The backlight unit comprises a bottom cover, a light guide plate on which a reflection layer is disposed on at least one side surface thereof, the light guide plate being disposed on an inside of the bottom cover, and a light emitting module disposed on at least one side surface of the light guide plate. A phosphorescing material may be exposed to an energy source that causes the material to stop phosphorescing. An area varying mechanism varies the area of the aperture of the diaphragm in response to a focal length varying operation of a projection lens. Another embodiment can include four slots per blade and four pre-attached upwardly protruding fasteners per blade arm. The amplified tachometer signal is used by the power management controller in controlling the rotational speed of the fan motor. A film type diffuser plate having predetermined tension is fabricated through traction by using a wire mesh instead of a diffuser plate based on an existing extruding method to improve egg mura generated in a backlight unit.