A bit late to the party but better than never right? The Left 4 Dead blog has posted part 2 of a series of posts dissecting the game's art direction. This part concerns the stylistic choices in regards to lighting within levels that Valve put into effect to streamline the visual information given to the player. Amongst those discussed is the light-infused fog:
Randy wrote: But while TF2 had a bright and colorful art direction, Left 4 Dead takes place in a variety of dimly lit nighttime environments. Because of this, playtesters weren't able to see zombie silhouettes in the midground and background. Because of this, they were repeatedly getting mobbed.
While sudden zombie attacks were inarguably scary, they were also frustrating—players weren't being given the information they needed to react. They wanted that "Here they come!" moment, and we weren't giving it to them. The solution? Light-colored fog:
While not as realistic-looking as actual fog in some settings, it meant playtesters could see attackers in the distance. Once they were able to anticipate attacks, playtesters started to have a much better time.
More importantly, these posts reveal some of the thought process when trying to straddle the divide between realism and fun as a developer. Read more of Left 4 Dead's behind-the-scenes analysis of its art direction by checking out both Part 1 and Part 2.