用主光确定方向和质感，用辅光控制阴影对比，再用轮廓光把主体从背景中分离。先关掉所有灯逐个建立关系，最后才补环境光，这样更容易复现。 Use a key light for direction and texture, a fill for contrast, and a backlight to separate the subject. Build the relationship one light at a time before adding ambient light so the setup remains repeatable.