An illuminating apparatus adapted to receive an input power which is a pulse DC includes a lighting unit, a detecting unit and a controlling unit. The lighting unit includes a plurality of lighting sets and a switching unit. The switching unit may be used to cause the lighting sets interconnected in a serial fashion and/or in a parallel manner. The detecting unit detects a state of the input power. The control unit couples the detecting unit and the lighting unit, and controls the switching unit according to the detecting unit detecting the state of the input power. As such, the turn-on voltages of the lighting unit may adjust at different stages of the input power.