A back light unit for a display, comprising: a light guide film, including: a base film having a width and a length, and including a high refractive film at the bottom side thereof and a low refractive film at the upper side thereof stacked on the high refractive film; an incident pattern (CHOE) including a holography diffraction pattern and being disposed at one side of a bottom surface of the base film for diffracting light into the high refractive film; a reflective pattern (RHOE) including a diffraction optical pattern and being disposed at an opposite side apart from the one side with the length of the bottom surface of the base film, and covering the width of the opposite side; and a light radiating pattern including a light diffractive film, a grating pattern or a holographic pattern and being disposed on an upper surface of the base film for radiating back light out of the low refractive film; a holographic film for controlling a viewing-window disposed on the light radiating pattern; and a light source being apart from the incident pattern and positioned to provide an incident light to the incident pattern (CHOE), wherein the incident pattern (CHOE) is configured to convert the incident light from the light source into expanded light so as to be corresponding to the width of the reflective pattern (RHOE), and so that the light diffracted into the high refractive film has a refraction angle at which the light is totally reflected at the interface between the high refractive film and the low refractive film, wherein the reflective pattern (RHOE) is configured to re-reflect the totally reflected light entering into the reflective pattern (RHOE) into the high refractive film with an angle smaller than the total reflection angle of the interface between the high refractive film and the low refractive film and larger than a critical angle for total reflection at an upper surface of the low refractive film. a base film having a width and a length, and including a high refractive film at the bottom side thereof and a low refractive film at the upper side thereof stacked on the high refractive film; an incident pattern (CHOE) including a holography diffraction pattern and being disposed at one side of a bottom surface of the base film for diffracting light into the high refractive film; a reflective pattern (RHOE) including a diffraction optical pattern and being disposed at an opposite side apart from the one side with the length of the bottom surface of the base film, and covering the width of the opposite side; and a light radiating pattern including a light diffractive film, a grating pattern or a holographic pattern and being disposed on an upper surface of the base film for radiating back light out of the low refractive film; a holographic film for controlling a viewing-window disposed on the light radiating pattern; and a light source being apart from the incident pattern and positioned to provide an incident light to the incident pattern (CHOE), wherein the incident pattern (CHOE) is configured to convert the incident light from the light source into expanded light so as to be corresponding to the width of the reflective pattern (RHOE), and so that the light diffracted into the high refractive film has a refraction angle at which the light is totally reflected at the interface between the high refractive film and the low refractive film, wherein the reflective pattern (RHOE) is configured to re-reflect the totally reflected light entering into the reflective pattern (RHOE) into the high refractive film with an angle smaller than the total reflection angle of the interface between the high refractive film and the low refractive film and larger than a critical angle for total reflection at an upper surface of the low refractive film.