Seasonal monitoring of light intensity reveals design-driven variability in naturally lit broiler houses

Since the broiler industry moved primarily to solid sidewall houses nearly twenty years ago, the goal of providing uniform light intensities by artificial bulbs has been the norm. However, increasing consumer demand for improved bird welfare has led to the provision of natural light via windows in some broiler houses and, consequently, to a more varied lighting environment. The effects of varying window configurations and seasonality on in-house light intensities have not been characterized for windowed houses. This study characterized light intensity using multiple sensor orientations in two Global Animal Partnership (GAP)–certified commercial broiler houses (18.3 × 183.9 m) with different window configurations: one-sided windows (1SW) and two-sided windows (2SW), across summer, winter, and fall flocks. The 1SW configuration included 23 translucent windows on the north sidewall, while the 2SW configuration included windows on both north and south sidewalls, along with two additional west end-wall windows. Two data acquisition units per house measured light intensity at one-minute intervals near bird height in five directions. Data were analyzed across three production phases: brooding (d 1–8), growout1 (d 9–20), and growout2 (d 20–42). Mean light intensity was significantly higher in the 2SW configuration (39.9 lx) compared to the 1SW configuration (27.2 lx) across all seasons and phases. Solar altitude strongly influenced indoor light intensity; mean indoor light intensity in summer (44.4 lx) was only 4% higher than in fall (42.7 lx), despite ambient sunlight being 56% greater in summer. Ceiling-facing sensors captured less than 17% of maximum light ingress, while north- and south-facing sensors captured 60% to 99% suggesting a rotational sweep with a single sensor may better represent the light environment experienced by birds. Relative light uniformity (coefficient of variation) did not statistically differ between window configurations but was better at lower artificial light levels. Overall, these findings demonstrate that window configuration and solar geometry strongly influence the indoor light environment in broiler houses, highlighting the need for improved measurement approaches and more refined design guidelines to ensure consistent and welfare-appropriate lighting conditions.