Well hens don't need any artificial light, but once they are laying eggs if they have 14 or more hours of light that is supposed to keep them laying. But that does not always work... here it is the middle of the summer and mine are laying at 34%. This article from the University of Nebraska seems to be fairly good read Proper Light Management for Your Home Laying Flock. You might note that they mention to not give young pullets extra light as it might stimulate them to start laying early, but I don't buy into that idea because a chick born in the early spring might be 4 months old and still have 14 hours of daylight. My RIR hens were 4 months old when they started laying.
JT
JT