First, of course, you need to be clear about exactly which mood you're after: sunny, dreamy, macho, scary or any of a score of other emotional states. For instance, midnight lighting is equally dark, blue and contrasty for both strolling lovers and lurking vampires. Beyond the basics, though, romantic and horrific are different animals.
So let's see how to paint emotional light pictures, using contrast, color and, first of all, key. As used here, "key" doesn't mean the main light on the subject, but the proportion of light to dark in the image. We'll work indoors, where you normally do most of your lighting and have the most control.
High-Key
High-key images are basically light-toned with darker accents. This doesn't mean low contrast; a good high-key lighting design includes a full range of tones from white …