Eighty Italian heavy pigs having an initial body weight of about 75 kg were allotted to two experimental groups: a low light intensity group (LL), in which pigs received the lowest level of illumination mandatory in piggeries (40 lux) and a high light intensity group (HL), in which pigs were exposed to a higher level of illumination (80 lux). For both groups the light phase lasted 12 hours per day. Pigs were slaughtered at about 160 kg body weight. Light intensity showed to have no effects on the growth traits, carcass parameters or neutrophil-to-lymphocyte ratio of heavy. With the exception of drinking (more frequently observed among LL pigs; P < 0.01) and sternal recumbency (more frequently observed among pigs belonging to HL group; P < 0.01), the behavioural observations, carried out on 20 pigs per group, indicated that light intensity did not affect the main behavioural traits of pigs. Agonistic interactions were significantly higher (P < 0.05) among pigs receiving a lower level of illumination (40 lux; LL group) and pigs exposed to the higher level of illumination (80 lux; HL group) showed a tendency (P < 0.1) towards a higher proportion of tactile social interactions. Our results confirm that a proper illumination level can be included among environmental conditions having a positive effect in order to preserve swine welfare.