Volumetric Light

The beam itself becomes visible, so light stops being something that lands on a subject and becomes an object in the frame with edges and a direction.

It also gives a flat image depth. A shaft crossing the frame at an angle separates the foreground from the background more clearly than any amount of focus pull.

The air has to hold something. Haze, smoke, dust or steam gives the beam particles to scatter off, and without them there is nothing between the source and the subject to see.

Backlight or three quarter backlight shows it best, because scattering is strongest when the light points roughly toward the camera. A source behind the subject aimed at the lens is the standard arrangement.

A hard source with a defined edge gives a defined shaft. Window frames, doorways, slatted roofs and gobos all work as the cutter that gives the beam its shape.

Use it for cathedrals, forests, warehouses and anywhere with height. It also sells a searchlight, a projector or a car headlight without showing what they are pointed at.

Skip it for clean interiors and product work. Haze lowers contrast across the whole frame and takes the snap out of a surface.

Backlight puts a source behind a subject and draws an edge on them. Volumetric light needs that same geometry and adds atmosphere, so the beam is visible on its way there.

The test is whether you can see the light in the air. If only the rim on the shoulder is lit, it is backlight. If the shaft itself is visible, it is volumetric.

Steven Spielberg and Vilmos Zsigmond fill the air with smoke through Close Encounters of the Third Kind (1977) so the light from the ships arrives as solid shafts. The beams do most of the work of making something enormous out of a light source.

The air comes back clear and the beams do not appear. Say the air carries haze or smoke, in the same sentence as the beam.

The second failure is a soft glow with no shape. Ask for defined edges to the shafts and name the opening that cuts them, such as a window or a doorway.