Holographic mirror film is used in cases where a hologram display case is not possible due to structural size, durability, or logistical constraints. On performance stages, for example, holographic mirror film can create large and impressive illusions of performing artists. Holographic mirror film works on the same principle as hologram display cases, reflecting the image formed on the actual projection surface into the eyes of the audience. The success of the illusion depends on several factors, the most important of which is preventing the audience from seeing the actual projection surface, which is usually built into the stage floor or a recess beneath it. It is also important that the mirror film is stretched perfectly flat. The illusion can also fail due to the choice of projection surface and projector, particularly if the screen contrast is not excellent.