Lighting management in broiler houses significantly affects bird welfare, with evidence that continuous or near-continuous lighting causes chronic sleep deprivation and associated suffering.
Broiler lighting programmes have historically been designed to maximise production rather than to meet birds' biological needs for rest. Continuous or near-continuous lighting causes chronic sleep deprivation with physiological consequences including impaired immune function and altered stress hormone profiles. The shift toward minimum darkness requirements represents welfare progress, but the quality of light - spectral composition, intensity, and uniformity - also matters for broiler welfare. Lighting that more closely resembles natural conditions supports normal diurnal behaviour patterns and reduces the chronic stress associated with inappropriate light regimes.