An electric device may include a first group and a first signal line coupled to the first group. The first group may include a first light-emitting diode (LED), a second LED and a first control circuit. The first LED and the second LED are coupled in series. The first control circuit is coupled to the first LED and the second LED for turning on one of the first LED and the second LED in a first mode, and turning on the first LED and the second LED in a second mode. Number of LEDs enabled in the first mode is less than number of LEDs enabled in the second mode.