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EP-4359862-B1 - ILLUMINATION APPARATUS

EP4359862B1EP 4359862 B1EP4359862 B1EP 4359862B1EP-4359862-B1

Inventors

  • ROBINSON, MICHAEL G.
  • HARROLD, JONATHAN
  • WOODGATE, GRAHAM J.

Dates

Publication Date
20260506
Application Date
20220620

Claims (14)

  1. A waveguide extending over a predetermined area, the waveguide (1) comprising front and rear light guiding surfaces (6,8) for guiding light along the waveguide, wherein: the rear light guiding surface (6) comprises: an array of light input wells (30) for arrangement over respective light emitting elements; and an array of light deflecting wells (40), each light input well (30) comprising a light input surface (32) extending towards the front light guiding surface (8) that is arranged to input light from the respective light emitting element into the waveguide, each light deflecting well (40) comprising a light deflecting surface (42) extending towards the front light guiding surface so that some guided light is incident thereon and some guided light passes over the light deflecting surface, the light deflecting surface being arranged to reflect at least some of the guided light that is incident thereon, and the light deflecting wells having an arrangement around each light input well that causes guided light that has been input through the light input surface of the light input well to be distributed around the light input well; and at least one of the front light guiding surface (8) and the rear light guiding surface (6) comprises light extraction features; (10) arranged to extract guided light from the waveguide as output light; and a light turning arrangement (50) to redirect at least some of the output light towards a normal to a plane of the waveguide; characterised in that the light input surface (32) of each light input well comprises four light input faces (32A, 32B, 32C, 32D) having surface normals with average components in a plane of the waveguide, which average components are oriented with respect to a reference axis at angles within at most 10°, preferably at most 5°, of 0°, 90°, 180°, and 270°.
  2. An illumination apparatus for providing illumination over a predetermined area, the illumination apparatus comprising: a waveguide as according to claim 1; and an array of light emitting elements (15) arrayed across the predetermined area behind the waveguide.
  3. An illumination apparatus according to claim 2, wherein the four light input faces are contiguous; and, optionally, either: each of the light input faces is planar; or each of the light input faces is convex in material of the waveguide.
  4. An illumination apparatus according to claim 3, wherein the light extraction features comprise an array of sets of four light extraction faces, each light extraction face having a surface normal with an average component in a plane of the waveguide, which average components are oriented with respect to the reference axis at angles within at most 10°, preferably at most 5°, of 0°, 90°, 180°, and 270°.
  5. An illumination apparatus according to any one of claims 2 to 4, wherein the light deflecting surfaces of the light deflecting wells comprise at least one light deflecting face having a surface normal with an average component in a plane of the waveguide, the average components in respect of the light deflecting surfaces of the light deflecting wells across the array of light deflecting wells being variously oriented with respect to the reference axis at angles within at most 10°, preferably at most 5°, of 45°, 135°, 225°, and 315°.
  6. An illumination apparatus according to claim 5, wherein the light deflecting surfaces of the light deflecting wells comprise first and second pairs of opposed light deflecting faces, the first pair of opposed faces having surface normals with average components in a plane of the waveguide that are oriented with respect to the reference axis at angles within at most 10°, preferably at most 5°, of 45° and 225°, respectively, and the second pair of opposed faces having surface normals with average components in a plane of the waveguide that are oriented with respect to the reference axis at angles within at most 10°, preferably at most 5°, of 135°, and 315°, respectively.
  7. An illumination apparatus according to claim 6, wherein the light deflecting surfaces of the light deflecting wells comprise four intermediate light deflecting faces extending between the light deflecting surfaces of the first and second pairs.
  8. An illumination apparatus according to claim 5, wherein the light deflecting wells are connected at ends of the pairs of opposed faces to form a grid of complete loops around the light input wells.
  9. An illumination apparatus according to any one of claims 2 to 8, wherein the light turning arrangement comprises a light turning optical component comprising an input surface extending across the front light guiding surface of the waveguide and arranged to receive output light from the waveguide, and an output surface facing the input surface, wherein the input surface is prismatic and arranged to provide deflection of the output light towards the normal to the plane of the waveguide.
  10. An illumination apparatus according to claim 9, wherein the deflection provided by the input surface of the light turning optical component varies in at least one direction across a plane of the light turning optical component so that the deflected light is directed towards a common optical window in front of the illumination apparatus.
  11. An illumination apparatus according to claim 9, wherein the input surface comprises an array of pyramidal recesses arranged to provide deflection of the output light towards the normal to the plane of the waveguide, each pyramidal recess comprising four light turning faces.
  12. An illumination apparatus according to claim 11, wherein: either the four light turning faces of the pyramidal recesses have surface normals with average components in a plane of the waveguide, which average components are oriented with respect to the reference axis at angles within at most 10°, preferably at most 5°, of 0°, 90°, 180°, and 270°, or the four light turning faces of the pyramidal recesses have surface normals with average components in a plane of the waveguide, which average components are oriented with respect to the reference axis at angles within at most 20°, preferably at most 10°, of 25°, 90°, 205°, and 270°; and, optionally, the surface normals of the faces of the pyramidal recesses have a tilt angle from the normal to a plane of the waveguide in a range from 35 to 80 degrees, and preferably in a range from 45 to 65 degrees.
  13. An illumination apparatus according to any one of claims 2 to 12, wherein the light input surfaces have surface normals that are inclined from a plane of the waveguide by at most 3°.
  14. An illumination apparatus according to any one of claims 2 to 13, wherein the illumination apparatus is arranged to emit light in a light output distribution, wherein a ratio of luminous intensity half maximum solid angle of the light output distribution to the luminous intensity half maximum solid angle of a Lambertian light distribution is less than 1, preferably less than 0.5, more preferably less than 0.25 and most preferably less than 0.1.

Description

TECHNICAL FIELD This disclosure generally relates to illumination from light modulation devices, and more specifically relates to optical stacks for providing illumination with reduced solid angle for use in display including privacy display, high efficiency display and high dynamic range display; and for use in environmental illumination. BACKGROUND Privacy displays provide image visibility to a primary user that is typically in an on-axis position and reduced visibility of image content to a snooper, that is typically in an off-axis position. A privacy function may be provided by micro-louvre optical films that transmit a high luminance from a display in an on-axis direction with low luminance in off-axis positions, however such films are not switchable, and thus the display is limited to privacy only function. Switchable privacy displays may be provided by control of the off-axis optical output from a spatial light modulator. Control may be provided by means of off-axis luminance reduction, for example by means of switchable polarisation control layers between display polarisers and additional polarisers. Backlights with reduced off-axis luminance can be used to provide or enhance the privacy function. Certain imaging directional backlights have the additional capability of directing the illumination through a display panel into viewing windows. An imaging system may be formed between multiple sources and the respective window images. One example of an imaging directional backlight is an optical valve that may employ a folded optical system and hence may also be an example of a folded imaging directional backlight. Light may propagate substantially without loss in one direction through the optical valve while counter-propagating light may be extracted by reflection off tilted faces as described in U.S. Patent No. 9,519,153. Backlights formed from arrays of individually controllable light sources arranged in series with a liquid crystal spatial light modulator can provide high dynamic range by reducing output luminous flux of the light sources in alignment with low luminance regions of the image displayed on the spatial light modulator. High dynamic range LCDs (HDR-LCD) can achieve dynamic ranges that are superior to that which can be provided by an LCD optical mode alone. An array of light sources such as LEDs (light emitting diodes) that is addressed with lower resolution image data is provided in a local dimming LCD backlight, such that dark areas of an image are illuminated by the backlight with low luminance, and bright areas are illuminated with high luminance. Thin substrate and polymer substrate LCD panels can provide mechanical characteristics such as flexibility that is similar to organic LED (OLED) displays. Such thin substrate LCDs desirably use backlights with similar mechanical characteristics. One type of LCD backlight comprises a light guide plate, and array of input light sources such as LEDs at one end of the light guide plate. Light that propagates by total internal reflection within the waveguide is output by means of surface features that adjust the propagation angle of light within the waveguide and allow extraction at angles close to grazing the outside of the waveguide. Such light is directed in a normal direction to the LCD by means of a turning film and/or rear reflectors. Such optical stacks may have high efficiency, but have multiple optical components with total backlight thickness typically 1mm or greater. Such an edge illuminated light guide plate is not typically appropriate for two-dimensional local dimming for HDR-LCD illumination, or free-form shaped LCD. Other known backlights incorporate an array of light emitting diodes (LEDs) in a matrix behind the LCD such as described in U.S. Patent Publ. No. 2017-0261179 comprises a plurality of spatially separated packaged LEDs and a multiple "batwing" optical elements, each batwing optical element arranged to direct light from the packaged LED in a lateral direction. Such light is strongly diffused to provide output illumination. Such backlights require expensive pick-and-place LED and individual optics alignment and have a high thickness and reduced efficiency in comparison to edge illuminated backlights. Illumination systems for environmental lighting such as automobile headlights, architectural, commercial or domestic lighting may provide a narrow directional light output distribution, for example by means of focussing optics to provide spotlighting effects, or can achieve a wide directional light output distribution for example by means of diffusing optics. White LED lighting sources can be comprised of separate spectral bands such as red, green, blue and yellow, each created by a separate LED element. Such sources enable users to resolve the separate colours, and as a result of the separation of the sources in the lamp, can create coloured illumination patches. Catadioptric elements combine refractive surfaces (dioptrics) a