The present invention introduces a backlight device, a backlight system, and a flat panel display device incorporated with the backlight device. The backlight device is configured by at least two backlight units detachably and electrically interconnected. The backlight unit comprises at least first and second leadframes each including longitudinal first and second ends and an intermediate portion located between the ends. A light emitting device is disposed at the intermediate portion. And at least a pair of first and seconds leads with the first pair of leads arranged at the first end, and the second pair of leads located at the second end. The backlight, backlight system, and the flat panel display device can be readily lengthened or shortened according to the field requirements. It features a simple configuration, while is easy to assemble, and is beneficial to cost down.