Reactive oxygen species (ROS) are fundamental for many biological activities; however, their uncontrolled production leads to oxidative stress, which can cause cellular transformations that contribute to a number of severe diseases including cancer, Alzheimer’s and Parkinson’s. Evaluating and linking the onset of these diseases to the levels of oxidative stress and the types of ROS involved will lead to an improved understanding of their role in the life-cycle of diseases. ROS are generated on activation of photosensitisers and it has long been hoped that these can be harnessed in a controlled way to damage and ultimately destroy tumour cells. In this study, a microbatch approach was developed to mimic the extracellular oxidative stress in a highly controlled fashion, and the method was applied to a well-established mammalian cancer cell line using a known photosensitiser aluminium(III) phthalocyanine chloride tetrasulfonic acid, and white light. The treated and control samples were analysed to determine cell recovery, viability, fragmentation and mode of cell death. It was found that in comparison to the controls, there were significant (p < 0.05) reductions in the total number of cells recovered and significant increases in cellular disintegration predominantly via necrosis.