We suggest the novel EEFL (External Electrode Fluorescent Lamp) Backlight System 3 types; the first aspect is a high optical efficiency second is reduction of mechanical size of Backlight, and the last is low power consumption in large LCD Backlight System. To gain a high optical efficiency, we consider the narrow diameter (φ 3.0) lamp of EEFL Backlight System. As the impedance of the narrow diameter (φ 3.0) lamp is higher than that of conventional (φ 4.0) EEFL. A high impedance of lamp is caused the increase of power consumption and a driving voltage of lamp. But its characteristic of an enhancement luminance could be possible for a high optical efficiency. We introduce a method for decrease of a mechanical size for large Backlight. The length of electrode for EEFL system must be increased as a small diameter and a long length of lamp. For that reason is caused the increase of Bezel Size For LCD TV. In this paper, we suggest a DEFL(Differential Diameter External Electrode Fluorescent Lamp). DEFL is made by junction between φ 4.0mm glass tube of emission part and φ 8.0mm glass tube of electrode part. Finally we explain φ 4.0mm EEFL system for low power consumption in comparison with φ 4.0mm CCFL backlight system.