Because of high aspect ratio and good conductivity, CNT is regarded as an excellent emitter for the field emission applications. In general, the field emission devices can be classified to diode structure and triode structure. As the figure shown below, a diode structure consists of (1) CNT mounted cathode, (2) phosphor coated anode, and (3) spacers to sustain a pressure below 10-7 torr With applying a bias voltage between cathode and anode, electrons will be emitted from cathode, travel through the high-vacuum space and, finally, bombard the phosphor in the anode. Electrons in the phosphors were therefore excited and emit visible light. Because of the restriction of the use of the mercury in the fluorescent lamp, CNT lighting is considered as the next generation lighting device.