I don't know that there is one set rule of thumb for lighting. we all have different sized coops, some with and some without electric, and some of us have hundreds of chickens, others have only 2 or 3.
Maybe it would help if you described your set-up in more detail and ask whether what you're doing is sufficient(objectively speaking because you'll still get varying responses)
a few times I've come across something saying 14 hours of light. but that doesn't mean that if they only get 12 they'll stop laying. some of us don't supplement any light at all and still get eggs, even through the short days of winter. I personally have my 11 chickens on my light schedule. when I wake up it's getting light out, I let them out. In the evenings, I turn on their light about the same time I would start needing artificial light in my own house, then before bed it's off. seems to be working, and putting the light on a timer means all I have to do at night is a headcount and close the coop door.
as far as watts, that really depends. I have a worklight in my coop, I think it's 40 or 60 watt, I dunno. It's plenty enough light for them though. now that it's getting colder here, I've thought about switching to a higher watt since my husband tells me that a higher watt bulb would give off just a little heat(but nothing like a heat lamp). but I also have to keep in mind that it's costing me power when really it's probably only my peace of mind I'm tending too.