Abstract: A backlight unit may include a turning film that receives light from a light guide layer. The turning film may have a plurality of elongated protrusions that extend across the turning film. Each protrusion may have a concave surface. The concave surface may be a curved surface that curves inward towards the interior of the turning film. Light from the light guide layer may pass through the turning film and be reflected towards a viewer by the concave surfaces of the protrusions. In a liquid crystal display, the turning film may be interposed between the light guide layer and a lower polarizer. In certain embodiments, the turning film may be the only optical layer interposed between the light guide layer and the lower polarizer. In other embodiments, the turning layer and a diffuser layer may be the only optical layers interposed between the light guide layer and the lower polarizer.

Abstract: A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a backlight unit. The backlight unit may include an array of light-emitting diodes and a light reflector that helps reflect light from the light-emitting diodes through the pixel array. A color conversion layer may be used to convert light from the light-emitting diodes from blue light to white light. A microlens array layer formed over the color conversion layer may spread the light from the color conversion layer to homogenize the light. To ensure light is emitted from the backlight with a uniform color, the microlens array layer may have different transmittance portions. A central portion of the microlens array layer may transmit more light and reflect less light than an edge portion of the microlens array layer.

Abstract: A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a backlight unit. The backlight unit may include a printed circuit board, a plurality of light-emitting diodes mounted on the printed circuit board, at least one light spreading layer formed over the printed circuit board that spreads light received from the plurality of light-emitting diodes, a partially reflective layer formed over the at least one light spreading layer, a color conversion layer formed over the partially reflective layer, a collimating layer formed over the color conversion layer, a brightness enhancement film formed over the collimating layer, and a diffuser formed over the brightness enhancement film. The at least one light spreading layer may include two light spreading layers with elongated protrusions that are rotated relative to each other.

Abstract: A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a backlight unit. The backlight unit may include a printed circuit board, a plurality of light-emitting diodes mounted on the printed circuit board, at least one light spreading layer formed over the printed circuit board that spreads light received from the plurality of light-emitting diodes, a partially reflective layer formed over the at least one light spreading layer, a color conversion layer formed over the partially reflective layer, a collimating layer formed over the color conversion layer, a brightness enhancement film formed over the collimating layer, and a diffuser formed over the brightness enhancement film. The at least one light spreading layer may include two light spreading layers with elongated protrusions that are rotated relative to each other.

Abstract: An array of pixels in a display may be illuminated by a backlight having an array of light-emitting diodes in an array of respective cells. A reflector is used to reflect light from the light-emitting diodes through the array of pixels. Within the cells, the reflector has cross-sectional profiles that help distribute light emitted from the light-emitting diodes toward edges of the cells. A light diffuser layer for the backlight may have a partially reflective layer such as a thin-film interference filter with an angularly dependent transmission. Within each cell, the reflector may have cross-sectional profiles with portions that are parabolic or elliptical.

Abstract: An electronic device may have a display with a backlight. The backlight provides backlight illumination for an array of pixels that is displaying images. The backlight may include an array of cells. Each cell may contain a light source with one or more light-emitting diodes and a cavity reflector that reflects light from the light source outwardly through a diffuser for use in forming the backlight illumination. The light sources may be mounted to a printed circuit. Support posts on the printed circuit may be used to maintain the diffuser at a fixed distance from the printed circuit. Sensors on the printed circuit may be used to measure separation distances between the printed circuit and diffuser. Adjustments to pixel gain profiles can be made based on the measured separation distances.

Abstract: An array of pixels in a display may be illuminated by a backlight having an array of light-emitting diodes in an array of respective light-emitting diode cells. A cavity reflector in each cell may help distribute blue light emitted from the light-emitting diode of that cell toward edges of the cell. Optical films in the backlight may include a photoluminescent layer such as a phosphor layer that converts blue light from the light-emitting diode array into white light and may include a dichroic filter for reflecting white light away from the diode array towards the pixel array. A light diffuser layer for the backlight may have printed white ink pads, recesses filled with a high index of refraction material, protrusions for light scattering, light-scattering particles, thin-film interference filters, partially reflective mirrors, and other structures for diffusing the light from the light-emitting diodes.

Abstract: A display such as a liquid crystal display may have an array of pixels that is illuminated using backlight illumination from a backlight. The backlight may have a light guide layer that distributes light from light-emitting diodes across the display. The light guide layer may have a planar portion that provides backlight illumination to the array of pixels and may have bent edge portions that curve out of the plane of the planar portion. Light scattering structures may be formed in the planar portion to extract backlight illumination from the light guide layer. A light sensor adjacent to the bent portion may monitor leaked light. The light guide layer may have two bent portions on opposing edges of the light guide layer.

Abstract: A backlight unit may include a turning film that receives light from a light guide layer. The turning film may have a plurality of elongated protrusions that extend across the turning film. Each protrusion may have a concave surface. The concave surface may be a curved surface that curves inward towards the interior of the turning film. Light from the light guide layer may pass through the turning film and be reflected towards a viewer by the concave surfaces of the protrusions. In a liquid crystal display, the turning film may be interposed between the light guide layer and a lower polarizer. In certain embodiments, the turning film may be the only optical layer interposed between the light guide layer and the lower polarizer. In other embodiments, the turning layer and a diffuser layer may be the only optical layers interposed between the light guide layer and the lower polarizer.