It doesn't matter if your walls are concrete. You can still have support beams at regular intervals, particularly in interesections. Square hallways are boring. (Granted, I didn't do much to mine either... too lazy LOL)
This is a cross section of what I had in mind for support beams -- with a reversed duplicate beam on the other side. They can be concrete supports. Or you can texture them like small steel girders or even wood. They also don't have to have support columns, they could just be a horizontal beam across the cieling. Or you don't need them at all. It's your map.
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You can run pipes along the cieling, or horizontally and verticallly along the walls. Metal brushes can be used to simulate wiring lines laid externally along the walls. This is how I laid out my lights for my tunnels.
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You could also build recessed areas in the walls. Texture the recess with a control panel, then put a fence texture in front of it that is flush with the wall. You can then add a small colored accent light to the paneled area.
I admit, a lot of this is stuff is probably more work than you want to put in a hallway, but if you think people will spend a lot of time down there, it is worth the extra time. My tunnels are just to get you from point A to point B so there is not a lot of fighting going on in there... but I've got some exploding barrels in there just in case
I like having the hole in the cieling to cast light into the tunnel. That will be most effective if the sunlight color contrasts with the tunnel lighting however you light it.
Bright colored lights really make an area come to life. I think that is probably because it took so about 6-8 years after DOOM for developers to be able to use them. (I remember getting my old Voodoo 16 card and playing Heritic 2 with it for the first time after ditching my Matrox Millienium... WOW was I stunned.)
But if the entire hallway is Blue like in your picture, it looks flat. It is difficult to judge distance and depth. I also can't see where the tunnels branch off. And it will be very hard to see other players in it. With creative lighting, you can lead the player's eye where you want him to look. Make the intersections more prominent so he doesn't get completely lost. But you can still have nice shadowy areas for people to hide in... Maybe a recessed alcove that just happens to be completely in shadow. Good place to ambush someone with a shotgun.
Ambient lighting is also a point of contention among mappers. A lot of guys are only using 5-10 % ambient light if at all. (Look at "The Canal" screens on the opening page. That's a daytime map but the shadows are almost completely black.) My own opinion is that is too dark unless it is a nighttime map. I'm leaning more to 20-25% on a daytime map. But since everyone's monitor and video brightness settings are different, it's a tough call.
If I play the stock maps on default settings, I think they are too dark. So I increase my video brightness enough to fill in the shadows so they are not completely black and I can see someone hiding there. But I never want to compromise the color integrity and wash out the map with brighter settings.
So when I lit my map, I started with a dim ambient light. Just enough to see by with my adjusted brightness settings. Then added my sun and lamps after that. I know that my ambient light will be too bright for some people's taste, and too dark for other's. But if you give the map enough ambient light to start with, everyone can always go darker. If they want to go brighter, they will hopefully not have to crank it up so high that the sun color get's washed out.
Also, if your dark areas are almost completely black, your video card will have no color information to rely on for a brightness increase. So when you do increase the brightness, you won't have black shadows, you will have Grey ones that just look flat.
(That's my only gripe about the Canal Map. You should download it if you haven't... it is still a beautiful map)
Sorry, that got a lot longer than I intended. I don't know if I would write a Tut on lighting. It's my specialty, but in the end, these are still just my opinion.