Well, there are many ways to trigger signals, two of the most popular are insulated rails and IR triggering devices along the track. Both options are discussed often and at some length here.
I'm sure you could rig something to kill the lights during daylight, personally I like to see lighted passenger cars, so I've never looked into that kind of option. The lights allow you to see the detail you've spent all that time to create in the interiors, even in the light you can't see much without internal lighting. 
