The Real Poop
Lighting design is one of those things you're not supposed to notice. In a movie, everyone looks good in each scene because a lighting designer knows all the ways to highlight the actors' best features.
In huge concert halls, or on game show sets, or in big fancy-shmancy homes, a lighting designer makes sure all the bulbs are just right. Subtlety is key, which is why you often only notice the lighting when it's really bad.
Any time you're in a space where light seems to be directed strategically, there was likely a lighting expert thinking through the problem. The guy who lit up that concert hall? Lighting designer. The gal who made that dark, shadowy scene in that movie look so ominous and foreboding? Lighting designer.
The fella who shined that flashlight in your eyes and asked to see your driver's license? Police officer. Sorry, different situation there—but you really shouldn't have been driving that fast.
There's more to this job than just figuring out where to point a bunch of lights, which is why the average salary is a respectable $52,000 per year (source). Lighting design is just one aspect of production, but all those production elements have to work together.
Consequently, there's a ton of overlap between lighting design and other production pieces like set design, stage direction, and camera work. In fact, many lighting designers help out with those other parts, too, so it helps to be knowledgeable about all areas of production design.
The important thing to remember is that you're a designer, not a technician—meaning you'd better have a clear, artistic vision every time you take on a project.
It isn't enough to be a wiz with lights and electronics; you need to have a deep understanding of a script, the characters within, and the director's own vision in order to create a world of lighting that enhances the overall project. If you're the type of person who has trouble generating artistic ideas, you'll burn out quickly in this biz.
All that said, if you grasp both the scientific and artistic aspects of lighting design, this could be a great career path for you. You have the potential to work on big-budget films that could stretch and challenge you (that's a good thing), or you might end up getting hired to light a regular television series, which may not be quite as glamorous but at least could mean a steadier paycheck.
It helps to be passionate not only about your lighting duties, but about each project you work on as a whole. You are, after all, a member of a team, and the ultimate goal is to come away with a win for the whole group—not just to pump up your own stats.
When you're working on a film or TV show, it's a special thing to be a part of that environment, part of that energy. If you let yourself be enveloped in the magic of the filming process, it'll only make your job that much more enjoyable.
At the end of the day (or scene), lighting design is a pretty good gig. You get to be creative and work in an interesting atmosphere, and your paycheck will probably be a bit heftier than most other "creative" types (which isn't saying much, but still).
When the audience applauds at the end of the show, you can close your eyes and pretend they're admiring your spotlight rigging. And they should—you really did a great job on that.