Daylight in barn - spectrum specification for light sources in poultry

摘要

According to the Order on the Protection of Animals and the Keeping of Production Animals ( 13 Abs. 3, 18 Abs. 5), artificial light in poultry production systems needs to be as equivalent to natural light as possible. This practice raises the question how natural light is defined and how birds perceive their environment as birds' eyes have a different spectral sensitivity when compared to the human eye. Contrary to the bird's perception, the entire visual spectrum of a human being excludes the UV-A range, whereas ultraviolet wavelengths contribute to brightness perception in birds. It can be assumed that natural daylight corresponds most closely to the requirements of a bird. In this study the spectral composition of daylight during the course of a year was determined from different measure points ("open air" and "under vegetation"). It was then compared to spectrophotometric measurement results taken in layer houses. These results allow an initial characterization of the spectrum and illustrate differences for different areas within the barn. These differences derive from the occurrence and absence of natural light sources. Under the influence of daylight the spectra are comparable to the 'open air' ones. The outdoor measurements show that daylight can be clearly defined, however, its composition varies depending on chosen measurement points due to the vegetation which acts as a filter. The natural habitats of productive poultry species vary. Chicken originally descends from South East Asian tropical and subtropical forests, whereas the original habitat of wild turkeys, are steppes, prairies and semi-open areas. Thus, animals preferring habitats shielded from light may have different requirements regarding light sources than animals favouring open air habitats. Therefore, a species specific illumination of the barn should be provided, supposedly even taking different functional areas within the barn into account. The results of the spectral analysis of daylight can be used for the development of daylight-like illuminants. The thesis of differentiated requirements needs further studies.