Abstract:
A light guide assembly for illuminating an instrument surface includes a continuous curved transition portion for uniformly directing and transmitting light from a light source to a backlight surface of the instrument surface. The curved shape of the transition portion is tailored to transmit a desired amount of light into the backlight portion and a desired amount outwardly against a back surface of the instrument surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The application claims priority to U.S. Provisional Application No. 60/692,193 which was filed on Jun. 20, 2005. 

   BACKGROUND OF THE INVENTION 
   This invention generally relates to light guide assembly for an illuminated dial. More particularly, this invention relates to a light guide assembly for an illuminated dial that increases light use efficiency. 
   Conventional illuminated dials utilize a light source such as a light emitting diode (LED) mounted to a circuit board and a light guide device. The light guide device directs light from the mounting location on the circuit board to the surface of the dial. In some applications it is desired to direct light parallel to the surface of the dial to provide the desired aesthetic appearance. Light is therefore directed by way of straight light guide portions connected at a relative angle to each other. The angular connection between straight light guide portions creates an over illuminated point that is not desirable. The over illuminated point or intersection between the straight light guide portions is typically blocked to prevent the over illumination from destroying a desired uniform appearance. For this reason, the angular portion is typically minimized so that the desired uniform lighted surface is available to illuminate more of the gauge. 
   Blocking light at the intersection points reduces the amount of light available for illuminating the dial gauge. In some instances as much, if not more than 30% of the available light is blocked, thereby reducing the efficiency of the light source and potentially requiring the use of an increased number of light sources, or the use of larger light sources that require more power to obtain the desired illumination. 
   Accordingly, it is desirable to design and develop a light guide assembly that increases the efficiency of light utilized for illuminating a dial or other instrument device. 
   SUMMARY OF THE INVENTION 
   An example light guide assembly for illuminating an instrument surface includes a transition portion for directing and transmitting light from a light source to a back lit surface. 
   The example light guide assembly includes the curved transition portion that directs light from a light source into a portion of the light guide behind the instrument surface. The transition portion between the light source and the surface behind the instrument surface also transmits a portion of light onto a back side of the instrument surface. The light is utilized to illuminate a further portion of the instrument surface, without the need for additional light sources. The transition portion includes a curved shape that provides a uniform illumination that does not produce over illuminated points that require blocking such that more light is available for illumination purposes. 
   Accordingly, the light guide assembly includes features that provide for the uniform illumination of an instrument surface and the increased utilization of available light. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of an example illuminated gauge assembly. 
       FIG. 2  is an exploded view of the example illuminated gauge assembly. 
       FIG. 3  is a top view of an example light guide assembly. 
       FIG. 4  is a cross-sectional view of the example light guide assembly. 
       FIG. 5  is a perspective view of the example light guide assembly. 
       FIG. 6  is a top view of an example light guide. 
       FIG. 7  is a front view of the example light guide. 
       FIG. 8  is a cross-sectional view of the example light guide. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , an instrument assembly  10  includes a dial face  14  with a plurality of markings indicating vehicle speed in miles per hour. The dial face  14  is illuminated in a circumferential region indicated at  12 . The circumferential region is back lit by way of a light guide  16  ( FIG. 2 ). The back lit region  12  receives light from underneath the dial face  14  to illuminate portions or the entire circumferential region  12 . As appreciated, although a round instrument assembly  10  is illustrated and described, other shapes for illuminated instrument cluster assemblies will also benefit from the disclosure of this invention. 
   Referring to  FIG. 2 , the instrument assembly  10  is illustrated in an exploded view and includes the light guide  16  mounted within a housing  18 . The housing  18  and light guide  16  are in turn mounted to a printed circuit board  20  that includes light emitting diodes (LED)  22 . The LEDs  22  emit light that is received and transmitted through the light guide  16 . 
   Referring to  FIGS. 3 and 4 , the light guide  16  receives light from the LEDs  22  through a light receiving surface  28 . The light guide  16  includes a transition portion  26  and a backlight portion  24 . Light from the LEDs  22  is directed through the light receiving surface  28  through the transition portion into the backlight portion  24 . A portion of light  36  within the light guide  16  illuminates the transition portion  26  to provide illumination for a portion of the dial face  14 . The remaining portion of light  34  is directed within the light guide  16  to illuminate the backlight portion  24  to provide illumination of the remaining portion of the dial face  14 . 
   The light guide  16  includes a backing  32  that is applied to block the transmission of light through a back side of the light guide  16 . The backing  32  can be a coating that is applied to the light guide  16  or a member such as plastic sheet that is attached or assembled within the housing and adjacent the bottom of the light guide to selectively block light. 
   The light guide  16  is semi-circularly shaped with two ends. At each end is the light receiving surface  28  that is disposed to receive light from the LEDs  22 . In the illustrated example, three LEDs  22  are disposed adjacent each light receiving surface  28 . The number of LEDs is dependent on desired illumination levels for the instrument assembly  10 . More or less LEDs  22  can be utilized to provide the desired intensity of illumination. 
   Referring to  FIG. 5 , the light guide  16  directs light from the circuit board  20  through the curved transition portion  26  to the flat backlight portion  24 . The light guide  16  directs light into a plane defined by the backlight portion  24  that is substantially parallel and spaced apart from the circuit board  20 . The curved path defined by the transition portion  26  from the LED  22  to the backlight portion  24  transmits a portion of the light  36  upwardly, and directs another portion of light  34  into the backlight portion  24 . 
   Utilizing the light emitted from the transition portion  26  provides a more efficient use of light from the LEDs  22 . Instead of blocking light due to over illumination at an intersection point between straight portions, the curved transition portion provides substantially uniform illumination that does not require blocking. Accordingly, more light is available for backlighting the dial face  14 . The intensity of the light  36  transmitted through the transition portion  26  is controlled and tailored by adjusting the curvature and arc of the transition portion  26  between the light receiving surface  28  and the backlight portion  24 . Further, because the curved transition portion  26  provides uniform illumination along a length, the length of the transition portion  26  can be increased without reducing lighting efficiency. 
   Referring to  FIGS. 6 ,  7  and  8 , the light guide  16  includes the curved transition portion  26 . The degree and shape of the curved transition portion  26  provides desirable features for the direction and distribution of light. One feature is the substantial elimination of any overly bright points or intersections that provides for use of the transition portion  26  for illuminating the dial face  14 . Further, a portion of light entering the light guide is directed through the transition portion  26  to the backlight portion  24  for illumination of a surface  30  that is disposed parallel to the surface to be illuminated, such as the dial face in the illustrated example. The curvature of the transition portion  26  can be modified to tailor the amount and intensity of light that exits the light guide  16  through the transition portion  26  to further illuminate the dial face  14 . 
   The transition portion  26  may also includes a textured surface finish  38  to further tailor the intensity and quality of light emitted through the transition portion  26 . The textured surface  38  can provide a desired uniformity in illumination through the transition portion  26 . 
   Accordingly, the example light guide  16  increases the efficient utilization of emitted light by providing a uniform illumination through a transition portion that provides for directing light that would otherwise require blocking through to the back of the dial face. Further, the intensity and uniformity of light transmitted through the light guide transition portion can be modified to tailor the light intensity directed to illuminate the dial face  14 . 
   Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.