Lighting a game level
Common mistake that beginners tend to make is to treat lighting as a no brainer tool that should simply render their levels. Usually, this ends up by placing one big lamp in every room and calling it done. Instead, lighting should be approached as a discipline that has it's own language. You can use this language not just to present your scenes and guide the player across your levels, but also to set the the mood and tell a certain story snippet.
The most basic example is the use of color. Colors similar to blue are seen as 'friendly', 'welcoming' and 'safe', like for example, a blue sky. On the other hand, colors like red are seen as 'evil', 'threatening' and 'dangerous', like for example, fire.
Here is a step by step example of how I use lighting and what goes thru my mind as I am doing it. It is using sci-fi setting, but it works for any setting from sci-fi cryo labs to ancient dungeons.
Step 1 - POI
First step is always to determine your goals. Primary goal for this scene is to draw player's attention to the locked door. Secondary goal is to make him notice the weapon rack. These two areas are called 'Points of Interest' or POI for short. So, we start off by placing Point Lights at these spots. Their are using default UDK values:
Falloff Exponent: 2.
Light Color: FFFFFF.
Step 2 - Mood
Next, we will adjust these two lights to set the basic mood for the scene.
Weapon rack light:
Falloff Exponent: 2.
Light Color: 75BFAC.
Falloff Exponent: 4.
Light Color: 68A4D0.
Step 3 - Contrast
Then, we will add a red light next to the doorway 'keycard' area:
Falloff Exponent: 2.
Light Color: EF521B.
We are using red, because we initially wanted this door to appear inaccessible; when player tries to use it, he will get a 'LOCKED! Use the Door Terminal to open this Door' type of message. Red is also contrasting the blue tones that make the remainder of the scene.
So, that would be the basic setup, in which we succesfully lit the scene's points of interest.
Step 4 - 'Connecting' the weapon rack
Currently, it is way too dark, so we will address that here. First we will clone weapon rack light and place it a bit down, so that it lits the floor, which is very important. By doing so, we are 'connecting' the rack with the rest of the room. Without it, the rack would be simply 'floating in the darkness' and not feeling so much as an integrated part of the room.
Placing this light below the rack will also provide the secondary lighting on the weapons, bringing out their features. Using two light sources on your subject like this is often seen in fashion and fitness photography.
Step 5 - Staircase
Next, we will make the staircase pop more by placing 2 lights next to the floor area:
Falloff Exponent: 2.
Light Color: 87C2DA.
Notice that lights are being placed behind the staircase railing. This way, the railing silhouette reads better and sends a 'Hey, this is a staircase!' type of message to the player.
This step was not as important as the previous one, but it makes the staircase read a lot better on approach. You can compare the two shots below and see the difference (Left Shot: with staircase lights, Right Shot: without staircase lights).
Step 6 - 'Connecting' the staircase
Lastly, we will duplicate the door light and place it directly above the staircase. It will connect staircase with the rest of the room. In this case, term 'connect' also means 'safe to step forward'. When something is in the dark, the player is more likely to slow down and approach that area with caution. By lighting it, you are saying: "Come on, it's safe to walk this way". This is one of the examples of how you can use lighting to control the pace of your level.
As you have probably noticed by now, none of these things are being done randomly and there is a reason for everything. One such example would be the setup for door and keycard area. Keycard light is on the left side and down, while door lights are on the right and above. That creates a contrast, making each area interesting to the eye.
Step 7 - Duplicating
Final step is to make lighting a bit more attractive. This is done by duplicating some of the lights and giving them lower Radius, but much higher Brightness and lighter Color. They are then moved a bit away from the original, usually closer to the place where your Static Mesh lamp will be.
Usually, Static Meshes like lamps are being placed after you finish placing all light sources in the scene. In this case it was the other way around, simply because it made it easier for me to make this tutorial.
Step 8 - Final look
This 'light duplicating' process has been done for 2 door lights, 2 weapon rack lights and 2 staircase lights. It wasn't done for keycard light, because it made the scene a bit strange. If I was doing fire at that same area, I would definitely duplicate that red light, as well.
Here is how the final scene looks like.
It is a common practice to zoom out your view from time to time or to 'blur' your eyes (a.k.a. 'squint test') and see if scene still 'reads' well, meaning, is everything instantly recognizable in a glance.
Another good test is to play your level backwards, as if you have completed your objective and your new goal is to backtrack all the way to the 'start' room.
Also, playing the level with different mindset is very useful. Meaning, first try playing your level completely focused, as you normally would be when playing it fresh and in the confort of your room. Then, play it in a 'distracted mode', as if you are in a room full of people; or if you are a bit tired, but still wanting to open that door and find out 'if something cool' is hidden behind.
If lighting works well in all of these situations, without having to guess where the POI is or where to go next, you did a good job. If not, keep re-arranging, tweaking and testing.
When doing world/level art, I usually like to look at my scenes thru some of the classic camera angles and see how that would feel inside of a top down game or in a cinematic, for example. More often than not, this can lead to 'happy accidents' which is always a good thing for any designer.