Abstract: A light-folding element includes an object-side surface, an image-side surface, a reflection surface and a connection surface. The reflection surface is configured to reflect imaging light passing through the object-side surface to the image-side surface. The connection surface is connected to the object-side, image-side and reflection surfaces. The light-folding element has a recessed structure located at the connection surface. The recessed structure is recessed from the connection surface an includes a top end portion, a bottom end portion and a tapered portion located between the top end and bottom end portions. The top end portion is located at an edge of the connection surface. The tapered portion has two tapered edges located on the connection surface. The tapered edges are connected to the top end and bottom end portions. A width of the tapered portion decreases in a direction from the top end portion towards the bottom end portion.

Abstract: A backlight module includes a light guide plate having a bottom surface, a light emitting surface, a first light incident surface, and microstructures. Each microstructure recesses into or protrudes from the bottom surface and has a first and a second surfaces. The first and the second surfaces of at least one of the microstructures are located on two sides of a first reference plane parallel to the first light incident surface. A section-line of each first surface on a second reference plane perpendicular to the first light incident surface and perpendicular to the light emitting surface is a straight line. A first angle between each first surface and a third reference plane parallel to the light emitting surface in the light guide plate is between 0 degrees and 20 degrees, and a thickness of each microstructure is between 0 micrometers and 20 micrometers.

Abstract: A planar light source including an LGP and first and second light sources are provided. The LGP has a first surface and a second surface opposite to each other and a first groove and a second groove. The first groove and the second groove are respectively located on the first surface and the second surface, and are respectively located at two sides of a center line of the LGP, where the center line equally divides the first surface and the second surface. The first groove has a first side surface and a first light incident surface, and the second groove has a second side surface and a second light incident surface, where the light sources are disposed in the grooves. The light sources are suitable for respectively providing a light beam entering the LGP through the corresponding light incident surface.

Abstract: A backlight module including an LGP, an optical film, a first light source is provided. The LGP has a bottom surface, a light emitting surface, a first light incident surface, and microstructures. Each microstructure is recessed into or protrudes out of the bottom surface and includes at least two structural units. A section line of each structural unit on a first reference plane is a curve, and the curve has a peak point. A distance between two peak points of two adjacent structural units along a first direction is greater than 0 and smaller than a half of a total width of the two structural units along the first direction. Each microstructure has a symmetric plane perpendicular to the light emitting surface and the first light incident surface. The optical film is located on the light emitting surface. The first light source is located beside the first light incident surface.

Abstract: A backlight module including an LGP, an optical film, a first light source is provided. The LGP has a bottom surface, a light emitting surface, a first light incident surface, and microstructures. Each microstructure is recessed into or protrudes out of the bottom surface and includes at least two structural units. A section line of each structural unit on a first reference plane is a curve, and the curve has a peak point. A distance between two peak points of two adjacent structural units along a first direction is greater than 0 and smaller than a half of a total width of the two structural units along the first direction. Each microstructure has a symmetric plane perpendicular to the light emitting surface and the first light incident surface. The optical film is located on the light emitting surface. The first light source is located beside the first light incident surface.

Abstract: A backlight module includes a light guide plate having a bottom surface, a light emitting surface, a first light incident surface, and microstructures. Each microstructure recesses into or protrudes from the bottom surface and has a first and a second surfaces. The first and the second surfaces of at least one of the microstructures are located on two sides of a first reference plane parallel to the first light incident surface. A section-line of each first surface on a second reference plane perpendicular to the first light incident surface and perpendicular to the light emitting surface is a straight line. A first angle between each first surface and a third reference plane parallel to the light emitting surface in the light guide plate is between 0 degrees and 20 degrees, and a thickness of each microstructure is between 0 micrometers and 20 micrometers.

Abstract: A planar light source including an LGP and first and second light sources are provided. The LGP has a first surface and a second surface opposite to each other and a first groove and a second groove. The first groove and the second groove are respectively located on the first surface and the second surface, and are respectively located at two sides of a center line of the LGP, where the center line equally divides the first surface and the second surface. The first groove has a first side surface and a first light incident surface, and the second groove has a second side surface and a second light incident surface, where the light sources are disposed in the grooves. The light sources are suitable for respectively providing a light beam entering the LGP through the corresponding light incident surface.