The industry standard is to keep the lights in the chicken houses on almost continuously, and to keep the lights dim. The lack of prolonged complete darkness discourages chickens from sleeping, which means the animals continue to eat around the clock (and therefore continue to rapidly gain weight around the clock). Long periods of illumination in a chicken house are associated with increased health problems in the birds, including leg disorders. Birds that are deprived of a regular dark period also have weakened immune systems.
Artificial light and darkness: Criteria key
maximum of 20 hours of illumination in a 24-hour period
maximum of 18 hours of illumination in a 24-hour period
maximum of 16 hours of illumination in a 24-hour period
Artificial light and darkness: How labels stack up against criteria
CHICKEN LABELS REPORT - Criteria: Artificial light and darkness