Lighting overview:
Lighting is one of the most important aspects of level design, and digital environments in general. it's responsible for bringing your environment to life. It ties your level into a whole, and sets the overall atmosphere and mood.

With current realtime rendering technology it's not possible to render photorealistic scenes. In order to overcome this limitation, environment artests must exaggerate many aspects of the scene, lighting in particular. this is true about all forms of art, and is essential for making a solid scene.

Hue, Brightness, Contrast and Saturation:
All these things are important to the outcome of your scene. They set an overall tone and they make your environment interesting, thereby catching a person eye, but it's even more important to use them wisely and keep consistently throughout your environment. These 4 lighting properties are the biggest lighting problems for people who are new to level design, and especially art in general.

Hue: this is where many beginners go wrong. Having too many colors in any given composition will ruin the atmosphere and believe ability of the scene, while not enough will cripple your scene,leaving it dull and boring. The goal is to fine a balance between the two, exaggerating based on the style your going for. The color wheel can be split into 2 categories, "warm" and "cool". The 3 complementary color sets you should be familiar with are(refer to the color wheel below):

Analogous: Analogous colors are colors that are close to each other on the color wheel(blue and blue-green for example).

complements: A complement color is the color that is directly across the color wheel from any given color. using complements is a great way to get contrast and atmosphere in your scene. A common example is blue with a complement of orange or yellow, blue being a cool color and orange being a warm color.

split complement: same as complements except that you use 2 complements of a color in a scene(eg. blue with complements of orange AND yellow).

Something you want to be careful of is mixing all 3 primary's(red, yellow, blue) in the same composition, they will most likely clash.

Brightness: Brightness (or value) is very important, use a good variety of this to get nice contrast. A great composition has a good deal of contrast. The eye (or player) is draw towards contrast shifts so use this to guide the player around the level(eg. if a player can't see a doorway, make a sharp contrast in that direction, such as having the general area dark and adding a high value, low radius light near the door.) this is also true about 2d compositions, except that your leading the viewers eye around the composition instead of the level. You must also think about the "key" of your level. a "key" is the overall value of a composition, is your level going to be high or low key?

Contrast: Contrast is always nice, compositions can be greatly enhanced with good use of contrast. Use it, but don't overuse it. If everything constantly shifting value your forms will be lost and your composition will be ruined.

Saturation: This is probably the biggest problem beginning level designers have. This along with too many colors causes very poor scene. Saturation should be varied and used in moderation. The amount of saturation depends on the style you want, generally lower saturation means higher "realism".

Saturation is one of the major things that decides your compositions mood and feeling. Many newer games use "screen overlays" which modify the overall look of the composition. A great example of this Gears of War, the designers wanted a really gritty and perhapses depressing world, in order to achieve this they use screen overlays to modify the the saturation, among other color properties. this can be seen on the following screenshots from Gears of Wars.

With Overlays	Without Overlays

Atmosphere and Mood:
Atmosphere is the biggest part of lighting, everything in this article deals with atmosphere, and for that reason i will only go over it generally in this section. For me it's the core reason someone should put so much time and energy into an environment. Atmosphere has the power to make the player excited, scared, happy, depressed, and any other emotion you can think of, and to waste that power should be a crime :)

Lighting describes atmosphere and mood better than any other aspect of an environment. For instance, If you want to scare the player you can make a transition from a high key scene to a low key scene. The player felt safe in the high key scene and let there guard down. This is a perfect opportunity to scare them, quickly lead the player into a low key environment and spring some surprises on them.

Mood is the effect of atmosphere, another great way of setting a mood is color. The human mind associates colors with moods and feelings. Red makes us think danger, blue gives a cool and safe feeling, and green can give a sickly or dirty feeling. There are countless color/mood associations. This is a great way to set an overall mood in your environment.

Shadows and Drama:
Cast shadows are shadows that are created when an object blocks light from hitting a surface. This type of shadow creates the most drama and is what you generally think of when you think of shadows. Again this is a great way to create sharp contrasts, and give a feeling of depth as well as scale.

Ambient shadows, unlike cast shadows this type shadow is not created when an object directly blocks light. Instead it's caused when either a light is too far away to light the surface enough, or if bouncing light has to bounce too many times before it hit's the surface(radiosity).

In the past realtime radiosity was not possible, so some game engines used their offline lightmap generators to create this effect(Half-Life 2, Max Payne 2). Fortunately with evolving graphics rendering technology this is becoming more and more possible to do in realtime. But at this time chances are you are working with an engine which does not supports any type of GI or radiosity so you must fake it. This is done by placing lights wisely. When working with static lighting there is really no limit to the number of lights you can use, but when working with realtime dynamic lighting you have to be careful not to fill your area with too many lights. Ambient shadows should not be pure black, there is nothing in reality that is not effect by light in some way, so don't let it happen in your environment.

Ambient Lighting Some beginners think it's ok to fill shadows with "ambient light" which sets a minimum brightness in an area. Please do not use this type of lighting unless it's on a per object basis and even then the ambient lighting must not illuminate any part of the object without the help of other "real" lights.

Cast shadow	Ambient shadow	Bad use of ambient lighting

Writen by Kurt Loeffler.
www.KeenLevelDesign.com

Contributers:

Sjoerd "Hourences" De Jong
Hourences.com
Work used: Ons-Adara, DM-1on1-Idoma, DM-Rankin, Verlan Island, Xidia Gold Mod, DM-Sion.

Florian 'Strogg' Oswald
Strogg.de
Work used: DM-1on1-Tangora, DM-1on1-Obsidian.

Oliver "dux" Hobbs
dux.interlopers.net
Work Used: DM_Drift.

Shawn "FMPONE" Snelling
Work used: DoD_Anemia.

Saroner
Work used: DM-Altena.

Other Contributers:

EpicGames

Valve

Warsow team