To place voile in front of light sources — soften without losing punch. French set-speak: "voiler le ciel" or "voiler la fenêtre".
Voiler is one of those French set terms that has stubbornly lodged itself in international film jargon—and for good reason. It describes the practice of stretching transparent or semi-transparent diffusion materials in front of a light source or an area to refract, scatter, or soften the incoming light. The term comes directly from the French word voile (veil), and that's precisely what the material does: it lays over the light like a fine veil, transforming its characteristics.
On set, this works concretely like this: you stretch voile—usually a synthetic silk fabric or specialized diffusion material like Silk or Light Silk—in a frame or directly in front of an HMI, a Dedolight, or even the windows of your set. This turns harsh, direct light into soft, diffused light. Voiler le ciel specifically means to matte the sky—for instance, by covering large overhead areas with voile to diffuse direct sunlight. Voiler la fenêtre works similarly: voile is attached to the set's windows to control and soften natural light before it hits the interior. This is work for the first assistant camera and the grip team—it costs time, but saves you a massive amount of interior lighting work later.
The practical difference from other diffusion methods lies in control and nuance. While a large bounce frame reflects light, voile absorbs it and scatters it in all directions—softer, more diffuse, less contrast. A voiled sky creates even, directional-indirect lighting without the sky becoming completely gray and flat. The light still retains a direction, but without hard shadows. Important: the density of the material determines the effect. A light silk costs you about one stop, a denser material two to three. You need to factor this into your light meter readings.
Professionals keep voile in various densities in their trucks—from transparent to opaque material. On smaller sets, where you need to save budget and manpower, you improvise with cheap white cotton or muslin. This works too, but costs more light and is less elegant. The French trick: don't attach voile directly to the source, but place it half a meter or a full meter in front of it—this creates a larger, softer light source and better control over hotspots.