The invention provides a backlight unit for a liquid crystal display and a method. In one embodiment, the backlight unit is provided with a plurality of luminous elements and a control unit. The control unit is electrically coupled to the plurality of luminous elements, so as to control the intensity of light emitted by each of the luminous elements according to the picture video data received bya plurality of pixels. When the picture video data is red, green or blue, the control unit may individually adjust each of the luminous elements to expand the color scope of the red, green or blue region of the liquid crystal panel, such that the emitted red, green or blue light has the maximal intensity. The invention can expand the color scope of a backlight device and reduce the power consumption.