We report observations of photocontrolled oscillatory behavior in the 1,4-cyclohexanedione- bromate reaction (CHD-cyclohexanedione). Experiments in a batch reactor show that illumination may exhibit qualitatively different effects on the reaction dynamics, where illumination with a moderate intensity favors oscillations while strong illumination quenches spontaneous oscillations. A transition from light-quenched to light-induced oscillations during the course of the reaction has also been observed. Investigations in a continuous flow stirred tank reactor further illustrate that the influence of light in the 1,4-CHD-bromate reaction depends not only on the intensity of the illumination but also on the phase at which the illumination is switched on. Mechanistic investigations suggest that 1,4-benzoquinone, a final product in the 1,4-CHD-bromate reaction system, plays a significant role in the occurrence of photoinduced oscillations. (C) 2004 American Institute of Physics.