An illumination device includes a light tube holder including two connectors for receiving either a light-emitting diode (LED) tube or a fluorescent tube. The connector includes three conductive elastic pieces therein. One elastic piece is electrically connected to an LED tube drive circuit board and a fluorescent tube, and the other two elastic pieces are respectively electrically connected to the LED and fluorescent tube drive circuit boards. A normally closed switch is located in the one of the connectors. The switch has a first end connected between a power supply and a first end of a ballast, and a second end connected to a second end of the ballast. When the LED tube is mounted to the holder, the switch is closed, and when the fluorescent tube is mounted to the holder the switch is open.