SUMMARY It is well known that the behaviour is a good indicator of welfare of laying hens. The present study which carried out in Hohenheim University, Stuttgart, Germany, includes four experiments. Three experiments were carried out with laying hens to study the effects of different light sources and its intensities in behaviour, egg quality and performance of laying hens. The fourth experiment was conducted in the different housing system to find out its effect in above mentioned parameters and signs of health in laying hens. 1st Experiment: The effects of different light sources on laying hens were tested under the same intensity (25 lux). A total of 80 Lohmann brown hens (35 weeks old) were kept in side by side pens at a climatic stall and were randomly allocated to four experimental groups of 20 hens each. These groups were exposed to different light sources (incandescent IL, fluorescent FL, day DL and blue BL) at the same intensity (25 lux) for eight weeks. The environmental conditions were automatically controlled; moreover 14 h lighting schedule was maintained during experiment. Behaviour (mainly abnormal behaviour), egg quality and performance of laying hens were recorded. The results showed that in laying hens: 1- Abnormal behaviour (feather pecking and aggression) were the highest under blue light (65.8+18.2 and 46.1+17.5, respectively) than other sources, but the observed difference did not reach the significance level. 2- There was no significantly differences (P>0.05) in the normal behaviour of laying hens. 3- Eggshell thickness was significantly higher under day light (43.2+2.2a) than other light sources. 4- There was a significantly differences (P<0.05) in yolk colour and haugh unit under the different light sources, especially the blue light (12.3+0.6a and 53.6+16.9a, respectively). 2nd Experiment: This experiment were carried out using the same light sources of experiment one but under two intensities (25&50 lux) on laying hens. A total of 80 Lohmann brown hens (70 weeks old) were used and randomly allocated to eight experimental groups of 10 hens each. Further husbandry condition, management and treatments were the same as in experiment one but in new pens in the same stall for six weeks. Recorded parameters were as experiment one. The result of this experiment was included the following: 1- Birds trend to rest more under fluorescent light (1.2+2.4a). 2- Egg weight was significantly higher under blue light (70.2+4.5a) than other sources. 3- The differences in other parameters between light sources and intensities did not reach the significance. 3rd Experiment: Studying the effects of different light sources with different intensities (5&50 lux) on laying hens. A total of 256 Lohmann brown hens (40 weeks old) were used and randomly allocated to eight groups of 32 hens in new pens for eight weeks. The obtained results indicated the following: 1- Highest pecking activity and aggressive behaviour were recorded in the group under blue light, with a significant difference in feather pecking (P=0.01). 2- Pecking activities and aggressive behaviour were significantly higher in birds under high light intensity. Therefore, the low light intensity can be used for controlling pecking activity and aggressive behaviour. 3- Neither light sources, nor light intensity have a significantly differences (P>0.05) in other behaviour, egg quality or performance of laying hens. 4th Experiment: The aim of experiment was to investigate the effect of different cage system on laying hens. A total, 1512 Lohmann breed (39 weeks old) were used and divided in to 720 hens in big dutchman and 792 hens in salmet system. The study was carried out from May, 2008 until April, 2009. The behaviour (mainly abnormal behaviour), egg quality, performance and signs of health in laying hens were recorded. The results obtained revealed that: 1- There was a significant differences in number of hens on upper perch (P=0.0001), number of hens on lower perch (P=0.0001), dust bathing (P=0.0002), number of hens on mat (P=0.001), resting (P=0.01) and feather pecking (P=0.03) in different cage system, especially under salmet system (13.55+8.20a, 13.92+5.48a, 3.67+4.91a, 1.96+4.28a, 10.34+8.99a, 7.42+7.96a, respectively). 2- Number of hens on upper perch, number of hens on lower perch, resting and feather pecking were significantly higher in upper tier (9.17+10.35a, 12.58+7.02a, 11.84+9.39a and 8.05+9.25a, respectively) than lower one(5.40+6.01b, 9.91+5.42b, 5.49+5.76b, 4.22+4.11b, respectively). While, number of hen on troughs was significantly higher in lower tier (23.88+13.16a) than upper one (17.97+11.92b). 3- Tier*cage system interaction has significant effects on number of hens on upper perch and resting behaviour, especially in upper tier of salmet system 17.37+5.67a and 14.77+5.62a, respectively). 4- Sign of health of breast and body weight were significantly higher under in big dutchman (2.63+0.82a and 1.85+0.22a, respectively) than salmet (1.64+0.43b and 1.68+0.06b, respectively). Nevertheless, foot hyperkeratosis was significantly higher in salmet (0.72+0.29a) than big dutchman (0.40+0.29b). 5- Although, no significant difference in the signs of health, but welfare scores were higher under big Dutchman system. 6- There was a significant difference (P=0.03) in toe hyperkeratosis in hens reared in lower tier (1.20+1.07a). 5- The welfare scores were higher in lower tier, although there was no a significant difference (P>0.05) in the other signs of health. 6- Tier*cage systems interaction was not significantly affected the signs of health. 7- Haugh unit and % number of egg out side nest were significantly higher in big dutchman (71+10a and 23.9+15.8a, respectively) than salmet system (69+11.6b and 1.9+0.9b, respectively). 8- Although, % egg production was higher under salmet (86.5+21.1) than big dutchman system (84.1+19.9), but the difference did not reach the significance level (P>0.05).