A driving circuit apparatus, including: a power converter, a reference light source, a light shield member, a luminance detection element, a comparison circuit, and a controller. The power converter outputs a driving voltage to drive a light string to emit light. The driving voltage continuously increases toward a maximum value. One end of the reference light source is electrically connected to the light string, and the other end is electrically grounded. The light shield member has an opaque chamber, and the reference light source and luminance detection element are disposed in the chamber. The comparison circuit receives a luminance signal from the detection element and determines whether the luminance signal strength is greater than a reference signal strength. When the luminance signal strength is greater than the reference signal strength, the controller sends an interrupt signal to the power converter to set an output value of the driving voltage.