Patent Publication Number: US-10309627-B2

Title: Light fixture retrofit kit with integrated light bar

Description:
The present application is continuation-in-part of, and claims the benefit of, U.S. patent application Ser. No. 13/672,592, entitled “Recessed Light Fixture Retrofit Kit, and filed on Nov. 8, 2012 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to retrofit systems and methods for lighting installations, and in particular, to retrofit systems and methods used to retrofit troffer-style lighting installations with LED light sources. 
     Description of the Related Art 
     Troffer-style fixtures are ubiquitous in commercial office and industrial spaces throughout the world. In many instances these troffers house elongated tubular fluorescent lamps or light bulbs that span the length of the troffer. Troffers may be mounted to or suspended from ceilings, such as being suspended by a “T-grid”. Often the troffer may be recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. Typically, elements of the troffer on the back side dissipate heat generated by the light source into the plenum where air can be circulated to facilitate the cooling mechanism. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures. 
     More recently, with the advent of the efficient solid state lighting sources, these troffers have been used with LEDs as their light source. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED. 
     LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. Current fluorescent lamp technology can exhibit low efficacy, short lifetime, and can use hazardous materials such as mercury which makes the lamps hard to dispose. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy. 
     In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs are attractive to many lighting suppliers and have resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving. 
     There has been recent interest in upgrading existing troffer style lighting systems with LED sources (or engines) to capitalize on the above advantages. Current options for upgrading include complete fixture replacement such as by the commercially available CR Series Architectural LED Troffer, provided by Cree, Inc. Some features of these troffers are described in U.S. patent application Ser. No. 12/873,303, titled “Troffer-style Fixture”, and assigned to Cree, Inc. Performing complete fixture replacement can require penetrating the ceiling plenum by a skilled technician. This can be time consuming and expensive, and in many locations, building codes can require that a licensed electrician perform any work in the plenum space above a ceiling. 
     SUMMARY OF THE INVENTION 
     Some embodiments of the present invention comprise a mechanical mounting system for installing an LED light engine, light source or light bar within an existing lighting system housing or pan, such as a troffer pan, without penetrating the ceiling plenum. Other embodiments of the present invention comprise light bars that are arranged for some of the features to be self-mounting. That is, they have features that allow for mounting to one another without the need for mounting mechanisms such as screws, rivets or brackets, or materials such as adhesives. Other embodiments provide mechanisms for allowing the light bars to be movably mounted in a light fixture housing. The light bars can then be moved on the housing to obtain the desired emission before permanently affixing the light bars in place. 
     One embodiment of a system for mounting a light source in a fixture comprises a solid state light source bar and mounting clips slidably mounted to said light source bar. The light source bar is arranged so that it can be movably mounted to a light fixture housing. A power supply is included for providing a drive signal compatible with solid state light sources. 
     One embodiment of a light bar according to the present invention comprises an elongated base and an elongated solid state light source on the elongated base. An elongated lens is included with the base and the lens comprising features to allow for self-mounting of the lens to the base. The elongated light source can be held in place by the lens and base. 
     One embodiment of a system for mounting an LED light source in a light fixture comprises a power supply capable of receiving a line voltage and generating a signal to drive LEDs. A LED light bar is included having a plurality of LEDs to accept an electrical signal from said power supply to illuminate the LEDs, wherein the light bar has a magnet for non-permanent and movable mounting of said light bar to a light fixture housing. 
     These and other further features and advantages of the invention would be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary lighting fixture to be retrofitted according to the present disclosure; 
         FIG. 2  is a perspective view of a lighting fixture with the raceway cover removed according to the present disclosure; 
         FIG. 3  is a top view of one embodiment of retrofit components according to the present disclosure; 
         FIG. 4 a    is a perspective view of the fixture of  FIG. 2  with one embodiment of mounting brackets in place according to the present disclosure; 
         FIG. 4 b    is a closer view of a portion of  FIG. 4 a    with the one embodiment of power supplies removed for ease of viewability according to the present disclosure; 
         FIG. 4 c    is a closer view of a portion of  FIG. 4 a    according to the present disclosure; 
         FIG. 5  is a perspective view of a light fixture during the retrofit process with one embodiment light source bars engaged according to the present disclosure; 
         FIG. 6  is a closer view of a portion of  FIG. 5  according to one embodiment of the present disclosure; 
         FIG. 7  is a perspective partial view of a retrofitted fixture after the raceway cover has been replaced in one embodiment according to the present disclosure; 
         FIG. 8  is a perspective full view of the fixture of  FIG. 7  according to the present disclosure; 
         FIG. 9  is a side cross section perspective view of one embodiment of a light source bar according to the present disclosure; 
         FIG. 10 a    is a side cross section view of another embodiment of a light source bar according to the present disclosure; 
         FIG. 10 b    is a side cross section view of another embodiment of a light source bar according to the present disclosure; 
         FIG. 11  is a perspective view of one embodiment of lighting retrofit system according to the present invention; 
         FIG. 12  is a perspective exploded view of one embodiment of a light source bar according to the present invention; 
         FIG. 13  is a sectional view of one embodiment of a light source bar according to the present invention; 
         FIG. 14  is an end view the light source bar shown in  FIG. 13 ; 
         FIG. 15  is a perspective exploded view of one embodiment of a power supply according to the present invention; 
         FIG. 16  is an end view of the power supply shown in  FIG. 15 ; 
         FIG. 17  is a section view of a troffer light fixture with one embodiment of a power supply according to the present invention; 
         FIG. 18  is a section view of another troffer light fixture with one embodiment of a power supply according to the present invention; 
         FIG. 19  is a section view of still another troffer light fixture with one embodiment of a power supply according to the present invention; 
         FIG. 20  is a schematic of one embodiment of a power supply driver board according to the present invention; 
         FIG. 21  is top view of one embodiment of light sources according to the present invention; 
         FIG. 22  is a schematic showing one embodiment of the interconnections of the LED is the light sources of  FIG. 21 ; 
         FIG. 23  is a sectional view of another embodiment of a light source bar according to the present invention; 
         FIG. 24  is a sectional view of another embodiment of a light source bar according to the present invention; and 
         FIG. 25  is a sectional view of still another embodiment of a light source bar according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention provide retrofit systems that can be used with different light fixtures, but that are particularly adapted for use with troffer-style fixtures. These retrofit systems can provide the same amount of light as traditional light fixtures, for example 1600-4000 lumens and above. The retrofit systems can be also used with many different light sources but are particularly well-suited for use with solid state light sources or light engines, such as those utilizing LEDs. The LED light engines can have an elongated form, similar to fluorescent light sources, and can comprise a generally linear array of LEDs. These LED light engines can be referred to herein as a “light source bar” or “light bar”. Some embodiments of the present invention comprise a mechanical mounting system for installing an LED light engine within an existing lighting system housing or pan, such as a troffer pan, without penetrating the ceiling plenum. 
     By leaving the existing troffer pan in place, embodiments of the present invention can rely on the troffer pan to act as a barrier against the spread of fire and smoke. In many areas, local codes may not allow for the use of plastic components inside the plenum space above the ceiling. This is due to concerns that if a fire occurred in one room, toxic smoke from burning plastics could be carried to other locations which share the air plenum. Maintaining the host fixture&#39;s troffer pan as a barrier to this spread of toxic smoke can allow for the use of lower cost plastic parts above the ceiling line in the troffer pan. Without the troffer pan barrier, these plastic parts might otherwise not be allowed in the plenum space. 
     During the upgrade process, contamination may also be a concern, particularly in a hospital or clean room environment. In upgrade processes where the entire fixture is replaced, the sheet metal pan or housing of an existing troffer lighting system is removed. Removing the “host fixture” pan can generate dust which must be contained, and the surrounding area must be cleaned prior to resuming normal operations within the environment. Preventing dust is of particular concern in the case of dust containing dangerous materials such as asbestos. In certain environments, construction permits may be required for an upgrade process that requires removal of the troffer pan, which can add additional complications and costs. 
     Another alternative upgrade option is by a fixture retrofit where a new LED based light engine or light source bar can be installed into the sheet metal pan of an existing troffer lighting system. This can provide the advantage of using light bars with design features such as reflectors, lenses, and power supplies which have been optimized for an LED-based system. It also allows light bars which are approved for use in other applications to be used in a retrofit application. Some retrofits can provide the advantage of not removing the existing troffer pan, with the pan acting as a barrier to the above-ceiling plenum space. Leaving the pan intact during the retrofit process does not disturb wiring connections, insulation, etc., found in the plenum space. Leaving the pan in place may also allow for work to be performed by non-licensed personal, which can result in a significant cost savings over work performed by licensed electricians. 
     Many upgrades involve replacing the fluorescent light bulbs/tubes with replacement tubes having LEDs along their length. This upgrade can fit existing fluorescent lamp fixtures and can rely on the fixture&#39;s electrical ballast and wiring. However, compared to light engines designed to capitalize on the characteristics of LEDs, these replacement lamps may utilize much more energy for a given light output (lower efficacy), and can provide little or no cost benefit. Furthermore, these upgrades require costly interface connectors to connect to the existing tombstone connections, and older fixtures may have significantly weakened tombstones. In addition, the retrofitter can be forced to rely upon the mechanical and electrical reliability of the original manufacturer and fixture. 
     The present invention is described herein with reference to certain embodiments, but it is understood that the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In particular, the present invention is described below in regards to certain retrofit systems that can be used to retrofit and/or upgrade troffer-style fixtures or lighting systems, but it is understood that the system can be used to retrofit and/or upgrade different types of lighting systems. The retrofit systems can also be used with many different light systems, sources and engines beyond those described herein, with many being LED based. 
     It is understood that when an element can be referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as “inner”, “outer”, “upper”, “above”, “lower”, “beneath”, and “below”, and similar terms, may be used herein to describe a relationship of one element to another. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     Although the ordinal, terms first, second, etc., may be used herein to describe various elements, components, regions and/or sections, these elements, components, regions, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, or section from another. Thus, unless expressly stated otherwise, a first element, component, region, or section discussed below could be termed a second element, component, region, or section without departing from the teachings of the present invention. 
     As used herein, the term “light source”, “LED” and “LED component” can be used to indicate a single light emitter or more than one light emitter functioning as a single source. For example, the term may be used to describe a single blue LED, or it may be used to describe a red LED and a green LED in proximity emitting as a single source. Thus, these terms should not be construed as a limitation indicating either a single-element or a multi-element configuration unless clearly stated otherwise. 
     Embodiments of the invention are described herein with reference to cross-sectional view illustrations that are schematic illustrations. As such, the actual thickness of elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Thus, the elements illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention. 
     As mentioned above, embodiments of the present invention can comprise a mechanical mounting system for installing an LED light engine or light bar within an existing lighting system pan, such as the opening of a troffer pan, without penetrating the ceiling plenum. The light bar can be provided with mounting features that quickly and easily engages the troffer pan. In some embodiments, these mounting features can comprise a mount bracket or mounting clips and different mount features can be arranged in different ways. Some can be provided as a single piece adaptor, and others being provided as a multiple piece adaptor. Additionally, mounting brackets may be provided with guides or other devices that allow for consistent and error free placement of the mounting bracket during the retrofit process. 
     In some configurations, the mount bracket may be a multi-function piece of equipment, which serves to correctly orient and space the light bars, hold the light bars in place, and provide a wiring path from the light bars to the power supply, both hiding the wiring and providing desired spacing or enclosures for electrical ratings, such as high voltage regulatory requirements. Initial installation of the mounting bracket may incorporate the use of a temporary holding mechanism to hold the bracket in place until further along in the process when the mounting bracket is secured in place. 
     In one exemplary retrofit system, the ballast or raceway cover of the original system is temporarily removed to begin the retrofit. Once the raceway or ballast cover is removed, mounting brackets may be placed within the troffer pan. The brackets may be shaped or sized to only fit in the proper installation location, or other types of markers or guides can be used to insure that the brackets are always consistently and correctly placed. Once the mounting bracket is placed in the correct location, and possibly temporarily fastened in place, light bars and wiring can be manipulated in place on the bracket. 
     If required, a new power supply may be placed in place of or adjacent to the existing power supply, under the raceway or ballast area, under its cover. In some configurations, the power supply may be designed to interface with existing fixture fastening features for ease of installation, such as holes, flanges, and cutouts. The power supply is responsible for delivering the electrical voltage and current to the light source bars. The power supply can receive line voltage from the fixture input (bypassing the existing ballast), for example 120 VAC. Wiring for this power supply may then be passed through a wire routing path in the mounting bracket between the light source and the power supply. This wire routing path may include a separate cover which can be put in place over the wires or a portion of the bracket itself may be used to cover the path, such as a living hinge cover of the wire path. 
     The mounting bracket may include features to receive and fasten light source bars. Light source bars may be fastened into place on the bracket using a variety of suitable methods, such as but not limited to snap fit, screws, adhesive, twist, interference fit, or press fit. Mounting brackets may be placed at each end of the troffer pan, additional mounting brackets may be included, or any other configuration of mounting brackets may be used. 
     The light source bars may be any appropriate light source which can be retrofitted in place of a fluorescent light bar. The light source in some configurations may be a plurality of LEDs or other solid state light chips spaced across a circuit board, such as a PCB which may be rigid or flexible. This circuit board with LEDs may be placed within a cover or other holding device. The LEDs may be in series or parallel or a combination of both. Also, the light source may include power supply components or circuitry, or this circuitry may be located separate from the light sources. The light sources may also include a heat sink; however, in configurations where high efficiency LEDs are used a heat sink may not be necessary as the traces on the PCB may be enough to dissipate heat. Previously, light source bars did not use heat sinks which resulted in light source failure. As heat sink and light source technology has matured, heat sinks now are used and required in all applications. Though, traditionally, heat sinks are required for adequate heat dissipation, it is possible in configurations of the light bars to exclude a heat sink and provide sufficient heat dissipation by only using the traces on the circuit board. Inclusion of a heat sink involves the added cost and manufacturing allowances for a heat sink. The light bars of the current disclosure, which do not require a heat sink, allow the light bars to be more efficient in terms of cost and manufacturing. 
     In some configurations, the light source bars includes a housing. This housing may include a cover over the LEDs. This cover may be translucent and in some configurations include a diffuser to provide a more uniform appearance of the light source. The housing includes a mechanism to hold the PCB in place, such as a snap fit, adhesive, a slide in channel, heat stake, vibration weld, sonic weld, or any other suitable mechanism. The housing may also include features to secure the light source bar to the mounting bracket. The housing provides a rigid form for the light source. Each light source bar may be one rigid piece or multiple rigid sections. Additionally, one light source bar may span an entire troffer pan or multiple portions may be strung together. The housing portion may include optional end caps for closing off or sealing each light source. 
     Each light source bar is connected to a power supply, directly or via another light source bar. This power supply is responsible for delivering electrical voltage and current to the light source and receives line voltage from the light fixture input. Though each light source may include power supply components, in some configurations, the power supply is separate from the light sources and fits inside the existing fixtures ballast or raceway cover. In some embodiments, the power supply may be designed to interface with the existing fixture fastening features for power supplies, such as holes, flanges and cutouts. In other configurations, the power supply can be fastened with other attachment methods. This power supply may replace the original power supply or simply be installed adjacent to it. 
     The retrofit systems according to the present invention can convert existing fluorescent fixtures, such as troffer fixtures, into long lasting LED luminaries. By using LED based light sources the cost of the retrofit can be paid back by cost saving from operating efficiency in a relatively short amount of time. The systems can use LED based light sources that offer high efficacy light with excellent color, long lifetime and improved performance. This systems can fit into common lensed and parabolic troffers, wraps, linears and other fixtures where linear fluorescent lamps are currently used. The systems are easy to install with little or no modification to the existing fixture. The upgrade systems can be very easy to install and do not rely on the lamp holders for installation. 
     In some embodiments the retrofit systems can comprise light bars having a metal/plastic base that can provide rigidity and is arranged to anchor the LED based light source between a lens and the base without the need for permanent mounting elements or materials such as screws, rivets, brackets or adhesives. The base can comprise a channel or opening along its length to provide space for the connectors behind the LED light source and for wires to pass. In some embodiments, the connectors are placed behind the LED board so that they do not cast shadows in the light path. This helps the light bar to provide uniform light emission along its length. 
     In some embodiment, the lens can clip onto the base and sandwich the LED light source between the two. End caps can be included on the light bars that allow for the connectors to be accessible to the installer and easily connect to the power supply. Mounting clips can be included on the base that allow for temporary placement and alignment of the light bars within the troffer. The light bars can then be permanently mounted to the troffer, such as by metal screws. The mounting clips can be arranged to slide along the metal extrusion and can be moved to desired location. This can allow for the metal clips to avoid any obstructing features within the troffer and can allow for the light bars to be compatible with a wide variety of fixtures. The systems according to the present invention can comprise a power supply that is designed to fit into the existing enclosures in troffers, with output connectors that can be easily plugged into the light bars. The upgrade/retrofit systems according to the present invention can be used in a wide variety of applications where current fluorescent lamps such as convention T8 or T12 lamps are used, and the systems can be used to retrofit different sizes of fixtures such as 2 feet and 4 feet fixtures. 
       FIGS. 1 and 2  show an existing light fixture with the legacy light engine removed, for example fluorescent light bulbs. The existing light fixture includes a troffer pan  10  and a ballast or raceway cover  12 . The legacy tombstone connections  14  can be seen at the top and bottom of the troffer pan  10 . The first step in retrofitting the troffer pan  10  with the new light engine or light bar begins with removing the raceway cover  12 , as shown in  FIG. 2 . The legacy power supply components  16  and associated wiring can be found under the raceway cover  12 . Following this step, the components of the retrofit light engine can be installed. 
       FIG. 3  shows exemplary components of a retrofit light engine of one configuration, such as light source bars  32 , mounting brackets  34 , and a power supply  36 . A new power supply  36 , which is more suitable for the retrofit system may be installed in place or in addition to the existing power supply  16 , shown in  FIG. 1 . In other configurations, the existing power supply  16  may be used for the retrofit system as well. In yet other configurations, the power supply components may be placed in the light source bars themselves. In another configuration, additional power supplies may be used for 2 or more light bars. 
       FIGS. 4 a -4 c    show the next step of the retrofit process which entails the installation of the mounting brackets  42  in the troffer pan  40 . This configuration shows both the new power supply  44  and legacy power supply  46  in place within the troffer pan  40 . The mounting brackets  42  may be made of any suitable material including plastics or metals. These may be manufactured using an extrusion and post processing method or any other suitable method (injection molding). Although only two mounting brackets  42  are shown in the figures, any number of them may be used in any location. Generally, at least two mounting brackets  42  will be used, with the first two being located proximate to the edges or ends of the troffer pan  40 . The mounting brackets  42  are multi-functional brackets as they serve to fix the light source bars in place, insure that the light source bars are oriented correctly, and also provide a wiring path for connecting the light source bars to power. 
     Considering that most retrofittings would occur while a light fixture is already installed in a ceiling, it is beneficial to provide features which make the retrofit process easier and as close to error free as possible, while working with a fixture that is overhead and cannot be manipulated. Therefore, in some configurations, the mounting brackets  42  will include guides or guiding features (not shown) to allow for consistent and error free mounting within the troffer pan  40 . Such guides or guide features may include shaping which prevents the mounting brackets from being mounted in a location other than the correct location. In another embodiment, the guide features may include extensions such as markers which can come in contact with the edges of the troffer pan and provide accurate orientation of the mounting brackets in relation to the troffer pan. In yet another embodiment, an installer may use marks or features of the troffer pan itself (or mounting brackets) to correctly orient and mount the mounting brackets. 
     Some configurations may include a temporary fastener to the troffer pan  40  to facilitate installation of the mounting brackets  42 . A temporary fastener may be a pressure sensitive fastener, such as an adhesive, or any other suitable temporary fastening mechanism such as screws, press fit, snap fit, twist, or interference fit. This would allow the installer to place the mounting bracket in the correct location and continue with the retrofit process without having to hold the mounting bracket in place until the mounting bracket can be fully secured. 
       FIGS. 4 b  and 4 c    show closer images of the mounting bracket  42  in place but not finally secured. As shown, the mounting bracket  42  extends across the troffer pan  40 , such that a portion of the mounting bracket  42  would be under the raceway cover when the raceway cover is reinstalled. In this configuration, the raceway cover would hold and secure the mounting bracket  42  in place (and relieve the temporary fastening mechanism of reliable mounting). The mounting bracket includes a ballast or raceway cover stand-off portion  48 , to space the raceway cover from the mounting bracket slightly, allowing wires to pass under the raceway cover to the wire path  49  without being pinched or chaffed. In other configurations other suitable methods may be used to prevent pinching of the wires, such as indentations in the mounting bracket. 
     Moving outward from the center of the mounting bracket  42 , past the wire path  49  is the light source bar mounting or engaging portion  46 . This area  46  is where light source bars engage or mount to the mounting bracket  42 . The mounting bracket  42  includes features to interface with the light source bar. In some configurations, the light source bars snap into place in the engaging portion  46 . However, in other configurations, the light source bar may be fastened using other mechanisms, such as press fit, screws, twist fit, adhesives, interference fit, or any other suitable fastening mechanism. In retrofits which have multiple light source bars, the mounting bracket may have predefined interface locations so the installer can position them correctly. 
     As can be seen in the troffer pans  50 ,  60  shown in  FIGS. 5 and 6 , the wires  54 ,  64  from a power supply  56  are passed through a wire path  66  of mounting brackets  52 ,  62  to light source bars  58 ,  68 . The wire path  66  provides an enclosure to both protect and hide the wiring, although neither may be necessary. Wire protection may prevent the wires from being cut, damaged, or otherwise harmed, as they may be when exposed. The wire path includes a way to provide access to pass the wires. Access to the wire path  66  may be provided by a hinged or removable portion. In  FIG. 4 c    the wire path is shown with the hinged or removable portion in place and therefore the wire path  49  is enclosed. In  FIG. 6  the wire path  66  is shown open with a hinged portion. This hinged portion may be constructed using a living hinge. A living hinge is preferable as it mitigates the need for a separate cover. (other hinges can also be used) Other embodiments may use a removable portion which could be a secondary snap cover or a cam in place cover. 
     Next, referring to  FIGS. 7 and 8 , after the mounting brackets  72 , optional power supply, light source bars  78  and wiring are in place, the ballast or raceway cover  74  may be reinstalled in its original position in the troffer pan  70 , now over and securing the mounting brackets  72 . The retrofit is complete at this stage. 
     The light source bars may be configured and constructed in a variety of manners.  FIGS. 9-10   b  show some configurations of light source bars and light source bar housings. Light source bar  90 ,  100  may include several components such as a housing  96 , circuit board  92 , and light source chips or LEDs  94 . Generally, the LEDs are spaced uniformly across the circuit board to provide uniform lighting; however, they may be placed or spaced in any way preferred for a particular lighting application. The housing  96  may include several portions as well, such as a translucent or diffuse top portion, which functions to both protect the LEDs and as a lens. A lens is not required and can be omitted in some configurations. The housing can be a single extrusion or can include multiple portions. It is only required that the areas through which light will be omitted be clear or diffuse; however, to simplify manufacturing the entire housing may be clear or diffuse. 
     The housing may also include holding features  98  to keep the circuit board  92  in place. The holding feature  98  may be advantageous in some configurations because it can also function to hold in place reflective layers or coatings on the circuit board which may come loose when the adhesive used to apply the layer fails. Holding features  98  may also be coextruded in a reflective white material to replace an often used reflective film. Some light source bars, such as the one shown in  FIG. 10 a   , may also include a heat sink  99 . However, as discussed previously it is possible, and may be advantageous, to omit the heat sink  99  in some configurations, using alternate methods to dissipate heat, such as the traces on the circuit board. 
     The circuit board  92  may be any suitable circuit board including those that are rigid or flexible. In the configuration shown in  FIGS. 9 and 10   b , the circuit board  92  is pivoted into place, or one may cam in the circuit board  92   a  and then snap it in place. The housing  96  should be at least in part rigid to support the circuit board and to aid in mounting and holding in place the light source bar  90 . The entire light source bar  90  may be a single rigid portion, or it may comprise of multiple rigid portions. 
     The light source bar  90 ,  100 , or housing portion of the light source bar  90 , includes features to engage it with the mounting bracket. These features may include screws, adhesives, twist fit, press fit, interference fit or snap fit features. In the configuration shown in  FIGS. 9 and 10   b , features to provide a snap fit  95  are shown. However, it will be understood that any appropriate engaging feature may be used. These engagement features may run across the entire length of the light source bar  90  or may only exist in designated portions which are known to possibly engage with a mounting bracket, such as the ends and in some cases intervening sections. Though not shown, the light source bar  90  may also include an end cap which includes features  95  to engage the light source bar. In some cases, multiple light source bars may be strung together across one troffer pan. 
     Different embodiments of the present invention can be arranged in many different ways and with many different features, and can be utilized in many different light fixtures. The light engines or light bars can utilize many different mounting mechanisms beyond those described above, and can comprise power supplies arranged in different ways.  FIG. 11  shows another embodiment of a system  120  for mounting LED based light engines or light bars in a light fixture such as a troffer pan, and FIGS.  12 - 14  show one embodiment of a light bar  122  that can be used in the systems according to the present invention. The system  120  can be used when retrofitting an existing troffer-type luminaire or when installing new troffer-type luminairs. The system  120  comprises one or more light bars  122  and a power supply  124 , with the power supply  124  arranged to provide an electrical signal to the light bars  122  causing them to emit light. It is understood that other systems according to the present invention can have more or fewer than two light bars, and can comprise more than one power supply. 
     Referring now to  FIG. 11  in conjunction with  FIG. 12-14 , each light bar  122  can be arranged to allow for convenient placement and mounting in light fixture (i.e. troffer pan), with some embodiments not utilizing mounting brackets as described above and shown in  FIGS. 3 and 4   a - 4   c . It is understood, however, that some embodiments can be used in combination with the mounting brackets described above. In the embodiment shown, each light bar  122  can comprise an elongated base  126 , an elongated lens  128 , and elongated light source  130 , and mounting clips  132 , all described in more detail below. End caps  134  can also be mounted at each end of the light bar  122  to protect its internal components. 
     The base  126  can be made of many different rigid materials, such as metal or plastic, and can be fabricated in many different ways. In some embodiments, the base  126  can comprise aluminum and can be fabricated using known extrusion methods. The base  126  can serve as the central mechanical mount or feature of the light bar, and in the embodiment shown, most of the remaining light bar elements can be mounted to the base  126  without mounting elements such as screws, rivets, brackets or adhesives as further described below. It is understood, however, that in other embodiments these mounting mechanisms can be used. The base can have openings or channels that reduce the amount of material necessary to form the base and also allow for formation of certain mounting features as described below, as well as passageways for the light source connector and connection wires. 
     The lens  128  can be made of many different materials and can be fabricated in many different ways. In some embodiments, the lens  128  can be made of a material that transmits the light from the light source  130 , while at the same time being UV stable to avoid yellowing over time. The lens  128  can comprise many different commercially available materials, such as commercially available plastics, and can be formed using known extrusion processes. The lens  128  can also comprise dispersing materials or other features to help mix light from the light source  130 . In the embodiment shown, the lens  128  has a top portion  128   a  with a substantially hemispheric cross-section, and a bottom portion  128   b  with features that allow for the lens  128  to cooperate with the base  126  so that it can be mounted to the base  126  without the use of mounting mechanisms or materials. The bottom portion of the lens  128  has two inward and opposing lens flanges  135 , and base  126  has two outward facing base flanges  136 . The lens  128  can be held in place to the base  126  by the overlapping of the lens and base flanges  135 ,  136 . 
     The light source  130  can be arranged in many different ways and can comprise many different light sources. In the embodiment shown, the light source  130  comprises LEDs  138  mounted on a PCB/submount  140  having conductive traces or wire bonds to interconnect the LEDs  138 . In submount embodiments, the submount can comprise sapphire, ceramic or silicon or any other suitable material, such as T-Clad thermal clad insulated substrate material, available from The Bergquist Company of Chanhassen, Minn. For PCB embodiments different PCB types can be used such as standard FR-4 PCB, metal core PCB, or any other type of printed circuit board. It is further understood that the PCB/submount can comprise many other elements made of different materials. In some embodiments it can comprise a reflective element made of a material that reflects or disperses light from the LEDs. In some embodiments this reflective element can be made of different material including plastics, various polymers, polycarbonates or combinations thereof. In some embodiments it can be reflective white material. In still other embodiments it can comprise a material with a layer of white or specular reflecting materials. Is these different reflective element embodiments, the LEDs can be interconnected in different ways such as by Copper Wire/Rails, magnet wire (e.g. copper wire coated with an insulator such as enamel), flex circuit, flattened braided wire, conductive foil, or a plastic or other non-conductive material selectively coated with a conductive material. The LEDs can be mounted to these different interconnections using different materials such as conductive Adhesives, low temperature solder, sonic/vibration welding, or conventional soldering. 
     The LEDs  138  can comprise many different LEDs, or LED components/packages such as those commercially available from Cree, Inc., including but not limited to the XLampCX, XLampM and XLampX family of LED packages. Embodiments having LEDs can comprise many different LEDs commercially available from Cree Inc., under its DA, EZ, MB, RT, TR, UT and XT families of LED chips. In the embodiment shown, the LEDs can comprise LED components described in U.S. patent application Ser. No. 13/649,052, entitled “LED Package With Encapsulant Having Planar Surfaces,” and U.S. patent application Ser. No. 13/649,067, entitled “LED Package With Multiple Element Light Source and Encapsulant Having Planar Surfaces,” both of which are assigned to Cree, Inc., and both of which are incorporated herein by reference. 
     The light source  130  can be mounted within the light bar  122  in many different ways, and in some embodiments can be mounted in place without the use of permanent mechanical mounting devices such as screws and rivet, or without the need for adhesives. In some embodiments, the light source  130  can be held in place by other elements of the light bar. In light bar  122 , the base can comprise an inner shelf  142 , with the light source  130  positioned on the shelf  142 . The lens  128  can comprise inner tabs  144  that extend from the inner surface of the lens  128  toward to light source  130 . When the lens  128  is mounted to the base  126 , the tabs  144  contact the top surface of the PCB  140  with a downward pressure. This allows for the light source  130  to be held in place between the tabs  144  and the shelf  142 . In some embodiment, at the tabs  144  can be made of a light reflective material to reflect light from the LEDs  138  to contribute to the desired emission from the light bar  122 . 
     The mounting clips  132  are also mounted to the base  126  and are arranged such that they can slide along the base  126  to the desired position. The mounting clips  132  have mounting clip extensions  146  that are positioned to contact the inner surface of the light fixture or troffer pan. The base has notches  148  shaped to cooperate with mounting clip tabs  150  to hold the mounting clips  132  on the base  126  while allowing the mounting clips  132  to slide along the base  126 . The mounting clips can have many different shapes and sizes and can be made of many different materials. In the embodiment shown, the mounting clips  132  can be made of plastic and can be formed by extrusion or injection molding processes. 
     The light bars according to the present invention can also comprise mechanisms to hold the light bars to the luminaire housing to allow positions of the light bars prior to permanent mounting. In some embodiments this can comprise materials such as non-permanent adhesives, while in other embodiments the light bars can have one or more magnets positioned to hold the light bar  122  to metallic troffer pans prior to permanently mounting the light bars (such as with screws). In some embodiments, the magnets can be in or one or more of the mounting clips  132 . In the embodiment shown, the mounting clips have longitudinal cavities  152  that can house magnets  154  such that the magnetic force from the magnets holds the light clip to the troffer pan. This in turn holds the light bar to the troffer pan. In other embodiments, the magnets can be in other locations, such as on the mounting clip extensions  146  or in/on other portion of the light bar, such as the base  126 , light source  130  or lens  128 . 
     The mounting clips can also have features that allow for the permanent mounting of the light bar to a light fixture. In some embodiments, the mounting clip extension can comprise mounting holes sized for a screw to pass and turn into a hole in the troffer pan. It is understood that other mounting mechanisms or permanent adhesives can be used. In different embodiments less than all of the mounting clips can be used for permanent mounting, and some can be used only for temporary mounting for light bar placement. It is also understood that light bars can be included where less than all of the mounting clips have magnets and where mounting clips of different shapes and sizes can be used with one of the mounting clips. In some embodiments the entire mounting clip can be made of a magnetic material, or as in the embodiment shown only a portion of the mounting clip can be magnetic. The magnets can be many different shapes and sizes such as rectangular, circular or triangular, and can have many different numbers, shapes and sizes of magnets. 
     It still other embodiments, the holding mechanisms or materials can be provided on the light fixture instead of on the light bar or its mounting clips. In these embodiments the temporary adhesive or magnets can be on, for example, the troffer pan and a portion of the light bar can be adhesive or magnet. In the embodiments where magnets are used, portions of the light bar or mounting clips should be made of a metallic material that is held by the magnetic field of the magnets. 
     The light bars  122  can also comprise end caps  134  that can be cover the ends and protect the components within the light bars  122 . The end caps can be made of many different materials, with some embodiments comprising a plastic fabricated by injection molding. The end caps  134  can be mounted to the light bars using mounting mechanisms or adhesives. In the embodiment shown, the end caps  134  are mounted to the base  126  using screws  158 , each of which is sized to pass through a hole in the end caps  134  and cooperate with hole  169  in the base. The end caps further comprise a wire hole  160  that allows a connecting wire (not shown) to pass through the end cap  134  for connection to the light source  130 . The other end of the connection wire can be coupled to a power supply, so that a drive signal from the power supply can be conducted to the light source  130 . The light source  130  can comprise many different mechanisms for connection to the connecting wire, with some embodiments comprising a bottom connector  162  that is arranged at the bottom of the PCB  140  and can be at one of the PCB to allow for easy access for wire connection. By being positioned at the bottom, the bottom connector  162  does not interfere with or block the emission of the LEDs  138 . 
     The components of the light bar  122  as described in the embodiment above allow for convenient and simple assembly and use. The base  126  serves as the central mechanical foundation with the remaining primary components mounted to the base without the need for mechanical mounting elements such as screws, rivets or brackets, or without adhesives. The light source  130  is arranged on the inner shelf  142  and the lens  128  can be slid or snapped in place to base  126 . The light source  130  is held in place between the base  126  and the lens  128 . Both the lens  128  and the light source can be easily removed by hand, such as by sliding the lens  128  off the base  126 . The mounting clips  132  can also be mounted to the base without screws, rivets, brackets or adhesives as described above, and can easily be removed. The end caps  134  are the only primary light bar elements that are mounted in place by a screw as described above. The mounting clips  132  also cooperate with the base so that after mounting of light bar  122  in a light fixture, the base  126  can be removed from the mounted mounting clips and a replacement light bar can be snapped into the mounting clips. 
     The light bars according to the present invention can have many different shapes and sizes, and in some embodiments the light bar can be in the range of approximately 5 to 200 inches. In some embodiments, the light bars can be approximately 21 inches long or approximately 42 inches long. The lens can have many different widths, such as in the range of 0.5 to 3 inches, with some embodiments having a width of approximately 1.10 inches. Similarly, the light bar can have many different heights, such as in the range of 0.5 to 4 inches, with some embodiments having a height of approximately 1.5 inches. The mounting clips according to the present invention can have many different lengths, such as in the range of 0.5 to 6 inches, with some embodiment having a length of approximately 2.0 inches. It is understood that these are only some examples of the different dimensions, and other embodiments can have that many others dimensions. 
     The system  120  can also comprise a power supply  180  with  FIGS. 11, 15 and 16  showing one embodiment of a power supply according to the present invention. The power supply  180  can be sized and arranged for mounting in a ballast or raceway of a troffer pan, as described above. The power supply  180  can receive line voltage from the fixture input, for example 120 VAC, and can comprise components that deliver an electrical voltage and current to the light bars  122  appropriate for driving LEDs. In some embodiments the voltage and current can be delivered through the connection wires. The power supply  180  generally comprises a driver board  182  arranged in a housing  184  that comprises a bottom  186  and top  188  held together by screws  190 . In other embodiments, the bottom and top  186 ,  188  can be arranged such that they can snap fit together, while in other embodiments the bottom and top  186 ,  188  can be glued together. There are only a few of the ways in which the housing  184  can be assembled, and other embodiments can comprise other pieces fitting together in different ways to form the housing  184 . The housing can be made of many different materials, such as plastics, metal or combinations thereof. 
     The driver board can be accessed by removing the screws  190  and removing the top  188  from the bottom  186 . The power supply also comprises mounting slots  192  that hold the power supply  180  in place to the troffer pan by screws. In some embodiments, the power supply can also provide dimming feature, while in other embodiments the power supply can provide for low voltage operation of the light bars  122 . This can provide the advantage of allowing for connection wiring between the power supply and light bars to pass outside of wire covers. This in turn can allow for less complex and less costly installation. 
     The power supply can be many different shapes beyond that shown in the  FIGS. 15 and 16 , and can be many different sizes. In some embodiment, the power supply can be in the range of 2 to 20 inches long, with some embodiments being approximately 9.5 inches long. In some embodiments is can have a width in the range of 0.5 to 6 inches, with some embodiment being approximately 2.3 inches wide. Some embodiments can have a height in the range of 0.5 to 5 inches, with some embodiments being approximately 1.3 inches high. 
       FIGS. 17, 18 and 19  show different types of conventional troffer light fixtures  200 ,  210  and  220 , each of which comprises a raceway  222 . The power supply  180  can be sized such that it fits under the raceway cover  224  for each of these different fixtures, making the power supply  180  compatible for retrofitting these fixtures.  FIG. 20  is a driver board schematic  230  showing one embodiment of the components that can be found on a driver board and their interconnections. The driver board has inputs  232  that can accept receipt line voltage at lines  1  and  2 , internal components  235  to convert the signal, and outputs  234  that can provide two or three drive signals to the light bars. 
     The system  120  can be arranged with different numbers of light bars  122  that can be arranged with different numbers of LEDs that can also be arranged in different serial/parallel combinations. As best shown in  FIG. 12 , the light source  130  can comprise different number of PCBs  148  connected in series, with the embodiment shown having three PCBs  140  connected in series. Each of the PCBs can have LEDs interconnected in different series and parallel combination.  FIG. 21  shows one embodiment of the PCBs  140  shown side by side for ease of illustration. Each of the PCBs  140  can have different numbers of LEDs  138 , and in the embodiment shown each PCB  140  has 39 interconnected LEDs  138 . The PCBs  140  can also have other features, such as a connector  162 . An electrical signal applied to the connector  162  causes the LEDs on each corresponding light source to emit light, and in some embodiments the PCBs  140  can be interconnected through their connectors  162 . 
       FIG. 22  is a schematic showing one embodiment of interconnections for the LED  138  on the PCBs  140  shown in  FIG. 21 . As mentioned above, the LEDs  138  can be interconnected in many different serial and parallel combinations. In the embodiment shown, the LEDs  138  on each PCB can comprise three sets of 13 parallel interconnected LEDs, with the sets interconnected in series. Each of the PCBs  140  can comprise 39 interconnected LEDs  138 , with a light bar having three interconnected PCB having 117 interconnected LEDs. It is understood that  FIGS. 21 and 22  illustrate only one embodiment, and that different embodiments can have different numbers of LEDs. In some embodiments the PCBs in one light bar can have different numbers of LEDs that can be interconnected in different serial and parallel combinations. It is further understood that in some embodiments, all the LEDs can be similar and emit the same or similar color of light. In other embodiments the LED can comprise different types of LEDs and/or different LED that emit different colors of light. 
     Different embodiments of the present invention can be used in retrofitting troffer pans and provide for flexibility and convenience in installation. The light bars can be placed in the troffer pan and can be held in place by the mounting clip magnets. The placement of the light bars can be adjusted as desired by simply moving the light bars, with the magnets holding the light bar in the new location. The mounting clips can also be slid up or down the light bars to the desired location. This can allow for aligning the mounting clip holes with existing holes in the troffer pan. The existing holes can be used again by the mounting clips to minimize the creation of new holes in the troffer pan. The power supply can then be mounted in the desired position, such as along the raceway of the troffer pan, and the power supply can be connected to the line supply and to the light bars. The light bars can then be illuminated to determine if they produce the desired troffer emission. The position of the light bars can then be further adjusted to achieve the desired emission. The light bars can then be mounted in place such as by screws passing through the mounting clip holes. 
     It is understood that the components of the light bars and power supplies according to the present invention can be arranged in many different ways with many different shapes and sizes. The base  126  can be made of many different materials and can have different numbers of channels or openings with different shapes and sizes. The light sources can similarly be arranged in many different ways with different numbers of LEDs, LED components or LED packages interconnected in different ways. The lens can also have many different shapes and sizes.  FIGS. 23, 24 and 25  show examples of different lens shapes  300 ,  310  and  320  that can be used in different light bars according to the present invention. It is understood that these are only a few of the shapes that can be used. 
     Although the present invention has been described in detail with reference to certain preferred configurations thereof, other versions are possible. Embodiments of the present invention can comprise any combination of compatible features shown in the various figures, and these embodiments should not be limited to those expressly illustrated and discussed. Therefore, the spirit and scope of the invention should not be limited to the versions described above.