A downlight apparatus includes a light source, a driver, a light holder, a metal rim and two elastic arms. The driver converts an external power to a driving current to be used by the light source. The light holder stores the light source in an holder space of the light holder. The light holder is placed inside a cavity of a ceiling. The metal rim is connected to a bottom side of the light holder. The two elastic arms are attached to one of the metal rim and the light holder for elastically pressing the metal rim to engage an cavity edge of the cavity of the ceiling for concealing the cavity and preventing an accidental fire to escape from the cavity of the ceiling to outside of the cavity of the ceiling.