An illuminating circuit includes an EMI filter rectifying circuit, an RC absorption circuit, a PWM control circuit, a DC-to-DC converter circuit, an output rectifier filter circuit and a flickfree automatic detection and shutdown circuit. The EMI filter rectifying circuit, the RC absorption circuit, the DC-to-DC converter circuit and the output rectifier filter circuit are in turn electrically connected in series. The PWM control circuit is electrically connected with the EMI filter rectifying circuit and the DC-to-DC converter circuit respectively. The flickfree automatic detection and shutdown circuit is electrically connected with the output rectifier filter circuit and the PWM control circuit respectively.