A light-emitting device includes an autotransformer, a circuit module and a light-emitting module. The autotransformer includes a first positive conductive wire for receiving a first input voltage within a first predetermined voltage range, a second positive conductive wire for receiving a second input voltage within a second predetermined voltage range, and a common negative conductive wire electrically mated to the first positive conductive wire and the second positive conductive wire. The first predetermined voltage range is larger than the second predetermined voltage range. The circuit module includes a driver electrically connected to the autotransformer, and a predetermined operating voltage value for driving the driver is substantially within the second predetermined voltage range. The light-emitting module is electrically connected to the driver. Therefore, one of both the first and the second positive conductive wires along with the common negative conductive wire are electrically connected to an AC power source.