The excitation balance between the two photosystems is regulated through state transitions (ST). Although shuttling of the light-harvesting complex II (LHCII) is considered the main player in ST, the dynamic modification of the intra-chloroplast LHCII distribution has never been visualized. Zhang et al. (on pp.872-882) used a self-developed excitation-spectral microscope to visualize the LHCII-derived fluorescence component within living Chlamydomonas reinhardtii cells. The technique enabled a rapid acquisition of the excitation spectrum at every pixel of a microscope image with sub-micron resolution. Since chlorophyll (Chl)-b is specifically bound to LHCII, the local excitation spectrum provides direct information about the local antenna size. From this analysis, Zhang et al. discovered an ST-driven reversible rearrangement of a Chl-b-related component reflecting the change in local antenna size.