When mine get about 9-10 hours of light a day they lay fine, as long as they get enough protein. They need more in winter, even if they free-range, like mine do, because they don't get all the yummy bugs in winter like they do in warmer weather. Black oil sunflower seeds help, too. Layer ration with 16% protein seems to be a minimum, IMO. Up the protein a bit and I bet you get eggs, with or without extra light, provided they aren't molting.
