In this reprint from the March 2005 issue of Game Developer magazine, technical artist Steve Theodore espouses classic design fundamentals for creating evocative lighting in your games.
"Light for the effect you need, and to hell with physics."
In this reprint from the March 2005 issue of Game Developer magazine, technical artist Steve Theodore espouses classic design fundamentals for creating evocative lighting in your games. Buzzwords like "fragment shading" and "per-pixel attenuation" might sound like pure geekery, but they're going to be critical to effective game art over the next five years. The most important advance in next-generation graphics quality will be a huge leap in quality of lighting. In most contemporary games, lighting is utilitarian at best: It helps players perceive the structure of 3D spaces, provides directional cues, and indicates places of concealment. In far too many games, the lighting doesn't even reach that basic level. In film and theater, though, it's universally recognized that lighting isn't simply about making things visible. Lighting is the instrument that controls the emotional pitch of a scene. For character and environment designs to engage the player's intellect, the lighting (much like music) must bypass the analytical, and works directly on emotions. If that sounds extreme, play a little game of mental mix-and-match with some familiar visual icons. Try to imagine Blade Runner shot under the florescent glaze of a Star Trek: The Next Generation set and you'll start to get the idea. Now that our lighting technology is finally starting to catch up to other media, it's time to revisit the fundamentals. A lot of us haven't worked with sophisticated lighting since we toyed idly with the MentalRay tutorials, so it's definitely a good idea to look back at the basics. With so many software packages and game engines to consider, we'll have to leave the mechanical aspects for another time; this discussion will focus on strategy rather than tactics. If terms like key light and kicker make you scratch your head, you might want to look at Jeremy Birn's book Digital Lighting and Rendering (New Riders Press, 2000). Although Birn's book has lots of technical detail that's irrelevant to real-time artists, it's also well stocked with useful insights into the universals of good lighting. In the meantime, let's look at how lighting can help establish moods in two ways: through control of color and contrast.
Obviously, color choice is the most straightforward way to manipulate a player's emotions with lighting. Colored lights can provoke some emotions among artists too — we all know games that outshine even Las Vegas in their tackiness. The reaction? Some artists swear off colored lights altogether. Neither extreme position is tenable. Subtlety and caution are certainly important, but in the end all light is colored light. Even direct natural sunlight has a distinctive color cast, which can vary a great deal based on the time of day, time of year, location, and weather. Likewise, every kind of artificial light, from a welcoming candle to a sickly fluorescent tube, has a signature tinge. If you own a digital camera, you know how complex and arbitrary the process of white balancing can be. The question, therefore, isn't whether to use color — it's how. 
The simplest kind of lighting designs work like a kind of coloring book. With strong key lights and appropriate fills, you can "paint" a scene to set a mood. We all know the basics of color association: red for danger, blue for peace, green for life, and so on. It can be very tempting to fall back on these old standbys as a shortcut to an emotion. This approach can work well — deep red emergency lights and inky shadows in the underground bunker might be just what you need to create tension and set the player's nerves tingling. Often, though, dominating color schemes can backfire. One of the important practical functions of good lighting, after all, is to help the characters pop off the screen and capture the player's attention. Your need for contrast between character and environment can easily work against your attempt to set an emotional tone. If your villain is clad in typically villainous purple and green, he's not going to stand out particularly well if the same sickly colors are washing the walls of his air. Some textures won't stand up to strong colored lighting either. Without careful planning, you might find a colored light reveals an annoying repeat pattern you never noticed in one of your textures, rather like a color-blindness test. So how do you set a mood with color when you also have to provide visual clarity?
When theatrical lighting designers need to pop a character out of the "canvas" of the screen or stage, they'll add a complementary rim light or kicker to provide a strong edge highlight. This separates the character from the backdrop without undercutting the color theme. Many games shy away from overtly theatrical lighting, fearing that players will wonder where that helpful little light is coming from. Audiences rarely notice or care, as long as the final effect makes a positive contribution to the scene. Lighting designers in film and theater seldom, if ever, rely on the actual physical lights on a set to create ambience. Only rarely is the pool of light below the reading lamp or the wash of daylight from the window actually produced by the prop or fixture. Usually there's a battery of theatrical lights just out of sight, providing a carefully stylized suggestion of "real" lighting. You can see the difference by comparing a typical Hollywood blockbuster with an arthouse film that relies exclusively on real-world lighting. In short, don't be afraid to get the look you need by using whatever collection of hacks and fakes will deliver the goods. This doesn't mean that there are no rules. You do need to remember that players are free to wander and can easily roam into areas where they can unveil our clever impostures. When lighting an environment, try not to place strong lights that don't have a possible physical source. Softer lights will usually escape scrutiny, particularly if they are colored to simulate radiosity bounces. However, the basic principle remains: Light for the effect you need, and to hell with physics.
Sometimes the overall ambience of your game can be undone by lighting that's too nakedly theatrical. Many of the best lighting designs are so subtle that you never catch the lighting designer at work. Rather than create strong color washes that hose the scene with a single dominant emotion, you can use the lighting to more subtly underscore the meaning of a scene. Working on a more subliminal level gives you great power over your audience's perceptions and still leaves you free to build a prosaic and realistic look. The lighting design of the original Star Wars is a particularly brilliant example of this. In conventional color terms, you'd expect the imperial sets to be drenched in reds and pooled with ominous shadows. But instead, the Death Star is lit up like a cross between a dentist's office and a meat locker. It's dominated by fluorescent haze and cool blue accent lights (see Figure 1). The cool colors reflect off the spotless plastic of the stormtroopers and the black vacuum of Darth Vader to perfectly embody the Empire's impersonal, bureaucratic brand of evil. By contrast, the rebels are always lit warmly; the classic shot that really establishes Luke Skywalker's character, as he watches the twin suns set on Tatooine, is as pink as the Barbie aisle in your local toy store. The warm/cool opposition is an extremely simple design, but it's absolutely critical for establishing the emotional underpinnings of the story. The opening levels of Half-Life 2 use the play of color temperature the opposite way: The player quickly learns to associate the warm colors of sunlight and open space with danger, while the blues and greens of murky sewers and tunnels become indicators of safety and concealment. The very consistent correlation between natural lighting and danger reinforces the player's paranoia and sense of powerlessness. By allowing the bad guys to "own" the daylight, the lighting subliminally underlines the overwhelming menace of the pursuing Combine forces in the early part of the game. (See Figure 2.) 
Figure 2: In Half-Life 2, warm lighting often connotes danger rather than safety and comfort.
Obviously, color choice is only the very beginning of good lighting design. Next month we'll take a a look at contrast — the roles that light fall-off, color blending, and shadow definition play in creating an effective lighting scheme. In the meantime, try playing with some of the fancy lighting tools that real-time artists have been denied for the last decade. We game developers like to think of ourselves as fearless pioneers, relentlessly pushing the boundaries of our medium. In fact, though, the last six or seven years have been a very conservative period in the evolution of 3D graphics. The basic feature list for a standard real-time rendering engine — Gouraud shading, colored lighting, light mapping, and so forth — hasn't changed that much since the days of Quake 3 and Half-Life. Our cozy little interlude of technological stability is just about over. It's exciting, but it's also going to be professionally challenging. We'll be handed a bunch of great new toys — pixel shading, dynamic lights, high dynamic range images, to name a few — which inevitably will mean a lot of time spent learning and experimenting with new technologies. But to really get the most out of the new tools, we have to stay focused on the timeless basics: making emotional connections with our audience. All the technology in the world won't ever provide that critical window into the player's subconscious.
KEY LIGHT. In a conventional lighting setup, the key light is the major source of light. Typically, the key light stands for the sun, the moon, or the main room lighting. Key lights are frequently positioned at about a 45 degree elevation and 45 degrees to one side of the main subject. FILL LIGHT. Typically, the fill light is positioned about 90 degrees away from the key light, and generally is a complementary color. The fill light is not as strong as the key and is intended to bring the major forms of the subject into relief. KICKER OR RIMLIGHT. In theatrical lighting, a kicker is a positioned behind the subject so that a glancing reflection forms a highlight around the subject's outline. Kickers are usually placed opposite from and lower than the fill light.
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