Quantification of three-dimensional light distribution in pig houses

Light intensity in swine buildings is regulated by European rules that define minimum standards for the welfare of pigs. This directive requires that "pigs must be kept in light with an intensity of at least 40 lux for a minimum period of eight hours per day" from 9:00 a.m. to 5:00 p.m. The objective of this study was to verify if the 40 lux light intensity level, as requested by EU rules for pig welfare, was achieved in a naturally versus artificially illuminated pig house under field conditions and to investigate the influence of the building structure on light intensity distribution within the building and the pens. Light intensity was monitored in an experimental swine facility comprising two different animal compartments in northern Italy. During the four-month trial, light intensity was recorded continuously at a frequency of 1 min using sensors located 1.50 m above the floor along the central corridor. As a second step, light intensity was measured in a three-dimensional grid at 0, 20, 75, 100, and 150 cm above the floor in six different positions within each pen to investigate how light was distributed in the pens at the heights of animals and humans. The results showed that, in the artificially illuminated areas, the light intensity required by EU rules for pig welfare was met a mean of 93% (89% in pens without dunging areas and 97% in pens with dunging areas) of the time between 9:00 a.m. and 5:00 p.m. In the areas illuminated only by natural light, the required light intensity level was achieved a mean of 41.5% of the time; in pens without dunging areas, the required light intensity level was never reached, while pens with dunging areas were illuminated at 40 lux 83% of the time. In general, based on EU rules, natural lighting was insufficient compared to artificial lighting in pens with no openings other than windows. Wider windows, positioned closer to the floor, could improve the lighting of the pen, avoiding the use of artificial light. Analysis of the 3-D distribution of light intensity, performed under clear sky conditions, revealed that light intensity at 150 cm height, as compared with lower heights, depends mostly on natural light coming from inlets and from the openings connecting the pens with the dunging areas. Nevertheless, even at this height, the light level remained very low (15 lux) and was totally insufficient for inspection of animals by the veterinarian or the farmer. For an identical light source, the 3-D distribution of light intensity in the compartment and in a pen depends on the type of pig building, the position of the pen in the building, and the presence of openings to the outside. The 3-D gradient of light intensity, or the variation of light intensity, measured in a single pen reached 3.98 lux m -1 while the gradient in a compartment reached 4.45 lux m -1 showing a non-homogeneous light distribution in the building.