A light source unit for use in a backlight unit, the light source unit comprising a light source and a lens; wherein the lens is a circular lens having a rotational symmetry about a central axis, the lens consisting of two bodies, namely a lens body and a light incidence part, the lens body comprising: a first curved surface on the side of the lens towards the light source and having a first variable curvature providing a convex shape, a second curved surface on the side of the lens away from the light source and having a second variable curvature providing a mainly concave shape with a protrusion formed on a center area of the second curved surface, and an edge surface connecting an end of the first curved surface and an end of the second curved surface at an outer edge of the lens; wherein the radius of the second variable curvature initially increases along the second curved surface from a point at a first radial distance from the central axis in a radial direction towards the outer edge of the lens to another point at a second radial distance from the central axis, and diminishes along the second curved surface from said another point towards the outer edge of the lens, the second radial distance being larger than the first radial distance; wherein the light incidence part is formed on the first curved surface, is cylindrically shaped and has a circular surface towards the light source; and wherein the light source unit is arranged such that light emitted by the light source enters the lens via the light incident part and exits the lens either at the second curved surface in case of lower angles of incidence with regard to the central axis or at the first curved surface with prior reflection on the second curved surface in case of higher angels of incidence with regard to the central axis or at the first curved surface without prior refection on the second curved surface in case of even higher angles of incidence, thereby dispersing the light of the light source. a first curved surface on the side of the lens towards the light source and having a first variable curvature providing a convex shape, a second curved surface on the side of the lens away from the light source and having a second variable curvature providing a mainly concave shape with a protrusion formed on a center area of the second curved surface, and an edge surface connecting an end of the first curved surface and an end of the second curved surface at an outer edge of the lens; wherein the radius of the second variable curvature initially increases along the second curved surface from a point at a first radial distance from the central axis in a radial direction towards the outer edge of the lens to another point at a second radial distance from the central axis, and diminishes along the second curved surface from said another point towards the outer edge of the lens, the second radial distance being larger than the first radial distance; wherein the light incidence part is formed on the first curved surface, is cylindrically shaped and has a circular surface towards the light source; and wherein the light source unit is arranged such that light emitted by the light source enters the lens via the light incident part and exits the lens either at the second curved surface in case of lower angles of incidence with regard to the central axis or at the first curved surface with prior reflection on the second curved surface in case of higher angels of incidence with regard to the central axis or at the first curved surface without prior refection on the second curved surface in case of even higher angles of incidence, thereby dispersing the light of the light source.