Indoor Flood Lighting
The easiest way of lighting the interior of models is to just run the wires out the back. If you just wish to take photos of the front and side of the buildings this is the quickest solution.
Simply piping bright LEDs into the bulding using small Technic blocks does the job
Hidden Outdoor Flood Lighting
The Magic Kingdom at Disneyworld is actually the second floor of a two story building. If you have ever visited you will note you walk uphill to the turnstiles from the monorail stations or the boat docks. When they dredged in order to achieve this, they created underneath the park a network of tunnels they call the Utilidoors. Over 5 million square feet of soil was taken to form the man-made Seven Seas Lagoon there to achieve this.
This underground area allow cables to run, prevent kids from seeing two Mickeys moving from area to are or simply supplying the shops and restaurants. Its well wirth the tour and its nicely air conditioned.
Abstracting this principle back to the Lego, we can nudge our models up a brick to hide wires in-between or underneath floors.
[Small LED in back of green block with clear cap]
Set 1930 and 1950
Copper wire under plates and between bricks.
Thin copper wire can be used in conjunction with LEDs or circuit stickers to hide wires within the bricks themselves
[Pictures of wires, breadboards with bent wires and chips]
Pop technic plates on the top to allow you to feed out the wires and LEDs without hiding thicker wires through the model.
I used technic pipe pieces to hide wires inside and make it look like aircondition ducting.
Drilling or Cutting
If you don’t mind altering a brick or two, you can cut grooves into them using a Dremel or similar: https://www.dremel.com