Aesthetics vs. Performance
"What do you mean I can't do that?"
As I mentioned earlier, in the film world, performance is not an issue. Yes, they have render times and schedules to deal with, but the film plays back at a given speed, and the only thing that can interfere with that is if the film breaks (old school) the digital projector somehow flakes out, or your DVD, or Blu-ray or whatever-comes-next player is having issues.
But performance is going to be your biggest issue when working on a game and getting it lit, and it will be the thing you will probably struggle with the most.
The truth is that there are all sorts of really cool things that Lighting Artists could do to make the game look even better...sometimes a LOT better, but we can't, because that thing we want to do negatively affects performance too much.
It would look fantastic, and then play at about 2 fps. And most people simply aren't going to put up with that. (It's a game, not a slide show.)
If you pay attention to things like lighting, odds are good that at some point you've been playing a game and reached an area where you said "Wow, the lighting here looks pretty crappy". The odds are also pretty good that there was a Lighting Artist who thought the same thing, and tried to improve things, only to get his or her knuckles rapped with a ruler by a programmer who said "YOU CAN'T DO THAT...IT'S TAKING 4 MILLISECONDS." So no pretty lighting for you!
So aesthetics vs performance is essentially: "How nice can we make this look while staying within our FPS budget?" If something that you do causes the framerate to drop to an unacceptable level, then you need to undo that thing you just did.
Torches on a Wall
Example: Imagine a hallway with several torches on the walls. What I'd like to be able to do is place a point light at the center of each torch, that casts shadows in all directions. But not hard-edged shadows mind you, I'd want to see soft-edges shadows. The light should be flickering in intensity, and moving in place slightly. This way the light would cast a realistic shadow of the part of the torch mesh, and any other parts of the model used as the torch holder, so of course the shadows are moving.
But I've never worked with an engine that would allow me to do that. Despite all the advances in technology to date, shadow-casting dynamic point lights are still too expensive, especially if you want a row of them, running down a wall. So it has to be faked somehow, and now you've got to balance the visual quality of what you want to see with gameplay performance.
I can't do this.
And speaking of performance, games were originally lit in a fairly static manner almost always, but then someone said "Hey, wouldn't it be cool if we actually saw the sun moving across the sky, and have the shadow position update?"
Which brings us to:
