Light placement relative to subject — front light (flat), side light (modeling), backlight (separation), top light (dimension). Defines depth and visual mood.
The positioning of your lights relative to the subject determines the sense of depth, dimensionality, and emotional impact of a scene—not just the intensity. You work with four basic directions that can be combined to create the desired visual language.
Front light comes from the front towards the actor (or your still life). It optically flattens the image—minimal shadows, even illumination. This appears friendly, neutral, sometimes even unfeeling. Classic for news interviews or portraits with high recognizability. If you use it too harshly, you immediately lose the sense of depth. That's why many cinematographers also use weak side light to still get contours.
Side light—your most important tool for modeling. The light comes from the left or right and creates volume through shadows and light. One half of the face is bright, the other dark (or filled in by reflectors). You use it to shape facial features, create drama or naturalness, depending on how hard or diffused you work. In feature films, this is your standard key light position—about 45 degrees to the side, 30-45 degrees elevated.
Back light is positioned behind the subject and shines back towards the camera. This is your separation tool: hair lights up, contours stand out from the background. Back light alone is invisible—you need it in combination with front or side light. For portraits, about 10-20% of the key light intensity; too harsh, it looks like a mistake rather than intentional design.
Top light comes from above and creates maximum dimensionality, especially on faces: eye sockets become darker, the forehead shines, the nose casts shadows downwards. Classic in film noir, for psychological scenes, in horror. Top light alone appears unnatural and eerie—you combine it with side light for realistic depth.
In practice, you play with all four directions simultaneously: key light from the side, fill light from the front (weaker), back light for separation, perhaps a top light for contours. The intensity ratios—your light ratio—determine the mood. Hard ratio (1:8) = drama. Flat ratio (1:2) = comedy or documentary. Experiment, measure with a light meter, and trust your eye.