A back light unit is provided to reduce a size by including an LED light source by COB(Chip On Board) and a pattern unit partially transmitting or reflecting in a diffusion plate. An LED(Light Emitting Diode) light source(120) includes a substrate(110), an LED chip(121), and a sealing unit(122). The LED chip is mounted on the substrate. The sealing unit seals the LED chip. A diffusion plate(130) is separated from the substrate and has a pattern unit(140) in one side. The pattern unit partially transmits and reflects the light emitted from the LED light source. The sealing unit includes a fluorescent material. The fluorescent material changes the wavelength of the light emitted from the LED light source.
