Abstract:
A light guide with optics accurately controls the light exiting the guide. The device achieves accurate control of the reflected light by extracting light from a limited area of the light guide. The configuration of the reflectors used for the selective extraction determines the nature of the output light. The reflectors are preferably located on a side of the light guide opposite to an output side of the light guide.

Description:
[0001]    Applicant incorporates by reference herein his co-pending application “TIR Switched Flat Panel Display”, filed concurrently with this application. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates generally to light display devices, and more particularly is an optical system to control the direction light travels as it exits a light guide. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many products require an optical system to spread light over a large area and control the direction of the light as it exits the system. Recent improvements in the performance of LEDs, coupled with a concurrent reduction in the cost of production, have made LEDs a more viable option for many applications. However, many applications; such as LCD backlights, signs with backlights, overhead lighting, and automotive lighting; require the concentrated light that is generated by an LED to be spread over a large area, while still controlling the direction of the light. These applications require an improved optic system to provide the desired light control. 
         [0004]    Displays based on LCD technology have been evolving for decades. Numerous patent references based on improvements to the basic technology are now available. However, current art displays still have several shortcomings. The chief shortcoming of current art devices is excessive energy consumption. A 65″ diagonal HDTV LCD TV typically draws around a half of a kilowatt. This is a result of the poor efficiency of the technology. 
         [0005]    One way to improve the efficiency of LCD displays is to direct as much as possible of the available light from the light source toward the area most easily seen by the viewer. With a hand held display device, where power consumption is clearly an important consideration, a narrowly angled light directed towards the viewer is desired. 
         [0006]    In a standing application, such as a TV, it is desirable to have the highest intensity segment of the light projected in a direction normal to the surface of the display. It is also important to provide a significant amount of light to the left and right of normal. This is required for viewers that are not in the optimal (normal to the screen) viewing position. It is also desirable in these applications to reduce the amount of light that is projected above and below the angel normal to the screen. If the light that is typically directed in the off normal directions is re-directed to the preferred angles, the intensity of the light transmitted in the preferred directions would be greater. 
         [0007]    Three groups of prior art references have addressed the control of light to LCD type displays. Among these, prism type “brightness enhancing films” (BEFs), comprise the most common class. One example of a BEF device is U.S. Pat. No. 5,467,208, “Liquid Crystal Display” by Shozo Kokawa, et al., issued Nov. 14, 1995. This reference discusses the prior art of prism type films and discloses improvements to the art. One drawback to prism films is that they have only limited control of the angles of the light output. Changes to the prism features result in only slight variations in the light output. The prism films are also limited to a two dimensional structure. If an application requires control of the light in three dimensions, at least two BEFs must be deployed. 
         [0008]    A second class of prior art is exemplified by U.S. Pat. No. 6,421,103, “Liquid Crystal Display Apparatus . . . ” by Akira Yamaguchi, issued Jul. 16, 2002. The Yamaguchi reference discloses another device to control light as it enters an LCD panel. The patent discloses light sources, a substrate (not used as a light guide), apertures, and reflective regions on the substrate. The light is either reflected by the reflective surface or passes through the apertures. The light that passes through the apertures is captured by a lens used to control the direction of the light. Yamaguchi teaches restriction of the angle of the output light to concentrate more light directly at the viewer of an LCD type display. The Yamaguchi device provides much greater control of the output light than can be had with a BEF device. But a drawback to the Yamaguchi device is that it is extremely inefficient. Light must reflect off of the reflective surface many times before it exits the aperture. Even when the reflective surface is made with a high reflectance material, the losses in intensity are substantial. Therefore while the control of light with this invention is superior to that of BEF devices, the efficiency is much poorer. 
         [0009]    U.S. Pat. No. 5,396,350, “Backlighting Apparatus . . . ” by Karl Beeson, issued Mar. 7, 1995; and U.S. Pat. No. 7,345,824, “Light Collimating Device” by Neil Lubart, issued Mar. 18, 2008; disclose devices in the third class of light control optics for LED light source devices. The Beeson and Lubart references disclose a reflective structure on the side of the light guide. The range of control of these reflective structures is limited, and is not equivalent to the control afforded by devices such as Yamaguchi. Further, the reflective structures are positioned very close to the LCD panel, which allows defects in their output to be easily seen by the viewer of the display. 
         [0010]    Accordingly, it is an object of the present invention to provide a light guide that is extremely efficient. 
         [0011]    It is another object of the present invention to provide a less complex light guide thereby reducing the cost to manufacture. 
         [0012]    It is a further object of the present invention to provide a light guide that will provide accurate control of the direction of light output. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention is an optic system for a light guide that controls the angle of the light as it exits the system. It can be used in many applications from LCD to overhead lighting. The LCD displays are of the type used in cellular phones, laptop computers, computer monitors, TVs and commercial displays. The light guide extracts light from the light guide at discrete points. Using the extraction elements in combination with a reflector, the output light of the device can be controlled to be parallel, divergent or convergent. The reflectors can be two dimensional or three dimensional. 
         [0014]    An advantage of the optic system of the present invention is that it accurately controls the angles of the output light. 
         [0015]    Another advantage of the optic system of the present invention is that it transmits light more efficiently than prior art devices. 
         [0016]    Yet another advantage of optic system of the present invention is that it is simple in construction, and therefore easy and economical to manufacture. 
         [0017]    These and other objectives and advantages of the present invention will become apparent to those skilled in the art in view of the description of the best presently known mode of carrying out the invention as described herein and as illustrated in the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of the light guide with optics of the present invention. 
           [0019]      FIG. 2  is a partial, magnified side view of the light guide with optics shown in  FIG. 1 . 
           [0020]      FIG. 3  illustrates three dimensional type reflectors. 
           [0021]      FIG. 4  shows two dimensional type reflectors. 
           [0022]      FIG. 5  is a broken side view of the light guide, LCD, and end reflectors. 
           [0023]      FIG. 6  is a partial, magnified side view of a different construction of the optic system. 
           [0024]      FIG. 7  shows a magnified side view of another construction of the optic system. 
           [0025]      FIG. 8  illustrates an optic system utilizing a divergent type reflector. 
           [0026]      FIG. 9  shows a magnified side view of another construction of the optic system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring first to  FIG. 1 , the light guide assembly  1  of the present invention comprises a light guide  2  with a planar surface and a plurality of LEDs  3 . The LEDs  3  are located along a lower edge of the light guide  2 . The number of colors of LEDs  3  and the side of the light guide  2  where the LEDs  3  are located would be a function of the size, shape and application of the light guide  2 . The LEDs  3  can be situated on more than one side of the light guide  2 . The LEDs  3  require electronics to drive them at the proper level. A person knowledgeable in LED driver electronics could devise many different circuits to accomplish this task. The preferred embodiment illustrated in  FIG. 1  comprises a total of  27  LEDs  3  shown generally equally spaced along the bottom edge of the light guide  2 . It should be recognized that other types of light sources such as incandescent or florescent, will suffice in the place of the LEDs  3 . 
         [0028]    The light guide  2  is shown in a magnified side view in  FIG. 2 .  FIG. 2  shows a sampling of light rays  17  emanating from the LED  3 . Upper light ray  10  is depicted as striking the upper surface  11  of the light guide  2 . When the contact angle of light ray  10  with the surface of the light guide  2  is shallow, the light reflects off of the surface of the light guide  2 . This reflection is governed by the equation: 
         [0000]        A =arcsine( Ns/Nlg )       Where Nlg is the index of refraction of the light guide         
         [0030]    And where Ns is the index of refraction of the medium outside the light guide
       A is the angle from normal to the surface of the light guide       
 
         [0032]    For air or another low index material, Ns would be 1.35 or less. For a plastic or glass light guide  2 , Nlg might be 1.5. Angle A for these values is 64°. 
         [0033]    If light strikes the surface of the light guide  2  at an angle less than A, light will reflect off of the surface, in total internal reflection (TIR). If the angle of incidence is greater than A, light will pass through the upper light guide surface  11  and would be refracted. In the case stated, the light reflects off the upper light guide surface  11 . The upper reflected light  13  continues in a downward direction where it encounters a contact dome  14 . The contact dome  14  is preferably the same or greater in index of refraction than the light guide  2 . If the indexes of the light guide  2  and the contact dome  14  are the same, the light  13  continues to travel in the same direction. If the indexes of refraction are slightly different, the light  13  is refracted. If the indexes are much different, and the contact dome  14  has a lessor index of refraction, light may again TIR. For most applications, it is undesirable to have any light TIR in the area where the contact dome  14  makes contact with the light guide  2 . Selecting a contact dome  14  with an index of refraction greater than that of the light guide  2  insures complete passage of the light. 
         [0034]    The upper reflected light  13  continues through the contact dome  14  and strikes a reflector  15 . If the angle at which the light  13  strikes the reflector  15  is not within the TIR range, the surface of the reflector  15  must be coated with a reflective material to reflect the light. The reflective material could be aluminum, silver, a dielectric interference type mirror, or other reflective materials or methods. If the reflector  15  is configured with angles that fall within the stated TIR formula, the reflector  15  need not be coated. The light TIR reflects off the surface of the reflector  15 . 
         [0035]    It should be noted that in all the configurations disclosed herein, the reflector  15  structures are optically isolated from the light guide  2 . In the configuration illustrated in  FIG. 2 , the isolation is accomplished by providing a slight air gap  16  between the light guide  2  and the structure comprising the reflectors  15 . (An alternative method, discussed below with reference to  FIG. 9 , is to install a layer of a low index material between the light guide  2  and the reflector  15  structure.) 
         [0036]    The shape of the reflectors  15  determines the direction the light is reflected and therefore the nature of the output light.  FIG. 2  illustrates the reflector  15  as being generally elliptical. An ellipse shaped reflector  15  focuses the light to a point, or causes the light to exit the reflector  15  at multiple angles. If reflector  15  is parabolic shaped, the light exiting the light guide  2  would be generally parallel. It should be noted that if an elliptical reflector or parabolic reflector is chosen, the focal point of the reflectors would most likely be located at the surface, where the contact dome  14  and the light guide  2  meet. Many other shapes could be used for the reflector  15 , the choice being dependent on a desired angular output of the light. 
         [0037]    Referring now to  FIG. 3 , the reflectors  15  are shown as three dimensional type reflectors. The reflectors  15  could as easily be selected to be two dimensional, linear type reflectors, such as that shown in  FIG. 4 . Again, the choice of which type of reflector  15  is used depends on the application being considered. A user could also select many combinations of reflector shapes, and could employ them in either a two dimensional or three dimensional type configuration. Both the two dimensional and the three dimensional reflectors are shown as an array of reflectors  15  in  FIGS. 3 and 4 . Those skilled in the art will recognize that many other types of reflector arrays could also be deployed. 
         [0038]      FIG. 5  shows a magnified side view of the light guide  2 , an LED  3 , and the end reflectors  20  and  21 . Light will often travel through the light guide from the LED  3  and not reflect off a contact dome  14  that is in an on position and therefore extracting light from the light guide  2 . In that situation, the light would travel the full length of the light guide  2 . When the light reaches the distal end of the light guide  2 , the end opposite the LEDs  3 , the light is reflected off the end reflector  21 . The reflection redirects the light in the opposite direction through the light guide  2 , back toward the originating LEDs  3 . Preferably, the end reflector  21  is formed from a material with high reflectance. Interference type or metal reflectors are two possible alternatives for the end reflector  21 . A third possibility would be an angled, retro type reflector. 
         [0039]    If the light continues to travel in the light guide  2  without contacting one of the contact domes  14 , the light will reach the originating end of the light guide  2 , the end where the LEDs  3  are located. At this end of the light guide  2 , the light will either strike the area between the LEDs  3  or it will strike the LEDs  3 . When the light strikes the area between the LEDs  3 , it will be reflected by the end reflector  20 . If the light guide  2  has only a few LEDs  3 , the light will almost always reflect off of the high reflectance end reflector  20 . In the cases of the light reflecting off an LED  3 , the LED  3  will absorb a portion of the light, and the remainder of the light will be reflected. Light may travel up and down the light guide  2  a number of times before it is extracted by a contact dome  14 . This would be the case when there are only a few contact domes  14  in the particular light guide assembly  1 . If many of the contact domes  14  were present in the light guide  2 , the likelihood of light making more than one or two passes along the light guide  2  is small. Even in the case of a large number of reflections with the light making multiple passes along the light guide  2 , the loss of light is small. The end reflectors  20 ,  21  have reflectance efficiencies of 98% or better, and good quality light guide material absorbs very little light. 
         [0040]    An alternate configuration of the light guide assembly  1  is shown in  FIG. 6 , in which the reflectors  15  are hollow rather than made from a solid material as is typically the case. In this configuration, the contact dome  14  employs a tapered or spherical surface  22  so the upper reflected light  13  passes through the contact dome  14  and continues along a generally straight path toward the surface of the reflector  15  when the contact dome is in the on position. The function of the light guide assembly  1  illustrated in  FIG. 6  is the same as for the guide assembly  1  illustrated in  FIG. 2 , the only difference being the utilization of hollow reflectors  15 ′. 
         [0041]    Another configuration of the light guide assembly  1  is illustrated in  FIG. 7 . In the configuration shown in  FIG. 7 , the features of the contact dome  14  are cut into the surface of the light guide  2 . This configuration is, in effect, a negative of the configuration illustrated in  FIG. 2 . As with the assembly  1  shown in  FIG. 6 , the function of the light guide assembly  1  shown in  FIG. 7  is the same as that shown in  FIG. 2 . Ease of manufacturing and desired output effects control which reflector construction is chosen for a given application. 
         [0042]      FIG. 8  shows a configuration of the light guide assembly  1  in which the output light is spread as opposed to being directed to a focal point. As discussed above, the shape of the reflectors  15  controls the output effect of the light. In  FIG. 8 , the shape of the reflectors  15  is chosen to scatter the reflected light rays  18 , as opposed to directing the light to a focal point. 
         [0043]      FIG. 9  discloses an alternative method for optically isolating the reflector  15  structures from the light guide  2 . In the configuration illustrated in  FIG. 9 , a thin layer  30  of a material with a low index of refraction separates the light guide  2  from the structure supporting the reflectors  15 . The contact domes  14 ″ are simply apertures in the thin, low index of refraction layer  30 . 
         [0044]    The thickness of the low index layer  30  in  FIG. 9  is not to scale. In practice, the low index layer  30  would be only microns thick. The thin layer  30  can be deposited with a lithographic process. The reflectors  15  and contact domes  14 ″ would then be molded in direct contact with the light guide  2  and the thin layer  30 . Adhesive can be used as the low index material  30 . Choosing an adhesive as the low index material  30  is often beneficial to the manufacturing process. 
         [0045]    The above disclosure is not intended as limiting. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the restrictions of the appended claims.