Exhibit: Phantom Filament

The bulb is really underneath the shelf in the exhibit and the one you see is only its image, formed by a curved mirror behind it. The mirror is so large and curved in such a way that the image appears to be real and can be seen over a very wide angle.

When light meets a shiny mirror surface, it bounces off. The angle of bounce depends on the angle at which the light meets the mirror. The mirror in the exhibit is spherical, but the light comes from a point just to one side of the centre of curvature. The bulb is upside-down and 4 feet from the mirror, so light from every point on the bulb reflects back to a corresponding image point above the shelf. So you see a floating image of the bulb which you think you can touch.