Pepper's Ghost: The Victorian Illusion Behind Modern Holograms
In December 1862, audiences at the Royal Polytechnic Institution in London watched a translucent ghost walk across the stage beside a living actor, in a staging of Charles Dickens's The Haunted Man. The method had been devised by the engineer Henry Dircks, whose version needed a purpose-built theatre. John Henry Pepper, a lecturer at the Polytechnic, found a way to fit it into an ordinary stage, and the effect has carried his name ever since.
The same idea later filled the ballroom of Disneyland's Haunted Mansion in 1969, put a life-size Tupac Shakur on the Coachella stage in 2012, and sits inside every plastic hologram pyramid on a phone. It is one of the few stage illusions you can build on a kitchen table in an evening.
How it works
A sheet of clear glass or plastic reflects a few percent of the light that reaches it and lets the rest through. Put a brightly lit object to one side of the sheet, angle the sheet at 45°, and a faint reflection of the object appears behind the glass, superimposed on whatever is really there. The reflection seems to sit as far behind the glass as the object is in front of it.
The illusion holds when two conditions are met. The object has to be much brighter than the scene behind the glass, because the reflection carries only a few percent of its light. And the object itself must be hidden from the audience, so the reflection seems to have no source. Pepper's actor stood brightly lit in a pit below the stage, out of the audience's sight; a modern version swaps the actor for a screen.
Building a tabletop version
The simplest version uses a tablet lying face up and a sheet of clear acrylic:
- Lay the tablet flat, screen up.
- Stand the acrylic over it at 45°, with its lower edge along the far edge of the screen and its upper edge leaning toward you.
- Put something black behind and around the glass, such as a box lined with black card, so nothing bright shows through it.
- Darken the room, turn the screen to full brightness, and look straight through the glass at the height of its middle.
The sheet needs to be at least as wide as the subject and about one and a half times as long as the subject is tall, since it crosses the screen on the diagonal.
Why HoloPath's layout looks the way it does
HoloPath's Pepper's Ghost layout follows from the geometry. A point on the screen appears in the glass at a height equal to its distance from the glass's lower edge, so whatever is near the far edge of the screen appears low, and whatever is near you appears high. The layout therefore:
- uses a wide 16:9 frame, 800 by 450 pixels at the default resolution setting, to suit a tablet or monitor turned sideways;
- scales the subject to 55% of the frame's height, about 248 pixels, and sets it near the bottom edge with a small margin;
- mirrors it, because a single reflection swaps left and right.
Place the tablet so the bottom of the picture lies along the far edge, under the glass's lower edge. From where you sit the picture on the screen looks upside down; that is correct. In the glass, the subject then stands on the floor of the box, upright and the right way round. On a tablet about 22 cm wide, it is about 7 cm tall.
Getting a clean picture
Most of a Pepper's Ghost frame is black, which used to cost GIFs dearly: on a test subject, the encoder's 256-colour palette held only 36 distinct colours, nearly all of them near-black, until a palette fix in October 2026 raised that to 196. That fix, and the remaining causes of banding, are covered in why hologram GIFs band. On a tablet, a video export with the player set to repeat avoids the question entirely.
A faint double outline means the reflection is coming from both surfaces of a thick sheet; thinner acrylic brings the two images together. If the subject looks tilted, the sheet is not at 45°.