Backlight modules. A backlight module for a flat display device includes a light guide element and a fluorescent lamp assembly. The fluorescent lamp assembly disposed on a first side of the light guide element includes a first fluorescent lamp and a second fluorescent lamp. The first fluorescent lamp comprises a first end, a second end and a first phosphor coating on an inner surface of the first fluorescent lamp, wherein the first phosphor near the first end is thicker than the second end. The second fluorescent lamp comprises a third end adjacent to the second end, a fourth end adjacent to the first end, and a second phosphor coating on an inner surface of the second fluorescent lamp, wherein the second phosphor near the third end is thicker than the fourth end.