We have a light on in the winter to give them 15 - 16 hours of light. Around here, the winter sun is only up for 7 3/4 hours which is not even close to being enough. Without the extra light, they will stop laying eggs and wait for spring! Chickens are photosensitive. The industrial system takes advantage of this and puts the chickens through two days (light and dark) within a 24 hour period. They do this so that they can raise a broiler from chick to dinner plate in 31 days. Absolutely gross and disgusting.