Production Lighting: How to Do Rim Lighting
In production lighting, you can often add a bit of glamor using a rim light. Lighting the person's face is always the primary objective, but you can create a greater aesthetic if you can go beyond merely achieving exposure.
Step 1: 3 point lighting
The basic lighting set up in film is a 3-point system. First, you have the key light which is the primary source of illumination on the subject. Second, you have a fill light to fill in any shadows caused by the key light. Finally, you have a back light, synonymous with rim light and hair light. This source originates from behind the subject pointing towards the general direction of the camera. This light that is now hitting the back of the person's head (assuming they are facing the camera) creates a luminescent outline around his hair and shoulders. There are many reasons that this effect would be desired.
Step 2: Separation
The primary reason to standardize a rim light is to separate the subject from the background. Lighting is one of the key ways to subliminally tell the audience where to look. If you look at a shot of a classroom, you will find yourself somehow being drawn to the lead character. You may excuse this as simply already knowing what they look like, but try comparing their lighting with the rest of the class. Perhaps this person has a rim light which separates them from everything else in the frame. The other students do not have a rim light and sort of blend into the setting.
Step 3: Hair and Glamor
In situations where you have a person with dark hair in a dark room, the separation problem is even more of an issue. In this instance, you absolutely cannot see the differentiation between where the person's hair ends and the background begins. Here, a hair light is absolutely critical. Even the most subtle amount of illumination is enough to outline the shape of the person against the blackness. In other instances, you may want to load the person's hair with light. The most cliche example of this is the gorgeous blond tossing her hair. A back light will accentuate the glamor of the moment.
Step 4: Flare
One issue to look out for when using a rim light is flare. If you have a source pointing in the direction of the lens, you may end up actually hitting the lens with light. In some cases, this can cause a desired flare effect. However, more often than not, flares are distracting or obtrusive. So, keep some tools around to block the light from the lens. Remember that if you try to fix the problem from the light source, you may end up affecting the light on the subject. So whenever possible, use a matte box near the lens to solve the issue.
Rim lighting can visually spice up your scene if used properly. The level of intensity is a matter of taste and purpose. Practice to discover what you like.