Fill Light

Light that softens the shadows made by the key light, controlling the difference in brightness between the two sides of the face (contrast). It usually sits 45° on the side opposite the key, dimmer than the key, and does not erase the shadows completely. A fill at half the key’s brightness is called 2:1, a quarter is 4:1; less fill is more dramatic, more fill is brighter and lighter. Light bounced off a reflector or wall also works as fill.

Lighting positions seen from above. A key 45° to the camera’s left, plus a soft fill at half strength from 45° on the right.

Camera view. The shadow side of the face brightens a little so its shape shows, but the shadow still remains.

How it feels

Softness
Friendly
Stable
Natural

When to use it

Interviews and ordinary narrative films
Filling with a reflector when shadows are too strong
Setting the mood through the brightness difference between the two sides of the face

In the movies

The Breakfast Club (1985) · Source: Movieclips (YouTube) · Original video

Lost in Translation (2003) · Source: Movieclips (YouTube) · Original video

Not to be confused with

Key Light: The key is the main light that sets the direction; fill is a supporting light that controls its shadows.
Bounce Light: Bounce is a way to make light by bouncing it off a wall or reflector; fill is a role. You can make fill with bounce.
Negative Fill: The opposite of fill. Instead of adding light, a black surface soaks it up to deepen shadows.

Prompt

Keyword

soft fill light

Descriptive

Gentle fill light from the opposite side keeps the shadows soft but visible.

Try these combinations

Fill light: topping up window light with a lamp
Medium close-up of a man at a kitchen table, soft window light with warm lamp fill, cool rim from hallway
Key + fill: a coolly filled interview
Interview close-up, warm 3000K main light from left, cool 6500K fill from right, soft fill shadows