I use a timer in the hen house in the winter to give the hens about 14 hours of light. I follow the advice given to me by a very old farmer who hatched my very first hens about 20 years ago.
Added light should be in the morning to add to the day not to extend it. I set my timer to turn on the lights 2 - 2 1/2 hours BEFORE sun rise and to turn them off just after sun rise. So, next month when the time changes and the sun is rising at 6am (and setting by 5:30pm!) the timer in my barn will turn on at 4am and will turn off just after 6am.
No light is added at the end of the day. The hens need the natural cycle of going to roost when the sun goes down.
The timer I use is a very inexpensive model from Lowes. I picked it up for $5.98.
It plugs into an outlet and your light plugs into the timer device.
I use a small florescent under the cabinet plug in light (12 - 18 inches long) that we got at Lowes for under $8 (- I think it might have been $6 on a clearance table -someone had returned it in a torn box).
I never have to worry about leaving the light on. I don't have hens who are confused and can't tell the difference between night and day. Also just adding the two hours of morning light if you notice a drop in production and really need your eggs you don't have to worry about burning out your hens long before their time of producing eggs is passed.
I have never had a problem with any hens over the years and a few occassions I haven't needed to use the light at all to maintain my normal egg supply.
Everyone has their own way of doing things and their own reasons as why they do what what they do. I just wanted to share the good advice I once got from an old farmer and how we have automated the source of two hours of extra light for my hens.