The resistance of photosynthetic apparatus of barley (Hordeum vulgare L.cv. Akcent) grown at low light (50 mmol. m-2 s–1) to short-term exposure (10 min) to different degree of excess irradiance was studied using the measurements of the 77 K chlorophyll a (Chl a) fluorescence spectra and room temperature Chl a fluorescence quenching. The protective down-regulation of the light-harvesting of photosystem II (PS II) as well photosystem I (PS I) was saturated at 850 mmol. m-2 s–1 and progressive PS II photodamage was induced at higher irradiances. After exposure of segments to excess irradiance (2410 mmol.m-2 s-1) a pronounced maximum at 700 nm appeared in emission spectrum of 77 K Chl a fluorescence. We suggest that this maximum reflects agregation of LHC II with part of inner PS II antenna during progressive PS II photodamage. The increased PS II emission at 77 K induced by exposure of plants at 2410 mmol. m-2s–1 was accompanied with reduced quenching of both maximum (FM) and minimum (F0) levels of room temperature Chl a fluorescence. The irradiance 2980 mmol. m-2 s –1 induced severe degree of photodamage associated with almost complete suppression of the long-wavelength emission maximum around 740 nm. This stage of photodamage was accompanied with extremely high values of nonphotochemical quenching of Chl a fluorescence at room temperature.