In connection with Sofia Lindkvist defending her doctoral thesis, her research is presented on SLU's external web, in Swedish.
The lighting environment in a barn affects the cows, and with LED technology it is possible to experiment with both brightness and color in the lighting. However, using red and blue light during parts of the day, which has been advocated, does not seem to offer any benefits. You shouldn't bother with it, an even white light and a clear difference between day and night seems to be the easiest and best for the cows. This is shown by Sofia Lindkvist in a thesis from SLU.