Back-light assembly

1. Field of the Invention

The present invention relates generally to back-light systems for uniform illumination of large area displays. More particularly the invention concerns collimating back-light systems for displays such as liquid crystals displays and micro-electromechanical light valve displays.

2. Discussion of the Prior Art

Back-light assemblies provide a planar light source for transmissive displays. More common light sources used in display back-lighting are cold cathode fluorescent lamps and light emitting diodes.

Based on arrangements of light sources the back-light systems may be grouped either “edge-lit” or “direct-lit”. In direct-lit, back-light's plural light sources are evenly distributed along the display area and each of the light sources directly illuminates a small segment of the display. In order to achieve relatively uniform illumination the light sources are placed at a great distance from the display panel. This increases the depth of the display. Additionally, diffractive optical components and diffusers are placed between the light sources and the display panel. Each light source must align with the diffractive optical components.

The only positive feature of direct-lit systems is that light sources and associated heat is evenly distributed along the display area.

Edge-lit back-light systems comprise a light source, a thin, rectangular optical waveguide, a reflector or a diffuser at the back of optical waveguide and prism films mounted between the waveguide and the display panel.

The primary limitation of edge-lit back-lights is its incapability of illuminating a large size display. Efficient light coupling and concentrated heat generated from the light sources limit the size of the edge-lit back-lights.

It is an object of the present invention to provide a homogenized, collimated and highly efficient back-light assembly for uniform illumination of large area display.

Another object of this invention is to provide a back-light assembly of the aforementioned character that exhibits an efficiency of greater than ninety-five percent.

It is another object of this invention to provide a back-light assembly that effectively overcomes the limitations of prior art direct-lit and edge-lit back-light systems.

It is another object of this invention to provide a back-light assembly that exhibits highly efficient light coupling between the light sources and the waveguide of the assembly.

It is another object of this invention to provide a back-light assembly of the character described in the preceding paragraphs that is easily scalable for displays of different sizes.

The foregoing as well as other objects of the invention will be achieved by the novel back-light assembly illustrated in the accompanying drawings and described in the specification that follows.

FIG. 1 is a generally perspective view of one form of the back-light assembly of the present invention.

FIG. 2 is a side-elevation view of the back-light system shown in FIG. 1 .

FIG. 3 is a side-elevation view of an alternate form of the back-light assembly of the invention.

FIG. 4 is a greatly enlarged view of the area designated in FIG. 3 as 4 - 4 .

FIG. 5 is a side-elevation view of still another form of back-light assembly of the invention.

FIG. 6 is a greatly enlarged view of the area designated in FIG. 5 as 6 - 6 .

Referring to the drawings and particularly to FIGS. 1 and 2 , one form of the back-light assembly of the invention for uniformly illuminating displays such as liquid crystal displays and micro-electromechanical light valve displays is there shown and generally designated by the numeral 14 . This embodiment of the invention comprises an optical waveguide 16 that has an upper, generally flat surface 18 , a first side surface 20 , a second side surface 22 and a specially configured lower surface 24 . Surface 24 uniquely includes a plurality of upwardly inclined optically flat first facets 26 with specularly reflective coatings and a plurality of downwardly inclined optically flat second facets 28 .

As best seen in FIG. 2 of the drawings, the first light-reflecting facets 26 are here inclined upwardly at an angle of between about two degrees and about fifteen degrees with respect to the plane of the upper surface 18 of the optical waveguide. The second light coupling facets 28 are inclined downwardly at a relatively steep angle of between about fifty degrees and about ninety degrees with respect to the plane of the upper surface 18 . As illustrated in the drawings, alternating facets 26 and 28 form generally V-shaped grooves that extend along lower surface 24 of the waveguide between sides 20 and 22 . Back-light assembly 14 also includes a light reflector panel 32 that is spaced-apart from the lower surface 24 of the optical waveguide.

Disposed between reflector panel 32 and lower surface 24 of the waveguide is a plurality of transversely spaced-apart light sources 34 . In this first embodiment of the invention, light sources 34 comprise side-mounted light emitting diodes having 120 degree emission angles that emit light in the direction of X-axis (see FIG. 2 ). It is to be understood that light sources 34 can be of various types including cold cathode fluorescent lamps with side-mounted reflectors the character of which presently is described.

Referring to FIG. 2 of the drawings, it is to be noted that certain of the light rays 36 that are generated by the light sources 34 enter into the waveguide 16 directly from the light coupling facets 28 . Additionally, depending on the angles that light rays 36 reflect from light-reflecting facets 26 and the upper surface of reflector panel 32 , and also enter the waveguide 16 from the light coupling facets 28 . Inside the waveguide 16 light rays 36 propagate in the X-axis direction by total internal reflections from the major upper surface 18 and light-reflecting facets 26 . As indicated in FIG. 2 , certain of the upwardly inclined light-reflecting facets 26 cause the light rays to exit the waveguide.

More particularly, the light rays exit the waveguide from the upper surface 18 when the light rays strike the upper surface at less than the critical angle.

Turning next to FIGS. 3 and 4 , an alternate form of the back-light assembly of the invention is there illustrated and generally designated by the numeral 40 . This latest embodiment is similar in some respects to the embodiment shown in FIGS. 1 and 2 of the drawings and like numbers are used in FIGS. 3 and 4 to identify like components. As indicated in FIG. 3 , back-light assembly 40 here comprises an optical waveguide 16 . An important feature of this second embodiment of the back-light assembly of the invention resides in the provision of a plurality of spaced-apart micro-prisms 56 that are disposed proximate lower surface 24 of the waveguide 16 . As indicated in FIGS. 3 and 4 of the drawings, each micro-prism 56 has a first facet 56 a optically coupled to a selected one of the light-reflecting facets 26 . In a similar fashion, a second facet 56 b is optically coupled to a selected one of the downwardly inclined facets 28 . Each micro-prism 56 also includes a light coupling third facet 56 c that interconnects the first and second facets 56 a and 56 b . To form the micro-prisms 56 , a UV hardening liquid polymer may be filled into the V-shaped grooves with approximately the same refractive index as the waveguide 16 .

Back-light assembly 40 also includes a light reflector panel 32 that is spaced-apart from the light coupling third facets 56 c of the micro-prisms 56 .

Disposed between reflector panel 32 and the third facets 56 c is a plurality of transversely spaced-apart light sources 34 . As in the first embodiment of the invention, light sources 34 comprise side-mounted light emitting diodes having 120 degree emission angles that emit light in the direction of the X-axis (see FIG. 3 ).

Referring to FIG. 3 of the drawings, it is to be noted that certain of the light rays 36 that are generated by the light sources 34 enter into micro-prism from the light coupling third facets 56 c.

Additionally, depending on the angles that light rays 36 reflect from the upper surface of reflector panel 32 and enter into micro-prism from the light coupling third facets 56 c.

Inside of the micro-prisms 56 light rays propagate in X-axis direction by total internal reflections from facets 56 a and 56 c and enter the waveguide 16 from facets 28 .

Inside the waveguide 16 light rays 36 propagate in the X-axis direction by total internal reflections from the major upper surface 18 and light-reflecting facets 26 . As indicated in FIG. 2 , certain of the upwardly inclined light-reflecting facets 26 cause the light rays to exit the waveguide.

More particularly, the light rays exit the waveguide from the upper surface 18 when the light rays strike the upper surface at less than the critical angle.

Referring now to FIG. 5 , still another form of the back-light assembly of the invention is there illustrated and generally designated by the 60 . This latest embodiment is similar in many respects to the embodiment shown in FIGS. 3 and 4 of the drawings and like numbers are used in FIG. 5 to identify like components. The main differences between this third embodiment of the invention and that shown in FIGS. 3 and 4 reside in the provision of a different type of light source and in the addition of a prism film 70 that is positioned adjacent the upper surface of the waveguide 16 .

As before, the back-light assembly 60 here comprises an optical waveguide 16 that includes an upper, generally flat surface 18 , a first side surface 20 , a second side surface 22 and a specially configured lower surface 24 that is identical to the lower surface described in connection with the embodiment of FIGS. 3 and 4 .

Like the embodiment in FIGS. 3 and 4 , this third embodiment of the invention includes a plurality of spaced-apart micros-prisms 56 that are disposed proximate lower surface 24 of the waveguide 16 and are identical in construction and operation to the micro-prisms described in connection with the second embodiment of the invention.

Back-light assembly 60 also includes a light reflector panel 32 that is spaced-apart from the third facets 56 c of the micro-prisms 56 .

Disposed between reflector panel 32 and the third facets 56 c is a plurality of transversely spaced-apart cold cathode fluorescent lamps 62 having side-mounted reflectors 64 (see FIG. 6 ).

As indicated in FIG. 5 of the drawings, certain of the light rays 36 that are generated by the light sources 62 enter into micro-prism from the light coupling third facets 56 c . Additionally, depending on the angles that light rays 36 reflect from the upper surface of reflector panel 32 and enter into micro-prism from the light coupling third facets 56 c . Inside of the micro-prisms 56 light rays propagate in X-axis direction by total internal reflections from facets 56 a and 56 c and enter the waveguide 16 from facets 28 .

As before, inside the waveguide 16 light rays 36 propagate in the X-axis direction by total internal reflections from the major upper surface 18 and light-reflecting facets 26 . As indicated in FIG. 2 , certain of the upwardly inclined light-reflecting facets 26 cause the light rays to exit the waveguide. More particularly, the light rays exit the waveguide from the upper surface 18 when the light rays strike the upper surface at less than the critical angle.

As previously mentioned, an important feature of this latest form of the invention is the prism film 70 that is positioned adjacent the upper surface 18 of the waveguide. As has been seen in FIG. 5 , prism film 70 is comprised of a planar upper surface 72 and a plurality alternating prismatic facets 74 a and 74 b that function to redirect the light exiting the waveguide 16 at an angle approximately perpendicular to the upper surface 72 of the prism film 70 . Light directed towards the normal is most effective for display panels such as liquid crystal displays.

Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirement or conditions. Such changes and modification may be made without departing from the scope and spirit of the invention, as set forth in the following claims.