Patent Publication Number: US-11396999-B2

Title: Sealed and sealable scalable lighting systems incorporating flexible light sheets and related methods

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/663,593, filed Oct. 25, 2019, which is a continuation-in-part of U.S. patent application Ser. No. 16/218,760, filed Dec. 13, 2018, which is a continuation of U.S. patent application Ser. No. 15/787,020, filed Oct. 18, 2017, which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/409,586, filed Oct. 18, 2016, the entire disclosure of each of which is hereby incorporated herein by reference. U.S. patent application Ser. No. 15/787,020, filed Oct. 18, 2017, is also a continuation-in-part of U.S. patent application Ser. No. 15/296,590, filed Oct. 18, 2016, which is a continuation of U.S. patent application Ser. No. 14/301,859, filed Jun. 11, 2014, which (i) claims the benefit of and priority to U.S. Provisional Patent Application No. 61/834,183, filed Jun. 12, 2013, the entire disclosure of which is hereby incorporated herein by reference, and (ii) is a continuation-in-part of U.S. patent application Ser. No. 14/195,175, filed on Mar. 3, 2014, which is a continuation of U.S. patent application Ser. No. 13/970,027, filed Aug. 19, 2013, now issued as U.S. Pat. No. 8,704,448, which is a continuation-in-part of U.S. patent application Ser. No. 13/799,807, filed Mar. 13, 2013, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/697,411, filed Sep. 6, 2012, the entire disclosure of each of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     In various embodiments, the present invention generally relates to electronic devices, and more specifically to array-based lighting devices. 
     BACKGROUND 
     Solid-state lighting is an attractive alternative to incandescent and fluorescent lighting systems for a wide range of lighting applications, and in particular for exterior applications, because of its relatively higher robustness, and long life. However, conventional solid-state lighting systems featuring light-emitting diodes (LEDs) have a number of limitations related to thermal management of heat generated by the LEDs that may complicate the fabrication of sealed, weatherproof or waterproof systems. Because of the sealing requirements, traditional exterior LED lighting systems typically have a rigid structure and a fixed size, making it difficult to illuminate arbitrarily sized areas. For example back lighting, either for decorative or signage purposes, is widely used in exterior applications, and in most cases, the size and shape of the area to be illuminated is not a perfect fit for traditional exterior lighting systems. Such backlighting systems may have very large sizes, for example hundreds of feet on a side, may have odd shapes, such as curve or non-right angle joints or may not be flat, but have a three-dimensional shape. The result is uneven illumination, for example relatively darker regions in between each illumination unit and at the edges of the area, which cannot effectively be illuminated by fixed size systems or relatively brighter areas associated with each illumination unit in the system. 
     Traditionally the issue of uneven illumination is addressed by increasing the depth of the lighting system and/or reducing the transmittance of the surface to be illuminated. While both of these approaches do address the issue of uneven illumination, these solutions come with increased cost, reduced efficiency and undesirable aesthetics. 
     In many lighting applications it is desirable to have lighting systems or luminaires that are thin, low-volume, and lightweight in order to meet certain building requirements, aesthetic design requirements or so that the lighting system is unobtrusive. In other applications it is desirable to be able to conform the illumination source to a curved surface. Increasing the depth of the system to achieve acceptable intensity uniformity is at odds with these needs and also increases the cost of the system because more material is required for the system itself as well as the mounting hardware. Reducing the transmittance of the illuminated surface also reduces the system efficiency. 
     In both cases, the actual flux from the LEDs typically must be increased to achieve the desired intensity of the illuminated surface, increasing the up-front and operating costs, as well as adding more cost and complexity for thermal management of the heat generated by the additional LEDs. In large measure the heat from LEDs is generally extracted by conduction, which typically requires relatively large amounts of material with a high thermal conductivity, such as metal core printed circuit boards (MCPCBs), heat sinks, and in some cases active (e.g., forced-air) cooling. Such thermal-management solutions are significantly more complicated when required to be located within a sealed system and are typically not sufficiently flexible to permit conforming to curved surfaces. Furthermore, they take up significantly more space than the LEDs themselves, resulting in increased size and volume of exterior LED-based lighting systems. In addition to higher cost, exterior LED lighting systems may have potentially reduced reliability and operational lifetime resulting from higher LED junction temperatures that may exist in sealed systems. 
     In view of the foregoing, a need exists for systems and techniques enabling the low-cost design and manufacture of sealed and sealable compact, reliable, high-brightness lighting systems able to produce uniform illumination over arbitrarily sized areas. 
     SUMMARY 
     In accordance with certain embodiments of the present invention, lighting systems incorporate flexible light sheets having light-emitting elements (e.g., light-emitting diodes such as packaged light-emitting diodes and bare-die light-emitting diodes) thereon. The light sheets may be utilized to fabricate a collection of assemblable, differently shaped illumination elements that may be assembled and electrically connected together in order to illuminate a two-dimensional area having an arbitrary shape. In various embodiments, the shape of each illumination element is defined by a one-dimensional or two-dimensional contiguous arrangement of “illumination unit cells,” each of which may encompass a minimum set of light-emitting elements (e.g., one or more light-emitting strings) such that the unit cell emits light at a predetermined luminous flux density. In this manner, since each of the illumination elements is composed of a number of the unit cells, each illumination element also emits light at approximately the same predetermined luminous flux density over its entire area. Thus, in various embodiments, each of the illumination elements emits light at a luminous flux density within ±10%, within ±5%, or even within ±2% of each of the other illumination elements, thereby enabling the illumination of arbitrary areas with a high degree of uniformity. Since each of the illumination elements has a different shape, one or more of each of the illumination elements may be assembled into a shape approximately conforming to the desired area for illumination. (As utilized herein, a shape “approximately conforming to” a desired area has an area within ±10%, within ±5%, or even within ±2% of the area to be illuminated; in various embodiments, the shape may conform to the area to within the geometric limits imposed by the shape and size of the illumination unit cells utilized to form the illumination units (for example, curved edges of an area to be illuminated may be approximated by angular edges in embodiments in which the illumination unit cells are polygons such as squares or rectangles).) 
     In various embodiments, top and/or bottom housings, either or both of which may be polymeric, may be utilized to seal at least portions of the light sheets and form sealed regions that may be water-resistant or waterproof. The housings may also be shaped to reflect, diffuse, and/or shape the light emitted by the light-emitting elements. The housings may even define structural features such as protruding ribs for mechanical stability. While most, if not all, of the light-emitting elements of the light sheets are preferably safely located within the sealed regions, the lighting systems typically incorporate conductive couplings that extend out of the sealed regions (without disrupting the seal over the light-emitting elements) and enable the provision of power from an external power source to the light-emitting elements. Lighting systems in accordance with embodiments of the invention may thus be advantageously deployed in harsher and/or moist environments where exposure to dirt, dust, moisture, etc. is possible or frequent. The lighting systems may be fabricated in bulk by, e.g., roll-to-roll processes and even separated from larger “sheets” of the lighting device components, preferably without disrupting the seal on and/or around each individual lighting system (or “partial” lighting system). As used herein, a “sealed region” refers to a portion of a light sheet or lighting system having a periphery at least partially defined by a seal between two housings, a housing and the light sheet, and/or a housing, light sheet, and/or another sealing material (e.g., a transparent material disposed between the light sheet and a housing. A sealed region may also include a portion of a light sheet coated with a housing, i.e., the housing may be a coating or sealant material conformally or non-conformally coating (and thus directly contacting) at least some portions of the light sheet (and, e.g., light-emitting elements, conductive traces, etc. on the light sheet) thereunder. Embodiments of the invention may incorporate aspects and details disclosed in U.S. patent application Ser. No. 14/301,859, filed on Jun. 11, 2014, the entire disclosure of which is incorporated by reference herein. 
     Various embodiments of the present invention feature a sealed thin light sheet that does not require any additional heat sinking or thermal management. In various embodiments, the light sheet may also be flexible and may be curved or folded to achieve one or more specific characteristics or attributes, for example, to permit manufacture of a compact, foldable system and/or to achieve a specific light-distribution pattern. In various embodiments of the present invention, the light sheet typically includes or consists essentially of an array of light-emitting elements (LEEs) electrically coupled by conductive elements formed on a flexible substrate, for example as described in U.S. patent application Ser. No. 13/799,807, filed Mar. 13, 2013 (the &#39;807 application), or U.S. patent application Ser. No. 13/970,027, filed Aug. 19, 2013 (the &#39;027 application), the entire disclosure of each of which is herein hereby incorporated by reference. 
     In an aspect, embodiments of the invention feature a system of lighting components for illuminating an arbitrary two-dimensional area. The system includes, consists essentially of, or consists of a plurality of assemblable illumination elements. Each illumination element includes, consists essentially of, or consists of a substrate, first and second spaced-apart power conductors disposed over the substrate, a plurality of light-emitting elements that are spaced apart and interconnected into one or more light-emitting strings, and one or more electrical connectors each electrically coupled to at least one of the first or second power conductors. Each light-emitting string (i) includes a control element disposed over the substrate and electrically connected to the light-emitting elements in the light-emitting string and configured to provide a predetermined current to the light-emitting elements in the light-emitting string, (ii) includes two or more of the light-emitting elements, (iii) has a first end electrically connected to the first power conductor, and (iv) has a second end electrically connected to the second power conductor. Each illumination element has a different shape defined by a one-dimensional or two-dimensional contiguous arrangement of illumination unit cells. Each illumination unit cell (i) is polygonal, (ii) encompasses at least one light-emitting string, and (ii) emits light at a predetermined luminous flux density, such that each of the illumination elements emits light at approximately the predetermined luminous flux density. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. The predetermined luminous flux density of each illumination element may be within ±10%, ±5%, or ±2% of the predetermined luminous flux density of any other illumination element. One or more of the illumination elements may be flexible. The system may include a power supply electrically coupled to the one or more electrical connectors of a first illumination element, and power from the power supply may be supplied to one or more other illumination elements via the first illumination element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. The power supply may be configured to adjust a light output of at least one illumination element by pulse-width-modulating a voltage or a current of the power supply. 
     The system may include a power-distribution element. The power-distribution element may include, consist essentially of, or consist of one or more first connector sets and one or more second connection point sets. The one or more first connector sets may each include, consist essentially of, or consist of one or more first electrical connectors each configured for connection to an electrical connector of an illumination element. The one or more second connection point sets may each include, consist essentially of, or consist of one or more second electrical connection points for receiving power from an external source of power. Any of the second electrical connection points may be a connection point for a bare wire or a flying lead, or may be a connector analogous to one or more of the electrical connectors found on the illumination elements. Power received via the one or more second connection point sets may be distributed, on the power-distribution element, to the one or more first connector sets. The system may include a power supply, and the power supply may be the external source of power for the power-distribution element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. The power supply may be configured to adjust a light output of at least one illumination element by pulse-width-modulating a voltage or a current of the power supply. The power supply may be directly coupled to the one or more second connection point sets (e.g., via a connection such as an electrical connector, a wire, or other connection). (In embodiments in which the power supply is “indirectly coupled” to the one or more second connection point sets, the power supply is directly coupled to a different element that is directly coupled to the one or more second connection point sets, such as one of the illumination elements, and power from the power supply flows through that different element to the power-distribution element.) The one or more second connection point sets may be directly coupled to one or more of the illumination elements, and power may be supplied to the power-distribution element via the one or more of the illumination elements. The power-distribution element may contain no light-emitting elements thereon. The power-distribution element may include a substrate, and the substrate may include, consist essentially of, or consist of the same substrate as that of one or more of the illumination elements. The power-distribution element may be flexible. 
     When the plurality of illumination elements are positioned adjacent to each other and connected together via the electrical connectors, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction, and the first pitch may be maintained between and among the plurality of illumination elements (i.e., the first pitch may be maintained even across interfaces between different illumination elements). When the plurality of illumination elements are positioned adjacent to each other and connected together via the electrical connectors, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from (e.g., substantially perpendicular to) the first direction, and the second pitch may be maintained between the plurality of illumination elements. The first pitch and the second pitch may be substantially equal. 
     At least one illumination element may include at least one optical element (e.g., a lens, prism, collimator, mirror, reflector, etc.), which may be configured for focusing and/or shaping light from the illumination element to a desired illumination pattern. An optic may be disposed on or over at least one illumination element. 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 at least one illumination element and the optic may be less than 500 mm. A collective thickness of the at least one illumination element and the optic may be at least 10 mm, at least 20 mm, at least 50 mm, or at least 100 mm. A collective thickness of the at least one illumination element and the optic may range from 100% to 500% of a spacing between the light-emitting elements disposed on the at least one illumination element. 
     At least one control element may be configured to receive a control signal representing the predetermined current. At least one power conductor may be configured to provide a control signal to the at least one control element. At least one illumination element may include a second control element (i) electrically connected to at least one light-emitting string, and (ii) configured to control the at least one light-emitting string to produce an optical characteristic of light emitted thereby. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. The plurality of light-emitting elements of at least one illumination element may include, consist essentially of, or consist of at least two groups of light-emitting elements, each group of light emitting-elements having a different optical characteristic. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. 
     One or more of the illumination elements may include a polymeric top housing sealed to the substrate to form a sealed region in which the light-emitting elements of the illumination element are disposed. The one or more of the illumination elements may be water-resistant or waterproof. The one or more of the illumination elements may have an ingress protection rating of at least IP X5, as specified by International Protection Marking in International Electrotechnical Commission (IEC) standard 60529. The substrate of the one or more of the illumination elements may have a first surface and a second surface opposite the second surface. The light-emitting elements of the one or more of the illumination elements may be disposed over the first surface. The one or more of the illumination elements may include a polymeric bottom housing disposed over the second surface of the substrate opposite the top housing. At least a portion of the bottom housing may contact the second surface of the substrate to form a second sealed region disposed between the bottom housing and the second surface of the substrate. The sealed region and/or the second sealed region may be water-resistant or waterproof. The bottom housing may be spaced away from the second surface (e.g., not in contact with or conforming to the shape of the second surface) in the second sealed region. The bottom housing may be in contact with at least a portion of the second surface in the second sealed region. 
     The substrate of the one or more of the illumination elements may have a first surface and a second surface opposite the second surface. The light-emitting elements of the one or more of the illumination elements may be disposed on over the first surface. The one or more of the illumination elements may include a polymeric bottom housing disposed over the second surface of the substrate opposite the top housing. At least a portion of the bottom housing may contact the top housing to form a second sealed region disposed between the bottom housing and the second surface of the substrate and/or the top housing. At least a portion of the bottom housing may contact the top housing to form a second sealed region disposed between the bottom housing and the top housing. The sealed region and/or the second sealed region may be water-resistant or waterproof. The top housing and/or the bottom housing may include, consist essentially of, or consist of polyester, acrylic, polystyrene, polyethylene, polyimide, polyethylene naphthalate, polyethylene terephthalate, polypropylene, polycarbonate, acrylonitrile butadiene styrene, polyurethane, silicone, and/or polydimethylsiloxane. The top housing and the bottom housing may include, consist essentially of, or consist of the same material or different materials. 
     The predetermined luminous flux density of each illumination element may be within ±10%, ±5%, or ±2% of the predetermined luminous flux density of any other illumination element. The one or more of the illumination elements may be flexible. The system may include a power supply electrically coupled to the one or more electrical connectors of a first illumination element, and power from the power supply may be supplied to one or more other illumination elements via the first illumination element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. The power supply may be configured to adjust a light output of at least one illumination element by pulse-width-modulating a voltage or a current of the power supply. 
     The system may include a power-distribution element. The power-distribution element may include, consist essentially of, or consist of one or more first connector sets and one or more second connection point sets. The one or more first connector sets may each include, consist essentially of, or consist of one or more first electrical connectors each configured for connection to an electrical connector of an illumination element. The one or more second connection point sets may each include, consist essentially of, or consist of one or more second electrical connection points for receiving power from an external source of power. Any of the second electrical connection points may be a connection point for a bare wire or a flying lead, or may be a connector analogous to one or more of the electrical connectors found on the illumination elements. Power received via the one or more second connection point sets may be distributed, on the power-distribution element, to the one or more first connector sets. When the one or more first connector sets are connected and the one or more second connection point sets are connected, the power-distribution element may be water-resistant or waterproof. The system may include a power supply, and the power supply may be the external source of power for the power-distribution element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. The power supply may be configured to adjust a light output of at least one illumination element by pulse-width-modulating a voltage or a current of the power supply. The power supply may be directly coupled to the one or more second connection point sets (e.g., via a connection such as an electrical connector, a wire, or other connection). The one or more second connection point sets may be directly coupled to one or more of the illumination elements, and power may be supplied to the power-distribution element via the one or more of the illumination elements. The power-distribution element may contain no light-emitting elements thereon. The power-distribution element may include a substrate, and the substrate may include, consist essentially of, or consist of the same substrate as that of one or more of the illumination elements. The power-distribution element may be flexible. 
     When the plurality of illumination elements are positioned adjacent to each other and connected together via the electrical connectors, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction, and the first pitch may be maintained between and among the plurality of illumination elements (i.e., the first pitch may be maintained even across interfaces between different illumination elements). When the plurality of illumination elements are positioned adjacent to each other and connected together via the electrical connectors, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from (e.g., substantially perpendicular to) the first direction, and the second pitch may be maintained between the plurality of illumination elements. The first pitch and the second pitch may be substantially equal. 
     At least one illumination element may include at least one optical element (e.g., a lens, prism, collimator, mirror, reflector, etc.), which may be configured for focusing and/or shaping light from the illumination element to a desired illumination pattern. An optic may be disposed on or over at least one illumination element. 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 at least one illumination element and the optic may be less than 500 mm. A collective thickness of the at least one illumination element and the optic may be at least 10 mm, at least 20 mm, at least 50 mm, or at least 100 mm. A collective thickness of the at least one illumination element and the optic may range from 100% to 500% of a spacing between the light-emitting elements disposed on the at least one illumination element. 
     At least one control element may be configured to receive a control signal representing the predetermined current. At least one power conductor may be configured to provide a control signal to the at least one control element. At least one illumination element may include a second control element (i) electrically connected to at least one light-emitting string, and (ii) configured to control the at least one light-emitting string to produce an optical characteristic of light emitted thereby. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. The plurality of light-emitting elements of at least one illumination element may include, consist essentially of, or consist of at least two groups of light-emitting elements, each group of light emitting-elements having a different optical characteristic. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. 
     One or more of the illumination elements may include (i) a polymeric top housing disposed over a first surface of the substrate, and (ii) a polymeric bottom housing disposed over a second surface of the substrate opposite the first surface. The top housing may be sealed to the bottom housing to form a sealed region in which the light-emitting elements of the illumination element are disposed. All or a portion of the substrate of the illumination element may be disposed within the sealed region. The one or more of the illumination elements may be water-resistant or waterproof. The one or more of the illumination elements may have an ingress protection rating of at least IP X5, as specified by International Protection Marking in International Electrotechnical Commission (IEC) standard 60529. 
     In another aspect, embodiments of the invention feature a method of illuminating an area. An area for illumination is defined. The area has an arbitrary size and two-dimensional shape. A plurality of assemblable illumination elements is provided. Each illumination element includes, consists essentially of, or consists of a substrate, first and second spaced-apart power conductors disposed over the substrate, a plurality of light-emitting elements that are spaced apart and interconnected into one or more light-emitting strings, and one or more electrical connectors each electrically coupled to at least one of the first or second power conductors. Each light-emitting string (i) includes a control element disposed over the substrate and electrically connected to the light-emitting elements in the light-emitting string and configured to provide a predetermined current to the light-emitting elements in the light-emitting string, (ii) includes two or more of the light-emitting elements, (iii) has a first end electrically connected to the first power conductor, and (iv) has a second end electrically connected to the second power conductor. Each illumination element has a different shape defined by a one-dimensional or two-dimensional contiguous arrangement of illumination unit cells. Each illumination unit cell (i) is polygonal, (ii) encompasses at least one light-emitting string, and (ii) emits light at a predetermined luminous flux density, such that each of the illumination elements emits light at approximately the predetermined luminous flux density. One or more of each of the illumination elements is assembled, via interconnection of electrical connectors of adjoining illumination elements, into a shape approximately conforming to the area. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. An area of the shape into which the one or more of each of the illumination elements is assembled may be within ±20%, within ±10%, within ±5%, or within ±2% of the area for illumination. The predetermined luminous flux density of each illumination element may be within ±10%, ±5%, or ±2% of the predetermined luminous flux density of any other illumination element. One or more of the illumination elements may be flexible. A power supply may be electrically coupled to the one or more electrical connectors of a first illumination element, and power from the power supply may be supplied to one or more other illumination elements via the first illumination element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. A voltage or a current of the power supply may be pulse-width-modulated to adjust a light output of at least one illumination element. 
     A power-distribution element may be provided. The power-distribution element may include, consist essentially of, or consist of one or more first connector sets and one or more second connection point sets. The one or more first connector sets may each include, consist essentially of, or consist of one or more first electrical connectors each configured for connection to an electrical connector of an illumination element. The one or more second connection point sets may each include, consist essentially of, or consist of one or more second electrical connection points for receiving power from an external source of power. Any of the second electrical connection points may be a connection point for a bare wire or a flying lead, or may be a connector analogous to one or more of the electrical connectors found on the illumination elements. Power received via the one or more second connection point sets may be distributed, on the power-distribution element, to the one or more first connector sets. A power supply may be provided, and the power supply may be the external source of power for the power-distribution element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. A voltage or a current of the power supply may be pulse-width-modulated to adjust a light output of at least one illumination element. Providing the power supply may include, consist essentially of, or consist of directly coupling the power supply to the one or more second connection point sets (e.g., via a connection such as an electrical connector, a wire, or other connection). (In embodiments in which the power supply is “indirectly coupled” to the one or more second connection point sets, the power supply is directly coupled to a different element that is directly coupled to the one or more second connection point sets, such as one of the illumination elements, and power from the power supply flows through that different element to the power-distribution element.) The one or more second connection point sets may be directly coupled to one or more of the illumination elements, and power may be supplied to the power-distribution element via the one or more of the illumination elements. The power-distribution element may contain no light-emitting elements thereon. The power-distribution element may include a substrate, and the substrate may include, consist essentially of, or consist of the same substrate as that of one or more of the illumination elements. The power-distribution element may be flexible. 
     When the one or more of each of the illumination elements are assembled into the shape, across the shape, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction, and the first pitch may be maintained between and among the plurality of illumination elements (i.e., the first pitch may be maintained even across interfaces between different illumination elements). When the one or more of each of the illumination elements are assembled into the shape, across the shape, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from (e.g., substantially perpendicular to) the first direction, and the second pitch may be maintained between the plurality of illumination elements. The first pitch and the second pitch may be substantially equal. 
     At least one optical element (e.g., a lens, prism, collimator, mirror, reflector, etc.) may be provided. The at least one optical element may be configured for focusing and/or shaping light from at least one illumination element to a desired illumination pattern. An optic may be positioned on or over at least one illumination element. 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 at least one illumination element and the optic may be less than 500 mm. A collective thickness of the at least one illumination element and the optic may be at least 10 mm, at least 20 mm, at least 50 mm, or at least 100 mm. A collective thickness of the at least one illumination element and the optic may range from 100% to 500% of a spacing between the light-emitting elements disposed on the at least one illumination element. 
     The predetermined current on an illumination element may be set by issuing a control signal to at least one control element via at least one of the power conductors. An optical characteristic of the emitted light of an illumination element may be controlled by issuing a control signal to a second control element electrically connected to at least one light-emitting string. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. The plurality of light-emitting elements of at least one illumination element may include, consist essentially of, or consist of at least two groups of light-emitting elements, each group of light emitting-elements having a different optical characteristic. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. 
     A polymeric top housing may be sealed to the substrate of an illumination element to form a sealed region in which the light-emitting elements of the illumination element are disposed. The illumination element may be water-resistant or waterproof. The illumination element may have an ingress protection rating of at least IP X5, as specified by International Protection Marking in International Electrotechnical Commission (IEC) standard 60529. The substrate of the illumination element may have a first surface and a second surface opposite the second surface, and the light-emitting elements of the illumination element may be disposed over the first surface. At least a portion of a polymeric bottom housing may be contacted to the second surface to form a second sealed region disposed between the bottom housing and the second surface of the substrate. The sealed region and/or the second sealed region may be water-resistant or waterproof. The bottom housing may be spaced away from the second surface in the second sealed region. The bottom housing may be in contact with at least a portion of the second surface in the second sealed region. At least a portion of a polymeric bottom housing may be contacted to the top housing to form a second sealed region disposed between the bottom housing and the top housing and/or the second surface of the substrate. The second sealed region may be water-resistant or waterproof. The top housing and/or the bottom housing may include, consist essentially of, or consist of polyester, acrylic, polystyrene, polyethylene, polyimide, polyethylene naphthalate, polyethylene terephthalate, polypropylene, polycarbonate, acrylonitrile butadiene styrene, polyurethane, silicone, and/or polydimethylsiloxane. The top housing and the bottom housing may include, consist essentially of, or consist of the same material or different materials. 
     The predetermined luminous flux density of each illumination element may be within ±10%, ±5%, or ±2% of the predetermined luminous flux density of any other illumination element. One or more of the illumination elements may be flexible. A power supply may be electrically coupled to the one or more electrical connectors of a first illumination element, and power from the power supply may be supplied to one or more other illumination elements via the first illumination element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. A voltage or a current of the power supply may be pulse-width-modulated to adjust a light output of at least one illumination element. 
     A power-distribution element may be provided. The power-distribution element may include, consist essentially of, or consist of one or more first connector sets and one or more second connection point sets. The one or more first connector sets may each include, consist essentially of, or consist of one or more first electrical connectors each configured for connection to an electrical connector of an illumination element. The one or more second connection point sets may each include, consist essentially of, or consist of one or more second electrical connection points for receiving power from an external source of power. Any of the second electrical connection points may be a connection point for a bare wire or a flying lead, or may be a connector analogous to one or more of the electrical connectors found on the illumination elements. Power received via the one or more second connection point sets may be distributed, on the power-distribution element, to the one or more first connector sets. When the one or more first connector sets are connected (i.e., to connectors on other objects such as illumination elements) and the one or more second connection point sets are connected (i.e., to other objects such as power supplies, other sources of power, illumination elements, etc.), the power-distribution element may be water-resistant or waterproof. A power supply may be provided, and the power supply may be the external source of power for the power-distribution element. The power supply may be configured to provide a substantially constant voltage to the illumination elements. A voltage or a current of the power supply may be pulse-width-modulated to adjust a light output of at least one illumination element. Providing the power supply may include, consist essentially of, or consist of directly coupling the power supply to the one or more second connection point sets (e.g., via a connection such as an electrical connector, a wire, or other connection). (In embodiments in which the power supply is “indirectly coupled” to the one or more second connection point sets, the power supply is directly coupled to a different element that is directly coupled to the one or more second connection point sets, such as one of the illumination elements, and power from the power supply flows through that different element to the power-distribution element.) The one or more second connection point sets may be directly coupled to one or more of the illumination elements, and power may be supplied to the power-distribution element via the one or more of the illumination elements. The power-distribution element may contain no light-emitting elements thereon. The power-distribution element may include a substrate, and the substrate may include, consist essentially of, or consist of the same substrate as that of one or more of the illumination elements. The power-distribution element may be flexible. 
     When the one or more of each of the illumination elements are assembled into the shape, across the shape, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction, and the first pitch may be maintained between and among the plurality of illumination elements (i.e., the first pitch may be maintained even across interfaces between different illumination elements). When the one or more of each of the illumination elements are assembled into the shape, across the shape, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from (e.g., substantially perpendicular to) the first direction, and the second pitch may be maintained between the plurality of illumination elements. The first pitch and the second pitch may be substantially equal. 
     At least one optical element (e.g., a lens, prism, collimator, mirror, reflector, etc.) may be provided. The at least one optical element may be configured for focusing and/or shaping light from at least one illumination element to a desired illumination pattern. An optic may be positioned on or over at least one illumination element. 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 at least one illumination element and the optic may be less than 500 mm. A collective thickness of the at least one illumination element and the optic may be at least 10 mm, at least 20 mm, at least 50 mm, or at least 100 mm. A collective thickness of the at least one illumination element and the optic may range from 100% to 500% of a spacing between the light-emitting elements disposed on the at least one illumination element. 
     The predetermined current on an illumination element may be set by issuing a control signal to at least one control element via at least one of the power conductors. An optical characteristic of the emitted light of an illumination element may be controlled by issuing a control signal to a second control element electrically connected to at least one light-emitting string. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. The plurality of light-emitting elements of at least one illumination element may include, consist essentially of, or consist of at least two groups of light-emitting elements, each group of light emitting-elements having a different optical characteristic. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. 
     A polymeric top housing disposed over a first surface of the substrate of an illumination element may be sealed to a polymeric bottom housing disposed over a second surface of the substrate opposite the first surface to form a sealed region in which the light-emitting elements of the illumination element are disposed. All or a portion of the substrate of the illumination element may be disposed within the sealed region. The illumination element may be water-resistant or waterproof. The illumination element may have an ingress protection rating of at least IP X5, as specified by International Protection Marking in International Electrotechnical Commission (IEC) standard 60529. 
     In an aspect, embodiments of the invention feature a system of lighting components for illuminating an arbitrary two-dimensional area. The system includes, consists essentially of, or consists of a plurality of illumination panels. Each panel is configured to emit light at a panel luminous flux density. Each panel includes, consists essentially of, or consists of (i) a backing support, and (ii) a plurality of illumination elements each (a) secured to the backing support and (b) electrically connected to at least one of the other illumination elements. Each illumination element may include, consist essentially of, or consist of a substrate and a plurality of light-emitting elements disposed thereover. Each illumination element may include, consist essentially of, or consist of (i) a substrate, (ii) first and second power conductors disposed over the substrate, (iii) a plurality of light-emitting elements that are spaced apart and interconnected into one or more light-emitting strings, and (iv) one or more electrical connectors each electrically coupled to at least one of the first or second power conductors. Each light-emitting string (a) may include, consist essentially of, or consist of two or more of the light-emitting elements, (b) may have a first end electrically connected to the first power conductor, and (c) may have a second end electrically connected to the second power conductor. Each illumination element has a shape defined by a one-dimensional or two-dimensional arrangement of illumination unit cells. Each illumination unit cell (i) is polygonal, (ii) encompasses a plurality of light-emitting elements, and (ii) is configured to emit light at a predetermined luminous flux density (which may be variable). Each illumination unit cell may encompass at least one light-emitting string. The predetermined luminous flux density of each illumination element is within ±10% of the predetermined luminous flux density of any other illumination element. The plurality of illumination panels collectively has a surface area greater than or equal to the two-dimensional area. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. At least one, or even each, of the panels may be configured to be electrically connected to at least one of the other panels. For at least one (or even all) of the panels, (i) a first one of the illumination elements may be configured to receive electrical power from a power supply or other external source of power, and (ii) one or more other illumination elements may be configured to receive power from the first one of the illumination elements. For at least one, or even each, panel, (i) the first power conductors of all of the illumination elements may be electrically coupled together, and (ii) the second power conductors of all of the illumination elements may be electrically coupled together. The first power conductors of all of the illumination elements on two or more, or even all, of the panels may be electrically coupled together. The second power conductors of all of the illumination elements on two or more, or even all, of the panels may be electrically coupled together. 
     A first one of the panels may be configured to receive electrical power from a power supply or other external source of power (e.g., AC mains). One or more, or even all, other panels may be configured to receive power from the first one of the panels. The system may include the power supply. The power supply may be electrically coupled to the first one of the panels. The power supply may be configured to provide a substantially constant voltage and/or substantially constant current to the illumination elements. The power supply may be configured to adjust a light output (e.g., a luminous flux density) of at least one illumination element by pulse-width-modulating a voltage or a current supplied by the power supply. The panel luminous flux density of each panel may be within ±10%, within ±55%, within ±2%, or within ±1% of the panel luminous flux density of one or more other panels or any other panel. The predetermined luminous flux density of each illumination element may be within ±5%, within ±2%, or within ±1% of the predetermined luminous flux density of any other illumination element. For at least one (or even all) of the panels, one or more (or even all) of the illumination elements may be flexible. The backing support to which the one or more of the illumination elements is secured may be rigid. 
     The system may include a power-distribution element. The power-distribution element may be flexible. The power-distribution element may be secured to a backing support, which may be different from the backing supports of the panels or the same as the backing support for one of the panels. The power-distribution element may include, consist essentially of, or consist of (i) one or more first connector sets each including, consisting essentially of, or consisting of one or more first electrical connectors each configured for electrical connection to an illumination element (e.g., for connection to an electrical connector of an illumination element), and (ii) one or more second connection point sets each including, consisting essentially of, or consisting of one or more second electrical connection points for receiving power from an external source of power (e.g., a power supply or AC mains). Power received via the one or more second connection point sets may be distributed, on the power-distribution element, to the one or more first connector sets. The system may include a power supply that is the external source of power. The power supply may be configured to provide a substantially constant voltage and/or substantially constant current to the power-distribution element. The power supply may be configured to adjust a light output (e.g., a luminous flux density) of at least one illumination element by pulse-width-modulating a voltage or a current supplied by the power supply. The power-distribution element may contain no light-emitting elements thereon. For at least one illumination element (or even for all of the illumination elements), the one or more electrical connectors may each include, consist essentially of, or consist of an insulation displacement connector. 
     For at least one (or even all) of the panels, when the plurality of illumination elements are positioned adjacent to each other and electrically connected together, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction, the first pitch being maintained across the plurality of illumination elements. For at least one (or even all) of the panels, when the plurality of illumination elements are positioned adjacent to each other and electrically connected together, across the plurality of illumination elements, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from the first direction, the second pitch being maintained across the plurality of illumination elements. The first pitch and the second pitch may be substantially equal to each other. The panel luminous flux density of each panel may be within ±10%, within ±5%, within ±2%, or within ±1% of the panel luminous flux density of one or more other panels or any other panel. 
     For at least one (or even all) of the illumination elements, a control element (i) may be disposed over the substrate, (ii) may be electrically connected to the light-emitting elements, and/or (iii) may be configured to provide a predetermined current to the light-emitting elements. The control element may be configured to receive a control signal representing the predetermined current. The first and/or second power conductors may be configured to provide the control signal to the control element. At least one (or even all) of the illumination elements may include a second control element. The second control element (i) may be electrically connected to at least one light-emitting string, and/or (ii) may be configured to control the at least one light-emitting string to produce an optical characteristic of light emitted thereby. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. The plurality of light-emitting elements of at least one illumination element (or even all of the illumination elements) may include, consist essentially of, or consist of at least two groups of light-emitting elements or groups of strings, and each group may be configured to emit light having a different optical characteristic. The optical characteristic may include, consist essentially of, or consist of light intensity, output power, color temperature, color point, spectral power distribution, color rendering index, and/or light distribution pattern. 
     For at least one (or even all) of the panels, one or more of the illumination elements may include a polymeric top housing sealed to the substrate to form a sealed region in which the light-emitting elements of the illumination element are disposed. The one or more of the illumination elements may be water-resistant or waterproof. For at least one (or even all) of the panels, the panel may include a polymeric top housing sealed to the backing support to form a sealed region in which at least a portion of each of the illumination elements secured to the backing support (e.g., at least the portion of each illumination element on which light-emitting elements are disposed) is disposed. The one or more of the panels may be water-resistant or waterproof. 
     For at least one (or even all) of the panels, at least one illumination element may include at least one optical element. The optical element may be configured for focusing and/or shaping light from the illumination element to a desired illumination pattern. For at least one (or even all) of the panels, one or more optics may be disposed over at least one illumination element. Each 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 at least one illumination element and the optic may be less than 500 mm. A collective thickness of the at least one illumination element and the optic may range from 100% to 500% of a spacing between the light-emitting elements of the at least one illumination element. 
     When the plurality of panels are positioned adjacent to each other, across the illumination elements of all of the panels, the light-emitting elements may be spaced apart at a substantially constant first pitch in a first direction. The first pitch may be maintained across the plurality of panels. When the plurality of panels are positioned adjacent to each other, across the illumination elements of all of the panels, the light-emitting elements may be spaced apart at a substantially constant second pitch in a second direction different from the first direction. The second pitch may be maintained across the plurality of panels. The first pitch and the second pitch may be substantially equal to each other. 
     In another aspect, embodiments of the invention feature a method of illuminating an area. An area for illumination is defined. The area has an arbitrary size and two-dimensional shape. A plurality of assemblable illumination elements is provided. A plurality of illumination panels is formed. Forming each illumination panel includes, consists essentially of, or consists of (i) securing a plurality of the illumination elements to one of the backing supports, and (ii) electrically connecting the illumination elements on the backing support. Thereafter, the plurality of panels is assembled into a shape approximately conforming to the area for illumination. The plurality of panels are electrically connected to a source of electrical power. Each illumination element may include, consist essentially of, or consist of a substrate and a plurality of light-emitting elements disposed thereover. Each illumination element may include, consist essentially of, or consist of (i) a substrate, (ii) first and second power conductors disposed over the substrate, (iii) a plurality of light-emitting elements that are spaced apart and interconnected into one or more light-emitting strings, and (iv) one or more electrical connectors each electrically coupled to at least one of the first or second power conductors. Each light-emitting string (a) may include, consist essentially of, or consist of two or more of the light-emitting elements, (b) may have a first end electrically connected to the first power conductor, and (c) may have a second end electrically connected to the second power conductor. Each illumination element has a shape defined by a one-dimensional or two-dimensional arrangement of illumination unit cells. Each illumination unit cell (i) is polygonal, (ii) encompasses a plurality of light-emitting elements, and (ii) is configured to emit light at a predetermined luminous flux density (which may be variable). Each illumination unit cell may encompass at least one light-emitting string. The predetermined luminous flux density of each illumination element is within ±10% of the predetermined luminous flux density of any other illumination element. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. The area of the shape into which the plurality of panels is assembled may be within ±100%, within ±5%, within ±2%, or within ±1% of the area for illumination. Electrically connecting the plurality of panels to the source of electrical power may include, consist essentially of, or consist of electrically connecting a first one of the panels to the source of electrical power. One or more (or even all) other panels may be configured to receive electrical power from the first one of the panels. 
     Electrically connecting the plurality of panels to the source of electrical power may include, consist essentially of, or consist of electrically connecting each of the panels to the source of electrical power via a separate electrical connection. The source of electrical power may include, consist essentially of, or consist of a power supply. For at least one (or even all) of the panels, (i) a first one of the illumination elements may be configured to receive electrical power from the source of electrical power, and (ii) one or more other illumination elements may be configured to receive power from the first one of the illumination elements. During formation of at least one (or even all) of the panels, the plurality of illumination elements may be secured to the backing support with gaps between adjacent illumination elements. 
     The panels may be formed at a manufacturing site different from a site at which the area for illumination is disposed. Before assembling the panels into the shape, the panels may be transported from the manufacturing site to the site at which the area for illumination is disposed. During formation of at least one (or even all) of the panels, the illumination elements may be secured to the backing support using an adhesive, tape, and/or one or more fasteners. Assembling the panels into the shape may include, consist essentially of, or consist of securing the panels onto a mounting surface. Assembling the panels into the shape may include, consist essentially of, or consist of disposing (e.g., suspending and/or affixing) the panels into one or more mounting frames. At least two of the panels may be electrically connected together via one or more jumpers. 
     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. 
     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 
       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: 
         FIG. 1A  is a circuit diagram of a portion of a light sheet in accordance with various embodiments of the invention; 
         FIGS. 1B and 1C  are schematic plan views of light sheets in accordance with various embodiments of the invention; 
         FIGS. 2A-2E  are schematic cross-sections of lighting devices in accordance with various embodiments of the invention; 
         FIG. 2F  is a schematic isometric view of a lighting device in accordance with various embodiments of the invention; 
         FIG. 2G  is a schematic cross-section of a lighting device in accordance with various embodiments of the invention; 
         FIGS. 3A and 3B  are schematic cross-sections of lighting devices in accordance with various embodiments of the invention; 
         FIGS. 3C-3E  are partial schematic cross-sections of a lighting device in accordance with various embodiments of the invention; 
         FIG. 4  is a schematic cross-section of a lighting device in accordance with various embodiments of the invention; 
         FIG. 5  is a schematic of a lighting device in accordance with various embodiments of the invention; 
         FIGS. 6A-6E  are schematic plan views of portions of a lighting-device in accordance with various embodiments of the invention; 
         FIGS. 6F and 6G  are schematic plan views of lighting systems in accordance with various embodiments of the invention; 
         FIGS. 6H-6M  are schematic plan views of portions of a lighting-device in accordance with various embodiments of the invention; 
         FIG. 7A  is a schematic plan view of a lighting system in accordance with various embodiments of the invention; 
         FIG. 7B  is a schematic plan view of a portion of a lighting system in accordance with various embodiments of the invention; 
         FIGS. 8A-8C  are schematic cross-sections of lighting devices in accordance with various embodiments of the invention; 
         FIG. 9  is a flowchart of a method of fabrication of lighting devices in accordance with various embodiments of the invention; 
         FIGS. 10A-10E  are schematic cross-sections of a lighting device during various stages of manufacture in accordance with various embodiments of the invention; 
         FIG. 11  is a schematic diagram of roll-to-roll processing apparatus for the fabrication of lighting devices in accordance with various embodiments of the invention; 
         FIG. 12  is a schematic plan view of a lighting system in accordance with various embodiments of the invention; 
         FIGS. 13A and 13B  are schematic plan views of lighting systems in accordance with various embodiments of the invention; 
         FIG. 13C  is a side view of the lighting system of  FIG. 13B ; 
         FIG. 13D  is an enlarged side view of a portion of the lighting system of  FIG. 13B ; 
         FIG. 13E  is an enlarged side view of a portion of a lighting system in accordance with various embodiments of the invention; 
         FIG. 13F  is an enlarged side view of a portion of a lighting system in accordance with various embodiments of the invention; 
         FIG. 13G  is a schematic plan view of a portion of the lighting system of  FIG. 13A ; 
         FIGS. 13H and 13I  are schematic diagrams of portions of lighting systems in accordance with various embodiments of the invention; 
         FIG. 14A  is a flowchart of a method of fabrication of a lighting system in accordance with various embodiments of the invention; and 
         FIG. 14B  is a schematic plan view of a lighting system in accordance with various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  depicts an exemplary circuit topology of one embodiment of a light sheet, in accordance with embodiments of the present invention, which features conductive elements  160 , at least two power conductors  120 ,  121 , multiple LEEs  140 , and control elements (CEs)  145 . In various embodiments, LEEs  140  may be configured in a regular periodic array, for example a substantially square or rectangular array, where LEEs  140  are separated by pitch (or “spacing”)  123  in one direction (for example, a vertical or intrastring direction) and by pitch  125  in a substantially orthogonal direction (for example, a horizontal or interstring direction). In various embodiments, pitch  125  is the same as or substantially the same as pitch  123 . While the geometrical layout and pitches  123 ,  125  are described in connection with the circuit schematic shown in  FIG. 1A , such geometry, layout, and pitches are not limitations of the present invention, and in other embodiments the physical layout of the circuit elements may be different than the circuit topology shown in  FIG. 1A . Additionally, other embodiments may have different circuit topologies, for example LEEs  140  may be electrically coupled in parallel, in a combination of series and parallel, or any other arrangement. In various embodiments, more than one group of electrically connected LEEs  140  may be electrically coupled to one CE  145 , while other embodiments may not require any CEs  145 . The specific circuit topology is not a limitation of the present invention. 
       FIG. 1A  shows two power conductors  120 ,  121 , which may be used to provide power to strings  150  of LEEs  140 . Each string  150  may include two or more electrically coupled LEEs  140 . LEEs  140  in string  150  may be electrically coupled in series, as shown in  FIG. 1A ; however, this is not a limitation of the present invention, and in other embodiments other examples of electrical coupling may be utilized, for example parallel connections or any combination of series and parallel connections.  FIG. 1A  shows CE  145  connected in series with LEEs  140  of string  150 ; however, this is not a limitation of the present invention, and in other embodiments CE  145  may have different electrical coupling between power conductors  120 ,  121 , or may be absent altogether. For example, in some embodiments CE  145  may be separately electrically coupled to power conductors  120 ,  121  and to the LEE string  150 , while in other embodiments each CE  145  may be electrically coupled to two or more strings. The number of strings electrically coupled to each CE  145  is not a limitation of the present invention. Combinations of structures described herein, as well as other electrical connections, all fall within the scope of the present invention. Power conductors  120 ,  121  may be used to provide power to strings  150 , for example AC power, DC power, or power modulated by any other means. 
     Referring to  FIGS. 1B and 1C  that depict schematics of exemplary light sheets  110 , a light sheet  110  may feature an array of LEEs  140  each electrically coupled between conductive traces  160 , as well as power conductors  120 ,  121  providing power to conductive traces  160  and CEs  145 , all of which are disposed over a substrate  165 . As utilized herein, a “wiring board” refers to a substrate for LEEs with or without additional elements such as conductive traces or CEs. A wiring board may also be referred to as a light sheet or a circuit board.  FIG. 1B  shows a portion of a light sheet  110 . In the exemplary embodiment depicted in  FIG. 1B , power conductors  120 ,  121  are spaced apart from each other and light-emitting strings (or simply “strings”)  150  are connected in parallel across power conductors  120 ,  121 . In various embodiments, for example as shown in  FIG. 1B , strings  150  do not cross (i.e., intersect) each other. In other words, power conductors  120 ,  121  are oriented in one direction and strings  150  are oriented such that they span power conductors  120 ,  121  in a different direction. As shown in  FIG. 1B , strings  150  are substantially perpendicular to power conductors  120 ,  121 . However, this is not a limitation of the present invention, and in other embodiments at least some segments (i.e., portions connecting two or more LEEs  140 ), or even the entire strings  150 , may define a line (not necessarily a straight line) that is not perpendicular to power conductors  120 ,  121  yet is (at least for an entire string  150 ) not parallel to power conductors  120 ,  121 . In other embodiments, strings  150  may intersect, for example one string  150  splitting into two or more strings  150 , or two or more strings  150  joining to form a reduced number of strings  150 . In various embodiments, conductive elements  160  may cross over each other without being electrically coupled to each other (i.e., they may be electrically insulated from each other), and in some embodiments strings  150  may cross over or under each other without being electrically coupled to each other. In some embodiments, all or a portion of one or more strings  150  may extend outside of the area bound by power conductors  120 ,  121 . Various examples of string geometries and conformations utilized in embodiments of the present invention are described in the &#39;807 and &#39;027 applications. 
     As shown in  FIGS. 1B and 1C , LEEs  140  may be positioned across substrate  165  in a regular periodic array, although this is not a limitation of the present invention, and in other embodiments LEEs  140  may occupy any positions on light sheet  110 . Power conductors  120 ,  121  provide power to each LEE string, for example the string  150  encircled by the dashed line in  FIG. 1B . Each LEE string  150  typically includes multiple conductive traces  160  that interconnect multiple LEEs  140 , as well as one or more CEs  145 , which in  FIG. 1B  is in series with LEEs  140 . String  150  shown in  FIG. 1B  is a folded string, i.e., a string that has three segments electrically coupled in series but positioned as three adjacent segments. A string segment is a portion of a string spanning all or a portion of the region between power conductors  120 ,  121  in  FIG. 1B . In light sheet  110 , some string segments may include LEEs  140  while others do not. However, in other embodiments the distribution and position of LEEs  140  along conductive elements  160  and string segments may be different. In various embodiments, a string  150  may be a straight string, i.e., a string with no folds, as shown in  FIG. 1C . One end of string  150  is electrically coupled to power conductor  120 , while the other end of string  150  is electrically coupled to power conductor  121 . As will be discussed, the number of segments in a string  150  is not a limitation of the present invention. Various examples of straight and folded strings utilized in embodiments of the present invention are detailed in the &#39;807 and &#39;027 applications. Note that the example shown in  FIG. 1C  does not include CEs  145 . In various embodiments of the present invention, CEs  145  may not be included or CEs  145  may be included but may not be mounted on substrate  165  or on light sheet  110 ; rather, they may be mounted on a separate structure (e.g., a separate submount) and electrically connected to one or more of the LEEs on the light sheet. 
       FIGS. 1A and 1B  illustrate three aspects in accordance with various embodiments of the present invention. The first is the multiple strings  150  that are powered by the set of power conductors  120 ,  121 . The second is the positional relationship between the locations of LEEs  140  and CE  145 , which is disposed between the conductive traces  160  and between power conductors  120 , 121 , such that the pitch between LEEs  140  is not disrupted by the placement or position of CE  145 . The third is the inclusion of a CE  145  in each string of series-connected LEEs  140 . Combinations of these three aspects enable light sheet  110  to be economically manufactured in very long lengths, for example in a roll-to-roll process, and cut to specified lengths, forming light sheets, while maintaining the ability to tile, or place light sheets adjacent to each other (e.g., in the length direction), with no or substantially no change in pitch between LEEs  140  or in the optical characteristics across the joint between two adjacent light sheets, as discussed in more detail in the &#39;807 and &#39;027 applications. 
     In an exemplary embodiment, CE  145  is configured to maintain a constant or substantially constant current through LEEs  140  of string  150 . For example, in some embodiments, a constant voltage may be applied to power conductors  120 ,  121 , which may, under certain circumstances may have some variation, or the sum of the forward voltages of LEEs  140  in different strings may be somewhat different, for example as a result of manufacturing tolerances, or the component and/or operational values of the element(s) within CE  145  may vary, for example as a result of manufacturing tolerances or changes in operating temperature, and CE  145  acts to maintain the current through LEEs  140  substantially constant in the face of these variations. In other words, in some embodiments the input to the light sheet is a constant voltage that is applied to power conductors  120 ,  121 , and CEs  145  convert the constant voltage to a constant or substantially constant current through LEEs  140 . The design of CE  145  may be varied to provide different levels of control or variation of the current through LEEs  140 . In some embodiments, CEs  145  may control the current through LEEs  140  to be substantially constant with a variation of less than about ±25%. In some embodiments, CEs  145  may control the current through LEEs  140  to be substantially constant with a variation of less than about ±15%. In some embodiments, CEs  145  may control the current through LEEs  140  to be substantially constant with a variation of less than about ±10%. In some embodiments, CEs  145  may control the current through LEEs  140  to be substantially constant with a variation of less than about ±5%. 
     In various embodiments, CEs  145  may, in response to a control signal, act to maintain a constant or substantially constant current through LEEs  140  until instructed to change to a different constant or substantially constant current, for example by an external control signal. In various embodiments, as detailed herein, all CEs  145  may act in concert, that is maintain or change the current through all associated LEEs  140 ; however, this is not a limitation of the present invention, and in other embodiments one or more CEs  145  may be individually addressed, instructed and/or energized. 
     Any of the CEs detailed herein (e.g., CE  145 ) may include, consist essentially of, or consist of one or more programmable control elements as described in U.S. patent application Ser. No. 15/457,172, filed Mar. 13, 2017, the entire disclosure of which is incorporated by reference herein. 
     In various embodiments, LEEs  140  may include, consist essentially of, or consist of light-emitting diodes (LEDs) or lasers. In various embodiments, light emitted from light sheet  110  is in the form of an array of bright spots, or light-emission points, resulting in a pixelated pattern. However, this is not a limitation of the present invention, and in other embodiments light sheet  110  includes different types of light emitters, for example organic LEDs (OLEDs). In various embodiments, light sheet  110  may emit light homogeneously or substantially homogeneously, for example light sheet  110  may include an array of LEEs  140  behind an optic or diffuser that spreads the light from LEEs  140  homogeneously or substantially homogeneously. In various embodiments, light sheet  110  may include one or more OLEDs emitting homogeneously or substantially homogeneously over light sheet  110 . 
     In the embodiment depicted in  FIG. 1B , LEEs  140  are distributed substantially uniformly over light sheet  110 ; however, this is not a limitation of the present invention, and in other embodiments, LEEs  140  may have a non-uniform distribution. As will be understood, the distributions of LEE  140  on light sheet  110  shown in  FIGS. 1B and 1C  are not limitations of the present invention, and other embodiments may have other distributions of LEEs  140 . In various embodiments, one or more portions of light sheet  110  may be unpopulated with LEEs  140 . In various embodiments, the distribution of LEEs  140  on light sheet  110  is specifically chosen to achieve one or more characteristics, for example optical, electrical, thermal or the like, as described herein. In various embodiments, the distribution of LEEs  140  on light sheet  110  may be chosen to create a certain decorative look. 
     In various embodiments, light sheet  110  may also be cut to length, as discussed in more detail in the &#39;807 and &#39;027 applications. For example, in various embodiments of the present invention light sheet  110  may be cut between strings  150 . 
     In various embodiments, light sheet  110  does not require any additional thermal management or heat-sinking, i.e., the heat generated by LEEs  140  is at least partially accommodated by the structure of light sheet  110  itself, for example substrate  165  and/or conductive elements  160  and/or power conductors  120 ,  121 . 
     In various embodiments of the present invention, substrate  165  is substantially covered with an array of LEEs  140  interconnected by conductive elements  160 ; however, in various embodiments one or more portions of substrate  165  may not be populated with LEEs  140 . 
     In various embodiments, all LEEs  140  in the lighting system may be driven at the same or substantially the same current; however, this is not a limitation of the present invention, and in other embodiments different LEEs  140  or different groups of LEEs  140  may be driven at different currents. 
     In various embodiments, all LEEs  140  in the lighting system may have the same optical characteristics, for example luminous or radiant flux, CCT, color point, CRI, R9, spectral power distribution, light distribution pattern, angular color uniformity, or the like; however, this is not a limitation of the present invention, and in other embodiments different LEEs  140  or different groups of LEEs  140  may have different optical characteristics. 
       FIGS. 2A-2G  depict exemplary lighting devices in accordance with embodiments of the present invention, although alternative devices or systems with similar functionality are also within the scope of the invention.  FIG. 2A  shows a cross-sectional view of a lighting device  200  of the present invention including or consisting essentially of LEEs  140  electrically coupled to conductive traces  160  that are formed over substrate  165 , and a top housing  210  adhered to the underlying structure with an adhesion agent  230 . Optional CEs  145  are not shown in  FIGS. 2A-2G  for clarity. While  FIG. 2A  shows top housing  210  adhered to the underlying structure (e.g., traces  160 ) with adhesion agent  230 , this is not a limitation of the present invention, and in other embodiments portions of adhesion agent  230  may also or instead be in contact with substrate  165 . 
     In various embodiments of the present invention, adhesion agent  230  may include, consist essentially of, or consist of an adhesive, an adhesive tape, a hot melt adhesive, polyurethane, thermoplastic polyurethane (TPU), ethylene vinyl acetate (EVA), a printed adhesive, or the like. In various embodiments, adhesion agent  230  may be optional and top housing  210  may be attached directly to the underlying structure without the use of adhesion agent  230  (e.g., via ultrasonic welding, heat welding, lamination, or clamps or other mechanical means). While  FIG. 2A  shows top housing  210  adhered to underlying substrate  165  in substantially all areas except in the LEE region, this is not a limitation of the present invention, and in other embodiments top housing  210  may be adhered or attached to underlying substrate  165  in only a portion of the area between top housing  210  and substrate  165 . 
       FIG. 2B  shows a cross-sectional view of a lighting device  201  in accordance with embodiments of the present invention and that is similar to lighting device  200  of  FIG. 2A , but with the addition of a bottom housing  220 . In lighting device  201 , bottom housing  220  is attached to the bottom of substrate  165  (i.e., in the depicted embodiment, the side opposite that to which LEEs  140  are attached). While  FIG. 2B  does not show an adhesion agent between bottom housing  220  and substrate  165 , this is not a limitation of the present invention, and in other embodiments adhesion agent(s) and/or alternative joining or bonding mechanisms or means may be utilized as detailed above. 
       FIG. 2C  shows a cross-sectional view of a lighting device  202  in accordance with embodiments of the present invention and that is similar to lighting device  201  of  FIG. 2B . In the case of lighting device  202 , the bottom housing  220  is at least partially sealed to top housing  210 . In various embodiments of the present invention, top housing  210  and bottom housing  220  may be joined at the periphery of lighting device  202 , for example in the region  225  in  FIG. 2C . While  FIG. 2C  shows bottom housing  220  shaped to wrap around substrate  165  and meet top housing  210 , this is not a limitation of the present invention, and in other embodiments top housing  210  may be shaped to meet bottom housing  220  or both top housing  210  and bottom housing  220  may be shaped or neither top housing  210  or bottom housing  220  may be shaped. While  FIG. 2C  does not show an adhesion agent between bottom housing  220  and substrate  165  or between top housing  210  and bottom housing  220 , this is not a limitation of the present invention, and in other embodiments adhesion agent(s) and/or alternative joining or bonding mechanisms or means may be utilized as detailed above. In various embodiments of the present invention, top housing  210  and bottom housing  220  may be joined by heat welding, high-frequency welding, ultrasonic welding, laser welding, adhesive, glue, tape, or the like. In various embodiments of the present invention, top housing  210  and/or bottom housing  220  may be joined to light sheet  110  or to each other within the periphery of lighting device  202 , e.g., to form one or more sealed regions. 
     In various embodiments, portions of top housing  210  and/or bottom housing  220  may be ribbed, i.e., have protruding segments or may be otherwise structured to provide rigidity to the lighting device. For example  FIG. 2D  shows a lighting system  203  having a rib  240 . 
     In various embodiments, substrate  165  and top housing  210  may have the same or substantially the same thermal coefficient of expansion (TCE). In various embodiments, choosing materials for substrate  165  and top housing  210  and/or bottom housing  220  having the same or substantially the same TCE may eliminate or reduce the tendency of the entire structure to curl and/or buckle when the lighting system is exposed to changing temperatures. 
     In various embodiments of the present invention, substrate  165  and top housing  210  and/or bottom housing  220  may have different TCE, in which case various techniques to reduce curling and/or buckling when exposed to changing temperatures may be employed. In various embodiments of the present invention, ribs or expansion joints, such as rib  240  shown in lighting device  203  of  FIG. 2D , may be incorporated to accommodate all or a portion of the expansion and contraction difference between top housing  210  and substrate  165 . While not shown in  FIG. 2D , similar ribs or joints may be included in bottom housing  220  to accomplish a similar purpose. 
     In various embodiments of the present invention, a layer of additional material having a TCE closer to (or even substantially equal to) that of substrate  165  than to top housing  210  may be formed over all or a portion of top housing  210 , to balance the stress in the structure.  FIG. 2E  shows a lighting system  204  including a cover layer or stress-balancing layer  250 . While  FIG. 2E  shows stress-balancing layer  250  as one layer this is not a limitation of the present invention, and in other embodiments stress-balancing layer may include, consist essentially of, or consist of two or more layers of the same or different materials. In various embodiments, substrate  165  and cover layer  250  have the same or similar TCEs. In various embodiments, substrate  165  and cover layer  250  are composed of the same material. In various embodiments, substrate  165  and cover layer  250  include, consist essentially of, or consist of PET, and top housing  210  includes, consists essentially of, or consists of acrylic. In various embodiments, substrate  165  has a thickness in the range of about 10 μm to about 150 μm, top housing  210  has a thickness in the range of about 50 μm to about 1000 μm, and cover layer  250  has a thickness in the range of about 25 μm to about 500 μm; however, these dimension are not a limit of the present invention, and in other embodiments the dimensions may be different. In various embodiments, substrate  165  and cover layer  250  include, consist essentially of, or consist of PET and have thicknesses of about 50 μm and about 50 μm respectively, and top housing  210  has a thickness of about 175 μm and includes, consists essentially of, or consists of acrylic. Cover layer  250  may be substantially transparent to light (e.g., to one or more wavelengths emitted by LEEs  140 ), or cover layer  250  may be translucent, opaque, or reflective to light or partially transparent, translucent, opaque, or reflective to light (e.g., to one or more wavelengths emitted by LEEs  140 ). 
     In various embodiments, portions of top housing  210  may be removed to reduce the area (and thus the magnitude) of stress generated by different in TCE between top housing  210  and substrate  165 , as shown in  FIG. 2F .  FIG. 2F  is an isometric view of lighting system  204  in which regions  213  of top housing  210 ′ are removed. 
     It should be noted that in the foregoing discussion regarding TCE, the conductive traces  160  may also affect the TCE of substrate  165 , and it will be understood by those skilled in the art that the TCE of the substrate includes the effect of the conductive traces, when they are present. 
     While  FIGS. 2A-2F  show the lighting systems as flat, this is not a limitation of the present invention, and in various embodiments the materials used in the lighting system may be flexible such that the lighting system may be curved or conformed to non-flat shapes, for example as shown in  FIG. 2G . 
     As used herein, the term “housing” broadly connotes any containment structure or medium for fully overlying a top and/or bottom surface of the light sheet  110 . A housing may be rigid or flexible, polymeric or other material (e.g., glass), and may interconnect with or be bondable to the light sheet or to another housing over the opposite surface of the light sheet to form a seal, e.g., a water-tight or water-resistant seal, around at least a portion of the light sheet. In various embodiments of the present invention, top housing  210  and bottom housing  220  are fabricated from plastic, for example polyester, acrylic, polystyrene, polyethylene, polyimide, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polypropylene, polycarbonate, acrylonitrile butadiene styrene (ABS), polyurethane, silicone, olydimethylsiloxane, or the like. In some embodiments of the present invention, top housing  210  and bottom housing  220  are fabricated by molding, vacuforming, and/or thermoforming. 
     In various embodiments of the present invention, the materials used in the lighting system may be similar or the same, while in other embodiments the lighting system may include, consist essentially of, or consist of two or portions, each portion including, consisting essentially of, or consisting of different materials having different properties or the same or similar materials having different properties. In various embodiments, the lighting system may include, consist essentially of, or consist of two or more portions. For example, in various embodiments the material of light sheet substrate  165  may be the same as that used for the top  210  and/or bottom housing  220 ; however, this is not a limitation of the present invention, and in other embodiments the material of top housing  210  and/or bottom housing  220  may include, consist essentially of, or consist of a material different from that used for substrate  165 . For example, in various embodiments the different components of the lighting system may include, consist essentially of, or consist of the same or similar materials having different shrinkage rates, thermal coefficients of expansion, transparency, brittleness, crystallinity, melting points, or the like. 
     In various embodiments of the present invention, all or a portion of top housing  210  is transparent to a wavelength of light emitted by LEEs  140 , for example having a transmittance to a wavelength of light emitted by LEEs  140  of at least 75%, or at least 85%, or at least 95%. In various embodiments of the present invention, all or a portion of top housing  210  may include a diffuser, for example to diffuse or scatter a wavelength of light emitted by LEEs  140 . 
     In various embodiments of the present invention, all or a portion of bottom housing  220  is transparent to a wavelength of light emitted by LEEs  140 , for example having a transmittance to a wavelength of light emitted by LEEs  140  of at least 75%, or at least 85%, or at least 95%, while in other embodiments all or a portion of bottom housing  220  may be translucent or opaque to a wavelength of light emitted by LEEs  140 . 
     In various embodiments of the present invention, all or a portion of bottom housing  220  or an inner surface  221  of bottom housing  220  may be reflective to a wavelength of light emitted by LEEs  140 , for example having a reflectance to a wavelength of light emitted by LEEs  140  of at least 75%, or at least 85%, or at least 95%. 
     In various embodiments of the present invention, the materials of construction, for example substrate  165 , top housing  210 , and/or bottom housing  220 , include, consist essentially of, or consist of materials having low flammability. One measure of flammability is defined by Underwriter Laboratories (UL) standard 94, the entire disclosure of which is incorporated by reference herein. UL94 includes various rating levels, for example UL94 V-1, UL94 V-2, UL94 V-0, UL94 V5B, UL94 V5A, and the like. In various embodiments of the present invention, the materials of construction are chosen to provide a certain level of flame retardance to the lighting system, for example, as measured by the UL94 flammability standard. In various embodiments of the present invention, the lighting system, for example as shown in  FIGS. 2A, 2C-2F, 3A-3E, 6B-6D , and the like, the lighting has a UL94 rating of at least UL94 V-1, or at least UL94 V-0, or at least UL94 5B, or at least UL94 5A. 
     In various embodiments of the present invention, housings  210 ,  220  may be configured to protect light sheet  110 , for example to provide mechanical protection, protection from dust, water, etc. One method for rating different levels of environmental protection is an IP rating as specified by International Protection Marking in International Electrotechnical Commission (IEC) standard 60529, providing classification of degrees of protection provided by enclosures for electrical equipment, the entirety of which is hereby incorporated by reference herein. In various embodiments, lighting devices of the present invention may have any IP rating, for example from IP00 to IP 69k, or any other IP rating. In various embodiments, lighting devices of the present invention have an IP 44 rating, or an IP65 rating or an IP66 rating or an IP67 rating or an IP68 rating. In general for an IP XY rating, “X” indicates the level of protection for access to electrical parts and ingress to solid foreign objects, while “Y” indicates the level of protection for ingress of harmful water. For example, an IP44 rating provides access and ingress protection for objects greater than about 1 mm and protection from water splashing on the system. In another example, an IP66 rating provides a dust-tight enclosure and protection from water jets incident on the system. In various embodiments an IP rating may be specified as IPX6, which indicates a rating including any level of protection for access to electrical parts and ingress to solid foreign objects and a specific (6) level for protection for ingress of harmful water. Specific details of the requirements and test method are detailed within the IP specification. 
     In various embodiments of the present invention, the interior region formed by housings  210 ,  220  may additionally contain a desiccant to absorb excess moisture and/or water vapor and prevent degradation or corrosion of light sheet  110  and associated components. In various embodiments of the present invention, the interior region formed by housings  210 ,  220  may be purged with an inert gas, for example nitrogen or argon, prior to sealing to reduce the moisture and/or water vapor concentration and prevent degradation or corrosion of light sheet  110  and associated components. 
     In various embodiments of the present invention, the interior region formed by housings  210 ,  220  may be evacuated to a relatively low pressure, or may be filled with air. In various embodiments of the present invention, all or portions of the interior region formed by housings  210 ,  220  may be filled with a material that is transparent or substantially transparent to a wavelength of light emitted by LEEs  140 . In various embodiments of the present invention, the transparent material includes, consists essentially of, or consists of silicone, polyurethane, epoxy, or other suitable materials. Examples of such transparent materials include materials from the ASP series of silicone phenyls manufactured by Shin Etsu, or the Sylgard series manufactured by Dow Corning. In various embodiments of the present invention, the transparent material may reduce total-internal-reflection (TIR) losses of LEEs  140  and may provide enhanced optical coupling between LEEs  140  and bottom housing  220 . In various embodiments of the present invention, the transparent material has an index of refraction greater than about 1.4, or greater than about 1.45. 
     In various embodiments of the present invention, a flexible membrane or diaphragm may be disposed within a portion of a housing or substrate  165  to accommodate expansion and contraction of the atmosphere within the sealed region that may occur during storage and/or operation, for example as a result of changes in temperature or altitude. In various embodiments of the present invention, all or a portion of a housing or substrate  165  has sufficient flexibility to accommodate such expansions and contractions of the atmosphere within the sealed region. 
     In various embodiments of the present invention, undesirable changes in one or more optical characteristics may occur if top housing  210  substantially changes the transmission, absorption and/or reflection of light at the emission surface of LEE  140 , and this may be of particular concern when LEE  140  includes, consists essentially of, or consists of a phosphor-converted LEE or LED. As discussed herein, this may occur in various configurations or geometric arrangements of LEE  140  and top housing  210 . The optical characteristics may include, but are not limited to, one or more of intensity, correlated color temperature (CCT), color point, color rendering index (CRI), R9, spectral power distribution, spatial intensity distribution, and angular color uniformity. 
     In various embodiments, phosphor-converted LEEs include a pump source and a wavelength-conversion material surrounding all or a portion of the pump source. The pump source produces radiation in a first radiation range; a portion of that radiation is absorbed by the wavelength conversion material and re-emitted at a second wavelength range different from the first wavelength range and the combination of the first and second wavelengths are what is observed. In some cases all or substantially all of the pump radiation is absorbed by the wavelength-conversion material. 
     Phosphor-converted LEDs typically use a LED chip and a phosphor for the pump source and the wavelength-conversion material. In white-emitting phosphor-converted LEDs, the LED typically has a relatively narrow emission in the UV and/or blue wavelength range and the phosphor has a relatively broad emission in the yellow-red range, the combination of these appearing as white light. Changes in the ratio of the intensity of the blue and converted light may thus result in a change in the observed color. 
     In typical white LEDs, the blue chip has a Lambertian intensity distribution while the phosphor (which may be, e.g., phosphor particles suspended in a transparent material such as silicone or epoxy) has an isotropic intensity distribution. This difference in spatial intensity distribution typically results in an angular non-uniformity of the observed color. As will be discussed herein, in various embodiments of the present invention interaction with top housing  210  may modify the relative intensities of the pump light and converted light and/or modify their intensity distributions, leading to undesirable changes in one or more optical characteristics of the lighting system. In particular this may lead to undesirable changes in the color, color point, or correlated color temperature (CCT). 
       FIG. 3A  shows a cross-sectional schematic of a generic phosphor-converted LED  310  including, consisting essentially of, or consisting of a blue-emitting chip  320  and a phosphor  330  (details of the LED package and electrical connections within the package are not shown for clarity). As will be understood by those skilled in the art, there are many different configurations of phosphor-converted LEEs and the structures shown in  FIG. 3A-3C  are used to demonstrate general characteristics of these devices and are not limiting to the present invention. 
     A portion of blue light  350  generated by blue chip  320  is absorbed by phosphor  330  and is converted to yellow/red light  355 , exiting LEE  310  as light  356 . A second portion of blue light  350 , identified as light  350 ′, reaches the top surface of phosphor  330 , exits the package without being absorbed by phosphor  330 , and is identified as light  351 . A third portion of blue light  350 , identified as  350 ″, is reflected back from the top surface of phosphor  330 , and is identified as light  352 . Blue light  352  may be absorbed by phosphor  330 , reflected back out of the package, or absorbed within the package. Reflection at the interface between phosphor  330  and air occurs because of the different indices of refraction of these materials. Typically, phosphor materials have an index of refraction in the range of about 1.3 to about 1.6, while air has an index of refraction of about 1. As described by Snell&#39;s Law, the difference in indices of refraction on opposite sides of an interface determines a critical angle, above which light incident on the interface is reflected—this is known as total internal reflection (TIR). 
     In various embodiments of the present invention, the phosphor-air interface is replaced by a phosphor-top housing interface, for example as shown in  FIG. 3B , and in various embodiments this may also change the optical properties of the lighting system. The top housing  353  has a different index of refraction than air (typically higher), and thus the amount and/or spatial distribution of the blue and converted light may be changed, leading to a change in optical properties, particularly color. Typically blue light TIR is reduced because the refractive index difference between the phosphor and the transparent layer is less than that between the phosphor and air, and consequently more blue light is extracted out of the LED. The greater amount of extracted blue light results in a higher CCT, as described with reference to  FIG. 3B . As shown in  FIG. 3B , a portion of blue light  350  generated by blue chip  320  is absorbed by phosphor  330  and is converted to yellow/red light  355 , exits LEE  310  as light  356  and is transmitted through top housing  353  as light  356 , and exits the system as light  356 ′. A second portion of blue light  350 , identified as  350 ′, reaches the top surface of phosphor  330 , exits LEE  310  without being absorbed by phosphor  330 , is identified as light  351 , and is transmitted through top housing  353  and exits the system as light  351 ′. A third portion of blue light  350 , identified as  350 ″, rather than being reflected back from the top surface of phosphor  330  as is the case in  FIG. 3A , is transmitted through the top housing  353  as light  354  and exits the system as light  354 ′. 
     While  FIG. 3B  shows all light being transmitted through top housing  353 , this may not always occur; in some cases light may be reflected from top housing  353 , for example as shown in  FIG. 3C .  FIG. 3C  shows blue light  350 ′, exiting the LEE as blue light  351 , reflecting off of housing  370 , the reflected light identified as light  360 , re-entering the LEE as light  361 , being absorbed by phosphor  330  and re-emitting as light  362 . Without housing  370  in place, the emitted light is blue, while with housing  370  in place the emitted light is the converted light, thus reducing the observed CCT. 
     In various embodiments of the present invention, it may be desirable for the top housing to have relatively minimal or no impact on the optical characteristics of the system. In various embodiments of the present invention, the optical impact of the top housing may be minimized or eliminated by various techniques. In various embodiments of the present invention, the top housing may be configured such that it does not change or does not substantially change the transmission and/or reflection of light at the emission surface of LEE  140 . In various embodiments, this may be accomplished by spacing the top housing apart from the LEEs, thus eliminating direct optical coupling (formation of a layer in direct contact with the emitting surface of the LEE having an index of refraction substantially different from that of air, or substantially larger than 1, for example less than about 1.1) between the two that may result in modification of the optical characteristics of the light emitted by the LEEs, as discussed with reference to  FIGS. 3A and 3B . For example, in various embodiments of the present invention the region under the top housing may include, consist essentially of, or consist of air or a gas or a partial or complete vacuum. 
     As shown in  FIG. 3C , even if the top housing is spaced apart from the LEE, changes may occur by virtue of light reflecting off of the top housing and re-entering the LEE. Re-entry of previously emitted light may be reduced or eliminated by, for example, appropriate design of the shape and spacing of the top housing. For example, as described herein with reference to  FIG. 3C , blue light  350 ′ exits the LEE as blue light  351 , reflecting off of housing  370 , the reflected light identified as light  360 , re-entering the LEE as light  361 , being absorbed by phosphor  330  and re-emitting as light  362 . Thus, reflection from housing  370  results in a reduction in the observed CCT. Referring to  FIG. 3D , which schematically shows housing  370 ′ having a different shape, blue light  350 ′ exits the LEE as blue light  351 , reflecting off of housing  370 ′. The reflected light identified as light  360 ′, instead of re-entering the LEE as shown in  FIG. 3C , is incident on the region adjacent to the LEE (for example the substrate) and is reflected as light  361 , which exits the lighting system without re-entering the LEE and being re-absorbed and color or wavelength shifted by phosphor  330 . 
       FIG. 3E  shows a schematic of a differently shaped housing  370 ″, again resulting in light  360 ″ that is reflected off of housing  370 ″ not re-entering the LEE the LEE and being re-absorbed and color or wavelength shifted by phosphor  330 . 
     Using known optical design techniques, and without undue experimentation, the shape of housing  370  may be designed in conjunction with the light-distribution pattern of the LEE to eliminate, substantially eliminate, or significantly reduce the amount of light that is reflected from housing  370 , or any other features in the lighting system, back into the LEE. In various embodiments, it may be desirable to form top housing  210  in such a way that it is in contact with the emitting surface of LEE  140  (for example where top housing includes, consists essentially of, or consists of a conformal coating), and in such cases the change in optical characteristics may be minimized or eliminated by, for example, choice of material and thickness of material. For example, lighting system  400  of  FIG. 4  includes a top housing  410  in contact with LEEs  140 . In various embodiments, top housing  410  may include, consist essentially of, or consist of a conformal coating, for example silicone, polyurethane, TPU, EVA, or the like. Using a material with an index of refraction that is matched to or substantially matched to that of the phosphor (typically this is the index of refraction of the binder in which the phosphor particles are suspended, typically silicone or epoxy), will in various embodiments minimize the impact of the differing indices of refraction. In addition, the impact of differing indices of refraction may be reduced by reducing the thickness of top housing  210 . 
     Table 1 below shows the measured CCT change for three different top housing thicknesses in an optically coupled structure similar to that shown in  FIG. 4 . In this example, LEEs  140  are conformally coated with TPU and the measurements are performed in an integrating sphere. As shown in Table 1, there is a relatively significant increase in CCT for TPU thicknesses between about 15 mil and about 25 mil, and then a much larger increase for a TPU thickness of about 50 mil. As also shown, the CCT increase is larger for higher starting CCT values. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 TPU Thickness 
                 CCT Change 
                 CCT Change 
               
               
                   
                 CCT 
                 (mil) 
                 (K) 
                 (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 2700 
                 15 
                 180 
                  7% 
               
               
                   
                   
                 25 
                 220 
                  8% 
               
               
                   
                   
                 50 
                 582 
                 22% 
               
               
                   
                 4000 
                 15 
                 436 
                 11% 
               
               
                   
                   
                 25 
                 495 
                 12% 
               
               
                   
                   
                 50 
                 1431 
                 36% 
               
               
                   
               
            
           
         
       
     
     Table 2 below shows the measured CCT change for a non-optically coupled structure similar to that shown in  FIGS. 2A-2G . In this example, top housing  210  is PET and has a thickness of about 100 μm and the measurements are performed in an integrating sphere. As shown, the change in CCT is relatively smaller than for the configuration discussed in reference to Table 1 and the change is also in the opposite direction. In this configuration, the CCT decreases slightly because of re-entry and re-emission of light from LEE  140 . 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 CCT Change 
                 CCT Change 
               
               
                 CCT 
                 (K) 
                 (%) 
               
               
                   
               
             
            
               
                 2700 
                  −48 
                 −1.7% 
               
               
                 5700 
                 −215 
                 −3.6% 
               
               
                   
               
            
           
         
       
     
     In various embodiments of the present invention, the configuration and material of top housing  210  may be chosen to minimize the impact on the optical characteristics of LEE  140  by following the overall principle of minimizing changes in the reflection and transmission of light at the light emission interface of LEE  140 . For example, top housing  210  may be chosen to have a high transparency to a wavelength of light emitted by LEE  140 , to minimize light reflection from top housing  210  back into LEE  140 . In various embodiments of the present invention, top housing  210  may have a transmittance of a wavelength of light emitted by LEE  140  of at least about 75% or at least about 85%, at least about 95% or at least 98%. In various embodiments of the present invention, all or portions of the interior surface of top housing  210  may be coated with an anti-reflection coating designed to minimize or eliminate reflection of light within the wavelength range of light emitted by LEE  140 . In various embodiments of the present invention, top housing  210  may be shaped to minimize or eliminate reflection of light from top housing  210  back into LEE  140 . Any of these techniques may be used alone or in combination or with other techniques for minimizing changes in the reflection and transmission of light at the light emission interface of LEE  140 . 
     In various embodiments of the present in invention, the lighting system may be cut or separated into more than one portion, with at least one or the cut portions retaining operability, as described in detail in the &#39;807 and &#39;027 applications and 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, all cut portions may retain operability. Referring to  FIG. 2A , if lighting system  200  is cut or separated at cut line  290 , the edge of conductive trace  160  may be exposed at the separation interface, that is at the cut line. In various embodiments of the present invention, it may be acceptable to leave the relatively small cross-sectional area of the conductive traces exposed; however, in other embodiments this may not be desirable. 
     Various techniques may be used to seal the edges of exposed conductive traces. For example, in various embodiments of the present invention the exposed edges of the conductive traces may be covered by a tape, gel, adhesive, silicone rubber or other material that is electrically insulating and/or that provides the desired level of protection, for example weather proof, water proof, IP65, or Ip67, or the like. In various embodiments of the present invention, a clip, cover, extrusion, or sleeve may be positioned over the exposed conductive trace edges after cutting. In various embodiments, such a clip may include, consist essentially of, or consist of silicone or polyurethane and may also employ gel insulation in the extrusion to improve the seal. 
       FIG. 5  shows an example of a sealed lighting system in accordance with various embodiments of the present invention that includes cuttable or separable light sheet  510  having an array of cut lines  520  and  521  defining a 4×4 array (16 in total) of elements  530  that may be removed as required.  FIG. 5  shows three elements  530  removed from one corner of light sheet  510  and clips or covers  540  covering all or a portion of cut edge  550 . In various embodiments of the present invention, covers  540  may cover all or substantially all of cut edge  550 ; however, this is not a limitation of the present invention, and in other embodiments cover  540  may cover only a portion of cut edge  550 , for example the portion of cut edge  550  that includes an exposed edge of a conductive trace. Various embodiments of the present invention may include a system that includes, consists essentially of, or consists of multiple sealed light sheets of different sizes and a connector system that matches the environmental or other requirements of the sealed light sheets. In various embodiments of the present invention the luminous flux of each sealed light sheet per unit area may be substantially the same, for example in various embodiments the difference between the luminous fluxes per unit area for the different sized sheets may be less than about 20%, or less than about 10%, or less than about 5%, or less than about 2%. 
     Such a system may be used to provide even, uniform illumination over different sized and shaped areas, without exposure of any live electrical components or conductors. In various embodiments of the present invention, the multiple sealed tiles and the connector system have the same or substantially the same characteristics with respect to protection from environmental impact, dust, abrasion and the like; however, this is not a limitation, and in other embodiments the characteristics of the sealed light sheets and connector system may be different. For example, the sealed light sheets and the electrical connectors may be designed to meet the desired requirements for water resistance, water proofing, dust resistance, or to meet various ingress protection ratings such as IP65, IP67, or the like. In various embodiments, such light sheets may include power conductors to transmit power to adjacent light sheets, while in other embodiments one or more power bus components may be utilized to provide power to multiple light sheets, as described in the &#39;149 application. In various embodiments of the present invention, sealing of the light sheets may use one or more techniques or structures discussed herein, for example sealed with one or more of a top housing, bottom housing, a conformal coating, or the like. The sealing mechanism is not shown in  FIGS. 5, 6A-6J and 7A and 7B  for clarity. 
       FIG. 6A  shows a schematic of a lighting system in accordance with various embodiments of the present invention including or consisting essentially of a sealed light sheet or tile  610  that features electrical connectors  620  and  630  that mate with electrical connectors  621  and  631  respectively. Light sheet  610  also includes an array of LEEs (not shown in  FIGS. 6A-6I  for clarity) formed over at least a portion of light sheet  610 , which are electrically coupled to and energized through the connector system (connectors  620 ,  621 ,  630 , and  631 ). In various embodiments, power conductors on the light sheet electrically couple connector  630  to connector  631  on the same sheet (for example, power conductors on the light sheet electrically couple connector  630  to connector  631 ′ on light sheet  610 ) and electrically couple connector  620  to connector  621  on the same sheet (for example, power conductors on the light sheet electrically couple connector  620  to connector  621 ′ on light sheet  610 ). Power is utilized from these power conductors to energize LEEs on the light sheet. In an installation of light sheets, power may be provided to one end of a column or set of light sheets ( FIG. 6A  shows part of a column of light sheets including light sheets  610 ″,  610 , and  610 ′). Such systems are described in detail in the &#39;807,&#39;027, and &#39;149 applications. The LEEs and wiring on light sheet  610  are not shown for clarity, and the specifics of the array size, layout of the array, and electrical connection scheme are not limitations of the present invention. This permits formation of a column of electrically connected light sheets, in which connectors  620  and  630  on light sheet  610  are mated with connectors  621  and  631  respectively on a second light sheet  610 ″ (shown not connected for clarity in  FIG. 6A ) and connectors  621  and  631  on light sheet  610  are mated with connectors  620  and  630  respectively on a third light sheet  610 ′. 
     In  FIG. 6A  and related figures, connectors  620  and  630  are shown as a relatively smaller circle than connectors  621  and  631 , and connectors  620  and  621  are shown with dashed lines. In various embodiments of the present invention, the connectors may be polarized to prevent misconnection. In various embodiments, the connectors may have a gender, for example connectors  620  and  630  may be male connectors while connectors  621  and  631  may be female connectors or vice-versa; however, this is not a limitation of the present invention, and in other embodiments the connectors may have other configurations. In various embodiments, connectors  621  and  631  may be formed on tabs that overlap connectors  620  and  630  (for example tab  602  in  FIG. 6A ); however, this is not a limitation of the present invention, and in other embodiments the connectors may have other configurations. 
     Light sheet  610  is composed of a number of elements or sub-units  615 ; in  FIG. 6A , light sheet  610  is a 5×4 array of 20 elements  615  that are defined by orthogonal lines  617  and  619 ; however, the number, size and/or shape of elements  615  are not a limitation of the present invention, and in other embodiments light sheet  610  may include, consist essentially of, or consist of fewer or more elements  615  that may have different shapes and/or sizes. Each element  615  includes one or more LEEs, and in various embodiments each element  615  has the same number, configuration and physical layout of LEEs; however, this is not a limitation of the present invention, and in other embodiments these may be different. In various embodiments of the present invention, the light intensity and light intensity uniformity is the same or substantially the same for each element  615 , such that forming elements  615  adjacent to each other provides uniform intensity over all of the elements  615  with no substantially brighter or darker areas at the interface between adjacent elements  615 . As discussed herein, any number or position of elements  615  may be present or not, permitting the lighting system to accommodate penetrations for example for sprinkler heads, light switches, other lighting fixtures, cameras, or the like. The minimum increment of resolution is the element (or “illumination unit cell”)  615 , and in various embodiments the element  615  size may be increased or decreased as required for the application. In various embodiments, each illumination unit cell  615  corresponds to one or more light-emitting strings, each of which features two or more interconnected LEEs and a control element for regulating the current to the LEEs. 
     While light sheets  610  in  FIG. 6A  may be utilized to provide a sealed lighting system in accordance with embodiments of the present invention, for example the use of a top and or bottom housing as well as connectors designed to meet the sealing requirements (e.g., IP54, IP65, IP67, or the like, as discussed herein), separation of such a lighting system into smaller units may result in the exposure of one or more conductive traces within lighting system  610  to the ambient environment. As discussed above, in various embodiments it may be advantageous to be able to provide a system that may be shaped and sized without exposure of conductive traces or other conductive elements. 
       FIG. 6B  shows a schematic of an embodiment of the present invention that includes sealed light sheet  610  as described in reference to  FIG. 6A , and in which light sheet  610  is electrically coupled to a power distribution system  640  that includes multiple connectors  620  and  630 . In various embodiments of the present invention, all connectors  620  on power distribution system  640  are electrically coupled together (but not to connectors  630 ), and all connectors  630  on power distribution system  640  are electrically coupled together (but not to connectors  620 ). Power is provided to power distribution system  640  from connectors  620  and  630  on light sheet  610  to connectors  620 ′ and  630 ′ on power distribution system  640  through jumpers  670  (only one jumper  670  is shown for clarity; unconnected jumper  670 ′ is also shown in  FIG. 6C ). In various embodiments jumper  670  includes, consists essentially of, or consists of a conductor or wire  672  electrically coupled at one end to a first connector and electrically coupled at an opposite end to a second connector. In various embodiments, the gender of the first connector may be different from the gender of the second connector; however, in other embodiments the connector gender at each end of the wire may be the same, or one or both connector may not be present. The power is then transferred through connectors  620  and  630  on power distribution system  640  to sub-tiles  660 ,  662  and  664 , to energize LEEs on the sub-tiles. 
     In various embodiments of the present invention, each sub-tile includes, consists essentially of, or consists of an integer number of elements  615  ( FIG. 6A ), for example sub-tiles  660  and  660 ′ include, consist essentially of, or consist essentially of one element  615 , sub-tile  664  includes, consists essentially of, or consists of two elements  615 , and sub-tile  662  includes, consists essentially of, or consists of three elements  615 . The connectors on the sub-tiles mate with connectors on power distribution system  640 , providing power to the LEEs on that element. As discussed with reference to  FIG. 6A , in various embodiments of the present invention each element has the same or substantially the same light intensity and light intensity uniformity; in addition, disposing or locating elements adjacent to each other provides uniform intensity over all of the elements with no substantially brighter or darker areas at the interfaces between adjacent elements. Sub-tile  660 ′ is shown in unconnected form in  FIG. 6D , while sub-tiles  660 ,  662  and  664  are shown as connected in  FIG. 6B . As shown in  FIG. 6B , sub-tiles with varying number of elements may be used to form a wide variety of uniformly illuminated shapes, to permit uniform illumination of a wide range of features or structures. While not shown for clarity, the components of the system shown in  FIG. 6B  are sealed as detailed herein (i.e., with a top housing and/or a bottom housing), for example including power distribution system  640 , jumpers, connectors, and sub-tiles. 
       FIG. 6E  shows an example of a variation of the system shown in  FIG. 6B  in accordance with various embodiments of the invention. In the case of the system of  FIG. 6E , the jumper system is replaced by connectors. While  FIG. 6E  shows the connectors that replace the jumpers as being the same as those that connect the light sheets or sub-tile elements, this is not a limitation of the present invention, and in other embodiments other connectors may be used. In the system of  FIG. 6E , light sheet  610  includes connectors  621  and  631  that mate and electrically couple with connectors  620 ′ and  630 ′ on power distribution system  641 . In various embodiments of the present invention, all connectors  620  on power distribution system  641  are electrically coupled together (but not to connectors  630 ) and all connectors  630  on power distribution system  641  are electrically coupled together (but not to connectors  620 ). Power is provided to power distribution system  641  from connectors  621  and  631  on light sheet  610  to connectors  620 ′ and  630 ′ on power distribution system  640  (power distribution system  641  in  FIG. 6E  is shown disconnected from light sheet  610 , for clarity). Tile elements are connected to power distribution system  641  in a similar fashion as that described in reference to  FIG. 6B . While not shown for clarity, in various embodiments the components of the system shown in  FIG. 6E  are sealed as detailed herein (i.e., utilizing a top housing and/or a bottom housing), for example including power distribution system  641 , jumpers, connectors, and sub-tiles. 
     In various embodiments of the present invention, the systems of  FIGS. 6B and 6E  may be used to provide uniform intensity illumination over areas having different shapes and sizes, for example over shape  605  shown in  FIG. 6F . In various embodiments, shape  605  may be defined by its application, for example back lighting a sign, in a piece of furniture, a luminous wall or ceiling, or the like. In various applications, it may also be necessary to be able to accommodate one or more penetrations or areas without light within the shape, not just at the edge, for example to remove all or a portion of light sheet  610  (the area in which all or a portion of the light sheet is removed is identified as  613 ′) in  FIG. 6F , leaving illuminated portion  613 , as shown in  FIG. 6G . Note that in various embodiments all or portions of power distribution system  642 ,  642 ′ may be positioned within non-illuminated portion  613 ′. 
       FIG. 6H  shows a schematic of a lighting system in accordance with various embodiments of the present invention designed to accommodate the need for penetrations or empty areas in the lighting system, without exposed conductors, as may be produced by cutting a light sheet into two or more portions. The configuration shown in  FIG. 6H  is designed to remove all or portions of the light sheet in area  613 ′ and leave illuminated portion  613 , as shown in  FIG. 6G ; however, this is not a limitation of the present invention and as will be discussed herein, different illuminated portions or non-illuminated (e.g., no light sheet present) portions and shapes may be produced. In various embodiments of the present invention, the system of  FIG. 6H  includes, consists essentially of, or consists of power distribution systems  642  and  642 ′ and various sub-tiles. The lighting system of  FIG. 6H  includes sub-tiles  680  and  683  while  FIG. 6  shows a set of sub-tiles  680 ,  681 ,  682 ,  683  and  684 .  FIG. 6I  also shows power distribution system  642 ′. Note that in various embodiments of the system there are two different power distribution systems for the left and right side, identified as  642 ′ and  642  respectively in  FIG. 6H . In the example shown in  FIGS. 6H and 6I , the connector order for sub-tile connectors is reversed in power distribution system  642  compared to power distribution system  642 ′ to permit connection of the same sub-tiles to both power distribution systems; however, this is not a limitation of the present invention, and in other embodiments other connector configurations may be used. In various embodiments, a full set of sub-tiles includes sub-tiles with the full complement of elements along the width of tile  610 . In the example of  FIGS. 6H and 6I , tile  610  has five elements across its width and a full complement of sub-tiles includes five sub-tiles with one, two, three, four, and five elements each, as shown in  FIG. 6I ; however, this is not a limitation of the present invention, and in various embodiments sub-tiles may have any shape or size. 
     Referring to  FIG. 6H , power distribution systems  642  and  642 ′ electrically connect light sheet  610 ″ to light sheet  610 ′ to transmit power from light sheet  610 ″ to light sheet  610 ′. In addition, all connectors  620  on power distribution systems  641  and  642 ′ are electrically connected together and all connectors  630  on power distribution systems  641  and  642 ′ are electrically connected together. This permits energization of sub-tiles by connecting them to a pair of connectors  620 ,  630  through connectors  631  and  621  on the sub-tiles. While  FIG. 6H  shows both power distribution systems  642  and  642 ′, this is not a limitation of the present invention, and in other embodiments only one may be utilized; for example, in  FIG. 6F  no sub-tiles are connected to power distribution system  642 ′ so it may be removed. In this case, power to light sheet  610 ′ is provided solely through power distribution system  642 . In the example shown in  FIG. 6H , sub-tile  683  includes four elements (as shown by the dashed element designation lines  617  and  619 ), while sub-tile  680  includes one element. With this arrangement any number or position of elements may be present or not, permitting the lighting system to accommodate penetrations for example for sprinkler heads, light switches, other lighting fixtures, cameras, or the like. The minimum increment of sub-tile is the element, and in various embodiments the element size may be increased or decreased as required for the application. While not shown for clarity, in various embodiments the components of the system shown in  FIGS. 6H and 6I  are sealed, for example including power distribution system  642  and sub-tiles. 
       FIG. 6J  shows a schematic of an embodiment of the present invention designed to accommodate the need for penetrations or empty areas in the lighting system, without exposed conductors, as may be produced by cutting a light sheet into two or more portions. In contrast to the system of  FIGS. 6H and 6I , the system of  FIGS. 6J and 6K  only uses sub-tiles and does not use power distribution systems.  FIG. 6K  shows a full complement of sub-tiles for a system having five elements across the width of the light sheet, including sub-tiles  690 ,  691 ,  692 ,  693  and  694 , having one, two, three, four, and five elements each respectively. As discussed herein, an element is an area of a light sheet  610  and in the example shown in  FIG. 6J , each element is defined by lines  617  and  619 , resulting in a 4×5 array for a total of 20 elements. The size of each element and thus the resolution or granularity of the system may be changed by using fewer or more elements, for example a 4×4 array, a 5×5 array, or the like. 
     In the example of  FIG. 6J , each tab has one connector positioned on it, in contrast to the systems of  FIGS. 6H and 6I , in which the two complementary connectors are positioned on one tab. By complementary, it is meant that in a system energized by a typical voltage or current, there are positive and negative terminals and these may correspond to connectors  621  and  631  respectively or connectors  620  and  630  respectively. In various embodiments, other energization schemes may be utilized, which may have more than just one positive and one negative line, in which case the number of connectors may be modified accordingly. For example, systems that may accommodate white color tuning, color tuning, or full color ability, or that incorporate addressability the ability to selectively energize portions of the system, may utilize more than two complementary connectors. While  FIGS. 6J and 6K  show one connector per tab, this is not a limitation of the present invention, and in other embodiments more than one connector may be positioned on a tab. 
     The system of  FIG. 6J  includes, consists essentially of, or consists of two two-element sub-tiles  691  and  691 ′, two one-element sub-tiles  690  and  690 ′, one three-element sub-tile  692 , and one five-element sub-tile  694 . Use of the different sub-tile sizes permits configuring a system with sub-tiles in any of the element areas. While not shown for clarity, the components of the system shown in  FIGS. 6J and 6K  are sealed as detailed herein (i.e., via use of a top housing and/or bottom housing). 
       FIG. 6L  shows an example of a system in accordance with embodiments of the present invention in which all sub-tiles have a size of one element area and the desired configuration is formed from multiple single element sub-tiles. In various embodiments of the present invention, the difference in the luminous flux per unit area of all of the different size sub-tiles is less than about 20%, or less than about 10%, or less than about 5%, or less than about 2%. 
     In various embodiments of the present invention, consistent light output (e.g., flux per unit area) may be incorporated into the design of the sub-tiles. For example,  FIG. 6K  shows five different sized sub-tiles, with each sub-tile including, consisting essentially of, or consisting of one, two, three, four or five elements. In various embodiments of the present invention, each element may be designed to have the same flux, which may be measured using well-known optical measurement tools and techniques, for example the flux may be measured in an integrating sphere. In various embodiments of the present invention in which each element has the same flux, a sub-tile made up of one element may be measured to have a flux of A (for example a luminous flux of A lumens). It then follows that a sub-tile made up of two elements (where each element has the same flux) would have a flux of 2 A, a sub-tile made up of three elements (where each element has the same flux) would have a flux of 3 A and so on, and, since the area also scales with the number of elements, the flux per unit area of a one element sub-tile is A/1, the flux of a two element sub-tile is 2 A/2 or A, the flux of a three element sub-tile is 3 A/3 or A, and so on, each of the sub-tiles designed in this fashion would have a flux of A per unit area (for example A lumens per the unit area of the element). 
     In various embodiments of the present invention, the luminous flux of each different sub-tile may be measured, for example using an integrating sphere, and that flux divided by the area of the sub-tile to validate the requirement of the flux per unit area being the same or the same within certain tolerances for all size sub-tiles. 
     In various embodiments of the present invention, consistent luminous output (e.g., flux per unit area) may be incorporated into the design of the sub-tiles. For example,  FIG. 6L  shows a lighting system including, consisting essentially of, or consisting of two large tiles  610 ′ and  610 ″ and multiple small sub-tiles  691  and a larger sub-tile  694 . In various embodiments, each tile and sub-tile may be populated with multiple LEEs  140 , with each LEE emitting the same or substantially the same flux, at a constant pitch (that is a constant spacing between each LEE), in which case the number of LEEs  140  per unit area is the same independent of the size of the tile or sub-tile. Again this may be validated by measuring the flux of each different sub-tile, for example using an integrating sphere, and that flux divided by the area of the sub-tile to validate the requirement of the flux per unit area being the same or the same within certain tolerances for all size sub-tiles. 
     In various embodiments, the single element sub-tiles may be connected by jumpers  670  and/or by connectors. In the example shown in  FIG. 6L , the system is configured to accommodate two circular penetrations, identified as  693  and  693 ′; however, any configuration with single-element resolution may be achieved by different arrangements of single-element sub-tiles. While not shown for clarity, the components of the system shown in  FIG. 6L  are sealed. LEEs  140  are shown in the system of  FIG. 6L . For example, sub-tile  691  includes, consists essentially of, or consists of four LEEs  140 ; however, the number of LEEs on a tile or sub-tile is not a limitation of the present invention, and in other embodiments tiles and sub-tiles may include fewer or more LEEs  140 . 
     In various configurations, not all of the connectors are actually connected to another sub-tile or light sheet. For example, in  FIG. 6J  connectors  621  and  631  on sub-tile  691 ′ are not connected in this example, as there is no sub-tile “above” them. In various embodiments of the present invention such non-connected connectors may be sealed in a permanent or reversible manner, for example to provide the same level of sealing as the remainder of the system or to provide the same or different level of ingress protection. In various embodiments, one or more connectors may be sealed using a liquid or gel sealant, for example polyurethane, silicone, RTV or the like; for example, the connector, and in some embodiments all or a portion of the tab on which the connector is disposed, is coated with the sealant to prevent exposure of the connector to the ambient environment. In various embodiments, one or more connectors may be sealed with a cap that covers substantially the entirety of the one or more connectors.  FIG. 6M  shows an example of a cap system  695  in accordance with embodiments of the present invention that includes, consists essentially of, or consists of cap  696  and cap  697  mechanically joined by connector  698 . In various embodiments, cap  696  and  697  may be sized to provide a seal to the electrical connectors on the light sheets. For example, in various embodiments cap  696  and  697  may have the same size or may have different sizes (as shown in  FIG. 6M ). While  FIG. 6M  shows a cap system  695  having two caps  696  and  697  that may mate to, for example connectors  621  and  631  on sub-tile  690  of  FIG. 6K , this is not a limitation of the present invention, and in other embodiments cap system  695  may include, consist essentially of, or consist of one cap or more than two caps. In various embodiments, cap system  695  may be manufactured by various means, for example additive manufacturing such as printing, injection molding or the like. In various embodiments, cap system  695  may include or consist of materials such as silicone, polyurethane, TPU, rubber, or the like. 
     While the systems described with reference to  FIGS. 6A-6L  show rectangular sub-tiles, this is not a limitation of the present invention, and in other embodiments other size sub-tile shapes may be utilized, for example circular, triangular, pentagonal, hexagonal, trapezoidal or any arbitrary shape. As noted in reference to  FIGS. 6A-6M , in various embodiments light sheets  610  may have one or two connector pairs; however, this is not a limitation of the present invention, and in other embodiments light sheets  610  may have other numbers of connector pairs, or connectors may not be configured in pairs. As noted in reference to  FIGS. 6A-6M , in various embodiments light sheets  610  may have connectors formed on one or more tabs; however, this is not a limitation of the present invention, and in other embodiments light sheets  610  may have no tabs, more than two tabs, or may have connectors formed on any portion of the light sheet. In various embodiments, connectors may be formed on a sub mount such as a circuit board, which may be disposed on light sheet  610 . In various embodiments of the present invention, one or more connectors may be replaced by jumpers or jumper wires. 
       FIG. 7A  shows an example of a light sheet in accordance with embodiments of the present invention (the seal for the light sheet in  FIGS. 7A and 7B  is not shown for clarity). Light sheet  710  in  FIG. 7A  includes, consists essentially of, or consists of a substrate  730  on which are disposed or mounted LEEs  720  and connectors  620 ,  621 ,  630 , and  631 . In various embodiments, on a light sheet, connectors  620  and  621  are electrically coupled and connectors  630  and  631  are electrically coupled, but connectors  620  and  621  are not electrically coupled to connectors  630  and  631 . Light sheet  710  also includes multiple conductive traces providing the electrical connection between connectors  620  and  621  and between connectors  630  and  631  (these conductive traces are also identified as power conductors) and other conductive traces interconnecting LEEs  720  and connecting LEEs  720  to the power conductors (conductive traces and power conductors not shown for clarity). In various embodiments, LEEs  720  may be electrically connected in series within each element  615 ; however this is not a limitation of the present invention, and in other embodiments LEEs  720  may be electrically connected in parallel or a series/parallel arrangement or any configuration within each element  615 . In various embodiments, LEEs  720  within each element  615  may be separately powered from the power conductors, while in other embodiments LEEs  720  from two or more elements  615  may be electrically coupled together and then electrically coupled to the power conductors. The electrical and/or physical configuration of LEEs  720  within an element  615  or on light sheet  710  is not a limitation of the present invention. 
       FIG. 7B  shows an expanded view of two elements  615  from the upper right corner of light sheet  710  of  FIG. 7A . Each element  615  includes six LEEs  720 ; however, this is not a limitation of the present invention, and in other embodiments an element may include fewer or a larger number of LEEs  720 . LEEs  720  are arranged in two staggered columns, with each column containing three LEEs  720 ; however, this is not a limitation of the present invention, and in other embodiments LEEs  720  may be positioned in a different configuration. The configuration of LEEs  720  is not a limitation of the present invention. 
     In various embodiments of the present invention, each element may additionally include a current control or current regulating circuit. In various embodiments, the circuit may be designed or configured to provide a constant or substantially constant current to LEEs  720 , for example within each element  615  or on light sheet  710 , as described further in the &#39;807 and &#39;027 applications. 
     As discussed herein, the systems discussed in reference to  FIGS. 5, 6A-6M, and 7A and 7B  provide for the ability to produce uniform or substantially uniform intensity over arbitrary shapes and sizes using lighting system of the present invention without any exposed conductors. 
     In various embodiments of the present invention, embodiments of the present invention may additionally include one or more optical elements to control one or more optical characteristics, for example luminous or radiant flux, CCT, CRI, R9, spectral power distribution, light-distribution pattern, angular color uniformity, or the like.  FIG. 8A  shows a cross-sectional schematic of lighting system  800  in accordance with various embodiments of the present invention, in which the optic includes an optic substrate  810  having multiple optical elements  820  on one side of optic substrate  810  and a second side (or “face”)  813  opposite the first side that is substantially flat and positioned adjacent to or in contact with substrate  165  and/or conductive traces  160 . In various embodiments, optic elements  820  may be spaced apart from LEEs  140 , as shown in  FIG. 8A ; however, this is not a limitation of the present invention, and in other embodiments optical elements  820  may be in contact with LEEs  140 . For example, in various embodiments of the present invention, optic elements  820  may include indentations into which fit one or more LEEs  140 , for example as in lighting system  810  shown in  FIG. 8B . 
       FIG. 8C  shows a cross-sectional schematic of lighting system  802  in accordance with various embodiments of the present invention, in which multiple individual optical elements  820 ′ are positioned over LEEs  140 . In contrast to the lighting systems of  FIGS. 8A and 8B , lighting system  802  does not include optical substrate  810 . 
     Optic substrate  810  and/or optic elements  820  may be attached to the underlying structure using a variety of techniques, for example using an adhesive, glue, heat-activated adhesive, mechanical fasteners, adhesive tape, a hot melt adhesive, TPU, EVA or the like. In various embodiments of the present invention, double-sided tape, such as 3M 467MP may be used to affix optic substrate  810  and/or optical elements  820  to the underlying structure and/or to form the seal. In various embodiments of the present invention, a liquid adhesive, such as Dymax 3099, may be used to affix optic substrate  810  and/or optical elements  820  to the underlying structure and/or to form the seal. In various embodiments of the present invention, optic substrate  810  and/or optical elements  820  may replace or partially replace top housing  210  and provide a seal to the underlying structure. 
     Optical elements  820  may all be the same or may be different from each other. Optical elements  820  may include, consist essentially of, or consist of, e.g., a refractive optic, a diffractive optic, a TIR optic, a Fresnel optic, or the like, or combinations of different types of optical elements. Optical elements  820  may be shaped or engineered to achieve a specific light-distribution pattern from the array of light emitters, phosphors and/or optical elements. 
     In various embodiments of the present invention one optical element  820  is associated with each LEE  140 , while in other embodiments multiple LEEs  140  are associated with one optical element  820 , or multiple optical elements  820  are associated with a single LEE  140 , or no engineered optical element is associated with any LEEs  140 , for example portions of optic substrate  810  thereover may merely be flat or roughened surfaces. In various embodiments, the optical elements  820  scatter, diffuse, and/or spread out light generated by LEEs  140 . 
       FIGS. 8A-8C  show the axis of each optical element  820  as substantially aligned with the center of an LEE  140 ; however, this is not a limitation of the present invention, and in other embodiments optical element  820  may be shifted in one or more lateral directions with respect to an LEE  140 , as detailed in U.S. Pat. No. 8,746,923, filed Dec. 4, 2012, the entire disclosure of which is incorporated by reference. It should be noted that alignment, as used herein, may mean that the center of one structure, for example an LEE  140 , is aligned with the center of another structure, for example an optical element  820 ; however, this is not a limitation of the present invention, and in other embodiments alignment refers to a specified relationship between the geometries of multiple structures. 
     Optical substrate  810  may be substantially optically transparent or translucent. For example, optical substrate  810  may exhibit a transmittance or reflectance greater than about 70%, or greater than 80%, or greater than 90% or greater than 95% for optical wavelengths ranging between about 400 nm and about 700 nm. Optical substrate  810  may include, consist essentially of, or consist of a material that is transparent to a wavelength of light emitted by LEEs  140 , for example having a transmittance greater than about 75%, or greater than about 85% or greater than about 95% to a wavelength of light emitted by LEEs  140 . Optical substrate  810  may be substantially flexible or rigid. Optical elements  820  may be formed in or on optical substrate  810 . For example, optical elements  820  may be formed by etching, polishing, grinding, machining, molding, embossing, extruding, casting, or the like. The method of formation of optical elements  260  is not a limitation of embodiments of the present invention. 
     Lighting systems in accordance with various embodiments of the present invention may have a thickness in the range of about 1 mm to about 50 mm, or in the range of about 2 mm to about 25 mm or in the range of about 2 mm to about 10 mm. 
     Lighting systems in accordance with various embodiments of the present invention may have a relatively light weight, for example having a weight per area of less than about 5 kg/m 2 , or less than about 3 kg/m 2  or less than about 1.5 kg/m 2 . It should be noted that the weights described herein do not necessarily include a driver that drives LEEs  140 . 
     Relatively lightweight lighting devices have several advantages. First, they reduce the weight load on the building, potentially permitting a reduction in new construction costs. Second, they are easier to handle and install. In some embodiments of the present invention, a lightweight lighting device may be installed, either temporarily or permanently, using hook-and-loop fasteners, adhesive, tape, dry wall hangers, nails, screws, or the like. Third, shipping costs typically depend on size and weight. The reduced weight of lighting devices of embodiments of the present invention may thus reduce shipping costs. The relatively thin profile of lighting devices of embodiments of the present invention permits increased shipping density, for example more lighting devices per shipping box or pallet, also resulting in lower shipping and storage costs. In some embodiments, lighting devices or ribbed lighting devices of embodiments of the present invention may be designed to stack relatively tightly, with little need for additional space or packing material for protection. 
     In various embodiments of the present invention the lighting systems, for example including a top housing, an optical substrate and/or optical elements, may be flexible or substantially flexible, for example having a radius of curvature of less than about 500 cm or less than about 250 cm or less than about 100 cm or less than about 50 cm. 
     Lighting systems in accordance with various embodiments of the present invention may be manufactured in a variety of ways.  FIG. 9  shows a flow chart of a process  900  for forming in accordance with various embodiments of the present invention. Process  900  is shown having six steps; however, this is not a limitation of the present invention, and in other embodiments the invention has more or fewer steps and/or the steps may be performed in different order. In step  910 , a light sheet is provided. In step  920 , housing material is provided, e.g., as a single piece or multiple pieces of material. In step  930 , one or more pieces of housing (i.e., housing components) are formed from the housing material. In step  940 , an electrical connector is provided. In step  950 , the electrical connectors are electrically coupled to the appropriate conductive traces and/or power conductors. In step  960 , the housing component(s) and light sheet are mated to form the lighting device. In various embodiments of the present invention, the electrical connectors are mated with the light sheet in step  960 ; however, this is not a limitation of the present invention, and in other embodiments the electrical connector may be mated with the light sheet in a different step or in a separate step. 
       FIGS. 10A-10E  depict one embodiment of process  900 . In this embodiment, a light sheet  110  is provided in step  910 , as shown in  FIG. 10A . The manufacture of the light sheet  110  includes provision of a substrate  165 , forming conductive traces  160  on the substrate  165 , attaching and electrically coupling LEEs  140  and optionally other components to the conductive traces  160  and the substrate  165 . Additional details may be found herein and in the &#39;807 and &#39;027 applications. However, the specific method of manufacture of light sheet  110  is not a limitation of the present invention, and in other embodiments other methods of manufacture of light sheet  110  may be utilized. For example, in some embodiments light sheet  110  may include, consist essentially of, or consist of an interconnected array of inorganic LEDs, while in other embodiments light sheet  110  may include one or more organic light emitting diode (OLED) elements. In step  920  the housing material is provided. Depending on the specific lighting device structure, this may be one piece of housing material or multiple pieces of housing material. In various embodiments, the material for all housing components is the same, while in other embodiments different housing components may include or consist essentially of different materials. For example, for the device described in reference to  FIG. 2A , material for the housing components is provided, as shown in  FIG. 10B .  FIG. 10B  shows of material  1010  that will be used to manufacture top housing  210 . In this example material  1010  is clear and has a transmittance to a wavelength of light emitted by LEEs  140  greater than about 90%. 
     In step  930  the housing components are formed. In various embodiments of the present invention, forming may be cutting to a specific shape, while in other embodiments this may include shaping the material, for example to have a specific three-dimensional shape. In other embodiments of the present invention, step  930  may include applying one or more coatings to the materials provided in step  920 . For example, for the device described in reference to  FIG. 2A , material  1010  is cut to size and bumps are formed therewithin by thermoforming to form top housing  210 , while material  520  is cut to size to form bottom housing  220 , as shown in  FIG. 10C . The method of cutting, shaping, and/or coating of materials is not a limitation of the present invention. In various embodiments of the present invention, forming the housing may include, consist essentially of, or consist of die cutting one or more materials and laminating and/or adhering two or more layers together. 
     In step  940  one or more electrical connectors to the light sheet are provided and in step  950  the electrical connectors are attached to the light sheet.  FIG. 10D  shows connector  1030  attached to conductive trace  160 . In various embodiments of the present invention all or a portion of the connectors may also be electrically and/or mechanically coupled and/or attached to appropriate conductive traces on substrate  165  during step  910 . 
     In various embodiments of the present invention, connectors may be attached using a variety of means, for example including soldering, adhesive, conductive adhesive, anisotropic conductive adhesive, crimping, eyeleting or the like. In various embodiments of the present invention, electrical connection includes providing power to light sheet  110 , for example to power conductors  120 ,  121 , while in other embodiments communication and/or control signals may also be required to be coupled to light sheet  110 . Electrical coupling to the conductive traces or power conductors on light sheet  110  may be accomplished in a variety of ways. In various embodiments of the present invention, electrical coupling to the conductive traces may be accomplished by attaching wires to the appropriate conductive traces. In various embodiments, electrical coupling to the conductive traces may be accomplished by a pressure connection. In various embodiments of the present invention, the connectors have the same or substantially the same or no worse characteristics with respect to ingress protection rating or requirements for the sealed lighting system. 
     In various embodiments of the present invention, electrical coupling to the conductive traces may be accomplished by attaching one or more wires directly to a conductive element, for example with solder or conductive adhesive or anisotropic conductive adhesive, and such wires are connected together or to other systems using connection systems with the appropriate ingress protection rating. In various embodiments of the present invention, electrical coupling to the conductive traces may be accomplished by attaching one or more wires to a conductive trace by crimping. Various crimp components may be used for this purpose, for example Autosplice TC series or Nicomatic Crimplex series crimp connectors; however, this is not a limitation of the present invention, and in other embodiments other crimp elements may be used. In various embodiments, wires attached to conductive traces  160  are sealed by top housing  210 . 
     In step  960 , the housing elements are mated with the light sheet  110  to form the lighting device.  FIG. 10E  shows the mated structure. Note that in this example, light sheet  110  extends beyond the edge of top housing  210  and electrical connection to conductive trace  160  is made using connector  1030  and that adhesive material  230  optionally forms a seal around connector  1030 .  FIG. 10E  also shows connector  1040  that mates to connector  1030 ; connector  1040  is a board-to-wire type connector, with wire  1041  electrically coupled to connector  1040 ; however, this is not a limitation of the present invention, and in other embodiments other types of connectors may be used. 
     In various embodiments of the present invention, top housing  210  and bottom housing  220  may be joined by lamination, heat welding, high-frequency welding, ultrasonic welding, laser welding, adhesive, glue, tape, or the like. In various embodiments of the present invention, light sheet  110  may be adhered to one or more portions of the housing, for example, top housing element  210  or bottom housing element  220 , before mating. In various embodiments of the present invention, light sheet  110  may be taped or glued to a portion of the housing before mating. 
     In various embodiments of the present invention, lighting devices may be manufactured in sheets or in a roll-to-roll process.  FIG. 11  shows one embodiment of the present invention featuring a roll-to-roll process for manufacture of lighting devices; however, this is not a limitation of the present invention, and in other embodiments the process has more or fewer steps and/or the steps may be performed in different order. The exemplary manufacturing process shown in  FIG. 11  begins with three material feed streams, although this is not a limitation of the present invention, and in other embodiments fewer or more material feed streams may be utilized. 
     A feed roll  1110  supplies material  1115  for top housing  210 , a feed roll  1120  supplies light sheet  1125  and a feed roll  1150  supplies adhesive material  230 . In various embodiments, top housing may be formed before the joining process (formed top housing material is supplied from feed roller  1110 ); however, this is not a limitation of the present invention, and in other embodiments forming of housing  210  may occur between feed roller  1110  and mating station  1140 . 
     In various embodiments, LEEs may be attached to light sheet material before the joining process (completed light sheet material is supplied from feed roller  1120 ); however, this is not a limitation of the present invention, and in other embodiments LEE attachment may occur between feed roller  1120  and mating station  1140 . In various embodiments, connectors may be attached to light sheet material before the joining process (completed light sheet material with connectors is supplied from feed roller  1120 ); however, this is not a limitation of the present invention, and in other embodiments connector attachment may occur between feed roller  1120  and mating station  1140 . 
     In various embodiments, adhesive material  230  may require die cutting before the joining process (for example to remove adhesive material in the region of the LEE) and this optional die cutting may be done prior to the joining process (die cut adhesive material is supplied from feed roller  1150 ); however, this is not a limitation of the present invention, and in other embodiments die cutting may occur between feed roller  1150  and mating station  1140 . 
     Light sheet  110 , adhesive material  230  and top housing  1115  are mated together in joining station  1140 . Joining station may include various processes such as cold rolling, hot rolling, lamination or the like. In the system shown in  FIG. 11  the completed sealed system  1135  in roll form is taken up by take-up roller  1130 ; however, this is not a limitation of the present invention, and in other embodiments take-up roller  1130  may be replaced by a sheeting system, that cuts the roll material  1135  into sheets or tiles or sub-tiles. 
     In various embodiments of the present invention, the electrical connection system has the same protection rating, for example IP rating, as the housing, resulting in a system having the desired rating, for example IP 65, IP 66, IP 67, or IP 68. 
     As discussed herein, other components may be formed on substrate  165  to provide additional functionality to the lighting devices, for example sensors, such as occupancy sensors, light sensors such as light intensity sensors, humidity sensors, fire and/or smoke sensors, communication systems, or the like. 
     In various embodiments of the present invention, CE  145  or one or more components making up CE  145  may be changed in the manufacturing process without stopping or significantly slowing down the roll-to-roll process, in a similar fashion as that described herein for changing the type of LEE. For example, feed roll  1120  in  FIG. 11  may include light sheet  110  with different portions, each portion having a different CE  145  or one or more different components making up CE  145  or a second light sheet  110  having a different CE  145  or one or more different components making up CE  145  may be spliced onto feed roll  1120 . In various embodiments of the present invention, CE  145  or the components making up CE  145  may be formed on substrate  165  between feed roll  120  and mating station  1140 . In various embodiments of the present invention, the type of CE  145  or one or more components of CE  145  making up CE  145  may be changed during the manufacturing process, without stopping or significantly slowing down the roll-to-roll manufacturing process. In various embodiments of the present invention, the pattern of conductive elements on substrate  165  may be varied during the manufacturing process, for between feed roll  1120  and mating station  1140 . 
     Such embodiments of the invention result in the ability to manufacture large volumes of lighting devices in a roll-to-roll process with a standardized product, with a semi-custom product or with a fully customized product. For example, customization may include different LEEs  140  having different properties, different conductive trace patterns, different pitch or patterns between LEEs, different drive currents for LEEs  140 , or different types of material for the housing. For example, housing elements  210 ,  220  may include, consist essentially of, or consist of different materials, for example a transparent housing element and a diffusing housing element, or a different thickness material for the housing. Customization may also include options for different substrate materials, for example transparent or opaque to a wavelength of light emitted by LEEs  140 , or different thickness substrate, different additional elements such as sensors, communication devices, or the like. In an automated system, in one embodiment of the present invention, the desired quantity and parts are programmed into the system, which then manufactures, in a continuous process, a wide range of differentiated or customized lighting devices having different electrical, optical or physical characteristics. 
     In various embodiments of the present invention, lighting devices may be manufactured entirely or in part by lamination. For example, the housing may be fabricated by lamination, as when a top housing  210  is formed over LEEs  140  and an optional bottom housing  220  by lamination. In the lamination process, a layer is formed and adhered to light sheet  140  over LEEs  140 , providing for example mechanical protection and/or electrical protection (covering conductive traces and other electrically active elements), water and/or moisture protection for example to achieve an LP rating, dust protection, and the like. 
     In various embodiments, the layer of film to be laminated is adhered to the light sheet using a liquid adhesive that is applied to the light sheet or the film or both before mating, or a dry adhesive that is applied to the film or light sheet or both before mating. In various embodiments, lamination may be performed on a sheet basis, while in other embodiments lamination may be performed using a roll-to-roll process. 
     In various embodiments, control and/or communication signals, either to or from the lighting system, or in two-way communication with the lighting system, may also be enabled in embodiments of the present invention. For example, such signals may include a dimming signal, signals providing sensor output (e.g., from a sensor such as a light sensor, occupancy sensor or the like), connection to a lighting control system (e.g., DALI, DMX or the like), or a facilities management system, a safety system, or the like. In some embodiments of the present invention, such sensors may be incorporated within power supplies or drivers or on light sheet  110 , while in other embodiments such sensors may be incorporated externally to light sheets and/or power supplies and drivers. 
     In various embodiments of the present invention, such signals may provide control information to the lighting system, for example to energize it, to de-energize it, to change the light level (e.g., dimming), to change the CCT, to change the spectral power density, to change the luminous intensity distribution or the like. In some embodiments of the present invention, such signals may provide information about the lighting system, for example a defect or failure in lighting and/or driver, the temperature of the lighting device and/or driver, the location of the lighting device and/or driver, the optical characteristics of the lighting device or the like. 
     In various embodiments of the present invention, control and/or communication signals may be transmitted to light sheets and/or drivers wirelessly, for example using light-based communication such as infra-red (IR) or ultra-violet (UV) or visible light, radio-based communication, for example WIFI, Bluetooth or the like. 
     In various embodiments, warning or other annunciation signals may be displayed by the lighting device. In various embodiments of the present invention, light sheet  110  or portions of light sheet  110  or a lighting system may be energized and de-energized to provide a blinking indication. In some embodiments of the present invention, light sheet  110  may be cut or formed into one or more shapes, symbols or letters, to provide additional information or indications. For example light sheet  110  may be shaped into an arrow, a stop sign, a cross, or other shapes. In various embodiments of the present invention, LEEs  140  on light sheet  110  may be positioned to form one or more shapes, symbols or letters, for example an arrow, a “DO NOT ENTER” sign, a no smoking symbol, a no entry symbol, a symbol for fire, or the like. 
     As described herein, lighting systems in accordance with embodiments of the present invention having uniform intensity illumination over areas may include, consist essentially of, or consist of an assembly of tiles and/or sub-tiles, for example as discussed in reference to  FIG. 6B, 6E, 6F , or  6 L. Such lighting systems may be sealed or un-sealed. As described herein, power may be carried by power conductors on the tile or sub-tile and may be distributed from one tile or sub-tile to the next (e.g., an adjacent tile or sub-tile and/or a tile or sub-tile in contact with the one tile or sub-tile) through connectors and/or jumper cables.  FIGS. 6F and 6G  show exemplary lighting systems in accordance with embodiments of the present invention, and these lighting systems include tiles and sub-tiles to create and/or illuminate shape or panel  605 . In various embodiments of the present invention, multiple panels  605  may be assembled together to form larger lighting systems. In various embodiments, multiple panels  605  may be mechanically and electrically separate from each other; however, this is not a limitation of the present invention, and in other embodiments multiple panels may be electrically and/or mechanically interconnected, for example as discussed with respect to  FIG. 14 . 
       FIG. 12  depicts a lighting system similar to that shown in  FIG. 6F ; however, the lighting system of  FIG. 12  includes, consists essentially of, or consists of three panels  1210 ,  1210 ′, and  1210 ″, with each panel including, consisting essentially of, or consisting of six tiles. Interconnects and/or other electrical and/or mechanical connections between panels  1210 ,  1210 ′, and  1210 ″ are not shown in  FIG. 12  for clarity. In various embodiments of the present invention, the light intensity for each tile may be the same or substantially the same as that for each of the other tiles. In various embodiments of the present invention, the light intensity for each panel may be the same or substantially the same as that for each of the other panels. In various embodiments of the present invention, the light intensity per unit area for each tile may be the same or substantially the same as for each of the other tiles and for each of the panels. While  FIG. 12  shows each panel  1210  having the same or substantially the same size, this is not a limitation of the present invention, and in other embodiments different panels may have different shapes and sizes. In various embodiments of the present invention, different panels may have different shapes and sizes while still maintaining the same or substantially the same light intensity per unit area. 
     In various embodiments, such panelized systems may be advantageous because each panel may be constructed in advance, leading to reduced installation time because of the need to handle fewer components at the installation phase. 
       FIG. 13A  depicts a lighting system including, consisting essentially of, or consisting of two panels  1320 ,  1320 ′, each panel including, consisting essentially of, or consisting of three tiles  1330 . In  FIG. 13A , the tiles or lighting units have a rectangular shape; however, this is not a limitation of the present invention, and in other embodiments tiles or lighting units may have a square, hexagonal, polygonal, or any other shape. While  FIG. 13A  shows panel  1320  featuring three tiles or lighting units  1330 , this is not a limitation of the present invention, and in other embodiments the number of tiles or lighting units may be less than or greater than two. While  FIG. 13A  shows a lighting system featuring two panels  1320 , this is not a limitation of the present invention, and in other embodiments lighting system may include one panel or more than two panels. While  FIG. 13A  shows a lighting system including two panels  1320  having the same size and shape, this is not a limitation of the present invention, and in other embodiments lighting system may include panels having different sizes and/or shapes. 
     In various embodiments of the present invention, panels  1320  may be pre-assembled at a manufacturing site and then used to create larger luminous surfaces at the place of use or deployment. In various embodiments, this permits a faster and lower-cost installation because it reduces the number of individual lighting elements that must be handled. For example, with reference to  FIG. 13A , each panel  1320  includes three tiles  1330 . If this were to all be installed on-site, it would require handling of six tiles  1330  as opposed to handling just two panels  1320  by using the panelized approach. This approach also permits using a different attachment or installation method and/or a different electrical coupling method for the tiles compared with the panels. In various embodiments it may also permit simplification of the alignment during installation, permitting alignment of a smaller number of relatively larger panels rather than a larger number of relatively small tiles. In various embodiments of the present invention, the size of panel  1320  may be at least 2× (2 times) or at least 3× (3 times) the size of tile  1330 . 
       FIG. 13C  shows a cross-sectional view of panel  1320  as shown in  FIG. 13B , showing tile  1330  mounted on or over backing support  1321 . In various embodiments of the present invention, backing support  1321  may include, consist essentially of, or consist of a rigid or relatively rigid panel, for example one constructed from wood, metal, foam core, foam board, Kapatech, Hylite or Dibond (manufactured by 3A Composites) plexiglass, or the like. Referring to  FIG. 13D , in various embodiments of the present invention tile  1320  may be attached or secured to backing support  1321  by an adhesive, by tape  1326 , for example single sided or double-sided tape, and/or one or more fasteners  1324 , for example a staple, nail, screw or the like, or by other means. 
       FIG. 13E  shows an enlarged side view of the portion  1327  of lighting panel  1320  from  FIG. 13B . In various embodiments, panel  1320  may be mounted to a mounting surface  1329 , for example a wall or ceiling, for example one constructed from wood, dry wall, concrete, or the like. The material of mounting panel  1320  is not a limitation of the present invention. In various embodiments of the present invention, panel  1320  may be attached or mounted to mounting surface  1329  using one or more fasteners  1328 , for example a screw, nail, clamp, or the like. While  FIG. 13E  shows panel  1320  mounted in a vertical orientation this is not a limitation of the present invention, and in other embodiments panel  1320  may be mounted in other orientations, for example horizontal, as shown in  FIG. 13F , or in any other orientation. 
       FIG. 13F  shows a schematic of a lighting system in accordance with embodiments of the present invention including lighting panels  1320  in a horizontal orientation. In various embodiments, panels  1320  may be mounted in a horizontal orientation over a region or area to provide illumination to that region or area. In various embodiments of the present invention, panels  1320  may be attached to a horizontal mounting surface, similar to that described in reference to  FIG. 13E  for a vertical surface, however, this is not a limitation of the present invention, and in other embodiments panels  1320  may be hung or laid into a mounting frame  1331 , as shown in  FIG. 13F . In various embodiments of the present invention, lighting panels  1320  may be installed in all or a portion of a grid ceiling, where mounting frame  1331  forms a portion of the grid ceiling support system. 
     In various embodiments of the present invention, lighting panels  1320  may be electrically coupled to each other, for example using one or more jumpers  1375 , as shown in  FIG. 13F . In various embodiments of the present invention, jumper  1375  may include, consist essentially of, or consist of a jumper wire  1374  and jumper connectors  1372 ; however, this is not a limitation of the present invention, and in other embodiments panels  1320  may be electrically coupled using other means, for example insulation displacement connectors, wires and screw terminals or poke-in connectors, or the like. In various embodiments of the present invention, lighting panels  1320  may include one or more panel connectors  1370  (and/or sockets) that mate with jumper connector  1372  on jumper  1375 . In various embodiments, one or more panels  1320  may be powered from a power source  1377 , which may be coupled to panel  1320  through panel connector  1370 ; however, this is not a limitation of the present invention, and in other embodiments each panel  1320  may be powered separately or may be electrically coupled and powered by other means. 
       FIG. 13F  shows panel connectors  1370  and jumper  1375  located on the back of panels  1320 , that is on the side that is opposite the side of panel  1320  on which tiles  1330  are mounted. In various embodiments of the present invention, this is advantageous as it does not afford an opportunity for jumpers  1370  and/or panel connectors  1370  to block or shadow light emitted by tile  1330 . However, this is not a limitation of the present invention, and in other embodiments panel connectors  1370  and jumper  1375  may be located on the same side of panel  1320  as tile  1330 . 
     In various embodiments of the present invention, the combination of tiles  1330  and panels  1320  may permit assembly of a large lighting unit (panel  1320 ) that is relatively robust as compared to tile  1330 . For example, in various embodiments of the present invention, tile  1330  may be manufactured using a flexible substrate or circuit board, for example including, consisting essentially of, or consisting of a substrate including at least one of polyethylene terephthalate (PET), polyimide (PI), glass, a polymer, paper or the like. Such a flexible tile  1330  may have a low cost but be more subject to damage during the installation process, for example from tools or rough handling. Mounting such low-cost tiles  1330  on a relatively more robust panel  1320  may reduce or eliminate such installation damage by increasing the robustness of the panels that need to be handled as well as reducing the total number of panels that need to be handled during the installation process. In various embodiments this may result in a lower overall cost. 
     In various embodiments of the present invention, one or more of the panels  1320  may include a top housing (e.g., a top housing  210  or other polymeric housing) disposed thereover and joined thereto. The panel  1320  and the top housing may be joined by one or more fasteners, lamination, heat welding, high-frequency welding, ultrasonic welding, laser welding, adhesive, glue, tape, or the like. In various embodiments, the top housing may provide, for example, mechanical protection and/or electrical protection (covering conductive traces and other electrically active elements, e.g., light-emitting elements), water and/or moisture protection for example to achieve an IP rating, dust protection, and the like. In various embodiments the top housing may be spaced apart from the LEEs. 
     Using known optical design techniques, and without undue experimentation, the shape of the top housing may be designed in conjunction with the light-distribution pattern of the LEEs to eliminate, substantially eliminate, or significantly reduce the amount of light that is reflected from the top housing, or any other features in the lighting system, back into the LEEs. In various embodiments, it may be desirable to form the top housing in such a way that it is in contact with the emitting surface of the LEEs (for example where the top housing includes, consists essentially of, or consists of a conformal coating), and in such cases the change in optical characteristics may be minimized or eliminated by, for example, choice of material and thickness of material. In various embodiments, the top housing may include, consist essentially of, or consist of a conformal coating, for example silicone, polyurethane, TPU, EVA, or the like. Using a material with an index of refraction that is matched to or substantially matched to that of the phosphor (typically this is the index of refraction of the binder in which the phosphor particles are suspended, typically silicone or epoxy) of the LEEs, will in various embodiments minimize the impact of the differing indices of refraction. In addition, the impact of differing indices of refraction may be reduced by reducing the thickness of the top housing. 
     In various embodiments, the top housing may be formed by lamination, and the layer of film to be laminated over the panel  1320  as a top housing is adhered to the panel using a liquid adhesive that is applied to the panel or the film or both before mating, or a dry adhesive that is applied to the film or panel or both before mating. 
     In various embodiments, the top housing may be sealed to the backing support of the panel  1320  (and/or one or more portions of one or more of the light sheets disposed thereover) to form a sealed region in which at least a portion of at least one of the light sheets is disposed. For example, the sealed region may encompass therewithin some or all of the light-emitting elements on the panel. 
     As discussed in reference to  FIGS. 1A and 1B , in various embodiments of the present invention, the pitch between LEEs on one tile or lighting unit or light sheet may be the same or substantially the same as the pitch between adjacent LEEs on adjacent lighting units or tiles. Furthermore, in various embodiments of the present invention, the spacing or pitch between LEEs on adjacent panels may have the same pitch, that is the same as between adjacent LEEs on one tile and between adjacent LEEs on adjacent tiles. 
       FIG. 13G  is an expanded view of region  1340  of  FIG. 13A  showing LEEs  1305  in a region between panels  1320  and  1320 ′ where four tiles or light sheets  1230  come together. In various embodiments of the present invention the light intensity per unit area for each tile  1330  may be the same or substantially the same as for each of the other tiles  1330 . 
     In various embodiments of the present invention, a pitch  1350  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as a pitch  1354  in the same or substantially the same direction on a different light sheet. 
     In various embodiments of the present invention, pitch  1350  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as a pitch  1352  in the same or substantially the same direction between adjacent LEEs  1305  on adjacent light sheets. 
     In various embodiments of the present invention, pitch  1350  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as the pitch  1352  in the same or substantially the same direction between adjacent LEEs  1305  on adjacent light sheets and on adjacent panels. 
     In various embodiments of the present invention, a pitch  1364  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as a pitch  1360  in the same or substantially the same direction on a different light sheet. 
     In various embodiments of the present invention, pitch  1364  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as a pitch  1362  in the same or substantially the same direction between adjacent LEEs  1305  on adjacent light sheets. 
     In various embodiments of the present invention, pitch  1364  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as the pitch  1362  in the same or substantially the same direction between adjacent LEEs  1305  on adjacent light sheets and on adjacent panels. 
     In various embodiments of the present invention, pitch  1350  between LEEs  1305  on one tile or light sheet in a first direction may be the same or substantially the same as the pitch  1360  in an orthogonal or substantially orthogonal direction on the same light sheet. 
     In various embodiments of the present invention, the pitches  1350  and  1360  between LEEs in first and second orthogonal directions respectively may be the same or substantially the same and may also be the same as or substantially the same as the pitch  1352  and/or the pitch  1362  between adjacent tiles or light sheets and may also be the same as or substantially the same as the pitch  1352  and/or the pitch  1362  between adjacent panels. 
     In various embodiments of the present invention in which LEE pitches are the same, as described above, and where each LEE emits the same or substantially the same amount of light, the light intensity per unit area for all tile may be the same or substantially the same. In various embodiments of the present invention, each LEE may be configured to emit the same or substantially the same amount of light in various ways, for example each LEE may be the same as all other LEEs and the current through each LEE may be controlled to be the same or substantially the same, while in other embodiments one or more LEEs may be different from one or more other LEEs and the current through each LEE may be controlled to result in the same amount of light from each of the different LEEs or by other means. 
     While the discussion in reference to  FIG. 13G  is for multiple or adjacent tile having the same LEE pitch, this is not a limitation of the present invention, and in other embodiments one or multiple or adjacent tile on one panel and/or one or multiple or adjacent tile on different panels may have a different LEE pitch and still exhibit the same or substantially the same light intensity per unit area, for example by adjusting the current through the LEEs such that LEEs having a first pitch have a light intensity per unit area that is the same or substantially the same as the light intensity per unit area of LEEs having a second pitch that are operating at a current different from that of the LEEs of the first pitch. 
       FIG. 13H  shows a schematic diagram of three tiles  1380 ,  1381 , and  1382  that may be used in lighting systems in accordance with various embodiments of the present invention. In various embodiments of the present invention, tiles  1380 ,  1381 , and  1382  may emit light with the same or substantially the same light intensity per unit area. In various embodiments of the present invention, LEEs  1385  may be the same on each tile  1380 ,  1381 , and  1382 ; however, this is not a limitation of the present invention, and in other embodiments different tile may utilize different LEEs, for example LEEs emitting a different light intensity level for a given current. 
     Referring to  FIG. 13H , tile  1380  has 3 LEEs  1385 , tile  1381  has 9 LEEs  1385 , and tile  1382  has 12 LEEs  1385 . LEEs  1385  are arranged in a periodic or substantially periodic array on tile  1380  (a 2×2 array of LEEs  1385 ) and on tile  1381  (a 3-3 array of LEEs  1385 ), while LEEs  1385  are arranged on tile  1382  in an irregular pattern. In various embodiments of the present invention, the current through LEEs  1385  on the different tiles may be adjusted so that the total light emitted from each tile is the same or substantially the same, thus resulting in the light intensity per tile (or per unit area of tile) being the same or substantially the same. The light output as a function of current is typically provided on specification sheets by the LEE manufacturers and may be validated by standard measurements known to those skilled in the art; thus, it is possible to determine the current required for each LEE  1385  to achieve the same light output per tile. For example, in various embodiments the light intensity may be linearly or substantially linearly proportional to the drive current over a particular region of operation of the LEE device (this is not an exact representation of every intensity-current relationship but is useful for illustrative purposes), and in this case if the light output of each LEE  1385  on tile  1380  is I, then the total light output of tile  1380  is 4I and the light output of tile  1381  may be made to have a value of 4I or substantially 4I by providing a current of (4/9)I to each LEE  1385  on tile  1381 . Similarly, the light output of tile  1382  may be made to have a value of 4 or substantially 4I by providing a current of (4/12)I to each LEE  1385  on tile  1382 . Thus, each tile  1380 ,  1381 , and  1382  has a light output of about 4I and as each tile  1380 ,  1381 , and  1382  has about the same area, the light intensity per unit area is substantially the same for each of tiles  1380 ,  1381 , and  1382 . 
     It should be noted that in various embodiments of the present invention a scale may be determined for evaluation of light intensity per unit area. In various embodiments of the present invention of lighting systems made up of scalable elements, for example sub-tiles, tiles, and panels, a useful unit area is that of the smallest sub-unit in the system. In various embodiments of the present invention, a useful unit area may be an integer multiple of the smallest sub-unit in the system. For example, in  FIG. 13H , each tile  1380 ,  1381 , and  1382  may represent the smallest sub-unit in a lighting system in accordance with elements of the present invention. Referring to  FIG. 6K , sub-tile  690  may represent the unit area for the lighting system of  FIG. 6K . Referring to  FIG. 6I , sub-tile  680  may represent the unit area for the lighting system of  FIG. 6I . Referring to  FIG. 12 , the lighting system of  FIG. 12  is composed of three panels  1210 ,  1210 ′, and  1210 ″, and each panel is composed of six tiles  610 . In various embodiments of the present invention, each tile  610  may be composed of sub-tiles, for example in  FIG. 12  tile  610 ′ is composed of twenty-five sub-tiles  620 , and thus a unit area for evaluation of the intensity per unit area of the lighting system of  FIG. 12  may be the area of sub-tile  620 . In various embodiments of the present invention, a larger unit area may be used for evaluation of the intensity per unit area of a lighting system; for example, in the lighting system of  FIG. 12  another possible unit area may be the area of tile  610  or the area of panel  1210 . 
       FIG. 14A  shows a flow chart of a process  1400  for forming a lighting system in accordance with various embodiments of the present invention. Process  1400  is shown having six steps; however, this is not a limitation of the present invention, and in other embodiments the invention has more or fewer steps and/or the steps may be performed in different order. In step  1402 , multiple tiles are provided. In step  1404 , at least two panels are provided. In step  1406 , two or more tiles are attached to each panel. In step  1408 , the tiles on each panel are electrically coupled together. In step  1410 , a power source for the lighting system is provided. In step  1412 , the panels are electrically coupled to the power source. 
     In various embodiments of the present invention, lighting systems composed of sub-tiles and/or tiles and/or panels may be configured with a diffuser to homogenize the light and significantly reduce or eliminate pixelization (i.e., eliminate the visualization or appearance of each individual LEE), resulting in a uniformly illuminated surface with relatively little visual variation in intensity across the diffuser. In various embodiments, the diffuser may be spaced apart from the LEEs to provide sufficient volume for mixing of the light to result in the uniform visual appearance. Referring to  FIG. 13I , the spacing or setback  1393  between diffuser  1390  and tile  1330  may be about 1 times the LEE spacing  1391 , or about 1.5 times the LEE spacing  1391 , or about 2 times the LEE spacing  1391 , or greater than about 2 times the LEE spacing  1391 . In various embodiments, it may be desirable to minimize the setback  1393  while maintaining the homogeneous light intensity beyond the diffuser, for example to minimize the size and weight of the lighting system or to achieve a specific aesthetic appearance of the lighting system. In various embodiments of the present invention, the unit area for determination of uniform intensity per unit area may be determined by the largest LEE spacing, for example referring to  FIG. 13G  the area encompassed by a length of 1350 and a width of  1364  (the lengths of the LEE pitch in orthogonal directions). In various embodiments of the present invention, the largest LEE pitch area may be used as the unit area for uniformity determination. In various embodiments of the present invention, different LEE pitches may be utilized on a sub-tile and/or a tile, and/or a panel. 
       FIG. 14B  shows a lighting system in accordance with embodiments of the present invention. As shown, the lighting system of  FIG. 14B  includes panels  1420  and  1420 ′, each panel including, consisting essentially of, or consisting of four light sheets or tiles  1430 , and in which the light sheets are electrically connected using power conductors  1440 ,  1440 ′, with connection points  1480  on each light sheet  1430 . In various embodiments, one or more tiles  1430  or panels  1420  may have a connection point or connector  1450  that is also electrically connected to power conductor  1440 ,  1440 ′ and which serves as a one-point connection for power and/or communication and/or control signals for all of the light sheets  1430  on the panel. In various embodiments, connection points or connectors  1450  may be positioned on one (or more) light sheets  1430 ; however, this is not a limitation of the present invention, and in other embodiments connection point or connector  1450  may be positioned on panel  1420 , for example on the side with light sheets  1430  or on the opposite side to provide back side electrical connection to panel  1420 . In various embodiments of the present invention, multiple panels  1420  may be electrically coupled from connection point or connector  1450  through a power/communication conductor  1470  (e.g., one or more wires or other electrical conductors) to power/control gear  1460 . In various embodiments power/control gear  1460  may include, consist essentially of, or consist of one or more of power supplies, drivers, control systems to set or modulate light intensity and/or color of the lighting system or other optical characteristics, timers or control systems to permit variation of optical characteristics of the lighting system in response to a time of day, a program, one or more sensors of the like, or systems for receiving information regarding the status, operational conditions, potential fault conditions or other aspects of the lighting system; however, these are not limitations of the present invention, and in other embodiments other control, power, or communication gear or systems may be incorporated into power/control gear  1460 . 
     In various embodiments, connection points  1480  on tiles  1430  may the different from connection points  1450  on panels  1420 . For example in various embodiments, connection points  1450  may be configured to carry a higher current level than connection points  1480  on tiles  1430 . In various embodiments of the present invention, a configuration to carry a higher current level may include having a lower resistance per unit length or a lower contact resistance, to reduce the voltage drop for a given current. For example, in various embodiments connection point  1450  on panels  1420  may be configured for a larger wire size (or smaller wire gauge (AWG)) than connection point  1480  on tiles  1430  to permit provision of higher currents with acceptable voltage drop to connection points  1450  compared to connection points  1480 . Similarly, in various embodiments of the present invention, conductor  1470  may have a larger diameter or larger cross-sectional area or lower resistance per unit length than conductor  1440 . In various embodiments of the present invention, connection points  1480  on tiles  1430  may be configured for lower cost and/or fewer mate/unmate operations, for example in various embodiments of the present invention tiles  1430  may be configured to be relatively permanently attached to panel  1420  and not designed to be individually replaced, while connection points  1450  may be configured for a higher level of mate/unmate operations because they would be the connection point to be removed and replaced if a failure on a panel were to occur. In various embodiments of the present invention, panels  1420  may be constructed in advance and large lighting systems may be constructed by assembling multiple panels  1420 . Such assembly is enabled to occur quickly and at low cost by the one point electrical connection system through connection point or connector  1450  and the reduction in the number of separate components that need to be handled at the assembly site by virtue of using pre-assembled panelized light sheets. 
     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, consists essentially of, or consists 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 “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. In some embodiments, an LEE may include, consist essentially of, or consist of an electronic device or circuit or a passive device or circuit. In some embodiments, an LEE includes, consists essentially of, or consists of multiple devices, for example an LED and a Zener diode for static-electricity protection. In some embodiments, an LEE may include, consist essentially of, or consist 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, consist essentially of, or consist of light emitted only by the light-conversion material, while in other embodiments the light from the LEE may include, consist essentially of, or consist 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, consist essentially of, or consist of light emitted only by an LED. 
     One or more non-LEE devices such as Zener diodes, transient voltage suppressors (TVSs), varistors, etc., may be placed on each light sheet to protect the LEEs  140  from damage that may be caused by high-voltage events, such as electrostatic discharge (ESD) or lightning strikes. In one embodiment, conductive trace segments shown in  FIG. 1B or 1C  between the LEE strings  150  may be used for placement of a single protection device per light sheet, where the device spans the positive and negative power traces, for example power conductors  120 , 121 . These trace segments also serve to provide a uniform visual pattern of lines in the web direction, which may be more aesthetically pleasing than a light sheet with noticeable gaps between LEE strings  150 . In a more general sense, in addition to conductive traces  160  that are part of string  150 , additional conductive traces  160  that may or may not be electrically coupled to other strings  150  and/or power conductors  120 , 121  may be formed on substrate  165 , for example to provide additional power conduction pathways or to achieve a decorative or aesthetically pleasing look to the pattern on the light sheet or to provide a communication pathway to one or more CEs  145 , for example to provide a control signal to the one or more CEs  145 . These trace segments also serve to provide a uniform visual pattern of lines in the web direction, which may be more aesthetically pleasing than a light sheet with noticeable gaps between LEE strings  150 . 
     In one embodiment, an LEE  140  includes, consists essentially of, or consists of a bare semiconductor die, while in other embodiments LEE  140  includes, consists essentially of, or consists of a packaged LED. 
     In various embodiments, an LEE  140  may include, consist essentially of, or consist 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. 
     In various embodiments, LEEs  140  may emit light in a relatively small wavelength range, for example having a full width at half maximum in the range of about 20 nm to about 200 nm. In various embodiments, all LEEs  140  may emit light of the same or substantially the same wavelength, while in other embodiments different LEEs  140  may emit light of different wavelengths. In various embodiments, LEEs  140  may emit white light, for example that is perceived as white light by the eye. In various embodiments, the white light may be visible light with a spectral power distribution the chromaticity of which is close to the blackbody locus in the CIE 1931 xy or similar color space. In various embodiments, white light has a color temperature in the range of about 2000 K to about 10,000 K. The emission wavelength, full width at half maximum (FWHM) of the emitted light or radiation or other optical characteristics of LEEs  140  may not be all the same and are not a limitation of the present invention. 
     Advantageously, embodiments of the present invention produce a light sheet  110  having controlled optical characteristics. In some embodiments of the present invention it is advantageous to have multiple light sheets, each of which as a similar CCT, preferably the average CCT of each light sheet during manufacture or use having a relatively narrow CCT distribution. One measure of white color temperature is defined as a MacAdam ellipse. A MacAdam ellipse represents a region of colors on a chromaticity chart, for example the CIE chromaticity diagram, and a one-step MacAdam ellipse represents the range of colors around the center of the ellipse that are indistinguishable to the average human eye, from the color at the center of the ellipse. The contour of a one-step MacAdam ellipse therefore represents barely noticeable differences of chromaticity. 
     Multiple-step MacAdam ellipses may be constructed that encompass larger ranges of color around the center point. While there are many recommendations as to how tight the color temperature uniformity should be (as measured by MacAdam ellipses or other units), a variation encompassed within a smaller step number of MacAdam ellipses (smaller ellipse) is more uniform than one encompassed within a larger step number of MacAdam ellipses (larger ellipse). For example, a four-step MacAdam ellipse encompasses about a 300K color temperature variation along the black body locus, centered at 3200K, while a two-step MacAdam ellipse encompasses about a 150K color temperature variation along the black body locus, centered at 3200K. 
     In various embodiments of the present invention, the variation in average CCT between different light sheets  110  is less than 4 MacAdam ellipses, or less than 3 MacAdam ellipses or less than 2 MacAdam ellipses. 
     Substrate  165  may include, consist essentially of, or consist of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, fiberglass, FR4, metal core printed circuit board, (MCPCB), and/or paper. Substrate  165  may include multiple layers, for example, a semicrystalline or amorphous material, e.g., PEN, PET, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper formed over a second substrate for example comprising, acrylic, aluminum, steel and the like. Depending upon the desired application for which embodiments of the invention are utilized, substrate  165  may be substantially optically transparent, translucent, or opaque. For example, substrate  165  may exhibit a transmittance or a reflectivity greater than 70% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. In some embodiments substrate  165  may exhibit a transmittance or a reflectivity of greater than 70% for one or more wavelengths emitted by LEEs  140 . Substrate  165  may also be substantially insulating, and may have an electrical resistivity greater than approximately 100 ohm-cm, greater than approximately 1×10 6  ohm-cm, or even greater than approximately 1×10 10  ohm-cm. In some embodiments, substrate  165  may have a thickness in the range of about 10 μm to about 500 μm. 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 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. 
     Conductive elements, e.g., power conductors  120 ,  121  and conductive traces  160 , may be formed via conventional deposition, photolithography, and etching processes, plating processes, lamination, lamination and patterning, evaporation sputtering or the like or may be formed using a variety of different printing processes. For example, power conductors  120 ,  121  and conductive traces  160  may be formed via screen printing, flexographic printing, ink-jet printing, and/or gravure printing. Power conductors  120 ,  121  and conductive traces  160  may include, consist essentially of, or consist of a conductive material (e.g., an ink or a metal, metal film or other conductive materials or the like), which may include one or more elements such as silver, gold, aluminum, chromium, copper, and/or carbon. Power conductors  120 ,  121  and conductive traces  160  may have a thickness in the range of about 50 nm to about 1000 μm. In some embodiments, the thickness of power conductors  120 ,  121  and conductive traces  160  may be determined by the current to be carried thereby. While the thickness of one or more of power conductors  120 ,  121  and conductive traces  160  may vary, the thickness is generally substantially uniform along the length of the trace to simplify processing. However, this is not a limitation of the present invention, and in other embodiments the thickness and/or material of power conductors  120 ,  121  and conductive traces  160  may vary. In some embodiments, all or a portion of power conductors  120 ,  121  and conductive traces  160  may be covered or encapsulated. In some embodiments, a layer of material, for example insulating material, may be formed over all or a portion of power conductors  120 ,  121  and conductive traces  160 . Such a material may include, e.g., a sheet of material such as used for substrate  165 , a printed layer, for example using screen, ink jet, stencil or other printing means, a laminated layer, or the like. Such a printed layer may include, for example, an ink, a plastic and oxide, or the like. The covering material and/or the method by which it is applied is not a limitation of the present invention. 
     In various embodiments of the present invention, all or a portion of substrate  165  and/or power conductors  120 ,  121  and conductive traces  160  may be covered by a layer having pre-determined optical properties. In various embodiments, the optical properties of substrate  165  or a coating material on substrate  165 , for example reflectance, transmittance and absorption, may be utilized to further control the optical characteristics of the lighting system. In various embodiments, substrate  165  or a coating on substrate  165  may be a diffuse reflector, while in other embodiments it may be a specular reflector, and in yet other embodiments it may be designed to have a relatively high absorbance for light emitted by LEEs  140 . In various embodiments of the present invention, substrate  165  may have a reflectance of at least 80% or at least 90% or at least 95% to a wavelength of light emitted by LEEs  140 . In various embodiments of the present invention, substrate  165  may be transparent or substantially transparent to a wavelength of light emitted by LEEs  140 , for example having a transmittance of at least 80% or at least 90% or at least 95% to a wavelength of light emitted by LEEs  140 . In various embodiments of the present invention, substrate  165  may be absorbing or substantially absorbing to a wavelength of light emitted by LEEs  140 , for example having an absorbance of at least 60% or at least 70% or at least 80% to a wavelength of light emitted by LEEs  140 . In various embodiments, substrate  165  or portions of substrate  165  may be configured to diffuse a wavelength of light emitted by LEEs  140 . In various embodiments, substrate  165  may have two or more regions, where different regions have different optical characteristics. In various embodiments, the transmittance of a diffuse region is at least 50%, or at least 70% or at least 80%, or at least 90% to a wavelength of light emitted by LEEs  140 . The remaining portion of substrate  165  in some embodiments has a reflecting surface, i.e., it is reflecting to a wavelength of light emitted by LEEs  140 . 
     In various embodiments, conductive traces  160  are formed with a gap between adjacent conductive traces  160 , and LEEs  140  and CEs  145  are electrically coupled to conductive traces  160  using conductive adhesive, e.g., an isotropically conductive adhesive and/or an ACA, as described in U.S. Pat. No. 8,384,121, filed on Jun. 29, 2011, the entire disclosure of which is incorporated herein by reference. ACAs may be utilized with or without stud bumps and embodiments of the present invention are not limited by the particular mode of operation of the ACA. For example, the ACA may utilize a magnetic field rather than pressure (e.g., the ZTACH ACA available from SunRay Scientific of Mt. Laurel, N.J., for which a magnetic field is applied during curing in order to align magnetic conductive particles to form electrically conductive “columns” in the desired conduction direction). Furthermore, various embodiments utilize one or more other electrically conductive adhesives, e.g., isotropically conductive adhesives, non-conductive adhesives, in addition to or instead of one or more ACAs. In other embodiments, LEEs  140  and CEs  145  may be attached to and/or electrically coupled to conductive traces  160  by other means, for example solder, reflow solder, wave solder, wire bonding, or the like. The method by which LEEs  140  and CEs  145  are attached to conductive traces  160  is not a limitation of the present invention. 
     CE  145  may be one component or multiple active and/or passive components. In one embodiment, power conductors  120 , 121  provide a DC voltage or substantially DC voltage and CE  145  includes, consists essentially of, or consists of a resistor, e.g. a current-limiting resistor. The choice of the resistance value may be a trade-off between a number of parameters and characteristics that may include, e.g., efficiency and current stability. In general, a larger resistance will result in reduced efficiency but greater current stability, while a smaller resistance will result in increased efficiency but reduced current stability. Variations in the current may result from variations in the input voltage (for example across power conductors  120 ,  121 ), variations in forward voltage of the LEEs  140  within the string, variations in the value of the current-limiting resistor, variations in current that may occur if one or more LEEs  140  in the string become short-circuited or the like. In the case of CE  145  including, consisting essentially of, or consisting of a resistor, in some embodiments CE  145  is a discrete resistor formed within or on conductive traces  160 , such as a chip resistor, a bare-die resistor or surface mount device (SMD) resistor. 
     As discussed above, in embodiments where CE  145  includes, consists essentially of, or consists of a resistor, there may be trade-offs between efficiency and current stability. While such trade-offs may be acceptable in certain products, other products may require relatively better current stability at higher efficiencies, and in these cases CE  145  may include, consist essentially of, or consist of multiple components or a circuit element, as discussed above. In various embodiments CE  145  includes, consists essentially of, or consists of a field-effect transistor (FET) and a resistor. In various embodiments CE  145  includes, consists essentially of, or consists of two bipolarjunction transistors (BJTs) and two resistors. 
     In various embodiments, the efficiency and current stability increase with the number of components, as does the cost. In some embodiments where CE  145  includes, consists essentially of, or consists of multiple components, the components may be in discrete form (i.e., each component individually electrically coupled to conductive traces  160 ) or in hybrid form (where multiple separate components are mounted on a submount, which is then electrically coupled to conductive traces  160 ), or in monolithic form (where multiple components are integrated on a semiconductor chip, for example a silicon-based or other semiconductor-based integrated circuit). In various embodiments, CE  145  may be in bare-die form, while in other embodiments CE  145  may be packaged or potted or the like. In some embodiments, CE  145  may include, consist essentially of, or consist of a bare-die integrated circuit. In some embodiments, the integrated circuit includes, consists essentially of, or consists of multiple active and/or passive devices that are fabricated on a common semiconductor substrate. 
     In various embodiments, power conductors  120 ,  121  may provide AC power, or power modulated at different frequencies and in these embodiments CEs  145  may be selected accordingly or may be omitted. In one embodiment, power conductors  120 ,  121  may provide a standard line voltage, for example about 120 VAC or about 240 VAC or about 277 VAC, for example at about 50 Hz or about 60 Hz. In various embodiments, CEs  145  may accommodate a plurality of input types, and thus be so-called “universal” CEs  145 , while in other embodiments different CEs  145  may be required for different input types. The actual component or components of CEs  145  are not limiting to this invention; however, in preferred embodiments of this invention, the positioning of CEs  145  does not disrupt the LEE pitch. In various embodiments of this invention, the positioning of CEs  145  is independent of LEE pitch. As discussed herein, CEs  145  and LEEs  140  may be electrically coupled to conductive traces  160  using a variety of means, for example solder, conductive adhesive or anisotropic conductive adhesive (ACA); however, the method of electrical coupling of CEs  145  and LEEs  140  is not a limitation of the present invention. 
     In general in the above discussion the arrays of semiconductor dies, light emitting elements, optics, and the like have been shown as square or rectangular arrays, however this is not a limitation of the present invention and in other embodiments these elements may be formed in other types of arrays, for example hexagonal, triangular or any arbitrary array. In some embodiments these elements may be grouped into different types of arrays on a single substrate. 
     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.