There are two main approaches you can take in the studio or on location. And which lane you choose will have a huge impact on the outcome of your images. You could choose to emulate window light, or you could choose to simulate sunlight.
Emotion in your portrait work comes from your subject almost entirely, for lots of obvious reasons. That said, other elements in your portraits can affect and enhance their overall mood—especially the lighting. Simple decisions about light diffusion can alter or augment the mood you are after. There are differing opinions on what light diffusion does to a portrait’s mood. It’s subjective. But there are some tried and true light diffusion techniques that work consistently to evoke or enhance specific moods in human subjects.