Not many people run their trains at night. A properly lit layout at night is a completely different model railroading experience. I have seen some fantastic scenes on the several layouts that I have observed over the years due to imaginative use of lighting at night. My own layout is set up for night running, and I believe that there is nothing as beautiful as your trains running with headlight and markers illuminated, or passenger cars lit, passing signals that change color, and passing illuminated stations, towns and individual houses.
When I originally constructed my layout, I buried extra Malibu wire along the areas where I thought I might need to tap in for lighting circuits. This wire was dormant for a few years until I went to a garage sale and bought a Malibu transformer and lights. I immediately started putting my lighting plan into operation. I like the Malibu system because it is made to be out in the weather, and is low voltage DC (12-14 Volts) so it is safe. Malibu makes some taps that allow you to cut into the main lines and add lights without any splicing or soldering. You can also buy similar taps from an auto parts store and save some money. They just squeeze over your wire with a pair of adjustable pliers, and immediately allow you to run a wire to a building or any other source of illumination that you might use.
When lighting a building, I always use yellow bulbs and paint over them with a light coat of black marker. The yellow bulb gives a warmer glow to the building, and the black marker dims the bulb so that it does not look like you have a spotlight shining inside. Most buildings for outside use have walls that are thick enough so that the light does not illuminate them like a plastic jack-o-lantern. If the walls and roof are thin, the inside of the building may have to be painted with black paint to make it opaque. Another trick with buildings, is to block off windows so that it does not look like all the lights are on in all the rooms. We have a two story farm house that has the first floor lit, but the second floor only has two windows lit. The barn has only a single light over the main door which gives a nice glow to the barnyard. This bulb is clear and is part of a Piko goose neck lamp.
One of my country stations, has a single tall post light, and the interior is softly lit with a yellow bulb, (colored black of course). My main yard has a series of tall double pole lights made by Pola, that provide some realistic illumination, and my town has street lights. If I can ever find some of that plastic stained glass material at the ceramics store, I will re-do my church windows, and illuminate the church. Any buildings that are not occupied at night, are of course, dark. Some of my stores, also have upper windows blocked off so that they are not all illuminated, and even the bottling plant has only a few windows showing light along with outside lamps.
The Malibu lights stay outside at all times. Buildings that have attached exterior lights, are equipped with quick-disconnect fittings, so that the building can be removed easily for storage.
Since my layout is really dark, I have placed some small Malibu spot lights in the oak tree to cast a small amount of light over the entire layout without overwhelming the lights on the layout. One layout that I have seen actually has a some soft blue spotlights shining on it to simulate moonlight. This produces is a very dramatic night time effect.
While running outdoors at night is not a fun thing in Florida during the summer due to mosquitoes, spring and fall may be ideal times to try some layout lighting to see if you like it. Experiment and enjoy yourself.