Besides making a dark shape (silhouette), how does light coming from *behindyour subject make it pop out strongly from the background?

Light coming from behind your subject makes it pop out strongly by creating a distinct, bright outline around its edges, a phenomenon known as rim lighting or a hair light. This occurs because the light source directly illuminates the very contours and fine textures of the subject that are closest to the light and furthest from the camera, causing those edges to glow brightly. This bright, illuminated edge then creates a significant value contrast against the comparatively darker or unlit background. Value contrast refers to the difference in lightness or darkness between adjacent areas in an image; the luminous outline of the subject (a light value) against a darker background (a dark value) establishes a strong visual separation. This high contrast at the subject's boundary visually detaches it from the background, enhancing the perception of its three-dimensional form and depth. The bright outline defines the subject's shape and volume, making it appear to lift off the background rather than blending into it.