Design Nomenclature / Light & Optics
Fill light
Also called fill
- Light & Optics
- Composition
- 2D & 3D
A secondary source that raises illuminance on the shadow side, controlling how much detail survives there. Fill sets the lighting ratio rather than the direction: it is placed so as to cast no visible shadow of its own, usually broad, low in contrast, and near the camera axis.
In practice
Fill is measured, not felt. The number that matters is the key-to-fill ratio in stops, not the wattage of whatever is producing it.
Not to be confused with
- Key lightThe dominant source in a setup — the one that establishes the direction of the light, the placement of the form shadow, and the exposure everything else is balanced against. Its height, angle, and angular size fix the character of the image; every other lamp is defined by its ratio to this one.
- Bounce lightLight redirected off a reflector — card, wall, ceiling, scrim — rather than aimed at the subject directly. The reflector becomes the effective source, so its size and distance, not the lamp's, govern shadow softness. Its colour is the reflector's albedo multiplied into the beam.
- Ambient lightIn a renderer, a constant added to every shaded point regardless of direction, occlusion, or distance — a flat lift with no physical referent, invented to fake indirect light before global illumination was affordable. In a room, the same phrase means the real diffuse light arriving from every direction at once.