The field emissions of the in-plane-type triode carbon nanotube emitters for the field emission backlight lamps were investigated in simulation by the finite element method in order to indicate ideal high efficient field emission fluorescent lamps (FELs). The anode current are commonly controlled by the gate bias voltages for the FEL triode emitters. The simulation of the in-plane-type triode emitter indicated that the ON/OFF ratio of the anode current density for the gate bias voltage of 0 V/-100 V was increased by decreasing the cathode to gate spacing, by decreasing the cathode and gate electrode width, and by using the lower ratio of the cathode to the gate electrode width. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3456180]