Chemical oscillations have been uncovered in the photo-mediated 4-aminophenol-bromate reaction. The presence of light is found essential both to the extent of the reaction and the oscillatory behavior, where turning-off (on) the light results in an immediate disappearance (revival) of the oscillation. The long induction time in this photochemical oscillator shows an exponential dependence on the light intensity. Phase diagrams show that illumination with intense light allows the otherwise non-oscillatory system to exhibit oscillations over broad 4-aminophenol, bromate and sulfuric acid concentrations. Preliminary mechanistic studies suggest that the reaction involves the production of N-bromo-1,4-benzoquinone-4-imine. (C) 2007 Elsevier B.V. All rights reserved.