Pepper's ghost — the ghost on stage (3D)

About this app

An angled pane of glass reflects a hidden, brightly lit figure onto the stage as a transparent ghost. Control stage and pit light separately, reflection after Fresnel, ray path and virtual image; scenes Theatre 1862, Haunted Mansion 1969 and foil today. Seen from the side, the trick falls apart.

Frequently asked questions

How does the Pepper’s ghost illusion work?

A sheet of glass or foil is placed at an angle between audience and stage, often around 45°. It lets the stage light through while also reflecting a brightly lit figure from a hidden area, so the audience sees both superimposed. The reflection appears as a translucent “ghost” where the figure would be if mirrored in the plane of the glass; nothing is actually standing there.

Why does the hidden figure need so much light?

Clear glass with a refractive index of about 1.5 reflects only a few percent of the light: about 4 % per surface at normal incidence, around 5 % at 45°, and a little over 9 % for a pane with two surfaces. For the reflection to show up against the stage behind it, the hidden figure has to be much brighter than the stage background. Black surfaces reflect nothing and stay invisible; dim the figure and the ghost disappears.

Are “hologram” concerts real holograms?

Often not. Many stage shows billed as holograms use the Pepper’s ghost principle with a thin foil stretched at an angle, reflecting a bright LED wall or projection from the orchestra pit. Holography, by contrast, records and reconstructs an object’s light waves through interference. The stage trick goes back to a model by Henry Dircks; John Henry Pepper brought it to the stage in London in 1862.

What can I explore in this app?

Choose one of three scenes (theatre 1862, Haunted Mansion 1969, modern foil) and set stage light and pit light separately to make the ghost appear or vanish. You can change the tilt of the pane, move the actor in the pit and show the ray paths and the virtual image; readouts give the Fresnel reflection of the pane and the brightness ratio between ghost and stage. The audience, free (cut-away model) and side views show why the trick only works from the front.

Subject: Architecture & scenography

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