Real hologram or not? How 3D images in fog and water work

If you have stood in front of one of our installations, you know the picture: a giant face of light hanging over a lake, or a tunnel of light you can walk into. People ask us all the time whether that is a real hologram. The honest answer has two parts.

What a hologram is in physics

The hologram was invented before it could be built. In 1947 the physicist Dennis Gabor, looking for a way to improve the electron microscope, proposed recording not just the brightness of light but the shape of its waves, so that the light could be rebuilt later. Holograms of real objects had to wait for the laser. In 1971 Gabor received the Nobel Prize in Physics “for his invention and development of the holographic method”.

A true hologram stores an interference pattern, a microscopic ripple of light and dark. Lit again, it bends the light back into the waves that once came off the object. Move your head and you look around the object, exactly as you would with the real thing. That precision has a price: moving holograms in this strict sense are still small and experimental, and the holograms most people own are the shimmering security patches on their banknotes.

Why everyone says hologram anyway

Stages had their ghosts long before physics had holograms. In London in 1862, John Henry Pepper, building on a design by the engineer Henry Dircks, hid a brightly lit actor out of sight and let his reflection appear in a large sheet of glass set at an angle on stage. The audience saw a transparent figure moving among the actors. The trick still carries his name: Pepper's ghost.

Cinema and television did the rest. An image floating in mid-air, visible without glasses, became “a hologram” in everyday language. When a digital Tupac Shakur appeared at Coachella in 2012, the headlines said hologram; technically it was a modern Pepper's ghost, a projected image reflected in a transparent foil.

Today “hologram” names an effect, not a method: a three-dimensional image in the air, no screen in sight, no glasses. By that definition, fog and water holograms are the real thing.

Five ways to put an image in the air

Every “hologram” you have seen at a concert, a trade fair or a festival hides its carrier in the dark. What changes is the carrier.

Walk-through fog screens were presented by researchers at Tampere University of Technology in 2002. Water screens are lit from behind; front projection only works with very powerful projectors in full darkness.

The last row is the oldest idea on the list and the one we work with most. In 1973 the artist Anthony McCall showed Line Describing a Cone: a projector slowly draws a circle, and in a hazy room the beam becomes a hollow cone of light that people step into. The work is the light in the room, not the picture on the wall.

How our volumetric lightfields work

Water and fog are almost invisible in the dark. Light hits them and stops in mid-air, and a form appears to hang there: in front of visitors, above them, around them. Technically these are volumetric lightfields. Everyone calls them holograms, unless they happen to be physicists, and we use both words. We build them in three ways.

Layers of water and fog

In Depth/100 at O.Z.O.R.A. Festival in Hungary in 2023, a pressurised water shield forms the first projection layer and two to three mist curtains stand several metres behind it. Foreground, middle ground and background each go onto a layer of their own, so the depth you see is real distance, not a trick of perspective. BEYOND takes the method to monumental scale: in its large outdoor configurations the light reaches about 100 metres into the space, depending on the site and the weather.

Walk-in fog

ÆTHER draws sheets and beams of coloured light through fog until they become walls, tunnels and floating shapes. Visitors walk into it, touch it and photograph it from inside, with spatial sound around them. It has been shown at Boom Festival in Portugal, on the Marx-Engels-Forum in Berlin, at Re:birth Festival in Japan and at Ramadan at Hafeet in Al Ain.

Fog on architecture

Projection mapping and fog can work together. In Tessellation at The Sixth Sense in Bengaluru, projection turns the concrete silo of a former glass factory into a transparent vessel, and layered fog carries the image off the surface and into the night air around it. Infinity Gate did the same with a façade in Weimar in 2019: light-forms seem to step out of the building's arches and hover among the audience.

Why it needs the dark, and what wind does

Water and fog do not glow; they scatter whatever light reaches them. A street lamp or the last blue of dusk lights the droplets too and washes the picture out. That is why our holographic works run after dark.

Wind is the second factor, and water and fog take it differently. A water screen is a surface: when the wind bends it, the picture bends with it. A field of fog has no surface to bend, because the light draws the form wherever the fog is.

• Fog: keeps working in winds up to about 40–50 km/h.
• Water screen: fine up to about 25–30 km/h; above that it deforms, and above about 35–40 km/h it is no longer practical.

A deforming water screen is not always a loss. Moving water can also give the image an interesting, living quality of its own.

Which word to use

• Hologram (physics): a recorded interference pattern that rebuilds a light wave. Precise, and small.
• Hologram (everyday): any three-dimensional image in the air, with no visible screen and no glasses.
• Pepper's ghost: a reflection in angled glass or foil; the classic stage hologram.
• Volumetric lightfield: projected light given form by water and fog in a real volume of space, often in several layers. Our term for what we build.

So when a client asks whether it will be a real hologram, our answer is simple: it will be real light in real space, and nobody will need glasses. That is usually what they meant. More about our hologram installations.