The present invention relates to a lighting apparatus. More particularly, the present invention relates to a low profile lighting apparatus utilizing a waveguide for illumination. The invention is particularly advantageous for use as a backlight for illuminating a display.
Backlights may be used to illuminate both mechanical displays, such as on analog watches or automobile gauges, as well as electronic displays, such as liquid crystal displays used with cellular phones, and pagers, and personal digital assistants. Because many backlight applications involve smaller displays where space is at a premium, it is desirable to reduce the thickness of such backlights while still maintaining the area of illumination. Backlights thus require reduced aspect ratios, defined as the ratio of the thickness of the backlight to the length of the illumination area.
One type of a backlight utilizes of a light source, such as a light-emitting diode (LED), that is coupled to a waveguide into which light is injected. The light source is typically mounted at an outer peripheral edge of the waveguide and is energized to emit light into the waveguide. The light undergoes several reflections between the surfaces of the waveguide until being transmitted through a top surface to illuminate the display.
One difficulty associated with such backlights is they do not produce a uniform intensity across the surface of the waveguide. The light loses intensity as it propagates outward from the light source. Consequently, as the distance from the light source increases, the intensity of the light transmitted out of the waveguide decreases. This results in the portions of the waveguide distal of the light source having reduced intensity.
There is therefore a need for an efficient backlight having a low aspect ratio that provides a substantially uniform illumination profile across the entire area of illumination.
One aspect of the present invention relates to a lighting apparatus for illuminating an illumination area of a display. The lighting apparatus comprises a waveguide adapted for mounting adjacent the display so as to illuminate the illumination area of the display. The waveguide comprises a top surface having an optical output area corresponding in size to the illumination area, a bottom surface spaced apart from the top surface, and a side surface extending between the top and bottom surfaces. Reflective material is positioned adjacent the bottom and side surfaces of the waveguide. At least one light source is mounted to input light proximate to a periphery of the waveguide between the top and bottom surfaces. The waveguide further comprises a light ejector on one of the top and bottom surfaces configured to redirect light propagating between the surfaces towards the top surface for transmission therethrough. The light ejector is arranged to provide a preselected illumination profile across the optical output area of the top surface.
Another aspect of the invention relates to a lighting apparatus comprising a waveguide having pair of opposed surfaces. Each of the surfaces is at least partially reflective and at least one of the surfaces is partially transmissive. Each of the surfaces have a reflectivity greater than the transmissivity of the at least one surface.
Another aspect of the invention relates to a lighting apparatus comprising a planar waveguide having a peripheral edge and a light source mounted proximate to the peripheral edge so as to direct light into the waveguide along a path extending from the light source towards an optical diverter in the waveguide. The optical diverter in the path redirects light rays away from the path towards the periphery of the waveguide.
Yet another aspect of the invention relates to a lighting apparatus comprising a top surface, a bottom surface in spaced relationship to the top surface and cooperating with the top surface to form a waveguide having a thickness defined by the distance between the top and bottom surfaces, and at least one solid state point light source mounted to input light into the waveguide between the surfaces. One of the surfaces has a curvature relative to the other surface which yields a substantial variation in the thickness of the waveguide in a selected region of the waveguide. The variation follows a geometric contour selected to redirect light propagating between the surfaces of the waveguide so that the redirected light exits the top surface of the waveguide.
Another aspect of the invention relates to a lighting apparatus comprising a waveguide having top and bottom surfaces and a peripheral edge. The waveguide has a thickness defined by the distance between the top and bottom surfaces. The thickness at the peripheral edge is substantially different than the thickness in a region intermediate opposing sides of the peripheral edge. The thickness has a geometry selected to enhance ejection of light from the top surface intermediate the opposing sides. At least one light source is disposed proximate to the peripheral edge to introduce light into the waveguide between the top and bottom surfaces.
Yet another aspect of the invention relates to a lighting apparatus comprising a waveguide of solid material, the waveguide having a top surface, a bottom surface and a side surface. A light source is mounted to input light into the waveguide and reflective material is juxtaposed with one of the top and bottom surfaces wherein at least a portion of one of the top and bottom surfaces has a pattern of elongate structures that generally increase in density with distance from the light source.
In yet another aspect of the invention, there is disclosed an illumination and display device comprising an optical waveguiding layer and an illumination coupler embedded in an interior region of the waveguiding layer. In one embodiment, the illumination coupler includes one or more semiconductor light emitting devices. A portion of the optical waveguiding layer has a pair of symmetric (a) nonplanar, curved surfaces, or (b) a plurality of flat, planar surfaces approximating the nonplanar, curved surface. The pair of symmetric surfaces form a cusp lying on the axis of the one or more semiconductor light emitting devices to produce total internal reflection of light from the one or more semiconductor light emitting devices into the waveguiding layer. Display elements are formed on surfaces of the waveguiding layer to cause light to be emitted from the waveguiding layer.
Another aspect of the invention relates to an illumination and display device, comprising an optical waveguiding layer, with an illumination coupler embedded in an interior region of the waveguiding layer, wherein the illumination coupler includes one or more semiconductor light emitting devices. Display elements formed on the surface of the waveguiding layer cause light to be emitted from the waveguiding layer.
Yet another aspect relates to an illumination and display device, comprising an optical waveguiding layer with an illumination coupler embedded in an interior region of the waveguiding layer. In one embodiment, the illumination coupler includes one or more semiconductor light emitting devices, each of the one or more semiconductor light emitting devices having a longitudinal axis that is parallel to the surface of the optical waveguiding layer. A hole or recess may be formed in the interior region of the waveguiding layer where the one or more semiconductor light emitting devices is placed. The device also may comprise display elements formed on the surface of the waveguiding layer to cause light to be emitted from the waveguiding layer.
A further aspect of the invention is directed to an illumination device comprising a waveguide having an illumination coupler embedded in an interior region thereof. The waveguide has generally parallel top and bottom surfaces outside of the interior region such that light is guided therebetween. The illumination coupler comprises a refractive index interface configured to capture light rays propagating along a line that forms less than the critical angle of total internal reflection with respect to at least one of the top and bottom surfaces, such that the captured light rays are injected therebetween for propagation outside of the interior region. In one embodiment, the illumination coupler comprises a surface configured for total internal reflection of light incident thereon. The illumination coupler of this embodiment is integrally formed with the waveguide from a single piece of transparent material, and the reflecting surface is uncoated. A point source of light is disposed at least partially, preferably fully, within a cavity formed in the waveguide adjacent the total internal reflecting surface. Display elements may be included on at least one of the surfaces for ejecting light from the waveguide. Additionally, diffusive reflective material may be included on at least one of the top and bottom surfaces.
In yet another aspect of the invention, there is disclosed a lighting apparatus, comprising a device that emits light and an optical cavity that is formed by diffusive reflective surfaces, the cavity having an output region through which light from the cavity passes. The light emitting device is mounted to supply light to the cavity while being hidden from direct view through the output region. The cavity has a diffusely reflective surface area and the output region also has an area. The ratio of the area of the output region to the sum of (i) the area of the output region and (ii) the surface area of the cavity is at least 0.05. Additionally, the cavity has a depth and the output region has an edge to edge bisector dimension, the ratio of the depth to the bisector dimension being significantly less than 0.1. The lighting apparatus additionally comprises an angular spectrum restrictor positioned to restrict output illumination through the output region to a predetermined range of angles.
Another aspect of the invention involves a method of lighting. The method comprises producing illumination from an optical cavity formed by diffusely reflecting surfaces and outputting illumination from the cavity through an output illumination region. Producing of the illumination comprises directing light rays from a source of illumination into the cavity such that the source of the illumination is not visible through the output illumination region. The method further comprises restricting the angular spectrum of illumination from the output illumination region to a predetermined range of angles, and mounting the optical cavity to illuminate at least a portion of a room.
In another aspect of the invention, there is disclosed a method of manufacturing a lighting apparatus. One embodiment of the method comprises wrapping a flexible sheet of reflective material around one side of a tubular light source, juxtaposing a member forming an optical cavity with another side of the tubular light source so that light from the source is introduced into the optical cavity, and attaching the flexible sheet to the member such that the sheet retains the tubular source in juxtaposition with the member.
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