Abstract:
A display assembly includes a light pipe that has a front face adapted for emitting light to illuminate a display. The light pipe defines a compartment for receiving a light source. A light shield is disposed overlying the compartment. Channel segments are formed in the rear face and are symmetrical about the compartment. Light from the light source is extracted through the front face to create glow regions about the light shield, over the channel segments, and adjacent the edges of the light pipe. This results in symmetrically uniform illumination of the display while utilizing a single central light source.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a display assembly comprising a light pipe to illuminate a display. More particularly, this invention relates to such assembly that comprises a light pipe defining a compartment for receiving a light source and light-extracting channel segments symmetrical about the compartment to provide improved illumination of the display. 
       BACKGROUND OF INVENTION 
       [0002]    It is known to manufacture a display assembly comprising a display device, such as a liquid crystal device, illuminated by light emitted by a light pipe. A light source, such as an LED, is located proximate an edge of the light pipe. Light from the light source enters the light pipe through the edge and is extracted through the front face toward the display device. For edge-lit light pipes, the light intensity needs to be sufficient to provide suitable light to remote areas of the display. Moreover, a significant portion of the light from the light source is emitted in directions away from the light pipe, and either needs to be reflected back toward the light pipe or is lost for purposes of illuminating the display. 
         [0003]    Therefore, what is needed is an improved display assembly that includes a light pipe for illuminating the display, wherein the light source is located relative to the light pipe in a manner that allows a greater proportion of the light from the light source to enter the light pipe and increased illumination of the display, and further provides more symmetrically uniform illumination of the display. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with this invention, a display assembly is adapted for emitting light to illuminate a display. The display assembly includes a light pipe having a front face and a rear face opposite the front face. The light pipe defines a compartment for receiving a light source. The light pipe also includes channel segments that are formed in the rear face and are symmetrical about the compartment. The channel segments have an outer wall and an inner wall effective to redirect light from the compartment toward the front face. By locating the light source within the compartment, and arranging light-extracting channel segments symmetrically about the compartment, the light pipe increases the proportion of light used to illuminate the display, and provides more uniform lighting of the display. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    This invention will be further described with reference to the accompanying drawings in which: 
           [0006]      FIG. 1  is an exploded view of a display assembly in accordance with this invention; 
           [0007]      FIG. 2  is a cross section view of the display assembly of  FIG. 1 ; 
           [0008]      FIG. 3  is a diagram of components of the display assembly of  FIG. 2 , showing light paths therethrough; 
           [0009]      FIG. 4  is a plan view of the light pipe in  FIG. 1 ; 
           [0010]      FIG. 5  is a view showing an exemplary illumination pattern from the light pipe in  FIG. 4 ; 
           [0011]      FIG. 6 . is a cross section view of a portion of a light pipe in accordance with an alternate embodiment; 
           [0012]      FIG. 7  is a cross section of a portion of a light pipe in accordance with an alternate embodiment; and 
           [0013]      FIG. 8  is a plan view of a light pipe in accordance with an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    In accordance with a preferred embodiment of this invention, referring to  FIGS. 1-5 , a display assembly  10  comprises a light pipe  12  for emitting light to illuminate a display device  14  overlying pipe  12 . A suitable display device is a liquid crystal display (LCD) device. In general, this invention may be used to illuminate any display device that requires backlighting to present visual information. 
         [0015]    Assembly  10  further comprises a diffuser  26  overlying pipe  12  and intermediate pipe  12  and display  14 . In general, the diffuser is used to spread out and scatter light emitted from the light pipe across the display. A preferred diffuser is formed of a white polymeric film, such as white polycarbonate film. In this embodiment, assembly  10  includes a brightness enhancing film  28  intermediate device  14  and diffuser  26  that further increases the luminance. 
         [0016]    Pipe  12  is formed of a transparent material. Suitable materials include glass and polymeric resin such as an acrylic or polycarbonate compound. Pipe  12  includes a front face  16  and a rear face  18  opposite front face  16  that are planar and parallel, and sides  19  intermediate faces  16 ,  18 . In this example, pipe  12  is rectangular. Pipe  12  defines a compartment  20  having an opening at rear face  18 . Compartment  20  is defined by a cylindrical wall  21  that is optically smooth. As used herein, an optically smooth surface refers to a surface that is highly polished to minimize scattering of light impinging thereon. Alternately, the surfaces may be textured to increase scattering. Compartment  20  has a diameter and height sufficient to accommodate and receive a light source, which in the embodiment is a light emitting diode  48 . 
         [0017]    Assembly  10  also comprises a light shield  22  overlying compartment  20  to intercept light from diode  48  that is emitted directly toward the display device. Referring to  FIGS. 2-3 , shield  22  is adhesively bonded to front face  16  by an adhesive  23 . A suitable adhesive is a transparent, ultraviolet curable acrylic adhesive. Shield  22  includes a reflective surface facing diode  48  that reflects the remainder of the light toward the light pipe. Adhesive  23  preferably bonds to face  16  with optical wetting to allow the reflected light to be admitted into the light pipe with minimal loss. Preferably, shield  22  is formed of polymeric material and is semi-opaque to reflect the major portion of the light, while allowing some light to be transmitted therethrough for illuminating the center of the display. Alternately, shield  22  may be substantially opaque to minimize light transmission toward the center of the display. Shield  22  is suitable to be large enough to overlie the diode such that the diode is not seen by viewer looking into front face  16  of pipe  12  at any viewing angle. 
         [0018]    Assembly  10  also includes a housing  24  that surrounds pipe  12  and is spaced apart from sides  19 . Housing  24  includes an inner surface  25  proximate to pipe  12  that is white and reflective. 
         [0019]    Referring to  FIG. 1 , light pipe  12  includes a first channel segment  30  and a second channel segment  32  formed in rear face  18  and symmetrical about compartment  20 . Pipe  12  also includes a third channel segment  34  and a forth channel segment  36 , also formed in rear face  18  and symmetrical about compartment  20 . In this embodiment, channel segments  30 ,  32 ,  34 ,  36  are linear and are interconnected to form a continuous, rectangular channel. Channel segments  30 ,  32 ,  34 ,  36  have an optically smooth surface. Referring to  FIG. 3 , channel segments  30 ,  32 ,  34 ,  36  have a predetermined width W and a predetermined depth Y. In this embodiment, depth Y is about one-third of pipe thickness t. The amount of light intercepted by channel segment is proportional to the depth, so that a depth of one-third of the pipe thickness intercepts approximately one-third of the light traversing in pipe  12 . In general, the width W and the depth Y are selected based upon the desired uniformity and brightness requirements for backlighting display  14 . 
         [0020]    Each channel segment  30 ,  32 ,  34 ,  36  includes an inner wall, an outer wall facing the inner wall and an end wall. Referring to  FIG. 2 , channel segment  30  has inner wall  38  facing away from compartment  20 , an outer wall  40  facing compartment  20 , and an end wall  42 . Inner wall  38  and outer wall  40  are planar and parallel, and are perpendicular to, and spaced apart from, front face  16 . End wall  42  is planar and is in parallel, spaced relationship to front face  16 . 
         [0021]    Diode  48  is preferably a thin, high flux device capable of producing high light illumination intensities. Diode  48  is mechanically and electrically attached to a circuit board  54  having connections for supplying electrical energy the diode. Pipe  12  is secured to circuit board  54  using mechanical fasteners (not shown). Circuit board  54  is typically formed of FR4 circuit board material, or the like. The surface of circuit board  54  proximate rear face  18  preferably comprises a reflective coating to increase the proportion and uniformity of light illuminating the display. Pipe  12  comprises stand-off feet  57  that prevents rear face  18  from resting directly on board  54  and defines an air space intermediate light pipe  12  and board  54 , thereby providing an air interface at rear face  18 . 
         [0022]    While not limited to any particular theory, pipe  12  is formed of a transparent material having an index of refraction effective to internally reflect light propagating longitudinally therethrough. In general, for light propagating through the light pipe at incident angles relative to the surfaces within a predetermined range, total internal reflection may be achieved when the index of refraction of the material is greater than the index of refraction of the adjacent material, typically air. Incident light outside the range is extracted through the front face and may be utilized for purposes of illuminating the display. In accordance with this invention, channel segments are provided that alter the path of light rays so that the incident angel is outside the range, and thus extract the light. 
         [0023]    When light emitting diode is activated, light is emitted from the light source for backlight illumination of display  14  of assembly  10 . Referring to  FIG. 5 , there is depicted a glow pattern of light extracted from light pipe  12  toward the display device. The glow pattern includes a glow regions  62 ,  66  and  70  and dark regions  61 ,  64  and  68 . As used herein, glow region refers to a region having relatively high luminance, whereas dark regions refer to regions having reduced luminance. Referring to  FIGS. 3 and 5 , more particularly, central dark region  61  is created by shield  22  that reflects light from the light emitting diode, as indicted by ray L 1 , wherein light reflected by the shield propagates through the light pipe and, because it is not within the range of incident angles that result in internal reflection, is reflected by circuit board and extracted, thereby resulting in glow region  62  immediately about shield  22 . Since in this embodiment, shield  22  is semi-opaque, region  61 , although darker than the surrounding glow region  62 , is illuminated by light that is transmitted through the shield, and so is not devoid of light. 
         [0024]    A substantial portion of light from diode  48  propagates within the light pipe at an angle that is internally reflected by the faces thereof, as indicated by rays L 2  and L 3 . In this manner, the internally reflected light propagates through the light pipe until encountering a surface that redirects the light so as to allow the light to be exit the light pipe. Because the light is internally reflected, minimal light is emitted by dark regions  64  and  68 . However, a portion of the light is intercepted by channel segments  30 ,  32 ,  34  and  36  and is redirected, as indicated by ray L 2 , at an angle that causes the light to be extracted, thereby resulting in glow region  66  and providing preferential backlighting for the middle region of display device  14 . Light refracted by the channel segments may also be refracted toward circuit board  54  and reflected or scattered toward the front face, further contributing to glow region  66 . A portion of the light propagating through the light pipe is not intercepted by the channel segments, for example, propagating within the light pipe between the front face and the end wall  42 , as indicated by ray L 3 . Upon reaching sides  19 , the light exits the light pipe and is reflected by housing  24  or circuit board  54 , thereby resulting in glow region  70 . Some light may be reflected back towards sides  19 , reenters pipe  12 , and propagates through the light pipe by internal reflection until being redirected by channel segments  30 ,  32 ,  34  and  36 , or by compartment  20 . 
         [0025]    Referring to  FIG. 5 , illumination uniformity and intensity of display  10  is a function of the combination of light from glow regions  62 ,  66 , and  70 . Following extraction, the light is diffused by diffuser  26  to provide more uniform illumination of display device  14 . Diffuser  26  combines and spreads out light emitted from the glow regions to provide illumination of the display, including in regions overlying dark regions  61 ,  64  and  68 . Additionally, diffuser  26  assists to obscure the contents of display assembly  10  from the viewer of display  14 . Brightness enhancing film  28  contains a series of parallel prisms (not shown) that allows light to exit substantially perpendicular to display  14 , thus, redirecting remaining light back into pipe  12  within housing  24 . The recycling of light in assembly  10  aids to produce uniform backlighting for display  14 . 
         [0026]    In the described embodiment shown in  FIGS. 1-5 , backlighting is provided by light pipe having a rectangular channel with linear segments symmetrical about a central compartment. Alternately, backlighting may be provided using channel segments that are arcuate, or channel segments that are not interconnected. Referring to  FIG. 8 , in an alternate embodiment, a light pipe  112  comprises a first channel segment  130  that is arcuate, a second channel segment  132  that is arcuate, a third channel segment  134  that is arcuate, and a forth channel segment  136  that is arcuate. Channel segments  130 ,  132 ,  134 ,  136  are in rear face  118 . First channel segment  130  and second channel segment  132  are symmetrical about a compartment  120 . Third channel segment  134  and fourth channel segment  136  are symmetrical about compartment  120 . Third channel segment  134  is remote from compartment  120  and first channel segment  130 . Forth channel segment  136  is remote from compartment  120  and second channel segment  132 . Additionally, a first vertical channel segment  137 , a second vertical channel segment  139 , a first horizontal channel segment  141 , and a second horizontal channel segment  143 , are linear. Vertical channel segments  137 ,  139  are symmetrical about compartment  120 . First vertical channel segment  137  is parallel to second vertical channel segment  139 . Horizontal channel segments  141 ,  143  are symmetrical about compartment  120 . First horizontal channel segment  141  is parallel to second horizontal channel segment  143 . Vertical channel segments  137 ,  139  are perpendicular to horizontal channel segments  141 ,  143 . 
         [0027]    Also, in the embodiment in  FIGS. 1-5 , the light shield is adhesively affixed to the front face of the light pipe. Alternately, the light shield may be suitably disposed in a recess formed in the front face about the central compartment. Referring to  FIG. 6 , a recess  276  is formed in the front face of pipe  212  about compartment  220  that contains diode  248 . A light shield  222  is disposed in the recess. The light shield may be secured by adhesive. Alternately, the light shield may be secured with a press, or interference fit securing to eliminate the need for adhesive. Still further, the light shield may be integrally molded (not shown) in the compartment of the light pipe. Recessing the light shield provides a front face for the light pipe that is planar, thereby allowing the overall height of the assembly to be reduced. Moreover, when a semi-opaque shield is used, positioning the shield closer to the light source may increase the portion of light transmitted therethrough to brighten illumination of the center of the display. 
         [0028]    In the embodiment in  FIGS. 1-5 , the channel segments included an end wall that is planar and parallel to the front face of the light pipe. In a further alternate embodiment, referring to  FIG. 7 , the channel segments include a concave end wall  142  intermediate the inner wall and the outer wall. The concave end wall facilitates manufacturing optically smooth channel surfaces that minimize light scattering. 
         [0029]    Thus, this invention provides a display assembly that provides improved backlight uniformity while achieving increased illumination levels. A light shield is provided overlying the compartment containing the light source to avoid an bright spot in the display. Channel segments in a rear face symmetrical about a compartment enhance illumination in the middle portion of the display. Light reflection about the sides of the light pipe provides enhanced illumination along an outer periphery of the display. This allows the light to be combined or spread out, for example, using a diffuser and a light enhancing film, to provide a desired illumination pattern for the display. 
         [0030]    While this invention has been described in terms of the preferred embodiment thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.