With ongoing deformation and bleb formation the hypericin fluorescence in the overall image steadily decreases, as shown in Fig. , where the sum of all photons emitted by hypericin and resorufin are displayed for each image in the series (for information on how the total fluorescence emitted by the individual dyes in each image is extracted see section 3.1 of the SI). This trend is also evident from the spatially resolved, steady state fluorescence spectra displayed in Fig. , acquired in the cell's ER after each FLIM acquisition. At the time point M1, the fluorescence spectrum shows a strong signal of Hypericin at 600 nm with a small contribution of resorufin (shoulder at 584 nm). Over the course of the PDT, the fluorescence signal of hypericin steadily decreases, whereas the resorufin signal increases. The decrease of the hypericin fluorescence intensity at the early stages (where the cell membrane is still intact) suggests that hypericin molecules are bleached during the PDT. Especially at Fig. strong increase of the resorufin fluorescence intensity can be observed, which is consistent with the average FLTs observed in the FLIM images. At Fig. M8, the cell is completely flooded with the surrounding medium and the fluorescence spectrum closely resembles the emission of resorufin with only a small contribution from hypericin. A second series of FLIM composite images for a hypericinincubated and resorufin surrounded cell is displayed in section 4 of the supporting information. The same mechanistic steps in the cell death are observed there, namely a contraction and rounding of the cell, a steadily decreasing hypericin contribution to the overall fluorescence, the formation of numerous small surface blebs that quickly merge to form larger surface protuberances, easing of the membrane stability and finally flooding of the cell with the surrounding medium.