Provided are a lighting system, a backlight unit and a 3D image display apparatus including the backlight unit. The backlight unit includes: a lighting system configured to selectively output collimated light and diverging light, a diffraction device, and a light guide plate configured to guide the collimated light and the diverging light from the lighting system to the diffraction device. An exit direction of the collimated light from the diffraction device depends on at least one of an angle of incidence of the collimated light and the wavelength of the collimated light.