Abstract:
A lighting device for lighting a display surface is provided. The lighting device includes a light source, a lighting well and a lens, which is arranged between the light source and the display surface. Due to the combined use of the lighting well and the lens, light scattered laterally is also reflected in the direction of the display surface.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a lighting device. 
   BACKGROUND INFORMATION 
   Lighting devices from other systems involve light sources for backlighting the display surface that are arranged on a side facing away from the user. To permit a homogeneous brightness distribution in backlighting the display surface, the light emitted by the light sources must be highly scattered, so that it may be distributed uniformly over the entire display surface. Furthermore, a light guide plate with light sources placed on its side faces may be arranged behind the display surface. The light of these light sources is injected into the light guide plate and deflected in the direction of the display surface. Light scatter may be omitted here, but provisions must be made for deflection of light and space must be provided for the light source in a lateral area of the display. 
   SUMMARY OF THE INVENTION 
   The exemplary lighting device according to the present invention may provide that light is distributed homogeneously over the entire display surface by using a reflector and a lens between the light source and the display surface, so that homogeneous lighting of the display surface may be achieved without additional films to be applied and without any additional light scatter. Due to the combined use of a reflector and a lens between the light source and the display surface, particularly efficient lighting of the display surface is allowed, because light scattered laterally is also reflected in the direction of the display surface. 
   The distance of the lens from the light source may be selected to be in the range of the focal distance of the lens. Then the lens does not function as an imaging optical system, but instead it homogenizes the light distribution of the light source. 
   The lighting well may be configured as a parabolic reflector to obtain a particularly homogeneous light distribution. 
   Light-emitting diodes may be used as the light sources because they are inexpensive and simple to install. Although traditional LEDs generally emit light in a preferential direction, a light cone emitted by the LED is widened for lighting a display surface by using the exemplary lighting device according to the present invention. 
   The lens may be located on a side of the lighting well facing away from the light source because in this manner the lens is integrally molded onto a light guide, for example, which is applied to the lighting well during the manufacture of the lighting device. A required plurality of lenses may be produced in one operation by integral molding onto a light guide for light sources arranged side-by-side. 
   A lens may be located on the light source, because in this manner the light source and the lens may be produced in one manufacturing operation, the lens may be molded onto a body of the LED and/or shaped by using an embossing stamp, for example. 
   The lens may be configured in an area around the optical axis of the lens as a dispersing lens and outside this area to configure it as a collecting lens. This makes the light distribution homogeneous due to the fact that the light is dispersed into central, very light areas of the light source and is collected and deflected in the direction of the display surface in edge areas where the light source is dark. 
   The exemplary lighting device according to the present invention may be used for backlighting a planar display because homogeneous backlighting is allowed using light sources, e.g., LEDs, due to the exemplary lighting device according to the present invention. 
   An exemplary lighting device according to the present invention may be used for a scale display in which individual segments of the scale are separately lightable and the particular lighting is separately controllable. Using an exemplary lighting device according to the present invention for each scale segment allows for implementation of a homogeneous, efficient and inexpensive backlighting, e.g., in comparison with regulating a scale segment lighting by using a liquid crystal cell. This exemplary lighting device according to the present invention may be used for a cruise control display in which individual segments are regularly activated or deactivated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  shows a first exemplary embodiment of a lighting device according to the present invention in a side view. 
       FIG. 1   b  shows a top view of the first exemplary embodiment. 
       FIG. 2   a  shows a first side view of another exemplary embodiment according to the present invention of a lighting device for a scale display. 
       FIG. 2   b  shows another side view of the second exemplary embodiment according to the present invention. 
       FIG. 2   c  shows a top view of the second exemplary embodiment according to the present invention. 
       FIG. 3  shows an exemplary embodiment of a light source according to the present invention in a cross section. 
       FIG. 4   a  shows an exemplary embodiment of a system of a lighting device according to the present invention for backlighting a planar display. 
       FIG. 4   b  shows a scale instrument which is lighted using an exemplary lighting device according to the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1   a  shows a side view of a first exemplary embodiment of a lighting device according to the present invention including a light source  1  provided on a circuit board  2 . A lens  3  which deflects the light into a lighting well  4  is provided on light source  1 . Lighting well  4  is bordered by a reflector  5  at the side. A diffuser  6  is provided on one end of lighting well  4  diametrically opposed to light source  1 . A liquid crystal cell  7  is provided on the side of diffuser  6  facing away from lighting well  4 . Light source  1  is configured as an LED. Light source  1  is supplied with an operating voltage via printed conductors (not shown in  FIG. 1   a ) over circuit board  2 . The light of light source  1  deflected by lens  3  either strikes diffuser  6  directly or strikes reflector  5  which forms the walls of lighting well  4 . Reflector  5  is configured as a rotating body including a parabolic cross section. Reflector  5  is made of a white nonreflective plastic material. A configuration as a metal reflector is also allowed. Diffuser  6  is made of a plastic material and in an exemplary embodiment it is made of a plastic material with light-scattering particles incorporated into it, e.g., particles of a different plastic material having a different refractive index.  FIG. 1   a  shows a liquid crystal cell  7  on diffuser  6 ; in an exemplary embodiment, the pixels of this liquid crystal cell are individually activatable electrically.  FIG. 1   a  does not show the details of liquid crystal cell  7 . The light guided from light source  1  through lens  3  either strikes diffuser  6  directly or first strikes reflector  5  and then is deflected to diffuser  6 . Diffuser  6  contributes toward further homogenization of the light and deflects the light to liquid crystal cell  7 . In one exemplary embodiment not shown in  FIG. 1   a , an invariable display, e.g., a dial or a warning field, e.g., made of a transparent plastic material including warning symbols printed on it, may be placed here instead of liquid crystal cell  7 . In an exemplary embodiment, a warning symbol may be printed directly on diffuser  6 . 
     FIG. 1   b  shows a view of the exemplary lighting device according to the present invention, which was described with regard to  FIG. 2   a , without diffuser  6  or liquid crystal cell  7 . Lighting well  4  is formed by reflector  5 . Light source  1  together with lens  3  is arranged at the center of reflector  5 . 
     FIG. 2   a  shows another exemplary embodiment of a lighting device according to the present invention in which a light source  10  is arranged on a circuit board  11 . On the side facing away from circuit board  11 , light source  10  is provided on a lighting well  12  and/or arranged so that it projects at least partially into lighting well  12  formed by a reflector  13 . Reflector  13  is molded from a support  14 . On the side of lighting well  12  facing away from light source  10 , a lens  15  is provided, integrally molded on a light guide  16  which rests on support  14 . Light from a light guide plate  18  which is arranged at the side next to light guide  16  and is adjacent to light guide  16  is injectable into a side face  17  of the light guide. Light guide plate  18  is lightable by another light source  19 . Light source  10  is optically separated from additional light source  19  by support  14  which forms lighting well  12 . A dial  20  is provided on the side of light guide  16  facing away from light source  10 . Dial  20 , which may be a numerical dial, includes first areas  21  which are opaque to light and second areas  22  which are permeable to light. Light source  10  is configured as an LED which is supplied with an operating voltage via circuit board  11 . In an exemplary embodiment, support  14  is made of a plastic material such as polycarbonate pigmented with white pigment particles. In this manner, reflector  13  may be formed by a surface of support  14 . In an exemplary embodiment not shown in  FIG. 2   a , metal coating of support  14  is also allowed. The light emitted by light source  10  either goes directly to lens  15  or is first deflected by reflector  13  to lens  15 . Dial  20 , which may be a numerical dial, is made of a transparent plastic material in which opaque first areas  21  may be applied by imprinting, for example. Symbols, scale segments or numbers may also be imaged through a suitable imprint. Light may be emitted to light guide plate  18  by additional light source  19 , the light guide plate is made of a light-scattering material. Light is emitted by light guide plate  18  through light-permeable second areas  22  on dial  20 . Furthermore, light is deflected by light guide plate  18  to first side face  17  of light guide  16  so that even for the case when light source  10  is not being operated, a segment  22 ′ is at least weakly illuminated on the side of lens  15  facing away from light source  10 . Segment  22 ′ is then discernable even when light source  10  is switched off. This ensures that switching is allowed between a weakly illuminated state, namely illumination by additional light source  19 , light guide plate  18 , and light guide  16 , and a brightly illuminated state when light source  10  is turned on. However, only an insignificant amount of light is sent from light source  10  into light guide plate  18  because the light is deflected by lens  15  in the direction of segment  22 ′. Light guide  16  and light guide plate  18  are made of polycarbonate in an exemplary embodiment, light guide  16  and lens  15  are configured to be transparent here. 
     FIG. 2   b  shows another side view of the exemplary lighting device according to the present invention as shown in  FIG. 2   a . Light guide  16  including an integral lens  15  sits on support  14  with contact faces  23 ,  23 ′. Lens  15  has a convex curvature in the direction of light source  10 . Additional lenses  15 ′ and  15 ″ belonging to other lighting devices provided in addition to the exemplary lighting device according to the present invention, all are similar in configuration, are connected to light guide  16  on contact faces  23  and  23 ′ of light guide  16  on support  14 . The distance between lens  15  and light source  10  is approximately equal to the focal distance of lens  15 . Therefore, lens  15  does not have an imaging function but instead performs a Fourier transform of the image in the focal plane, so that segment  22 ′ is homogeneously backlighted. Segment  22 ′ is separated from other transparent regions, i.e., segments  24 ,  24 ′ of dial  20  by opaque first regions  21 , so that separate backlighting of segments  22 ′,  24 ′ and  24  is allowed. Reflector  13  in the exemplary embodiment according to  FIGS. 2   a  and  2   b  includes walls running linearly. In an exemplary embodiment, lighting well  12  bordered by reflector  13  includes a rectangular section in a plane parallel to the plane of the lens of lens  15 . 
     FIG. 2   c  shows a top view of dial  20  behind which is arranged the exemplary lighting device according to the present invention as described in conjunction with  FIGS. 2   a  and  2   b . A section through the exemplary lighting device according to the present invention is shown by broken lines in  FIG. 2   c , the section according to  FIG. 2   a  is represented by the letters a and the section according to  FIG. 2   b  is represented by the letters b. In addition to opaque first regions  21 , second light-permeable regions  22  represent a number formed by transparent regions on dial  20 . The number is backlightable by additional light source  19  and light guide plate  18 . Segment  22 ′ is lighted by light source  10  separately from segments  24  and  24 ′ which in an exemplary embodiment are each individually activatable by a lighting device according to the present invention. A basic brightness of the segments is ensured by light guide plate  18  even when the light sources behind segments  22 ′,  24  and  24 ′ are turned off. 
     FIG. 3  shows an exemplary embodiment of a location of the lens according to the present invention directly at the light source. The light source described in conjunction with  FIG. 3  is used in particular as light source  1  in the exemplary embodiment explained with reference to  FIG. 1   a . Instead of an LED, an incandescent lamp, a glow lamp, and/or a fluorescent lamp may be used.  FIG. 3  shows the location of a lens at a light source  1  configured as an LED, which may be a top LED. Light source  1  includes a light-producing region  30  which is made of a semiconductor material which is excited by trigger lines (not shown in the figure) to emit light. Light source  1  also includes a housing  31  in which is arranged lens  3 , configured to have rotational symmetry with an optical axis  40  in light-producing region  30 . Lens  3  includes a first region  33  and a second region  32 , first region  33  is arranged beneath a surface  34  of housing  31 , surface  34  facing in the direction of diffuser  6 . Second region  32  is arranged on the side of surface  34  facing diffuser  6 . First region  33  includes light-producing region  30  and has a pot shape. Side faces  36  running linearly to surface  34  of housing  31  are connected to pot bottom  35  running parallel to surface  34 . Side faces  36  are configured to be reflective in an exemplary embodiment and, like housing  31 , are made of a white plastic material. A transition between first region  33  and second region  32  is represented by a dotted line  39 , which defines a diameter of lens  3 , i.e., a double lens radius. Second region  32  is divided into an internal region  38  and an external region  37  with respect to optical axis  40  running perpendicular to surface  34 . A border of the internal region is defined by a predefined radius about optical axis  40  which is smaller than the lens radius. In internal region  38 , a surface of lens  3  has a concave curvature so that lens  3  acts to disperse light in internal region  38 . A first ray of light  41  from light-producing region  30  is shown in the figure, passing through internal region  38  and leaving lens  3  in internal region  38 . First ray of light  41  is diffracted away from optical axis  40 . The walls of lens  3  are connected to surface  34  of housing  31  in external region  37  and are also connected in internal region  38 . A surface of lens  3  runs linearly in external region  37 , forming a wall running around internal region  38 . A second ray of light  42  begins at light-producing region  30 , leaves the lens in external region  37  and is diffracted toward optical axis  40 . 
     FIG. 4   b  shows a scale display including a dial  60  on which is displayed a numerical value on a scale  64  by a pointer. In an exemplary embodiment, the scale display is used for the speed display in a motor vehicle. A pointer  61  is movable on a pointer shaft  63  and points to a value on a scale  64  which is marked with numerical values 65.  FIG. 4   b  shows numerical values 65 of “0,” “20,” “40,” “60” and “80” on scale  64 . Scale  64  includes individual scale segments  66 , only one scale segment  66  of which is provided with a reference number in the figure for reasons of simplicity. Scale segments  66  are provided with one lighting device each on the side of dial  60  facing away from pointer  61 , the lighting devices are electrically activatable separately so that individual scale segments  66  may be lighted up individually. Numerical values  65  are all lightable by one source for which light is also injected into scale segments  66  in the manner according to the present invention, as described in conjunction with  FIG. 2   a , when light sources  10  behind scale segments  66  are turned off. The exemplary lighting devices are controllable by a computing device (not shown in  FIG. 4   b ) just as pointer  61  is controllable by a stepping motor mounted on pointer shaft  63  and also connected to the computing device. If a numerical value of “60” is preselected by user input, e.g., a speed of 60 kilometers per hour is selected, then all scale segments starting from numerical value 0 up to numerical value “60” are lighted up by the exemplary lighting devices according to the present invention. Scale segments from “60” to “100” to remain dark and are lighted only faintly by additional light source  19 , which also lights up numerical values 65. A speed of 60 km per hour in an exemplary embodiment is a preselected speed in a cruise control in a motor vehicle in which a speed is input into the computing device and an automotive drive is regulated by the computing device so that the vehicle travels at the selected speed. The actual vehicle speed is then displayed by counter  61  on scale  64 , so that a user constantly has an opportunity to compare a setpoint speed, namely the speed which is represented by the brightly lighted scale segments, e.g., 60 km/h with the actual vehicle speed. Since scale segments  66  are individually activatable, any other desired speed values may be preselected and displayed as a setpoint speed by a corresponding lighting of the scale segments.