Lighting programmes in commercial poultry houses significantly affect bird welfare through their effects on growth, behaviour, sleep, and natural rhythm expression.
Poultry lighting welfare illustrates how a seemingly technical production variable has profound effects on bird welfare across multiple domains. Commercial broiler production has historically used near-continuous bright lighting to maximise feeding time and growth rate - a practice that disrupts normal circadian rhythms, prevents adequate sleep, and contributes to the rapid growth that causes skeletal and cardiovascular problems. The minimum 8-hour darkness period now required in UK law represents a baseline below which the circadian disruption is severe. Higher-welfare lighting programmes that include gradual dawn-dusk transitions, appropriate daytime light intensity not so bright as to cause eye discomfort, and adequate dark periods for sleep and behaviour synchronisation significantly improve welfare outcomes. Research has shown that poultry given adequate dark periods show better leg health, reduced fear responses, and more natural behaviour patterns. The wavelength of light also matters: poultry have four types of colour receptors (compared to three in humans) and can see into the UV range, meaning light spectrum affects their experience of the environment in ways that human intuition does not capture. Blue-green enriched light reduces stress responses and supports more normal behaviour in both broilers and laying hens.