Neils right on the 12 on 12 off thing, it just doesn't work. Neil.... where's my waters??? You get my e-mail? : )
However it's tough to do on a backyard setup. I've kind of modified this lighting to better fit what I do here. The chickens get full light until they are about 10 days old or so sometimes three weeks if they need the extra heat. The lights are needed because of the heat.... especially in buildings / brooders that aren't insulated.
Once they hit 4-5 weeks I give them 6 hours of darkness and it seems to work perfect. 12 hours is just too long for these birds to go without feed, trust me... they will hurt each other trying to get feed, especially if you don't have feeders that can feed all the birds at once.
HUGE mistake for people is feeding too much protein like Neil said... I learned from him that it's unnecessary and a complete waste of money after 21 days.
One way to make it easy as for lighting goes is to have timers set up in your brooders. Have them go off at 12:00 in the morning that way there is complete darkness and the chicks will just lay down instead of piling like they will do if the sunlight is able to shine. Sunlight will gradually disappear and the birds tend to pile as the light goes less and less. Have the lights come back on at 6:00 that night, way before the sun goes done so they are able to not distinguish the changing of the day.
As for tractors, when I move the tractors I have little push button lights that I turn on after I make the last move before nightfall. Around 11:00-12:00 I go out and turn them off, I like checking on things around that time. I have the luxury of working for myself and I'm able to do this, but they make solar lights with timers on them that you could use. I like to check on mine, gives me the security of knowing what's going on, after midnight, the dog does all the work. She comes inside at 6:00 and the day starts all over.
Find what works for you... but feed a 16 % protein after 3 weeks and have about a 6 hour period of darkness for them.