The issue with the lights is the SHOCK of them suddenly coming on or suddenly going off. Some folks suggested using a dimmer to gradually introduce and terminate the light. I never went that far with my girls... I only had issues with the marans. The other birds in the same coop never produced meat or blood spots.perhaps the new rage for vegetarian chicken feeds is contributing to the problem? Also if it's worse in winter, when bugs and green forage are scarce, would certainly explain the problem. Some report it's worse when they have lights on. Perhaps because the lights are inducing the birds to lay even tho they are lacking in certain vital nutrients? Certainly something to think about.