If your girls are from this year's hatch they will most likely lay through the winter even if you don't add light.  Mine always do the first winter.  Chickens molt at about 18 months old, just about the time of their second winter will start.  That is when you can add light if you want them to lay through their second winter.  I don't add light, preferring to let the girls have a rest if they need one. 
If you want eggs year round a good solution is to always have some first year pullets.  I have a friend who gets 10 new chicks each spring.  He rotates between Red Star, Black Star, and Barred Rock.  As the new pullets start to lay he culls the chickens that are oldest.  With him getting a different breed every year it's easy to tell which ones are the oldest.