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 . <EOS>