Just like anything else, rules were made to be broken. If you understand the principle of 3-point lighting, then you can begin modifying your setup to meet your specific needs. Have you noticed the look of interviews on shows like 20/20 or Dateline? Their interviews are often in support of a serious or dramatic topic, and they use the lighting on the interviewee to enhance the mood of the piece. Many times, they will use no fill light at all. This creates a bit of mystery, especially when the key light is on the side of the face away from the camera as you see in my example above. Sports segments leading up to the beginning of a game will take this concept to the max, often using very stark single-point lighting (from directly overhead, for example) to cast distinctive shadows across the face. On the other hand, lighting an interview for the Today show might call for four or five point lighting on the subject. This could include not only a key, fill, rim and additional edge light, but also a broad fill (often bounced off a white card from below the subject) to raise the overall base illumination and eliminate shadows under the chin. In addition to that, you might use several lights on the background in order to create the happier atmosphere you need on a morning show.
You have a lot of choices when lighting a scene, and though we are talking about interviews here, these same principles apply to narrative storytelling--it just becomes a little more complicated when people are moving around. The basic take-away here is to know the story you are shooting and light accordingly. Your story will be enhanced and the look of your overall piece will have a consistent feel to it.
