Abstract:
A lighting device includes a light emitting module including a substrate and a light emitting device mounted on the substrate; a case body receiving the light emitting module; a gap member contacting the case body and wider than the substrate; a lens on the light emitting module and contacting the gap member; a first ring provided on a peripheral portion of the lens; and a case cover coupled with the case body and having an opening, wherein the case body is provided therein with a coupling cavity in which the gap member is seated, and wherein the lens includes a first portion between the ring and the gap member and a second portion that extends outward from the first portion through the opening of the case cover.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 13/745,307 filed Jan. 18, 2013, which is a continuation of U.S. application Ser. No. 13/099,761 filed May 3, 2011 (now U.S. Pat. No. 8,186,848), which is a continuation of U.S. application Ser. No. 12/656,501 filed on Feb. 1, 2010 (now U.S. Pat. No. 8,366,299), which claims priority under 35 U.S.C. 119 of Korean Patent Application No. 10-2009-0049987 filed on Jun. 5, 2009, which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments relate to a lighting device. 
     Light emitting diodes (LEDs) are semiconductor devices configured to convert electrical energy to light. Such LEDs have low power consumption, semi-permanent service life, rapid response speed, stability, and environmentally-friendly properties, relative to related art light sources such as fluorescent lamps and incandescent lamps. Thus, much research has been carried out to replace related art light sources with LEDs, which are increasingly being employed as the light sources of lighting devices used indoors and outdoors, including various lamps, liquid crystal display devices, electronic display boards, and street lamps. 
     2. Background 
     In one embodiment, a lighting device comprises: a case body comprising a receiving cavity and at least a portion including at least one first hole; a light emitting module in the receiving cavity, the light emitting module including a plurality of light emitting devices; a lens on the light emitting module; and a case cover including an opening through which the lens is exposed, the case cover being disposed on the case body; and a heat sink between the light emitting module and the case body to transfer heat from the light emitting module to the case body, wherein the case body acts as a conduit to transfer heat from the lighting emitting module to the portion of the case body including at least one first hole and the case cover has at least a portion including at least one second hole and the first hole of the case body corresponds with the second hole of the case cover. 
     In another embodiment, a lighting device comprises: a case body including a cavity; a light emitting module disposed in the cavity of the case body, the light emitting module including a plurality of light emitting devices; a lens on the light emitting module; and a case cover including an opening through which the lens is exposed, the case cover being disposed on a circumference of the lens and the case body, wherein the case body has an inner wall and an outer wall forming at least one first heat dissipating portion and the case cover has an inner wall and an outer wall forming at least one second heat dissipating portion, wherein the first heat dissipating portion corresponds with the second heat dissipating portion. 
     In further another embodiment, a lighting device comprises: a case body including a cavity and a through-hole in a bottom surface of the cavity; a light emitting module in the cavity, the light emitting module including a plurality of light emitting devices; a lead electrode electrically connected to the light emitting module, the lead electrode being exposed to the outside through the through-hole; a gap member on the light emitting module, the gap member including an electrode penetration portion through which the lead electrode passes; a lens on the gap member; and a case cover including an opening through which the lens is exposed, the case cover being disposed on the lens and the case body. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is an exploded perspective view of a lighting device according to a first embodiment. 
         FIG. 2  is a perspective view of the lighting device according to the first embodiment when viewed from above. 
         FIG. 3  is a perspective view of the lighting device according to the first embodiment when viewed from below. 
         FIG. 4  is a sectional view of the lighting device according to the first embodiment. 
         FIG. 5  is a view illustrating a light emitting module of the lighting device. 
         FIG. 6  is a view illustrating a gap member of the lighting device when viewed from above. 
         FIG. 7  is a sectional view illustrating the gap member and the light emitting module of the lighting device. 
         FIG. 8  is a view illustrating an example of a lens of the lighting device. 
         FIG. 9  is a perspective view of a lighting device according to a second embodiment when viewed from above. 
         FIG. 10  is a sectional view of a lighting device according to a third embodiment. 
         FIG. 11  is a perspective view of a lighting device according to a fourth embodiment when viewed from below. 
     
    
    
     DETAILED DESCRIPTION 
     In the descriptions of embodiments, it will be understood that when a layer (or film), a region, a pattern, or a structure is referred to as being ‘on/above/over/upper’ substrate, each layer (or film), a region, a pad, or patterns, it can be directly on substrate each layer (or film), the region, the pad, or the patterns, or intervening layers may also be present. In addition, spatially relative terms, such as “upper” and “lower” are used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the drawings. 
     In the drawings, thicknesses and sizes of layers are exaggerated, omitted, or schematically illustrated for clarity. In addition, the sizes of elements illustrated in the drawings may not correspond to their actual sizes. 
     Hereinafter, a lighting device according to a first embodiment will be described with reference to the accompanying drawings. 
       FIG. 1  is an exploded perspective view of a lighting device according to a first embodiment, and  FIG. 2  is a perspective view of the lighting device according to the first embodiment when viewed from above.  FIG. 3  is a perspective view of the lighting device according to the first embodiment when viewed from below, and  FIG. 4  is a sectional view of the lighting device according to the first embodiment. 
     Referring to  FIGS. 1 to 4 , a lighting device according to a first embodiment includes a case body  30 , a heatsink plate  20  in a receiving cavity of the case body  30 , a light emitting module  10  on the heatsink plate  20 , a gap member  40  on the light emitting module  10 , a lens  50  on the gap member  40 , a first protection ring  60  on an edge  51  of the lens  50 , and a case cover  70  on the first protection ring  60  and the case body  30 . 
     The case body  30  and the case cover  70  are coupled and fixed to each other by a coupling screw  80  to form a case  90  of the lighting device. 
     The heatsink plate  20  radiates heat generated from the light emitting module  10 . 
     The light emitting module  10  may include a substrate  12 , a plurality of light emitting devices  11  mounted on the substrate  12 , and a lead electrode  17  transmitting power to the plurality of light emitting devices  11 . 
     A portion of the lead electrode  17  may be exposed to the outside through a through-hole  35  passing through a bottom surface of the case body  30  and electrically connected to an external power source. 
     A protection tube  18  may surround the exposed lead electrode  17  to protect the exposed portion of the lead electrode  17  from exterior environment such as heat or moisture. A connection terminal  19  may be disposed on an end of the lead electrode  17  to connect the lead electrode  17  to the external power source through the connection terminal  19 . 
     The lens  50  adjusts light generated from the light emitting module  10  to realize desired light distribution. 
     The gap member  40  may space the light emitting module  10  from the lens  50  by a predetermined gap G 1  to form a space between the light emitting muddle  10  and the lens  50 , thereby inducing a desired light emitting angle and the desired light distribution. 
     The first protection ring  60  is disposed between the case cover  70  and the lens  50  to prevent moisture from being permeated into the lighting device. 
     A second protection ring  65  may be disposed on an outer circumference of a circumference surface of the through-hole  35  of the bottom surface of the case body  30  when the lighting device is attached to an external support member. 
     Hereinafter, components of the lighting device according to the first embodiment will be described in detail. 
     Referring to  FIGS. 1 to 4 , the case body  30  may have a circular-shaped body with a receiving space such as a receiving cavity. Also, the case cover  70  may have a circular ring shape corresponding to that of the case body  30 . 
     The case body  30  and the case cover  70  are coupled to each other to form the case  90 . The case  90  constitutes a body of the lighting device to receive the heatsink plate  20 , the light emitting module  10 , the gap member  40 , the lens  50 , and the first protection ring  60 . 
     The heatsink plate  20  is disposed in the receiving space such as the receiving cavity of the case body  30 , and the light emitting module  10  is disposed on the heatsink plate  20 . The gap member  40  is disposed on a circumference of the light emitting module  10 , and the lens  50  is disposed on the gap member  40 . The first protection ring  60  is disposed on the edge  51  of the lens  50 , and the case cover  70  is disposed on the first protection ring  60  and the case body  30 . Here, the lens  50  is exposed through an opening of the case cover  70 . 
     A shape of the case  90 , e.g., the shapes of the circumference surfaces of the case body  30  and the case cover  70  are not limited to the circular shape and may be variously varied. 
     The case  90  may be formed of a material having a superior thermal dissipation property. For example, the case  90  may be formed of a metal material, e.g., at least one of aluminum (Al), nickel (Ni), copper (Cu), silver (Ag), and tin (Sn). Also, plating may be disposed on a surface of the case  90 . 
     Alternatively, the case  90  may be formed of a resin material, but is not limited thereto. 
     The circumference surface of the case body  30  may have an inner wall and an outer wall. A first hole  31 , a second hole  32 , and a first heatsink hole  33  may be disposed between the inner wall and the outer wall. 
     Also, the circumference surface of the case cover  70  may have an inner wall and an outer wall. A protrusion  71  and a second heatsink hole  73  may be disposed between the inner wall and the outer wall. 
     Here, the outer walls may not be disposed at a portion of the circumference surfaces of the case body  30  and the case cover  70  in which the second hole  32  is disposed. 
     Referring to  FIG. 4 , the protrusion  71  may include a screw groove  75 . The protrusion  71  is inserted into the first hole  31 , and the coupling screw  80  is inserted into the screw groove  75  and the first hole  31 . As a result, the case body  30  and the case cover  70  may be firmly fixed and coupled to each other. 
     The coupling screw  80  may be inserted from the first hole  31  of the case body  30  into the screw groove  75  of the protrusion  71  of the case cover  70  so that the head  81  of the coupling screw  80  faces down. Thus, when the coupling screw  80  is inserted from the first hole  31 , the coupling screw  80  may not be exposed to a top surface of the case cover  70 . However, a coupling method of the coupling screw  80  may be various changed. 
     The case  90 , e.g., the case body  30  and the case cover  70  may be coupled or separated to/from each other using the coupling screw  80 . Thus, when the lighting device has broken down, the coupling screw  80  is inserted or removed to easily perform maintenance and repair of the lighting device. 
     Referring to  FIGS. 1 to 3 , a screw may be inserted into the second hole  32  of the case body  30  to couple the lighting device to the external support member such as a wall surface, a streetlight, or an automobile as necessary. Here, as described above, the outer walls may not be disposed at the portion of the circumference surfaces of the case body  30  and the case cover  70  in which the second hole  32  is disposed, so that the screw is smoothly inserted into the second hole  32 . 
     The first heatsink hole  33  of the case body  30  and the second heatsink hole  73  of the case cover  70  constitute a heatsink hole  93  of the case  90 . The heatsink hole  93  may enlarge a surface area of the case  90  to effectively radiate the heat generated from the light emitting module  10 . Also, when compared to a case in which the heatsink hole  93  is not formed, the lighting device may be reduced in weight. 
     Referring to  FIGS. 3 and 4 , the through-hole  35  may be disposed in the bottom surface of the case body  30 . The portion of the lead electrode  17  of the light emitting module is exposed to the outside through the through-hole  35  and connected to the external power source. 
     A circumference surface  36  of the through-hole  35  may protrude from the bottom surface of the case body  30 . Since the circumference surface  36  of the through-hole  35  protrudes, the lighting device may be exactly installed to the external support member. 
     Also, the second protection ring  65  may be disposed on the outer circumference of the circumference surface of the through-hole  35 . When the lighting device is attached to the external support member, the second protection ring  65  may prevent the moisture from being permeated into the lighting device through the through-hole  35  to improve reliability of the lighting device. 
     A ring groove  66  having a shape corresponding to that of the second protection ring  65  may be disposed in the outer circumference of the circumference surface of the through-hole  35  so that the second protection ring  65  is smoothly installed. 
     Referring to  FIGS. 1 ,  2 , and  4 , an inner surface  77  of the case cover  70  may be inclined to effectively radiate the light emitted from the lens  50 . Also, the inner surface  77  of the case cover  70  may fix the heatsink plate  20 , the light emitting module  10 , the gap member  40 , the lens  50 , and the first protection ring  60 , which are received inside the case  90 . 
       FIG. 5  is a view illustrating the light emitting module  10  of the lighting device. 
     Referring to  FIGS. 1 and 5 , the light emitting module  10  may include the substrate  12 , the plurality of light emitting devices  11  mounted on the substrate  12 , and a lead electrode  17  transmitting a power to the plurality of light emitting devices  11 . The light emitting module  10  provides light to the lighting device. 
     The light emitting module  10  has a shape corresponding to that of the receiving cavity of the case  90  such that it is received into the case  90 . As shown in  FIGS. 1 and 5 , the light emitting module  10  may have a circular plate shape, but is not limited thereto. 
     A circuitry is printed on a dielectric to form the substrate  12 . The substrate  12  may include an aluminum substrate, a ceramic substrate, a metal core printed circuit board, and a general printed circuit board. 
     The substrate  12  may have a colored surface, for example, a white colored surface to efficiently reflect light. 
     The plurality of light emitting devices  11  may be mounted on the substrate  12  in an array form. The mounted configuration and the number of the plurality of light emitting device  11  may be variously changed as necessary. 
     The plurality of light emitting device  11  may include at least one light emitting diode (LED). The LED may include at least one of a red LED, a green LED, a blue LED, and a white LED, which respectively emit red light, green light, blue light, and white light. 
     The lead electrode  17  may have one end connected to the substrate  12  and the other end exposed to the outside through the through-hole  35  passing through the bottom surface of the case body  30  and electrically connected to the external power source. 
     The protection tube  18  may surround the lead electrode  17  exposed to the outside to protect the exposed other end of the lead electrode  17  from the exterior environment such heat or moisture. The connection terminal  19  may be disposed on the exposed terminal end of the other end of the lead electrode  17  to connect the lead electrode  17  to the external power source through the connection terminal  19 . 
     A DC converter for converting an alternating current (AC) into direct current (DC) to supply the converted DC or a protection device for protecting the lighting device from an electrostatic discharge (ESD) effect or a surge effect may be further disposed on the substrate  12 . 
     The heatsink plate  20  may be attached to a floor surface of the light emitting module  10 . The heatsink plate  20  may radiate the heat generated from the light emitting module  10  to transmit the heat to the case  90 . 
     The heatsink plate  20  may be formed of a material having thermal conductivity. For example, the heatsink plate  20  may include one of a thermally conductive silicon pad and a thermally conductive tape. 
       FIG. 6  is a view illustrating a gap member of the lighting device when viewed from above, and  FIG. 7  is a sectional view illustrating the gap member and the light emitting module of the lighting device. 
     Referring to  FIGS. 1 ,  4 ,  6 , and  7 , the gap member  40  may be disposed on a circumference between the light emitting module  10  and the lens  50 . The gap member  40  may have a circular ring shape with an opening to expose the light emitting devices  11  of the light emitting module  10 . Also, an electrode penetration portion  41  through which the lead electrode  17  of the light emitting module  10  passes may be disposed in the gap member  40 . 
     The gap member  40  may be formed of an insulation material, e.g., the resin material, but is not limited thereto. When the gap member  40  is formed of the insulation material, insulation resistivity of the lighting device may be improved. 
     The gap member  40  may be formed of a material having high reflectivity or have a color having high reflectivity. The color may be a white color. The gap member  40  may increase an amount of light incident from the light emitting module  10  to the lens  50 . 
     Referring to  FIGS. 1 and 4 , the gap member  40  spaces the light emitting module  10  from the lens  50  by a predetermined gap G 1 . Light is emitted from the light emitting device  11  of the light emitting module  10  at an angle of about 120°. Thus, to obtain the desired light distribution using the light, the predetermined gap G 1  between the light emitting module  10  and the lens  50  may be required. 
     A space  42  between the lens  50  and the light emitting module  10  is defined by the gap G 1  to easily induce the desired light distribution. 
     A resin material may be filled into the space  42 , but is not limited thereto. A phosphor may be contained in the resin material. 
     An inner surface  43  of the gap member  40  may be inclined at a predetermined angle. The inner surface  43  of the gap member  40  may be inclined such that a thickness of the inner surface  43  of the gap member  40  is tapered from the outside toward the inside. Thus, the light generated from the light emitting module  10  may be effectively led to the lens  50  along the inner surface  43  of the gap member  40 . 
     Referring to  FIGS. 4 and 7 , the gap member  40  may have a diameter greater than that of the light emitting module  10 . A module fixing part  45  may be disposed on the circumference of the bottom surface of the gap member  40  to fix the gap member  40  to the light emitting module  10 . Alternatively, the module fixing part  45  may not be provided. 
     The gap member may not be included in the lighting device if not necessary. 
       FIG. 8  is a view illustrating an example of a lens of the lighting device. 
     Referring to  FIGS. 1 ,  2 ,  4 , and  8 , the lens  50  may be disposed on the gap member  40 . The lens  50  may include a light emitting part  52  and an edge  51 . 
     The light emitting part  52  adjusts the light distribution of the light generated from the light emitting module  10  to emit the adjusted light. The light emitting part  52  may be exposed through the opening of the case cover  70  to distribute the light. 
     The edge  51  may be disposed on a circumference of a bottom surface of the light emitting part  52  and have a circular ring shape. The first protection ring  60  may be disposed on the edge  51 . 
     The lens  50  may be injection-molded using a light transmitting material. The light transmitting material may be realized using a plastic material such as glass, poly methyl methacrylate (PMMA), or polycarbonate (PC). 
     Although the lens  50  has a hemispherical shape, the present disclosure is not limited thereto. As necessary, the lens  50  may have various shapes such as convex and concave shapes. 
     Also, as shown in  FIG. 8 , a floor surface of the lens  50 , for instance, an incident surface of the lens  50  may have an uneven shape or a prism shape to improve light extraction efficiency and obtain the desired light distribution.  FIG. 8  illustrates an example of the floor surface shape of the lens  50 , but is not limited thereto. 
     The case body  30  and the case cover  70  may be separated from each other to replace the lens  50  with a lens having the desired light distribution. Thus, the lighting device may be used for various purposes. 
     The first protection ring  60  is disposed on the edge  51  of the lens  50 . 
     Referring to  FIG. 4 , the first protection ring  60  may have a circular ring shape to surround top and circumference surfaces of the edge  51 . As shown in  FIG. 4 , the first protection ring  60  may be disposed between the edge  51  of the lens  50  and the inner surface  77  of the case cover  70 . 
     The first protection ring  60  may be formed of a material through which moisture does not pass. For example, the first protection ring  60  may be formed of rubber for waterproof or a silicon material. 
     Since first protection ring  60  surrounds the top and circumference surfaces of the edge  51  to fill a space between the lens  50  and the case cover  70 , the moisture is not penetrated through the space to improve reliability of the lighting device. 
     Referring to  FIGS. 3 and 4 , the second protection ring  65  may be disposed on the outer circumference of the circumference surface  36  of the through-hole  35  disposed in the bottom surface of the case body  30 . When the lighting device is attached to the external support member, the second protection ring  65  may prevent the moisture from being permeated into the lighting device through the through-hole  35  to improve reliability of the lighting device. 
     Here, the ring groove  66  may be disposed in the outer circumference of the circumference surface  36  of the through-hole  35  so that the second protection ring  65  is smoothly installed. 
     The second protection ring  65  may be formed of a material through which the moisture does not pass. For example, the second protection ring  65  may be formed of rubber for waterproof or a silicon material. 
     Hereinafter, components of a lighting device according to a second embodiment will be described in detail. In descriptions of the second embodiment, the same components as those of the first embodiment will be described with reference to the first embodiment, and the duplicated descriptions will be omitted. 
       FIG. 9  is a perspective view of a lighting device according to a second embodiment when viewed from above. 
     Referring to  FIG. 9 , a case body  30  has a square-shaped body with a receiving space such as a receiving cavity. Also, a case cover  70  has a square ring shape corresponding to that of the case body  30 . 
     The case body  30  and the case cover  70  are coupled to each other to form the case  90  having a square shape. The case  90  constitutes a body of the lighting device to receive a heatsink plate  20 , a light emitting module  10 , a gap member  40 , a lens  50 , and a first protection ring  60 . 
     That is, the case  90  may have various shapes within the technical range of the present disclosure. For example, the case  90  may have a circular shape, a square shape, a polygonal shape, or an oval shape. 
     Hereinafter, components of a lighting device according to a third embodiment will be described in detail. In descriptions of the third embodiment, the same components as those of the first embodiment will be described with reference to the first embodiment, and the duplicated descriptions will be omitted. 
       FIG. 10  is a sectional view of a lighting device according to a third embodiment. 
     Referring to  FIG. 10 , a circumference surface of a case body  30  may have an inner wall and an outer wall. A first groove  31 , a second hole (not shown), and a first heatsink hole (not shown) may be disposed between the inner wall and the outer wall. 
     Also, a circumference surface of a case cover  70  may have an inner wall and an outer wall. A protrusion  71  and a second heatsink hole (not shown) may be disposed between the inner wall and the outer wall. 
     Referring again to  FIG. 10 , a protrusion  71  may include a screw hole  75 . The protrusion  71  is inserted into the first groove  31 , and a coupling screw  80  is inserted into the screw hole  75  and the first groove  31 . As a result, the case body  30  and the case cover  70  may be firmly fixed and coupled to each other. 
     The coupling screw  80  may be inserted from the screw hole  75  of the protrusion  71  of the case cover  70  into the first groove  31  of the case body  30  so that a head  81  of the coupling screw  80  faces upward. Thus, when the coupling screw  80  is inserted from the screw hole  75 , the coupling screw  80  may be exposed to a top surface of the case cover  70 . As a result, the coupling screw  80  may be easily inserted or removed. 
     Thus, when the lighting device has broken down, the coupling screw  80  is inserted or removed to easily perform maintenance and repair of the lighting device. 
     A method of coupling and fixing the case cover  70  to the case body  30  is not limited to the first and third embodiments and may be various changed. 
     Hereinafter, components of a lighting device according to a fourth embodiment will be described in detail. In descriptions of the fourth embodiment, the same components as those of the first embodiment will be described with reference to the first embodiment, and the duplicated descriptions will be omitted. 
       FIG. 11  is a perspective view of a lighting device according to a fourth embodiment when viewed from below. 
     Referring to  FIG. 11 , a case body  30  has a receiving space such as a receiving cavity. A case cover  70  has a ring shape corresponding to that of the case body  30 . 
     The case body  30  and the case cover  70  are coupled to each other to form a case  90 . The case  90  constitutes a body of the lighting device to receive a heatsink plate, a light emitting module, a gap member, a lens, and a first protection ring. 
     According to the fourth embodiment, a helix  32  instead of the second hole formed for attaching the lighting device to the wall surface in the first embodiment is disposed on a circumference surface of the case  90 . A screw groove (not shown) corresponding to the helix  32  may be disposed in a position at which the lighting device is attached to an external support member such as a wall surface, a streetlight, or an automobile. Thus, the helix  32  is fitted into the screw groove (not shown) to attach the lighting device to the external support member such as the wall surface, the streetlight, or the automobile. 
     Therefore, the lighting device may be easily attached to the external support member such as the wall surface, the streetlight, or the automobile without using a screw. 
     A method of attaching the lighting device to the external support member such as the wall surface, the streetlight, or the automobile is not limited to the first and third embodiments and may be various changed as necessary. 
     According to the embodiments, the lighting device having the superior thermal dissipation property and waterproof property may be provided. 
     According to the embodiments, the lighting device capable of easily obtaining the desired light distribution may be provided. 
     According to the embodiments, the lighting device having the improved insulation resistivity may be provided. 
     According to the embodiments, the lighting device that can easily perform maintenance and repair thereof may be provided. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.