Chlorophyll molecules in a leaf can use light energy in three pathways: it can be used in photosynthesis, dissipated as heat or re-emitted as light, which is called chlorophyll fluorescence. Having images of the whole leaf area allows the observation of stress-induced changes in fluorescence emission. Fluorescence yield is quantified by exposing a leaf to a known and constant light intensity and then applying a saturating light pulse. The relative amount of re-emitted (fluorescence) light energy (of longer wavelength than the applied pulse) is measured with a modulated fluorometer.

PI curves are a graphical representation of the relationship between solar irradiance and photosynthesis, which show the efficiency and capacity of plant photosynthesis with respect to light intensity. Samples were exposed to dark for 30 minutes and then to different light intensities every 10 minutes. After each light intensity, the oxygen production of the sample was measured.