Rearing broilers on 6-h photoperiods and transferring them to 23 h at 21 d has been shown to reduce mortality and the incidence of leg disorders without adversely affecting final body weight or feed conversion efficiency. However, in many countries, welfare codes for meat chickens currently stipulate a minimum photoperiod of 8 h, and are likely to specify a minimum uninterrupted dark period of 8 h in the future. This paper reports a study of the response of two genotypes of broiler females to a lighting regimen that complies with these requirements: an initial 8-h photoperiod followed by a 16-h photoperiod from 21 to 42 d. Constant 8- and 16-h photoperiods were provided as controls. The two breeds responded similarly to all lighting treatments. Constant 8-h and photostimulated birds had significantly heavier body weights, and strong tendencies towards larger feed intakes and superior feed conversion, than the 16-h controls. Lighting treatment had no significant effect on mortality or the incidence of leg problems. Ross birds had a significantly slower growth to 21 d, higher feed intake after 21 d, and inferior feed conversion efficiency throughout than Cobb birds. Ross birds had significantly lower mortality and fewer leg disorders than Cobb, due possibly to their slower initial growth.