Abstract:
A lighting apparatus includes a light-diffusive plate having opposing faces bounded by one or more sides. The plate has disruptions on a first face of the opposing faces and a first channel along at least a portion of a first side of the one or more sides. A first cover has first and second surfaces disposed over the first channel with the first surface facing the first side of the light-diffusive plate. A plurality of light-emitting diodes (LEDs) is disposed on the first surface of the first cover and within the first channel. The LEDs electrically coupled with wiring are integrated with the first cover.

Description:
FIELD OF THE INVENTION 
     The embodiments of the present invention generally relate to an LED apparatus. 
     BACKGROUND 
     LED-based lighting is becoming more popular due in part to the energy efficient qualities and durability of LEDs. One popular application is advertising and public information signage. In some implementations, LEDs are placed along one or more edges of a light-transmitting panel, and the light-transmitting panel is configured to evenly emit light from the LEDs through a surface of the panel. 
     With an edge-lit light-transmitting panel, light from the LEDs is spread evenly through the panel by total internal reflection. Disruptions formed on the surface of the panel scatter incident light so that light is emitted from the surface of the panel. 
     SUMMARY 
     In one embodiment, a lighting apparatus includes a light-diffusive plate having opposing faces bounded by one or more sides. The light-diffusive plate has a plurality of disruptions on a first face of the opposing faces and a first channel along at least a portion of a first side of the one or more sides. A first cover has first and second surfaces and is disposed over the first channel with the first surface of the cover facing the first side of the light-diffusive plate. A plurality of light-emitting diodes (LEDs) is disposed on the first surface of the first cover and within the first channel. The LEDs are electrically coupled with wiring integrated with the first cover. 
     A method of making a lighting apparatus is provided in another embodiment. The method includes forming disruptions on a first face of opposing faces of a light-diffusive plate. The opposing faces of the light-diffusive plate are bounded by one or more sides. A first channel is formed along at least a portion of a first side of the one or more sides. A plurality of light-emitting diodes (LEDs) is attached on a first surface of a first cover, and the first cover is attached to the light-diffusive plate over the first channel such that the plurality of LEDs are disposed in the channel. 
     In another embodiment, a lighting apparatus includes a light-diffusive plate having opposing faces bounded by one or more sides. The light-diffusive plate has disruptions on a first face of the opposing faces and a first channel along at least a portion of a first side of the one or more sides. A first cover includes a polyimide substrate, and the polyimide substrate has a first surface and a second surface. The first cover is disposed over the first channel with the first surface of the polyimide substrate facing the first side of the light-diffusive plate. A plurality of light-emitting diodes (LEDs) is disposed on the first surface of the polyimide substrate and within the first channel. The LEDs are electrically coupled with wiring integrated with the polyimide substrate. At least one positive connector lead and at least one negative connector lead are disposed on the second surface of the polyimide substrate. The at least one positive connector lead is electrically coupled to a positive power line of the LEDs, and the at least one negative connector lead is electrically coupled to a negative power line of the LEDs. An ultra-violet (UV) curable encapsulant fills the first channel. 
     The above summary of the present invention is not intended to describe each disclosed embodiment of the present invention. The figures and detailed description that follow provide additional example embodiments and aspects of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects and advantages of the invention will become apparent upon review of the Detailed Description and upon reference to the drawings in which: 
         FIG. 1  shows a perspective view of a lighting apparatus; 
         FIG. 2  shows an example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source; 
         FIG. 3  shows another example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source; 
         FIG. 4  shows another example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source; 
         FIG. 5  shows a cross-sectional view of the lighting apparatus of  FIG. 1  taken in the direction of cross-section lines  5 ; and 
         FIG. 6  is a flowchart of a process for constructing a lighting apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure describes an LED lighting apparatus that provides efficient dissipation of heat from the LEDs and that is adaptable for various applications, including signage or general lighting. The LED lighting apparatus may be adapted for use in outdoor applications which require protection against weather elements. Since the LEDs are embedded in the light-diffusive plate rather than supported by a frame outside the plate, the lighting apparatus can be deployed and adapted for particular functional and aesthetic requirements. 
     The lighting apparatus includes a light-diffusive plate. The plate has opposing faces and sides that surround the opposing faces. The intersections between the faces and the sides of the plate are the edges of the plate. The plate has at least one channel that extends along at least a portion of at least one of the sides of the plate. A number of LEDs, which are electrically connected, are disposed in the channel. The electrical connections may include only power lines or both power and control lines. 
       FIG. 1  shows a perspective view of the lighting apparatus  100 . The lighting apparatus includes light-diffusive plate  102  having a channel  104  formed on side  106 . The channel forms a recess large enough to accommodate the string of LEDs  108 . The LEDs are mounted on channel cover  110 , and the channel cover is disposed over the channel  104  such that the LEDs are within the channel. 
     The channel cover includes a metal coated dielectric in an example implementation. In a particular implementation, the cover may include an aluminum-coated polyimide substrate. In other implementations, the channel cover may be a rigid printed circuit board rather than flexible. Also, the cover may include multiple dielectric and/or conductive layers. Conductive traces  112  are disposed on and integrated with the polyimide substrate, which insulates the traces from the aluminum coating. The aluminum coating effectively dissipates heat emitted from the LEDs when the lighting apparatus is operated. A circuit-side surface of the metal-coated polyimide substrate has the LEDs mounted thereon and faces the channel  104 . The metal-coated surface of the metal-coated polyimide substrate faces away from the channel. 
     In one implementation, the channel cover may be shaped to wrap around edges of the side having the channel as shown. Alternatively, the width or breadth of the channel cover may be slightly larger than the channel such that the channel is fully covered when the channel cover is disposed on the side having the channel. The conductive traces include power lines  114  and  116  and may also include control lines (not shown). 
     In one implementation, the light-diffusive plate is made from a transparent thermoplastic such as polymethyl methacrylate (PMMA or “acrylic glass”). In an example implementation, the light-diffusive plate is rectangular as shown. Other implementations may call for different shapes such as other polygons, or circular, elliptical, or irregular shapes. 
     Though not shown in  FIG. 1 , the light-diffusive plate has disruptions formed on one face  122  of the opposing faces of the plate. With an edge-lit lighting apparatus, light from the LEDs is spread evenly through the light-diffusive plate by total internal reflection. The disruptions formed on the surface of the plate scatter incident light so that light is emitted from the face of the plate having the disruptions. Another implementation has disruptions formed on both face  122  and the opposing face (not shown) of the light-diffusive plate. 
     The arrangement of LEDs in the channel may be varied according to implementation requirements. For example, different implementations may call for different sizes, numbers, and/or spacing of LEDs. Also, there may be more than one row of LEDs disposed in the channel. Another implementation may have more than one channel formed on the light-diffusive plate. For example, in addition to channel  104 , another channel (e.g., channel  464  in  FIG. 5 ) may be formed along side  124 , and another channel cover (e.g., channel  466  in  FIG. 5 ) with LEDs (e.g., LED  468  in  FIG. 5 ) may be disposed over the channel. Other implementations may have multiple channels on a single side of the light-diffusive plate. 
       FIG. 2  shows an example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source. A portion of a channel cover  202  is shown with a partial string of LEDs  204 . Metallic connector leads  206  and  208  are attached to the channel cover and connected to the positive and negative power lines of the LED string. It will be appreciated that additional connector leads may be similarly provided for connecting the LED string to control signal lines. 
     The connector leads may be an aluminum or copper foil and may be attached to the channel cover and connected to the power lines with a conductive adhesive or by a solder attachment. The connector leads may be bent as shown to conform to the edge of the light-diffusive plate (not shown), which may be useful for insertion of the completed lighting apparatus into a socket (not shown) for providing power. 
       FIG. 3  shows another example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source. A portion of a channel cover  302  is shown with a partial string of LEDs  304 . Metallic connector leads  306  and  308  are attached to the channel cover and connected to the positive and negative power lines of the LED string. It will be appreciated that additional connector leads may be similarly provided for connecting the LED string to control signal lines. 
     The connector leads may be an aluminum or copper foil and may be attached to the channel cover and connected to the power lines with a conductive adhesive or by a solder attachment. The connector leads may be bent as shown to wrap from one surface of the channel cover, around the edge, to the other surface of the channel cover, which may be useful for insertion of the completed lighting apparatus into a socket (not shown) for providing power. Though not shown, it will be appreciated that connector lead  306  includes a portion that is disposed on the surface of the channel cover  302  that is opposite the surface of the channel cover that faces the light-diffusive plate. In other words, connector lead  306  has a portion that is similar to the portion of connector lead  308  that is shown in the diagram. Similarly, connector lead  308  includes a portion (not shown) that is similar to the portion of connector lead  306  shown in the diagram. Since channel cover  302  is metal coated, an insulator (not shown) may be disposed between the connector lead and the metal coated surface  310  of the channel cover. 
       FIG. 4  shows another example implementation of connector leads on the channel cover for electrically connecting the string of LEDs to a power source. A portion of a channel cover  402  is shown with a partial string of LEDs  404 . 
     The structure of  FIG. 4  differs from the structures of  FIGS. 2 and 3  in that the polyimide substrate is not metal-coated. Instead, metallic connector leads, for example leads  406  and  408 , are provided in a circuit layer on the side of the substrate opposite the side on which the LED string is disposed. The connector leads may be copper, for example. 
     The connector leads are disposed in an alternating pattern of positive and negative connections to the string of LEDs. Connector lead  406  extends from one wall  410  of the channel cover to the other wall  412  of the channel cover. In the perspective view, the connector leads are not visible on wall  412  and base  414  of the channel cover. All of the positive and negative connector leads may be disposed in this manner. 
     The connector leads are electrically connected to the positive and negative power lines  416  and  418  by vias. For example, via  422  connects connector lead  406  to the positive power line  416 , and via  424  connects connector lead  426  to the positive power line  416 . The connector leads  408  and  428  are similarly connected to the negative power line  418  by vias which are not visible in the perspective view. The alternating pattern provides a number of choices for connecting power lines  416  and  418  to an external power source. The connections can be made at any of the connector leads, with solder joints for example. In addition, the number and size of the metallic connector leads provide for heat dissipation from the LED string. An insulative sleeve (not shown) may be disposed over the connector leads. 
     Though a particular pattern of connector leads is shown in  FIG. 4 , it will be appreciated that the pattern and number of connector leads may be varied according to application requirements. For example, it is not necessary that the leads alternate between positive and negative or have the same size. A single positive connector lead and a single negative connector lead could be printed in a pattern that provides alternating locations for making positive and negative connections. However, it is desirable to have sufficient metal in the connector leads in order to provide sufficient heat dissipation from the LED string. 
       FIG. 5  shows a cross-sectional view of the lighting apparatus of  FIG. 1  taken in the direction of cross-section lines  5 . The cross-sectional view shows light-diffusive plate  102  in which channel  104  is covered by channel cover  110 . In the example implementation, the channel cover is an aluminum-coated polyimide, which is illustrated with polyimide layer  442  and metal coating  444 . 
     LED  108  is mounted on the polyimide layer  442  and connected to conductive traces (not shown) that are either on the surface of the polyimide layer or in a layer of conductive traces in a multilayer arrangement. Because the channel cover is metal coated, the metal coating  444  provides an effective heat sink for dissipating heat generated by the LEDs. This may simplify the support structure needed for the lighting apparatus and make the lighting apparatus suitable for a variety of applications. 
     In an example implementation, the channel  104  is filled with an ultra-violet (UV) curable encapsulant  446 . In one implementation, the encapsulant serves to secure the channel cover  110  to the light-diffusive plate  102  as well as to seal the components of the lighting apparatus from weather elements for outdoor applications. The encapsulant should be transparent and non-yellowing. In another implementation, a separate weather-tight adhesive may be used to secure the channel cover to the light-diffusive plate. 
     For many signage applications, emission of an even level of light from the entire surface of the light-diffusive plate may be desirable. Different patterns of disruptions on light-diffusive plates have been used to different effect. One pattern that has been found to be particularly useful is an edge-to-edge pattern of disruptions formed on the surface of the plate. Disruptions  448 ,  450 , and  452  are examples of the disruptions on surface  454  of the light-diffusive plate  102 . The disruptions may be laser etched as is known in the art. For applications in which multiple ones of the light-diffusive plates are disposed side by side, the pitch between the disruptions on two separate plates is equal to the pitch between disruptions on the same plate. In another implementation, disruptions  470 ,  472 , and  474  may be formed on surface  458  as well as on surface  454 . 
     In another implementation, a reflector plate  476  may be attached to the surface of the light-diffusive plate having the disruptions. 
       FIG. 6  is a flowchart of an example process for making a lighting apparatus. At block  502 , disruptions and a channel are formed in a light-diffusive plate. The disruptions may be formed on a surface of the light-diffusive plate using laser etching as is known in the art. The channel may be formed by laser ablation. 
     At block  504 , a string of LEDs is attached to a channel cover. As explained above, in one implementation the channel cover is a flexible substrate, such as a polyimide, and the substrate is aluminum-coated. In other embodiments, the substrate may be a polyimide substrate that is not metal coated, but has connector leads for providing electrical connections to the LEDs and for dissipating heat from the LEDs. The LEDs may be attached to the substrate and connected to metal traces using techniques known in the art. 
     The channel in the light-diffusive plate is filled with an encapsulant at block  506 . The encapsulant may be transparent and UV-curable. At block  508 , the cover is placed over the channel such that the string of LEDs is disposed in the channel. The encapsulant in the channel is cured at block  510  with a UV light source. 
     Though aspects and features may in some cases be described in individual figures, it will be appreciated that features from one figure can be combined with features of another figure even though the combination is not explicitly shown or explicitly described as a combination. 
     The present invention is thought to be applicable to a variety of lighting applications. Other aspects and embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the disclosed apparatus and method be considered as examples only, with a true scope of the invention being indicated by the following claims.