In this article I will list a few things which are good to keep in mind when doing the functional lighting of a level. This will not be about the artistic aspect of lighting, but aimed more towards how lighting affects the gameplay of a level and how big of a role it plays in player guidance and the playability of a level. This article is targeted towards singleplayer design, but most, if not all, of the points can be translated to multiplayer design as well.
I'll be using a scene which I made in Half-Life 2 as an example throughout the article, which will showcase the specific lighting which is talked about in each section.
Each section will showcase the scene in its basic stage with very simplistic lighting, alongside a more developed scene where the lighting has been further tweaked to fit the geometry. Remember that you can click on each image to see a larger version of it!
Player guidance is what lighting is all about. Player guidance means that when the player enters an area in the level, he or she receives enough information to be able to know where to go and what the goal of the area is. Before I get started, I just want to mention that a pitch dark level is usually bad unless you're working with gameplay mechanics which requires it (Amnesia, Doom 3 etc.). If you intend the player to be able to make decisions regarding where to take cover or where to go next, he or she needs to be able to read the environment in the first place. With that being said, let's move on!
Let's start out with taking a look at our scene below. As you can see in the image, it's well lit, the player can see everything, but nothing really stands out or draws your eyes in. Let's modify the lighting to better inform the player about the area.
Exit highlighting is when the goal of the player is made very obvious. In this example the scene is mostly plainly lit, but the intensity of the exit-area draws the player in and tells him or her that there's something interesting over there. There really isn't much to say about this since it's quite obvious, but if you find yourself getting playtesting feedback that an area is hard to navigate or confusing, then highlighting the correct way forwards can be a great way of getting the player on the right track again.
When a scene is getting a bit more complex it can be a good idea to use path highlighting, which emphasizes the correct route through the area. This is basically an extension of exit highlighting, where we show each step the player needs to take to get through the area. In this scene, we want the player to go through the door at the far end of the room, then continue over the catwalk into a new area.
When introducing enemies into the scene, it can be easier on the player if they're introduced in a proper way so that the player has time to identify the threats, make decisions about cover and so forth. Presenting enemies can be done in several ways and depends on the type of enemy you're working with. If the area has several levels of height and the enemies will attack from top-down, it's a good idea to backlight them to enhance their silhouettes, making them easier to target. If enemies will be introduced to the scene via an entrance-point, dynamic light can make it much more obvious where the enemy is coming from, such as light streaking out from a door opening. In this example I've put focus on the area the enemies will be coming from. I've also lit up the main floor, which gives the player more information about cover and makes it easier to keep tabs on enemy movement.
Hinting is just what the name implies, when you give the player hints of alternate passages, pickups or other items of interest. Don't make the hint too obvious, since that will lessen the feeling of discovery. Make sure that the hint doesn't interfer with the main lighting, but that it still sticks out noticeably. In this scene the left side is lit up slightly to give it a higher chance of being explored by the player.
For basic functional lighting that is really all there is to it. Remember to continously playtest your level with new people to get some fresh eyes on it, when designing a level you can miss obvious things since you know every last square meter of the level and can play through it blindfolded.
I hope you've enjoyed reading this article on functional lighting. If you have any questions or comments I can be reached at firstname.lastname@example.org
Thanks for reading!