets to meet a variety of different requirements. 
         [0011]    As utilized herein, the term “light-emitting element” (LEE) refers to any device that emits electromagnetic radiation within a wavelength regime of interest, for example, visible, infrared or ultraviolet regime, when activated, by applying a potential difference across the device or passing a current through the device. Examples of light-emitting elements include solid-state, organic, polymer, phosphor-coated or high-flux LEDs, laser diodes or other similar devices as would be readily understood. The emitted radiation of an LEE may be visible, such as red, blue or green, or invisible, such as infrared or ultraviolet. An LEE may produce radiation of a continuous or discontinuous spread of wavelengths. An LEE may feature a phosphorescent or fluorescent material, also known as a light-conversion material, for converting a portion of its emissions from one set of wavelengths to another. In some embodiments, the light from an LEE includes or consists essentially of a combination of light directly emitted by the LEE and light emitted by an adjacent or surrounding light-conversion material. An LEE may include multiple LEEs, each emitting essentially the same or different wavelengths. In some embodiments, a LEE is an LED that may feature a reflector over all or a portion of its surface upon which electrical contacts are positioned. The reflector may also be formed over all or a portion of the contacts themselves. In some embodiments, the contacts are themselves reflective. Herein the term “reflective” is defined as having a reflectivity greater than 65% for a wavelength of light emitted by the LEE on which the contacts are disposed unless otherwise defined. In some embodiments, an LEE may include or consist essentially of an electronic device or circuit or a passive device or circuit. In some embodiments, an LEE includes or consists essentially of multiple devices, for example an LED and a Zener diode for static-electricity protection. In some embodiments, an LEE may include or consist essentially of a packaged LED, i.e., a bare LED die encased or partially encased in a package. In some embodiments, the packaged LED may also include a light-conversion material. In some embodiments, the light from the LEE may include or consist essentially of light emitted only by the light-conversion material, while in other embodiments the light from the LEE may include or consist essentially of a combination of light emitted from an LED and from the light-conversion material. In some embodiments, the light from the LEE may include or consist essentially of light emitted only by an LED. 
         [0012]    In one embodiment, an LEE includes or consists essentially of a bare semiconductor die, while in other embodiments an LEE includes or consists essentially of a packaged LED. In some embodiments, LEE may include or consist essentially of a “white die” that includes an LED that is integrated with a light-conversion material (e.g., a phosphor) before being attached to the light sheet, as described in U.S. patent application Ser. No. 13/748,864, filed Jan. 24, 2013, or U.S. patent application Ser. No. 13/949,543, filed Jul. 24, 2013, the entire disclosure of each of which is incorporated by reference herein. 
         [0013]    In an aspect, embodiments of the invention feature a lighting system that includes, consists essentially of, or consists of a lightsheet. The lightsheet includes, consists essentially of, or consists of a substrate, a first power conductor disposed on the substrate, a second power conductor disposed on the substrate and electrically isolated from the first power conductor, and a plurality of light-emitting strings each electrically connected between and being energizable via the first and second power conductors. Each light-emitting string includes, consists essentially of, or consists of a plurality of electrically connected illumination units. Each illumination unit includes, consists essentially of, or consists of (i) one or more electrically connected light-emitting elements, and (ii) a bypass element (a) electrically connected across the first and second power conductors and (b) configured to transition from a high-impedance state to a low-impedance state and thereby complete a circuit between the first and second power conductors upon removal of the one or more light-emitting elements of the illumination unit from the lightsheet, whereby energization of unremoved light-emitting elements within the light-emitting string is maintained. 
         [0014]    Embodiments of the invention may include one or more of the following in any of a variety of combinations. At least one of the bypass elements (or even each of the bypass elements) may include, consist essentially of, or consist of a switch, a relay, a Zener diode, and/or a circuit including, consisting essentially of, or consisting of at least one transistor and at least one resistor. The illumination units within at least one light-emitting string (or even each light-emitting string) may be electrically connected in series. The illumination units within at least one light-emitting string (or even each light-emitting string) may be electrically connected in parallel. At least one light-emitting string may include a second illumination unit that includes, consists essentially of, or consists of one or more electrically connected light-emitting elements without a bypass element associated therewith. The lighting system may include a power supply electrically connected to the first and second power conductors. The at least one light-emitting string may extend from a proximal end proximate the power supply to a distal end away from the power supply. The second illumination unit may be disposed at the proximal end. For at least one light-emitting string, at least one illumination unit may include (i) a voltage-drop element and (ii) a shunt configured to (a) prevent voltage drop across the voltage-drop element when the one or more light-emitting elements of the illumination unit are present on the lightsheet, and (b) upon removal of the one or more light-emitting elements of the illumination unit, cause a voltage drop across the voltage-drop element. The shunt may be configured to be at least partially removed upon removal of the one or more light-emitting elements of the illumination unit, thereby causing the voltage drop across the voltage-drop element. The voltage drop across the voltage-drop element may be approximately equal to a voltage drop across the one or more light-emitting elements of the illumination unit when the one or more light-emitting elements of the illumination unit are present on the lightsheet. The voltage-drop element may include, consist essentially of, or consist of one or more resistors. 
         [0015]    The lighting system may include one or more control elements configured to control current to at least one of the light-emitting strings. The one or more control elements may include, consist essentially of, or consist of a plurality of control elements. Each light-emitting string may have a different control element electrically coupled thereto. At least one light-emitting element of at least one illumination unit may include, consist essentially of, or consist of a light-emitting diode. The light-emitting diode may emit substantially white light. The substrate may be flexible. A string pitch at which the light-emitting strings are spaced across the substrate may be substantially constant across the substrate. Along each light-emitting string, a pitch at which the light-emitting elements are spaced may be substantially constant. 
         [0016]    The lighting system may include a third power conductor disposed on the substrate, a fourth power conductor disposed on the substrate and electrically isolated from the third power conductor, and a plurality of second light-emitting strings each electrically connected between and being energizable via the third and fourth power conductors. Each second light-emitting string may include, consist essentially of, or consist of a plurality of electrically connected third illumination units. Each third illumination unit may include, consist essentially of, or consist of (i) one or more electrically connected second light-emitting elements having an optical characteristic different from a corresponding optical characteristic of the light-emitting elements, and (ii) a second bypass element (a) electrically connected across the third and fourth power conductors and (b) configured to transition from a high-impedance state to a low-impedance state and thereby complete a circuit between the third and fourth power conductors upon removal of the one or more second light-emitting elements of the third illumination unit from the lightsheet, whereby energization of unremoved second light-emitting elements within the second light-emitting string is maintained. At least one second light-emitting string may include a fourth illumination unit including, consisting essentially of, or consisting of one or more electrically connected light-emitting elements without a second bypass element associated therewith. The lighting system may include a second power supply electrically connected to the third and fourth power conductors. The power supply and the second power supply may be the same power supply, or they may be different and discrete from each other. The at least one second light-emitting string may extend from a proximal end proximate the second power supply to a distal end away from the second power supply. The fourth illumination unit may be disposed at the proximal end. The third power conductor may be electrically isolated from the first and second power conductors. The fourth power conductor may be electrically isolated from the first and second power conductors. The optical characteristic may include, consist essentially of, or consist of correlated color temperature, color rendering index, R9, spectral power distribution, and/or spatial light intensity distribution. 
         [0017]    The lightsheet may include one or more connectors for mechanical and/or electrical connection to an adjoining lightsheet. At least one of the connectors may include, consist essentially of, or consist of a snap connector. A second lightsheet may be mechanically and/or electrically connected to the lightsheet. The lighting system may include a first snap connector electrically connected to the first power conductor, a second snap connector electrically connected to the second power conductor, and a second lightsheet. The second lightsheet may include, consist essentially of, or consist of a second substrate (which may be flexible or rigid), third and fourth power conductors disposed on the second substrate, a plurality of second light-emitting elements disposed on the second substrate and electrically connected to the third and fourth power conductors, a third snap connector electrically connected to the third power conductor, and a fourth snap connector electrically connected to the fourth power conductor. The first snap connector may be configured for connection to the third snap connector, thereby electrically coupling the first power conductor to the third power conductor. The second snap connector may be configured for connection to the fourth snap connector, thereby electrically coupling the second power conductor to the fourth power conductor. The lightsheet may define therethrough a hole proximate a bypass element. The hole may be defined by removal of one or more light-emitting elements of an illumination unit. 
         [0018]    At least one bypass element (or even each bypass element) may have a resistance of at least 10 6  ohms in the high-impedance state. At least one bypass element (or even each bypass element) may have a resistance no greater than 10 3  ohms in the low-impedance state. The lightsheet may have a thickness in the range of 0.25 mm to 25 mm. The lighting system may include an optic disposed over at least a portion of the lightsheet. The optic may include, consist essentially of, or consist of a lens, a diffuser, a refractive optic, a reflective optic, a Fresnel optic, a fabric, a translucent material panel, a graphic panel, and/or a membrane. A collective thickness of the lightsheet and the optic may be in the range of 0.5 cm to 20 cm. Within at least one illumination unit (or even each illumination unit), the light-emitting elements may be spaced apart at a substantially constant pitch. The substrate may define a tab extending therefrom. A portion of the first and/or second power conductors may be disposed on the tab. The substrate may define first and second tabs extending therefrom. A portion of the first power conductors may be disposed on the first tab. A portion of the second power conductor may be disposed on the second tab. 
         [0019]    In another aspect, embodiments of the invention feature a lighting system that includes, consists essentially of, or consists of a lightsheet. The lightsheet includes, consists essentially of, or consists of a substrate, one or more first electrical contacts disposed on the substrate and electrically connected to each other, one or more second electrical contacts disposed on the substrate and electrically connected to each other, and a plurality of illumination modules disposed on the substrate and electrically connected to each other. The one or more first electrical contacts are electrically isolated from the one or more second electrical contacts. Each illumination module includes, consists essentially of, or consists of (i) one or more electrically connected light-emitting elements, (ii) a first power conductor, and (iii) a second power conductor electrically isolated from the first power conductor. The one or more light-emitting elements are electrically connected between and energizable by the first and second power conductors. The first power conductors of the illumination modules are electrically connected to the one or more first electrical contacts. The second power conductors of the illumination modules are electrically connected to the one or more second electrical contacts. The illumination modules are collectively energizable via application of power to a first electrical contact and a second electrical contact. The first and second power conductors of the illumination modules are electrically connected to enable energization of all remaining illumination modules upon removal of any illumination module from the lightsheet. 
         [0020]    Embodiments of the invention may include one or more of the following in any of a variety of combinations. The first and second power conductors of each illumination module may form an independent path electrically connected to at least one first electrical contact and at least one second electrical contact. Removal of any illumination module may not sever the independent path formed by the first and second power conductors of any other illumination module. The lighting system may include one or more control elements configured to control current to at least one of the illumination modules. The one or more control elements may include, consist essentially of, or consist of a plurality of control elements. Each illumination module may have a different control element electrically coupled thereto. At least one illumination module may include one or more connectors for mechanical and/or electrical connection to an adjoining illumination module. At least one of the connectors may include, consist essentially of, or consist of a snap connector or a portion thereof. The light-emitting elements of at least one illumination module (or even each illumination module) may include, consist essentially of, or consist of light-emitting diodes. The light-emitting diodes may emit substantially white light. The one or more light-emitting elements of at least one illumination module may include, consist essentially of, or consist of a plurality of light-emitting elements that are electrically connected in series. The one or more light-emitting elements of at least one illumination module may include, consist essentially of, or consist of a plurality of light-emitting elements that are electrically connected in parallel. 
         [0021]    Each illumination module may include, consist essentially of, or consist of a plurality of electrically connected illumination units. Each illumination unit may include, consist essentially of, or consist of (i) one or more electrically connected light-emitting elements, and (ii) a bypass element (a) electrically connected across the first and second power conductors and (b) configured to transition from a high-impedance state to a low-impedance state and thereby complete a circuit between the first and second power conductors upon removal of the one or more light-emitting elements of the illumination unit from the lightsheet, whereby energization of unremoved light-emitting elements within the illumination module is maintained. At least one bypass element (or even each bypass element) may have a resistance of at least 10 6  ohms in the high-impedance state. At least one bypass element (or even each bypass element) may have a resistance no greater than 10 3  ohms in the low-impedance state. At least one bypass element (or even each bypass element) may include, consist essentially of, or consist of a switch, a relay, a Zener diode, and/or a circuit including, consisting essentially of, or consisting of at least one transistor and at least one resistor. The illumination units within at least one illumination module (or even within each illumination module) may be electrically connected in series. The illumination units within at least one illumination module (or even within each illumination module) may be electrically connected in parallel. At least one illumination module may include a second illumination unit that includes, consists essentially of, or consists of one or more electrically connected light-emitting elements without a bypass element associated therewith. The lighting system may include a power supply electrically connected to at least one of the first electrical contacts and at least one of the second electrical contacts. The at least one illumination module may extend from a proximal end proximate the power supply to a distal end away from the power supply. The second illumination unit may be disposed at the proximal end. For at least one illumination module (or even for each illumination module), at least one illumination unit may include (i) a voltage-drop element and (ii) a shunt configured to (a) prevent voltage drop across the voltage-drop element when the one or more light-emitting elements of the illumination unit are present on the lightsheet, and (b) upon removal of the one or more light-emitting elements of the illumination unit, cause a voltage drop across the voltage-drop element. The shunt may be configured to be at least partially removed upon removal of the one or more light-emitting elements of the illumination unit, thereby causing the voltage drop across the voltage-drop element. The voltage drop across the voltage-drop element may be approximately equal to a voltage drop across the one or more light-emitting elements of the illumination unit when the one or more light-emitting elements of the illumination unit are present on the lightsheet. The voltage-drop element may include, consist essentially of, or consist of one or more resistors. 
         [0022]    The substrate may be flexible. Along each illumination unit, a pitch at which the light-emitting elements are spaced may be substantially constant. A pitch at which the illumination modules are spaced across the substrate may be substantially constant. The lighting system may include a second lightsheet mechanically and/or electrically connected to the lightsheet. The lightsheet may include one or more connectors for mechanical and/or electrical connection to an adjoining lightsheet. At least one of the connectors may include, consist essentially of, or consist of a snap connector or a portion thereof. The lighting system may include a first snap connector electrically connected to the first electrical contacts, a second snap connector electrically connected to the second electrical contacts, and a second lightsheet. The second lightsheet may include, consist essentially of, or consist of a second substrate, third and fourth power conductors disposed on the second substrate, a plurality of second light-emitting elements disposed on the second substrate and electrically connected to the third and fourth power conductors, a third snap connector electrically connected to the third power conductor, and a fourth snap connector electrically connected to the fourth power conductor. The first snap connector may be configured for connection to the third snap connector, thereby electrically coupling the first electrical contacts to the third power conductor. The second snap connector may be configured for connection to the fourth snap connector, thereby electrically coupling the second electrical contacts to the fourth power conductor. 
         [0023]    The lightsheet may define therethrough a hole. The hole may be defined by removal of one or more light-emitting elements of one or more illumination modules. The lightsheet may have a thickness in the range of 0.25 mm to 25 mm. The lighting system may include an optic disposed over at least a portion of the lightsheet. The optic may include, consist essentially of, or consist of a lens, a diffuser, a refractive optic, a reflective optic, a Fresnel optic, a fabric, a translucent material panel, a graphic panel, and/or a membrane. A collective thickness of the lightsheet and the optic may be in the range of 0.5 cm to 20 cm. The substrate may define a tab extending therefrom. A portion of the first and/or second power conductors may be disposed on the tab. The substrate may define first and second tabs extending therefrom. A portion of the first power conductors may be disposed on the first tab. A portion of the second power conductor may be disposed on the second tab. An optical characteristic of one or more of the illumination units may be different from a corresponding optical characteristic of one or more other illumination units. The optical characteristic may include, consist essentially of, or consist of correlated color temperature, color rendering index, R9, spectral power distribution, and/or spatial light intensity distribution. 
         [0024]    These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. As used herein, the terms “about,” “approximately,” and “substantially” mean±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. 
         [0025]    Herein, two components such as light-emitting elements and/or optical elements being “aligned” or “associated” with each other may refer to such components being mechanically and/or optically aligned. By “mechanically aligned” is meant coaxial or situated along a parallel axis. By “optically aligned” is meant that at least some light (or other electromagnetic signal) emitted by or passing through one component passes through and/or is emitted by the other. Substrates, light sheets, components, and/or portions thereof described as “reflective” may be specularly reflective or diffusively reflective unless otherwise indicated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
           [0027]      FIGS. 1A and 1B  are, respectively, a circuit diagram and schematic of a lighting system; 
           [0028]      FIGS. 1C-1E  are schematic illustrations of areas illuminated by lighting systems; 
           [0029]      FIG. 2A  is a circuit diagram of an illumination system in accordance with various embodiments of the invention; 
           [0030]      FIGS. 2B-2D, 3A, and 3B  are partial circuit diagrams of illumination systems in accordance with various embodiments of the invention; 
           [0031]      FIGS. 4A-4G and 5  are circuit diagrams of illumination systems in accordance with various embodiments of the invention; 
           [0032]      FIG. 6A  is a circuit diagram of an illumination system in accordance with various embodiments of the invention; 
           [0033]      FIGS. 6B and 6C  are partial circuit diagrams of illumination systems in accordance with various embodiments of the invention; 
           [0034]      FIG. 6D  is a circuit diagram of an illumination system in accordance with various embodiments of the invention; 
           [0035]      FIGS. 7A-7E  are circuit diagrams of illumination systems in accordance with various embodiments of the invention; 
           [0036]      FIGS. 8A-8H  are schematic diagrams of illumination systems in accordance with various embodiments of the invention; 
           [0037]      FIG. 9A  is a circuit diagram of an illumination system in accordance with various embodiments of the invention; 
           [0038]      FIGS. 9B-9D  are partial circuit diagrams of illumination systems in accordance with various embodiments of the invention; and 
           [0039]      FIG. 10  is a partial circuit diagram of an illumination system in accordance with various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]      FIG. 2A  depicts an exemplary lighting apparatus  200  in accordance with various embodiments of the present invention. Lighting apparatus  200  includes substrate  165  on which are disposed conductive elements  160 , power conductors  120 ,  121 , control elements  145 , light-emitting elements (LEEs)  220  and bypass elements  210 . The circuit on substrate  165  may be powered by a power supply  230 . Lighting apparatus  200  includes three strings  240 ,  241 ,  242  of series-connected LEEs  220 ; however, this is not a limitation of the present invention, and in other embodiments lighting apparatus  200  may include fewer or more strings. In  FIG. 2A , each string contains four LEEs  220 ; however, this is not a limitation of the present invention, and in other embodiments each string of lighting apparatus  200  may include fewer or more LEEs  220 . In  FIG. 2A , strings  220  are electrically connected in parallel; however, this is not a limitation of the present invention, and in other embodiments strings  220  may have other electrical configurations. In various embodiments, LEEs  220  may be electrically connected in other configurations, for example parallel or a combination of series and parallel. In various embodiments of the present invention, each LEE  220  may represent one LEE or may represent a group of two or more LEEs, as will be discussed herein. While the description in reference to  FIG. 2A  describes one physical configuration (a substrate with conductive traces), this is not a limitation of the present invention and in other embodiments other physical configurations may be utilized. 
         [0041]    Substrate  165  may be shortened (i.e., reduced in size) in a direction  250  by removing first string  240  (for example, by cutting along cut line A-A′) and then string  241  (for example, by cutting along cut line B-B′). In various embodiments of the present invention, the size increment removed when each string removed is equal to or substantially equal to pitch  125 . In various embodiments, pitch  125  may be in the range of about 3 mm to about 200 mm or pitch  125  may be in the range of about 5 mm to about 50 mm; however, this is not a limitation of the present invention, and in other embodiments other values of pitch may be utilized. This structure permits relatively fine control of the size increment when configuring sheet  165 , as described herein. 
         [0042]    Reduction of the size of sheet  165  in the perpendicular or substantially perpendicular direction  252  may be accomplished by removing first LEE group  221  (for example, by cutting along cut line C-C′), then by removing LEE group  222  (for example, by cutting along cut line D-D′), then removing LEE group  223  (for example, by cutting along cut line E-E′). When the first LEE group  221  is removed, it leaves an open circuit that is shunted by bypass element  210 . The LEE(s) of a group and the associated bypass element may be referred to as an illumination unit, for example illumination unit  227 , as shown in  FIG. 2A . In various embodiments, the LEE(s) of an illumination unit is/are removed, while the associated bypass element of that illumination unit remains on the light sheet to complete the circuit, as is discussed herein. In various embodiments, bypass element  210  is or provides a high-impedance path (i.e., an open circuit or a substantially high resistance to current flow sufficiently high to prevent direct current flow between power conductors  120 ,  121 ) when the LEEs of group  221  are present, and is or provides a low-impedance path (i.e., a short circuit or substantially low resistance to current flow to enable direct current flow between power conductors  120 ,  121 ) when LEEs of group  221  are removed. In various embodiments of the present invention, a high-impedance path may have a resistance of at least about 10 5  ohms or at least about 10 6  ohms or at least about 10 8  ohms. In various embodiments of the present invention, a low-impedance path may have a resistance of no greater than about 1000 ohms or no greater than about 100 ohms or no greater than about 10 ohms. 
         [0043]    In various embodiments of the present invention, bypass element  210  may include or consist essentially of a switch. For example, bypass element  210  may include or consist essentially of a manually operated switch, for example a DIP switch that may in some embodiments be mounted on substrate  165 . When an LEE or a group of LEEs is removed, the associated switch is closed, completing the circuit. For example, referring to  FIG. 2B , if LEE  220 ′″ is removed, then switch  210 ′ is closed. Note that it is not necessary to remove all LEEs  220  in a group, for example group  221  or  222  in  FIG. 2A  (that is, it is not necessary to remove an LEE  220  from all strings in a group)—for example, LEE  220 ′ may be removed from string  240  but not from string  241  (in this case bypass element  210 ′ from string  240  would be closed but bypass element  210 ′″ from string  241  would remain open. 
         [0044]    In various embodiments of the present invention, bypass element  210  may be automatically activated by the action of cutting or shortening the sheet.  FIG. 2C  shows an example of such an embodiment, in which bypass element  210  includes or consists essentially of a normally closed relay (only a portion of the circuit is shown for clarity). Relay  210  includes a switch  232  and a coil  231 . Before cutting along cut line C-C′ to remove LEE  220 ′, coil  231  is energized by current flowing from wire  235  to the coil and returning to wire  236 , thus holding switch  232  open, ensuring normal circuit operation. However, when LEE  220 ′ is removed by cutting along cut line C-C′, this also cuts wires  235  and  236 , which de-energizes coil  231 , permitting switch  232  to close, thus completing the circuit. As will be understood by those skilled in the art, the function performed by relay  210  may be accomplished by means other than a conventional relay, for example a solid-state relay or other solid-state components acting as a switch or substantially like a switch, for example transistors such as bipolar transistors and/or field-effect transistors, diodes, or the like. As will be understood by those skilled in the art, the circuit of  FIG. 2C  may include other components required for normal operation of well-known components. For example, in various embodiments, a means to limit the current through coil  231  may be included in series with coil  231 . As utilized herein, the term “relay” encompasses not only relays but other devices or groups of devices exhibiting the functionality of a relay or switch. 
         [0045]      FIG. 2D  shows an example of an embodiment of the present invention in which bypass element  210  includes or consists essentially of a transistor-based circuit. In this example bypass element  210  includes transistor  239  and resistor  238 . Before cutting along cut line C-C′ to remove LEE  220 ′, the base of transistor  239  is tied to ground by wire  237 , the base-emitter voltage (VBE) of transistor  239  is essentially zero, resulting in no current flow from the collector to the emitter, in essence an open circuit, thus ensuring normal circuit operation. However, when LEE  220 ′ is removed by cutting along cut line C-C′, this also cuts wire  237 , which removes the short across the base and emitter of transistor  239 . VBE increases by virtue of current flowing through resistor  238 , turning on transistor  239  which then acts like a closed switch, completing the circuit. 
         [0046]    In various embodiments of this approach, removing one or more LEEs  220  may result in a reduction in the string voltage, i.e., the voltage of the series-connected string of LEEs  220 .  FIG. 3A  shows a schematic of one string of an exemplary lighting system including current control element  145  and 10 LEEs  310 - 319 . The voltage between points A and B is given by the sum of the voltage drop across current control element  145  and the voltage drop across LEEs  310 - 319 , for example VCCE+n×VLEE, where VCCE is the voltage drop across current control element  145 , n is the number of LEEs in series, and VLEE is the voltage drop across each LEE. In various embodiments, each LEE may include or consist essentially of a light-emitting diode (LED), and VLEE thus may represent the forward voltage Vf of the LED at the operating current. For the present discussion it is assumed that each LEE or LED has the same VLEE or Vf respectively; however, in various embodiments, VLEE or Vf may have a range of values, for example because of manufacturing variations, component aging, temperature variations across the components, or the like. In various embodiments, different LEEs may have different Vf because they have different bandgaps and/or turn-on voltages. 
         [0047]    When one or more LEEs are removed from the circuit, the string voltage decreases. For a constant-voltage system, in which, for example, a constant voltage is applied between points A and B in  FIG. 3A , it is desired that the string voltage remain constant or substantially constant even when one or more LEEs are removed from the circuit. In various embodiments of the present invention, the additional voltage (that is, the forward voltage of the removed LEEs) may be taken up across current control element  145 .  FIG. 3B  shows an exemplary embodiment of the present invention in which a resistor takes up the additional voltage.  FIG. 3B  also includes the transistor-based bypass circuit discussed in reference to  FIG. 2D . The value of resistors  360  and  361  is selected to generate the same or substantially the same voltage across the resistor at the operating current as is dropped across the LEE. Resistor  360  is shunted by loop  370 , while resistor  361  is shunted by loop  371 . Loop  370  and  371  are spatially located on the sheet or substrate so that the loop is cut when an associated portion of the circuit is removed. When the loop is cut, the shunt around the resistor is removed and current flows through the resistor, creating the additionally required voltage drop. For example, when a cut is made at cut line C-C′ to shorten the sheet by removing LEE  312 , this opens loop  370 , permitting current to flow through resistor  360 , which generates the same or substantially the same voltage as was dropped across LEE  312 , and thus keeps the string voltage constant or substantially constant. Cutting across cut line C-C′ also opens wire  237 , causing transistor  239  to turn on, thus completing the circuit. Similarly, if a cut is made at D-D′ to remove both LEEs  311  and  312 , both loops  370  and  371  are cut, forcing current to flow through both resistors  360  and  361 , which then generate the same voltage or substantially the same voltage as was dropped across LEEs  311  and  312 , thus keeping the string voltage constant or substantially constant. Cutting across cut line D-D′ also opens wire  237 ′, causing transistor  239 ′ to turn on, thus completing the circuit. The values of the resistors  360  and  361  may be determined by well-known techniques using the driving current value for the LEE and the forward voltage of the LEE at that current value, for example using Ohm&#39;s Law. 
         [0048]      FIG. 4A  is a schematic of an embodiment of one string of an exemplary circuit of the present invention. In this schematic, each LEE  220  of  FIG. 2A  includes or consists essentially of four LEDs, and resistor  360  of  FIG. 3B  includes or consists essentially of two resistors. The circuit of  FIG. 4A  includes four groups  410 - 440 , each of which may be individually removed. Cutting between groups  430  and  440  (cut line C-C′) removes LEDs D 45 -D 48 , cutting between groups  420  and  430  (cut line D-D′) additionally removes LEDs D 41 -D 44 , and cutting between groups  410  and  420  (cut line E-E′) additionally removes LEDs D 37 -D 40 . 
         [0049]    In various embodiments, more than one resistor may be utilized to produce the voltage drop when one or more LEEs is removed. In various embodiments, more than one resistor may be used to distribute the heat generated in the resistor across a larger portion or area of the sheet or substrate, if necessary. 
         [0050]      FIG. 4B  shows a schematic of an exemplary panel or tile including a 4×4 grid of LEEs numbered  450 - 465 . Each grid element includes four individual LEEs; however, this is not a limitation of the present invention, and in other embodiments each grid element may include fewer or more LEEs. In the example shown in  FIG. 4B , current control element  145  includes a two-transistor, two-resistor circuit, for example as described in the &#39;807 and &#39;027 applications. In various embodiments, this circuit is designed to be operated at a constant voltage, which is applied between terminals A and B. While  FIG. 4B  shows an exemplary system having a 4×4 grid or array of LEEs, this is not a limitation of the present invention, and in other embodiments systems of the present invention may have other configurations, for example 5×5 or 4×5 or any number of groups of LEEs. While  FIG. 4B  shows an exemplary system having a rectilinear array of grids, i.e., organized in an arrangement of orthogonal or substantially orthogonal dimensions, this is not a limitation of the present invention, and in other embodiments other configurations, for example triangular or hexagonal or any arbitrary configuration may be utilized. In one exemplary embodiment of the present invention, the circuit of  FIG. 4B  is designed to operate at a voltage in the range of about 56 to about 60 V, which is applied to terminals A and B; however, in other embodiments the system may be designed to operate at a different voltage or within a different voltage range. The circuit is designed to fit on a panel or substrate  499  having a substantially square shape, for example as shown in  FIG. 4C ; however, this is not a limitation of the present invention, and in other embodiments the panel or substrate may have a different shape, and in different embodiments the circuit may be designed to operate within different voltage ranges. In various embodiments, the panel may be square and have a side dimension in the range of about 250 mm to about 1000 mm, or in the range of about 150 mm to about 250 mm; however, the size of the panel is not a limitation of the present invention. In various embodiments of the present invention, the panel, including LEEs and optional other components (for example current control elements), may have a thickness in the range of about 0.25 mm to about 25 mm, or in the range of about 0.5 mm to about 5 mm. In this example, four separate strings are mounted on each panel. The first string occupies grid elements  462 ,  458 ,  454 , and  450 , the second string occupies grid elements  463 ,  459 ,  455 , and  451 , the third string occupies grid elements  464 ,  460 ,  456 , and  452 , and the fourth string occupies grid elements  465 ,  461 ,  457 , and  453 . In various embodiments, LEEs  220  each include or consist essentially of LEDs, for example LEDs that emit in a variety of wavelength ranges, for example red, green, blue, amber, violet, ultraviolet, infrared, or the like. In various embodiments, LEEs  220  may include or consist essentially of phosphor-converted LEDs, for example that emit white light or substantially white light, for example having a correlated color temperature in the range of about 1500K to about 10,000K, each of which may have V f  in the range of about 2.5 V to about 3.5 V, or in the range of about 2.7 V to about 3.1 V. In various embodiments, LEEs or LEDs may emit in any wavelength range or region and may have a V f  appropriate to the bandgap of the LED or LEE. The voltage from each grid element is compensated for by two resistors, as discussed herein. The tile or sheet may have one or more portions removed to adjust its size to provide improved and/or customized fit during installation. 
         [0051]    For example,  FIG. 4D  shows the tile being reduced in width by one grid element, by removing grids  453 ,  452 ,  451 , and  450  (in  FIGS. 4D-4G  the removed grids are darkened). The tile may be reduced further in width, for example by removing grids  457 ,  456 ,  455 , and  454 , and further by removing grids  461 ,  460 ,  459 , and  458 .  FIG. 4E  shows the tile being reduced in height by one grid element, by removing grids  453 ,  457 ,  461 , and  465 . The tile may be reduced further in height, for example by removing grids  452 ,  456 ,  460 , and  464  and further by removing grids  451 ,  455 ,  459 , and  463 . 
         [0052]    While  FIGS. 4D and 4E  show an entire row or column being removed, this is not a limitation of the present invention, and in other embodiments less than an entire row or column may be removed. For example,  FIG. 4F  shows a system with only grid  453  removed, while  FIG. 4G  shows grids  450 ,  451 ,  455 ,  459 ,  453 , and  457  removed. FIGS.  4 B- 4 G show only one example of a design with several different options for removing grids, but embodiments of the present invention include designs with fewer or more grids and the ability to remove grids not shown as removed in  FIGS. 4B-4G . 
         [0053]    In various embodiments of the present invention, bypass element  210  may include or consist essentially of a Zener diode or a similar Zener-based protection device, for example Littelfuse PLED series devices.  FIG. 5  shows a simplified circuit incorporating a Zener diode  510 , power supply  230 , current control device  145  and two LEEs  220  and  220 ′. The circuit of  FIG. 5  is a simplified circuit and actual embodiments may have more components or different electrical topologies, as required and/or as discussed herein. In various embodiments of the present invention, Zener diode  510  is selected to have a breakdown voltage greater than the forward voltage of LEE  220 ′. Thus, when LEE  220 ′ is in the circuit, all or substantially all the current flows through LEE  220 ′ because the voltage across Zener diode  510  is less than the breakdown voltage, thus no or virtually no current flows through Zener diode  510 . However, when LEE  220  is removed from the circuit (for example by cutting along cut line A-A′), the voltage from power supply  230  may increase to drive the current to the desired value. When the voltage increases to a value larger than the breakdown voltage of Zener diode  510 , it will conduct current and complete the circuit. Current regulator  145  may control the current to the desired or substantially desired value; however, with Zener diode  510  in the circuit (replacing LEE  210 ′) the voltage supplied by power supply  230  may be higher than without Zener diode  510  replacing LEE  210 ′, for example by an amount about equal to the difference between the Zener breakdown voltage of Zener diode  510  and the forward voltage of LEE  210 ′. 
         [0054]    In various embodiments of the present invention, a panel or substrate may be divided into a number of segments (or grid elements similar to those described in reference to  FIGS. 2A and 4B ), where each grid segment or grid element contains one string of LEEs and cutting or separation removes one or more complete strings. In addition, the embodiment discussed in reference to  FIG. 5  and similar embodiments permit removal of a portion of a string. 
         [0055]      FIG. 6A  depicts an exemplary lighting apparatus  600  in accordance with various embodiments of the present invention. Lighting apparatus  600  includes substrate  165  on which are disposed conductive elements  160 , power conductors  120 ,  121  and LEEs  620 . The circuit on substrate  165  is powered by power supply  630 . Lighting apparatus  600  includes a 3×3 array of LEEs  620 ; however, this is not a limitation of the present invention, and in other embodiments lighting apparatus  600  may include fewer or more LEEs  620 . In various embodiments, each LEE  620  may include or consist essentially of one or more individual LEEs. In various embodiments, each LEE  620  may include or consist essentially of one or more individual LEEs and one or more control elements, for example a current-control element, or one or more other components, as will be discussed herein. 
         [0056]    Substrate  165  may be shortened in the direction  250  by removing LEEs  620  in row  640  (for example, by cutting along cut line A-A′) and then further shortened by removing LEEs  620  in row  641  (for example, by cutting along cut line B-B′). In various embodiments of the present invention, the size increment removed when each string removed is equal to or substantially equal to an LEE pitch  690 ; however, this is not a limitation of the present invention, and in other embodiments the size increment may be different from pitch  690 . In various embodiments, pitch  690  may be in the range of about 3 mm to about 200 mm or in the range of about 5 mm to about 50 mm; however, this is not a limitation of the present invention, and in other embodiments the pitch may have any value. This structure permits relatively fine control of the size increment when configuring sheet  165 , as described herein. As discussed herein, in  FIG. 6A  each LEE  620  may include or consist essentially of one or more individual LEEs, in which case the pitch between each LEEs  620  and the cut increment may be different. 
         [0057]    In addition to removing an entire row, a portion of a row may also be removed. For example, LEE  620 ′ may be removed by cutting out the area bounded by the edge of substrate  165  and cut lines E-E′, D-D′, and A-A′. In this embodiment, portions of sheet  165  are preferably first removed from the top (in the region of cut line A-A′) to ensure power is available to remaining LEEs  620 . For example, if LEE  620  bounded by the edge of substrate  165  and cut lines A-A′, D-D′, and B-B′ is removed, this will also cut power to LEE  620  situated above (that is bounded by cut lines A-A′, D-D′ and the edge of substrate  165 ). Thus, in various embodiments, LEEs  620  are preferably removed from the sheet  165  from the distal ends of the strings, i.e., the ends of the strings opposite the ends closest to power supply  630 . 
         [0058]    Reduction of the size of sheet  165  in the perpendicular or substantially perpendicular direction  252  may be accomplished by removing LEEs  620  in column  621 , (for example, by cutting along cut line D-D′) and then further reduced by removing LEEs  620  in row  622  (for example, by cutting along cut line E-E′). In various embodiments of the present invention, the size increment removed when each string removed is equal to or substantially equal to an LEE or string pitch  691 ; however, this is not a limitation of the present invention, and in other embodiments the size increment may be different from pitch  691 . In various embodiments, pitch  691  may be in the range of about 3 mm to about 200 mm or in the range of about 5 mm to about 50 mm; however, this is not a limitation of the present invention, and in other embodiments the pitch may have any value. This structure permits relatively fine control of the size increment when configuring sheet  165 , as described herein. 
         [0059]    In various embodiments, each LEE  620  may include or consist essentially of a string of LEEs, for example LEEs  220  as described with reference to  FIG. 2A .  FIG. 6B  shows an example of an embodiment of the present invention in which LEE  620  includes or consists essentially of nine LEEs  220  electrically connected in series. However, this is not a limitation of the present invention, and in other embodiments LEE  620  may include or consist essentially of any number of LEEs  220 , and these may be connected in series, parallel, a combination of series or parallel or any other arrangement. In various embodiments LEE  620  may also include additional elements, for example resistors, capacitors, transistors, inductors, integrated circuits, or the like.  FIG. 6C  shows an example of LEE  620  that includes or consists essentially of 18 LEEs  220  and control element  145 , all connected in series. As described with reference to  FIG. 6A , when one LEE  620  is removed, this is equivalent to removing an entire string of LEEs  220  in  FIG. 6B or 6C , instead of a portion of a string, as is the case with the circuit of  FIG. 2A . An advantage of the approach described in reference to  FIG. 6A  is that a bypass element may not be required to complete the circuit after cutting or separation. While  FIG. 6C  shows control element  145  as part of LEE (or string)  620 , in various embodiments, control element  145  may not be removed along with LEEs  220 , while in other embodiments control element  145  may be removed along with LEEs  220 . 
         [0060]      FIG. 6D  shows a schematic of an embodiment of the present invention of a structure in which each removable portion includes or consists essentially of one string. In  FIG. 6D , cut lines are designated by dashed lines and each LEE  620  includes or consists essentially of 12 LEEs  220 , control element  145 , and resistors  610 . In various embodiments of the present invention, resistors  610  may be included in the string to permit use of a string voltage larger than the voltage drop across LEEs  220  and control element  145 . While in various embodiments this may reduce luminous efficacy, this approach may be utilized to control the number of LEEs  220  within the string or within LEE  620 . 
         [0061]      FIG. 7A  shows a schematic of an embodiment of the present invention similar to that shown in  FIG. 6A ; however, in the structure of  FIG. 7A , additional power conductors are added to permit arbitrary removal of an LEE  620 , i.e., removal independent of its position on sheet  165 . Specifically, the LEEs within each string of LEEs are directly connected to opposing power conductors and thus are connected in parallel to each other; removal of an interior LEE without removing one or more LEEs at the distal end of the string may be accomplished via removing the LEE without removing an associated portion of at least one of the power conductors connected to that LEE.  FIG. 7B  shows removal of a portion  720  (removed portion indicated by light grey square), while  FIG. 7C  shows removal of portions  720  and  722 . Note that in  FIGS. 7B and 7C  the removed portions include removal of an edge portion of sheet  165  and removal only of LEEs  620  adjacent to the edge of sheet  165 .  FIG. 7D  shows additional removal of LEE  730 . In  FIG. 7D  removed portion  724  includes LEEs  730  and  730 ′.  FIG. 7E  shows removal of portions  722 ,  725 ,  726 , and  727 . In this case, portion  727  is in the interior of sheet  165 , i.e., it does not include an edge of sheet  165 . Note that portion  725  is different from portion  720  in  FIG. 7A , as portion  725  does not include the conductive trace attached to LEE  730  in portion  725  (this portion of the conductive trace is encircled in a dashed area identified as  740  in  FIG. 7E ). In this fashion, multiple interior and edge or exterior regions may be removed from the sheet, for example to modify the shape of the sheet to fit a specific installation area, or to permit accommodation of various features in the installation environment, for example smoke detectors, fire sprinkler heads, heating, ventilation and air conditioning ducts and/or sensors, various other sensors or cameras or the like. 
         [0062]      FIG. 8A  shows a schematic layout of an exemplary panel or tile including a 5×5 grid of LEE groups, similar to that described in reference to  FIGS. 7A-7E . Lighting panel  800  (also referred to as a lighting tile, tile, or lighting unit) includes a 5×5 grid of LEE groups  810  and connector or connection regions  820 ,  821 ,  830  and  831 . In various embodiments, one or more of the connectors or connector regions may be configured as a tab or extension to the body of the panel or tile. For example,  FIG. 8A  shows connector or connector regions  821  and  831  are disposed and/or configured on tabs or extensions  899 . In various embodiments, connector regions  820  and  821  may be electrically coupled together by conductive traces on lighting panel  800  and connector regions  830  and  831  may be electrically coupled together by conductive traces on lighting panel  800 . In various embodiments, one or more connectors, for example a snap connector (for example a connector having one of two parts that clip or snap together, e.g., a button and/or a button socket such as a 9V battery connector), slide connector, or other type of connector, may be electrically coupled to each connector region, permitting electrical and potentially mechanical coupling between multiple lighting panels  800 . In various embodiments, lighting panel  800  may incorporate features and/or connectors as described in U.S. patent application Ser. No. 14/699,149, filed on Apr. 29, 2015 (“the &#39;149 application”), the entire disclosure of which is incorporated by reference herein. In various embodiments, power may be supplied to lighting panel  800 , for example to connector regions  820  and  830 . In various embodiments power may be supplied to lighting system  800 , for example to connector regions  821  and  831 . In various embodiments, connector region  820  is electrically coupled to connector region  821  within lighting panel  800  and connector region  830  is electrically coupled to connector region  821  within lighting panel  800 . In various embodiments, a second lighting panel  800  may be electrically connected to the first, for example connector regions  820  and  830  of the second lighting panel  800  may be electrically coupled to connector regions  821  and  831 , respectively, of the first lighting panel  800 , permitting transfer of power from connector regions  821  and  831  from the first lighting panel  800  to connector regions  820  and  830  of the second lighting panel  800 . 
         [0063]      FIG. 8B  shows a schematic of a lighting system  803  including two lighting units or panels  800 , identified as  800  and  800 ′, powered by power supply  230  that is electrically coupled to connector regions  820  and  830  through conductors  891  and  890  respectively; connector regions  821  and  831  of lighting unit  800  are electrically coupled to connector regions  820 ′ and  830 ′ of lighting unit  800 ′. In various embodiments, conductors  890  and  891  may be configured as part of a power distribution bus that includes or consists essentially of power distribution lines  890  and  891  and connectors (not shown in  FIG. 8B  for clarity) that electrically couple power distribution line  890  to connector or connector region  830  and that electrically couple power distribution line  891  to connector or connector region  820 . 
         [0064]    As connector region  820  is electrically coupled to connector region  821  and connector region  830  is electrically coupled to connector region  831 , shown schematically by dashed lines  895  and  895 ′ respectively, power is thus transferred from lighting unit  800  to lighting unit  800 ′ without the need for additional power conductors between the two lighting units. While  FIG. 8B  shows two electrically connected lighting units, this is not a limitation of the present invention, and in other embodiments more than two lighting units may be configured and electrically coupled and powered as described herein. 
         [0065]    While  FIG. 8B  shows two lighting units that are the same or substantially the same, this is not a limitation of the present invention, and in other embodiments lighting units that have different shapes, sizes or configurations may be electrically coupled as described herein; preferably, such embodiments feature lighting systems configured to be powered or energized from the same power source. For example, in various embodiments of the present invention, one or more lighting units may be similar to those described in the &#39;149 application, i.e., they are separable in only one direction, or one or more lighting units may be of fixed size and not separable. In various embodiments of the present invention, the light intensity or luminous flux emitted by light sheets or lighting units is engineered to be the same or substantially the same as that emitted by other lighting units that may be incorporated into the lighting system.  FIG. 8C  shows lighting system  803  that includes multiple lighting units  800 , including a lighting unit  800 ′, a lighting unit  800 ″ that is shortened in one direction, a lighting unit  800 ′″ including a hole  888 , a lighting unit  800 ″″ that is shortened in one direction a different amount than lighting unit  800 ″, a lighting unit  800 ′″″ in which a corner is removed, and lighting unit  800 ″″″ having a portion removed along the outer edge of the lighting unit. As shown in  FIG. 8C , lighting system  803  also includes power supply  230  that provides power along bus  892  (in various embodiments power bus  892  includes or consists essentially of power distribution lines  890  and  891 ). As described herein, in various embodiments, each column of lighting units  800  is powered from power bus  892 ; however, this is not a limitation of the present invention, and in other embodiments more than one column may be powered with only one connection to power bus  892  or other power supply configurations may be utilized. 
         [0066]      FIG. 8D  shows an embodiment of a lighting system  804  of the present invention including or consisting essentially of light panels  800 ′,  800 ″″, and  800 ′″″ attached to a support  862  and covered or partially covered by an optic  865  (the details of support  862  and of optic  865  are not shown for clarity, nor are they limitations of the present invention). As shown in  FIG. 8D , optic  865  is spaced apart from light panels  800 ′,  800 ″″, and  800 ′″″ by a spacing  864 . In various embodiments of the present invention, optic  865  may be in contact with light panels  800 ′,  800 ″″, and  800 ′″″ or substantially in contact with light panels  800 ′,  800 ″″, and  800 ′″″, while in other embodiments optic  865  may be in contact or substantially in contact with the LEEs on light panels  800 ′,  800 ″″, and  800 ′″″, or may be spaced apart from light panels  800 ′,  800 ″″, and  800 ′″″ as shown in  FIG. 8D . In various embodiments of the present invention, spacing  864  may be in the range of about 0.5× to about 5×, or in the range of about 1× to about 2×, the spacing or pitch of LEEs on panels  800 ′,  800 ″″, and  800 ′″″. In various embodiments of the present invention, spacing  864  may be in the range of about 5 mm to about 500 mm, or in the range of about 10 mm to about 100 mm. In various embodiments of the present invention, support  862  may include or consist essentially of a wall, ceiling, floor, column, sub-structure, substrate, or other feature to which light panel panels  800 ′,  800 ″″, and  800 ′″″ may be attached or mounted. In various embodiments of the present invention, optic  865  may include or consist essentially of a lens, a diffuser, a refractive optic, a reflective optic, a Fresnel optic, a fabric, a translucent material such as plastic or stone, a graphic panel, a membrane or the like. In various embodiments of the present invention, optic  865  may include or consist essentially of a plurality of optical elements, for example as described in U.S. patent application Ser. No. 13/693,632, filed on Dec. 4, 2012, the entire disclosure of which is incorporated by reference herein. In various embodiments of the present invention, optic  865  may include or consist essentially of glass, stone, plastic, fabric, foam, paper, or the like. 
         [0067]    In various embodiments of the present invention, the total thickness  866  of the lighting system  804  shown in  FIG. 8D , i.e., the distance between the back of light panel  862  to the front of optic  865 , may be in the range of about 1× to about 5× the spacing or pitch of LEEs on light panels  800 ′,  800 ″″, and  800 ′″″, or in the range of about 1.5× to about 4× the spacing or pitch of LEEs on light panels  800 ′,  800 ″″, and  800 ′″″. In various embodiments of the present invention, a total thickness  866  of the lighting system shown in  FIG. 8D  may be in the range of about 0.5 cm to about 20 cm, or in the range of about 1 cm to about 10 cm, or in the range of about 1.5 cm to about 5 cm. 
         [0068]    In various embodiments, the pitch of LEEs and/or the pitch of light-emitting strings on light sheets of the present invention are engineered to provide the same or substantially the same setback behind a diffuser, graphic panel or other overlying feature as the setback for other lighting units that may be incorporated into the lighting system. In various embodiments of the present invention, the setback spacing may be the same or substantially the same despite a different pitch between LEEs on the different light sheets. In various embodiments of the present invention, the operating current may be different and may be adjusted to achieve the same or substantially the same setback spacing in a system including different light sheets. 
         [0069]    Such lighting systems  803  and  804  and similar lighting systems of the present invention provide substantially uniform illumination over large areas. The systems are also configurable to fit different shapes and sizes of areas and also permit formation of holes or penetrations, for example for sprinkler heads, standoffs, heating, and/or air conditioning, and/or ventilation ducts, and the like. In various embodiments of the present invention, the variation in luminous flux across the surface area of a lighting system  803  may be less than about 25%, or less than about 20%, or less than about 15% or less than about 10%. 
         [0070]    In various embodiments, LEE group  810  may include or consist essentially of multiple LEEs, for example LEEs  140  and optionally one or more control elements, for example to control the intensity, color, or one or more other characteristics of LEEs  140 .  FIG. 8E  shows an enlarged portion of the circuit layout of  FIG. 8A , showing LEE group  810  containing multiple positions for LEEs  140 , identified as LEE positions  840  in  FIGS. 8A and 8E . While  FIGS. 8A and 8E  show LEE group  810  having 16 LEE positions  840 , this is not a limitation of the present invention, and in other embodiments LEE group  810  may have fewer or more LEE positions  840 . 
         [0071]      FIG. 8F  shows a schematic of an embodiment of a LEE  140  of the present invention, having contacts  854  and  856 .  FIG. 8G  shows a magnified view of the contact side of an embodiment of LEE position  840  of the present invention, having a first contact area  844  and a second contact area  846 , separated by a gap  842 . In various embodiments of the present invention, contact  854  of LEE  140  is electrically coupled to contact area  844  and contact  856  of LEE  140  is electrically coupled to contact area  846 , as shown in  FIG. 8H . 
         [0072]      FIG. 9A  shows an electrical schematic of an exemplary embodiment of the present invention including a panel or tile including a 5×5 grid of LEE groups and that is representative of the layout structure shown in  FIG. 8A . In various embodiments of the present invention, the circuit of  FIG. 9A  is energized through contacts  910  and  920 . In  FIG. 9A , the circuit may be energized through multiple contacts  910 , identified as  910 ,  910 ′,  910 ″ and  910 ′″ and contacts  920 , identified as  920 ,  920 ′,  920 ″ and  920 ′″. The circuit of  FIG. 9A  includes multiple LEE groups  810 —in  FIG. 9A  the circuit has 25 LEE groups  810 ; however, this is not a limitation of the present invention, and in other embodiments the system may have fewer or more LEE groups  810 . As discussed with respect to  FIGS. 8A and 8C , each LEE group  810  may include or consist essentially of multiple LEEs  140 . In the embodiment shown in  FIG. 9A , each LEE group  810  has 16 LEEs  140 ; however, this is not a limitation of the present invention, and in other embodiments each LEE group  810  may include a different number of LEEs  140 . 
         [0073]      FIG. 9B  shows an enlarged portion of the electrical schematic of  FIG. 9A , showing connector areas  910  and  920  and four LEE groups  810 . In various embodiments the structure of  FIG. 8A  corresponding to the electrical layout of  FIG. 9A  may have one or more LEE groups  810  removed without affecting the operation of the remaining LEE groups  810 . The straight dashed lines shown in  FIGS. 9A and 9B  show schematic cut lines that permit such removal of each LEE group  810  without affecting the operation of the remaining LEE groups  810 . As may be seen in  FIGS. 9A and 9B , each LEE group  810  is electrically connected through power conductors  120 ,  121  to the other LEE groups  810  through multiple connections, permitting one or more LEE groups  810  to be removed from the lighting system without affecting the operation of the remaining LEE groups  810 . 
         [0074]      FIG. 9B  shows four complete LEE groups  810  and portions of two surrounding LEE groups  810 . As shown in  FIG. 9B , in various embodiments the lighting system may be energized through connector areas  910  and  920 ; for example, power may be applied to connector areas  910  and  920 . In various embodiments of the present invention, the lighting system or panel may be energized using a constant or substantially constant voltage or constant current. In various embodiments of the present invention, the lighting system or panel may be energized using a constant or substantially constant DC voltage. In various embodiments of the present invention, the power may be modulated, for example pulse width modulated to modify the light intensity level or to dim the lighting system or panel. As shown in  FIG. 9A , multiple connector areas  910  and  920  may be configured on the lighting panel or tile, identified with one or more apostrophes (′), to permit electrical coupling between multiple panels or tiles. In various embodiments a connector, for example a snap connector as described in the &#39;149 application, may be disposed in the area of connector areas  910 ,  920  and be electrically coupled to connector areas  910 ,  920 ; however, this is not a limitation of the present invention, and in other embodiments different connectors or methods of electrically coupling to and between panels and tiles may be utilized. 
         [0075]    Referring to  FIG. 9B , power may be applied to the lighting tile or panel by way of connector areas  910  and  920 . In various embodiments, the tile or panel may be energized by a constant or substantially constant voltage. As shown in  FIG. 9C , each LEE group  810  includes or consists essentially of 16 LEEs  140 , a control circuit  960 , and two resistors  962  and  964 . In various embodiments of the present invention, control circuit  960  may be configured to regulate the current to LEEs  140 , for example to provide a constant or substantially constant current to LEEs  140 ; however, this is not a limitation of the present invention, and in other embodiments control circuit  960  may be configured for other purposes, for example to control an optical characteristic of LEEs  140 , for example, luminous flux, CCT, CRI, spatial light distribution, angular color uniformity, or the like. In various embodiments of the present invention, control circuit  960  may be addressable, for example to permit separate control of each or groups of LEE groups  810 . In various embodiments of the present invention, one or more resistors, for example resistors  962  and  964 , may be included in the circuit of LEEs  140 , for example in series with the series-connected LEEs  140 , as shown in  FIG. 9C . In various embodiments of the present invention, resistors  962  and  964  may be included in the string to permit use of a string voltage larger than the voltage drop across LEEs  140  and control circuit  960 . While in various embodiments this may reduce luminous efficacy, this approach may be utilized to control the number of LEEs  140  within LEE group  810 . 
         [0076]    Referring to  FIG. 9B , connector area  910  is electrically coupled to multiple conductors  120 ,  120 ′,  120 ″,  120 ′″ and  120 ″″. If LEE group  810 ′ is removed, conductor  120 ′ will be cut at cut line B′ and at cut line B and conductor  120 ″ will be cut at cut line A′; however, power will be delivered around the removed LEE group  810 ′ through conductors  120 ′″ and  120 ″″ and the remainder of the tile. A similar configuration is utilized for connector area  920 . 
         [0077]    Referring to  FIG. 9C , if LEE group  810 ″ is removed, conductor  120  will be cut at cut line A′ and A, and conductor  120 ′″ will be cut at cut line B; however, power will be delivered around the removed LEE group  810 ″ through conductors  120 ′ and  120 ″ to conductors  120 ′″″ and  120 ″″″ and the remainder of the tile. 
         [0078]    Referring to  FIG. 9D , if an interior LEE group, for example group  810 ′″ is removed, conductor  120 ′″″ will be severed, but power will be delivered around the removed LEE group  810 ′″, for example by way of conductor  120  and conductor  120 ″″″. 
         [0079]    In  FIGS. 9A-9C , similar configurations are utilized for conductor area  920  and conductors  121 , to permit delivery of power around removed LEE groups  810 . 
         [0080]    While  FIGS. 9A-9C  show one example of redundant wiring, to permit removal of one or more LEE groups  810 , for the edge or interior of the lighting panel or tile, the specific physical layout is not a limitation of the present invention and in other embodiments different physical layouts may be utilized. 
         [0081]    While the systems discussed heretofore have been discussed with respect to all LEEs on a tile or panel having the same or substantially the characteristics, this is not a limitation of the present invention, and in other embodiments such systems and methods may be extended to grids or sections having more than one type of LEE per grid. For example, in various embodiments of the present invention a system may have two types of LEEs having different characteristics in each separable grid element or section, for example in grid element or section  450  of  FIG. 4B . 
         [0082]      FIG. 10  shows a schematic of a partial system in accordance with various embodiments of the present invention showing each section or grid having two groups of LEEs. The structure of  FIG. 10  shows two grids, identified as  1040  and  1041 . The sections shown in  FIG. 10  are similar to those shown in  FIG. 4A , except that each section or grid has two groups of LEEs in  FIG. 10 , whereas in  FIG. 4A  each section or grid has one group of LEEs. Each grid or section in  FIG. 10  has two types of LEEs, four LEEs identified as type  1010  and four LEEs identified as type  1020 ; thus, each grid or section has eight total LEEs. In various embodiments of the present invention, each type of LEE may have a different optical characteristic. For example, in various embodiments each type of LEE may have a different CCT, for example a relatively cool CCT for one group and a relatively warm CCT for a second group. In various embodiments, a cool CCT may have values in the range of about 4000K to about 10,000K and a warm CCT may have values in the range of about 1500K to about 3000K. In various embodiments of the present invention, each grid or section may have its associated current control circuitry identified as  1012  for LEEs  1010  and  1022  for LEEs  1020 . In various embodiments of the present invention, power may be applied to each type of LEE through connections  1014  for LEEs  1010  and through connections  1024  for LEEs  1020 . In various embodiments of the present invention, each group may be independently energized or powered, for example through connections  1014  and  1024 ; however, this is not a limitation of the present invention, and in other embodiments the amount of power to each type of LEE may be fixed, or may be limited to two or more pre-set values or may be controlled in any other manner. 
         [0083]    In various embodiments of the present invention, the different types of LEEs may have one or more different electrical and/or optical characteristics, such as correlated color temperature (CCT), color rendering index (CRI), luminous flux, radiant flux, R9, spatial intensity distribution pattern, spectral power density, forward voltage or the like. For example, in various embodiments of the present invention, each group of LEEs may have a different CCT, for example a relatively cool CCT for one group and a relatively warm CCT for a second group, and the intensity of each group may be separately and/or independently adjusted, for example by the amount of power applied to terminals  1014  and  1024 , to permit tuning of the value of the CCT of the light emitted from the system between the CCTs of each group, that is from warm to cool. In various embodiments of the present invention, the two types of LEEs may have different spatial intensity distribution patterns and the overall spatial intensity distribution pattern may varied by varying the power to the two types of LEEs. In various embodiments of the present invention, the two types of LEEs may have different spectral power distributions and the overall spectral power distribution may varied by varying the power to the two types of LEEs. 
         [0084]    In various embodiments of the present invention, a group may include more than two different types of LEEs. For example a group may have three or more LEE types, each having a different CCT, for example a relatively warm CCT, a relatively cool CCT, and a CCT in between the relatively warm and relatively cool CCT. In such embodiments, the CCT may be varied between the warm and cool CCTs while maintaining the color point on or substantially on the black body locus. 
         [0085]    As discussed herein, the number of LEEs in each group is not a limitation of the present invention; while  FIG. 10  shows four LEEs of each type in each group, other numbers of LEEs per group and configurations are within the scope of the present invention. 
         [0086]    While removal of a portion of the sheet or substrate has been referred to as cutting or shortening, this is not a limitation of the present invention, and in other embodiments removal of a portion of the sheet may be accomplished by other means, for example breaking or tearing, die cutting, sawing, or the like. The method of removing a portion of the sheet or substrate is not a limitation of the present invention. In various embodiments, the sheet or substrate may have guide lines (e.g., features such as dashed lines printed on the sheet or substrate) to aid in the separation process. In various embodiments, the guide lines may provide a guide for the separation process, while in other embodiments the guide lines may incorporate one or more features to aid in separation, for example perforations in the substrate, a reduction in the thickness of the substrate, the absence of conductive trace material in the separation region, or the like. 
         [0087]    In various embodiments of the present invention, substrate  165  is flexible, while in other embodiments substrate  165  may be rigid or semi-rigid. The rigidity of substrate  165  is not a limitation of the present invention. In various embodiments of the present invention, substrate  165  may include, consist essentially of, or consist of one or more of the following: fiberglass, FR4, FR2, acrylic, cloth, polyester, polyimide, polyethylene, polyethersulfone, polyethylene napthalate (PEN), polyetherimide (PEI), polyethylene terephthalate, aluminum, metal, metal core printed circuit board, (MCPCB), fabric, paper, or glass. In various embodiments of the present invention, conductive elements interconnecting LEEs may include, consist essentially of, or consist of one or more of the following: copper, aluminum, carbon, conductive fibers, gold, silver, transparent conductive materials (e.g., transparent conductive oxides such as indium tin oxide), conductive nanocomposites, or conductive ink. The materials of substrate  165  and the conductive elements are not limitations of the present invention. 
         [0088]    In some embodiments, a flexible substrate  165  is configurable to a radius of curvature of about 1 m or less, or about 0.5 m or less, or even about 0.1 m or less. In some embodiments, a flexible substrate  165  has a Young&#39;s Modulus less than about 100 N/m 2 , less than about 1 N/m 2 , less than about 0.1 N/m 2 , or even less than about 0.05 N/m 2 . In some embodiments, a flexible substrate  165  has a Shore A hardness value less than about 100; a Shore D hardness less than about 100; and/or a Rockwell hardness less than about 150. 
         [0089]    In various embodiments of the present invention, removal of a portion of a light sheet, for example to remove a LEE, may be performed using scissors or a knife or another cutting tool. In various embodiments of the present invention, lines or shapes demarking cut lines may be marked on the light sheet, for example as a pattern in the conductive metal on the substrate or printed on the light sheet or by other means. In various embodiments of the present invention, portions of the substrate and/or the conductive traces may be perforated or scored to indicate cut lines and/or to facilitate removal of a portion of the light sheet. 
         [0090]    The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.