Rapid changes in the intensity of chlorophyll a fluorescence induction (CFI) during dark-light transition reflect the various reactions of photosynthesis, especially of electron transport. The analysis of CFI transients in plant leaves in situ is a sensitive and non-destructive assay of the functional state of the photosynthetic apparatus. We earlier developed an image instrumentation system for analyzing CFI transients. The system gives information on the location of different photosynthetic activities in whole leaves in situ and can allow identification of sites of inhibition caused by environmental stresses. The recent addition of a scanning laser enables us to diagnose photosynthetic injuries to plants at a distance from the instruments.