Updated: Oct 2, 2019
Form. We don't know what a shape is without defining it with light. As most experienced artists know, we fundamentally start with what is called a three-point lighting setup. This concept applied to real-world and 3D compositions, so it's essential to not neglect. This system is composed of a key, rim, and fill lights.
The "key" is what you'd think; it's the leading light, and often times, it is the most pronounced and focusing on highlighting the most crucial part of the subject. The "rim," on the other hand, hits the subject from behind, and well, rims the back of the subject, making the background pop from the foreground.
Finally, we have the "fill" light; Its purpose is to fill in the form to make it all blend and harmonious by reducing hard shadows and balancing the shot.
All lights work in tandem, and you can add or even subtract, but it's important to remember that it all starts with the fundamentals.
As you can see with Peter Pan, simple lights as mentioned above help define him, and with a little bit of color temperature in the lights, we can add some great mood.