Light for dairy cows : methods to measure light in dairy barns

Abstract: Cows presumably perceive light differently from humans, due to physiological dif-ferences and the eyes’ position. When designing light in dairy barns, a lux meter is the most commonly used instrument, and the design is often calculated without any daylight inlet. A lux meter has the same sensitivity spectrum of wavelengths as visi-ble light for human’s eye. Light to dairy cows is frequently discussed and it is known to affect both production and behaviour. The most commonly used method for quan-tifying light is lux meter but there are other options. The aim of this study was to investigate and compare a lux meter and other methods to measure light; a spectro-photometer and the ELF-method, with a cows’ possibility to perceive light according to existing literature. The ELF-method is an innovation to quantify light that possibly reach an eye. Several research studies have tested the effects of different light treatments on dairy cows production and welfare. However, the illuminance is often mentioned but not how the lux was measured. The results in this study showed that a lux meter is not optimal when measuring light for a dairy cow, since a lux meter does not show color occurrence nor the variation of photon flux over the wavelength spectrum. A spectrophotometer or the ELF-method would be recommended, due to the results that shows light intensities and the distribution of colors within a specific wavelength spectrum. The position of the instrument, vertical or horizontal, can affect the meas-ured values and the reliability of the measurement. To measure a cow’s field of vi-sion, the ELF method is the best option. Also, the measurements showed significant differences in light intensity between different times during one day, in a barn with daylight inlets, and great differences in light intensity in one barn. In conclusion, it is probably possible to measure light in a way that corresponds well with how light can reach the cow’s eye. Measurements either with a spectropho-tometer or with the ELF-method is recommended due to the results with light inten-sity and color occurrence. A lux meter is not the optimal choice since it does not have the same sensitivity for light as the cow’s eye. The actual light intensity treatment is of great importance when measuring how the light affect dairy cows’ production and welfare. One universal light unit when measuring light for dairy cows is requested.