A light emitting diode (LED) lamp tube includes a lamp device including a circuit board, and a plurality of LEDs mounted on the circuit board. The circuit board is disposed in a tubular enclosure such that an inner peripheral surface of the enclosure is divided into a non-illuminated portion and a light-receiving portion. The tubular enclosure has a plurality of tapered protrusions extending from the light-receiving portion toward the LEDs. Each of the tapered protrusions converges from the light-receiving portion toward the LEDs. Each of the tapered protrusions further has a maximum width at an outer end thereof, which increases gradually from a middle portion of the light-receiving portion toward junctions of the light-receiving portion and the non-illuminated portion.