It is expected that hydrated lichen thalli are more susceptible to negative effects of high light (HL) under low rather then optimum temperature of thallus. In our experiments, we investigated response of foliose lichen species (Lasallia pustulata) to HL stress at low temperature under laboratory conditions. Hydrated thalli were exposed to HL of 500 mmol (CO2) m-2 s-1 for 30 min under 5 oC. Response of photosynthetic parameters (Fv/Fm - potential yield of PS II photochemistry, FII - quantum yield of PS II photochemistry, qN - non-photochemical quenching, qT+I - photoinhibition-related quenching) was monitored during HL treatment and subsequent 6 h recovery in dark using chlorophyll (Chl) fluorescence imaging technique False color images of lichen thallus showing heterogeneity of the above-specified Chl fluorescence parameters over the thalli were taken using a kinetic fluorometric CCD Camera (FluorCam FL-400, PSI, Czech Republic). Subsequent image analysis allowed us to specify zones and anatomic structures exhibiting different values of Chl fluorescence parameters. When considering whole lichen thallus, HL treatment led to 23 and 20 % decrease in Fv/Fm and FII, respectively. Dark recovery led to a gradual increase in both parameters. Fast phase of recovery, attributed to regulatory and protective mechanisms, was finished after 90 min recovery in dark. Slow phase of recovery, attributed to reparatory mechanisms, lasted several hours. When considering different thallus zones, there were big differences in Chl fluorescence parameters. Before HL treatment, Fv/Fm and FII, reached 0.585 and 0.446 in umbilicus zone. Close-to-umbilicus zones showed higher values of 0.649 and 0.523, resp. Marginal zones showed Fv/Fm and FII ranges of 0.599-0.699 and 0.312-0.615. HL treatment led to differential decrease of Fv/Fm and FII in the above-specified zones showing their different sensitivity to HL effects on photosynthesis.