I recently upgrade from LR4 to LR5 (and to Yosemite at the same time). I have have an iMac and an HP monitor. I prefer to run LR on the HP and leave the iMac for other applications. Since upgrading to LR5, I now have a loupe image on the iMac and the full LR program on the HP. I cannot find a way to free up the iMac monitor, and more important the Lights Out toggle only affects the iMac. I have tried various combinations of checkboxes in Yosemite's Mission Control without success. Perhaps the issue is some setting in LR%?