A display device comprising: a display panel configured to display an image; a light source module comprising a plurality of light sources; and an optical sheet provided between the display panel and the light source module, the optical sheet being configured to guide light radiated by the light source module to the display panel, wherein the optical sheet comprises: a first transparent layer comprising a plurality of grooves provided on a first surface of the optical sheet that is opposite to a second surface of the optical sheet facing the display panel, the first transparent layer having a first refraction index, a second transparent layer provided in each groove of the plurality of grooves, and a reflective layer covering the second transparent layer such that it is not exposed from the first surface and comprising a light-reflective material, wherein the first surface further comprises a plurality of transmission portions provided between the plurality of grooves, the plurality of transmission portions being configured to transmit incident light exiting the light source module, characterised in that the second transparent layer has a second refraction index that is smaller than the first refraction index, and in that the reflective layer is provided in each groove of the plurality of grooves in a form of filling in the remainder of the inside of each groove of the plurality of grooves that is not filled by the second transparent layer. a display panel configured to display an image; a light source module comprising a plurality of light sources; and an optical sheet provided between the display panel and the light source module, the optical sheet being configured to guide light radiated by the light source module to the display panel, wherein the optical sheet comprises: a first transparent layer comprising a plurality of grooves provided on a first surface of the optical sheet that is opposite to a second surface of the optical sheet facing the display panel, the first transparent layer having a first refraction index, a second transparent layer provided in each groove of the plurality of grooves, and a reflective layer covering the second transparent layer such that it is not exposed from the first surface and comprising a light-reflective material, a first transparent layer comprising a plurality of grooves provided on a first surface of the optical sheet that is opposite to a second surface of the optical sheet facing the display panel, the first transparent layer having a first refraction index, a second transparent layer provided in each groove of the plurality of grooves, and a reflective layer covering the second transparent layer such that it is not exposed from the first surface and comprising a light-reflective material, wherein the first surface further comprises a plurality of transmission portions provided between the plurality of grooves, the plurality of transmission portions being configured to transmit incident light exiting the light source module, characterised in that the second transparent layer has a second refraction index that is smaller than the first refraction index, and in that the reflective layer is provided in each groove of the plurality of grooves in a form of filling in the remainder of the inside of each groove of the plurality of grooves that is not filled by the second transparent layer.