Abstract: A concentrated light emitting device includes a transparent casing, a printed circuit board in the transparent casing, a drive module and a light emitting element, which is a single element, plural elements arranged alternately or a module, on the printed circuit board. The drive module and the light emitting element are on one or two sides of the printed circuit board, the drive module includes a regulator circuit without electrolytic capacitors and the light emitting element is an LED or an organic LED. The light emitting device is used in a fluorescent lamp of a smaller diameter, like a T5 fluorescent lamp (i.e., a fluorescent lamp of a diameter of ?? or 16 mm). The present invention is capable of matching with an external drive module and providing a dedicated bracket for the external drive module, which can reduce production cost and can be installed more conveniently.