A displaying device, comprising: a calculating unit, configured to calculate position and size of an active display area according to an interface content, comprising calculating pixel coordinates values <x,y,x',y'> in the active display area, <x,y> stands for the pixel coordinates values at the upper left corner of the active display area and <x',y'> stands for the pixel coordinates values at the lower right corner of the active display area and all of the interface content is configured within the area of <x,y,x',y'>; a creating unit configured to create interface image data comprising the interface content in the active display area and black or other single color image data outside the active display area and to write the interface image data in a displaying unit;the displaying unit configured to display the interface image data, the displaying unit includes an LCD screen and backlights (132, L1 to L8); and a controlling unit, configured to control the backlights (132, L1 to L8) of the displaying unit according to a backlights control command that is generated according to the active display area, wherein the backlights (132, L1 to L8) are configured to be controlled individually by the controlling unit; and wherein the backlights (132, L1 to L8) are light sources of equal brightness that provide the LCD screen with light, most of the backlights (132, L1 to L8) are uniformly distributed on two opposing sides of the LCD screen when seen in top view, and some others of the backlights (132, L1 to L8) are located below the LCD screen, wherein the backlights (132, L1 to L8) are configured to be turned on/off according to the position and size of the active display area, so that when much information is to be displayed, on the full LCD screen, the controlling unit is configured to generate the backlights control command to turn on all the backlights (132, L1 to L8), and when only little information is to be displayed, on part of the LCD screen, the controlling unit is configured to generate the backlights control command according to the active display area to turn on part of the backlights (132, L1 to L8) only and remaining backlights outside the active display area are turned off; wherein the size of the active display area is smaller than a size of the full LCD screen when only little information is to be displayed on part of the LCD screen. a calculating unit, configured to calculate position and size of an active display area according to an interface content, comprising calculating pixel coordinates values <x,y,x',y'> in the active display area, <x,y> stands for the pixel coordinates values at the upper left corner of the active display area and <x',y'> stands for the pixel coordinates values at the lower right corner of the active display area and all of the interface content is configured within the area of <x,y,x',y'>; a creating unit configured to create interface image data comprising the interface content in the active display area and black or other single color image data outside the active display area and to write the interface image data in a displaying unit;the displaying unit configured to display the interface image data, the displaying unit includes an LCD screen and backlights (132, L1 to L8); and a controlling unit, configured to control the backlights (132, L1 to L8) of the displaying unit according to a backlights control command that is generated according to the active display area, wherein the backlights (132, L1 to L8) are configured to be controlled individually by the controlling unit; and wherein the backlights (132, L1 to L8) are light sources of equal brightness that provide the LCD screen with light, most of the backlights (132, L1 to L8) are uniformly distributed on two opposing sides of the LCD screen when seen in top view, and some others of the backlights (132, L1 to L8) are located below the LCD screen, wherein the backlights (132, L1 to L8) are configured to be turned on/off according to the position and size of the active display area, so that when much information is to be displayed, on the full LCD screen, the controlling unit is configured to generate the backlights control command to turn on all the backlights (132, L1 to L8), and when only little information is to be displayed, on part of the LCD screen, the controlling unit is configured to generate the backlights control command according to the active display area to turn on part of the backlights (132, L1 to L8) only and remaining backlights outside the active display area are turned off; wherein the size of the active display area is smaller than a size of the full LCD screen when only little information is to be displayed on part of the LCD screen.