What is one-way vision film?

The effect comes from perforation and colour rather than from anything exotic. The film is punched with a regular pattern of small holes — commonly around half its area — and is printed white on the outer face and black on the inner face.

From outside, the eye is drawn to the brightly lit printed surface and the small dark holes disappear into it, so the image reads as continuous. From inside, the black backing absorbs light so there is nothing to look at, and the eye focuses instead through the holes at the brighter scene outside. It is the same principle that makes a net curtain work.

The consequence is that it depends on a light imbalance. It works well in daylight, when outside is brighter than inside. After dark with interior lights on, the relationship reverses: the graphic becomes hard to read from outside and people outside can see in. For premises whose signage has to work at night, that is a genuine limitation to plan around rather than a defect.

Because half the surface is missing, printed colours look lighter on the window than on screen, so artwork is usually built slightly denser than it would be for solid vinyl. It is applied to the outside of the glass and is a consumable — expect a couple of years outdoors rather than a permanent installation.