When the lights in the chicken house are on, they are generally kept dim to keep the chickens mellow, which helps direct their energy away from physical activity and toward rapid growth. Dim light leads to inactivity, which is in turn associated with leg problems such as lameness. Dim light can also cause damage to the eye and lead to blindness.
Natural v. dim light: Criteria key
minimum average illumination of 10 lux
minimum average illumination of 20 lux
the chickens have access to the outdoors to access sunlight and natural daylight (see criterion "outdoor access")
Natural v. dim light: How labels stack up against criteria
CHICKEN LABELS REPORT - Criteria: Natural v. dim light