Recent information from trials has suggested that: • After 7 days of age around 5 hours of darkness may be optimum (4-6 hours). • There is no reduction in growth rate to 39 days and possibly an increase to 49 days of age. Feed conversion efficiency improves particularly in the later stages of growth. • Mortality due to sudden death syndrome (SDS or flips) and mortality and morbidity from ascites and skeletal disorders are reduced. • Bird mobility is improved and the severity of footpad lesions may be reduced. • The proportion of meat as leg meat may be increased. • The welfare of the birds is improved as a more normal biological rhythm including rest is facilitated