Moholy-Nagy described his Light Prop for an Electric Stage, better known as the Light Space Modulator, 1929-30, as an ‘apparatus for the demonstration of the effects of light and movement’ or the ‘light-requisite for an electrical stage.’ With the aid of an engineer and technician, the work was constructed to provide lighting effects for plays and other performances. It consists of a box with a circular opening at the front (the stage) and a second board with a parallel circular opening inside the box. The backs of both of these openings are surrounded by bulbs of various colours, which flicker on and off at pre-determined times, illuminating moving discs and pieces of glass and metal. These, in turn, cast complex shadows on the back wall of the box. The wall can also be removed, allowing the light to project onto a backdrop of any size. A hybrid of light and movement, the kinetic quality of this work was captured in motion in Moholy-Nagy’s film Motion Picture Black-White-Grey, 1930. The artist also made photographs of the work, shown here. ‘It is indeed foreseeable that this or similar motion pictures may be transmitted by radio,’ he prophesied, ‘[i]n part with the support of telescopal prospects, in part as real light plays, whereby the listener owns a private lighting apparatus which can be remotely conducted from the radio station via electrically controlled colour filters.’
The Busch Reisinger Museum at Harvard University, Cambridge, MA holds the original and a 2006 reproduction. Earlier reproductions from 1970 are held at the Van Abbemuseum in Eindhoven, Netherlands and the Bauhaus Archiv in Darmstadt, Germany. Different sources provide different dates for the work, 1922-1930, 1923-30, 1929-30. In any case, it is a key work in the history of kinetic art, light art, and installation.
“This piece of lighting equipment is a device used for demonstrating both plays of light and manifestations of movement. The model consists of a cube-like body or box, 120 x 120 cm in size, with a circular opening (stage opening) at its front side. On the back of the panel, mounted around the opening are a number of yellow, green, blue, rot, and white-toned electric bulbs (approximately 70 illuminating bulbs of 15 watts each, and 5 headlamps of 100 watts). Located inside the body, parallel to its front side, is a second panel; this panel too, bears a circular opening about which are mounted electric lightbulbs of different colors. In accordance with a predetermined plan, individual bulbs glow at different points. They illuminate a continually moving mechanism built of partly translucent, partly transparent, and partly fretted materials, in order to cause the best possible play of shadow formations on the back wall of the closed box.” 
 Edward A Shanken, Art and Electronic Media, 2009, p 85.
 Ibid, p 18. Moholy-Nagy quoted from The New Vision, 1928.
 Greg Allen, “So Many Light Space Modulators” http://greg.org/archive/2010/08/09/so-many-light-space-modulators.html
 Media Art Net, http://www.medienkunstnetz.de/works/licht-raum-modulator/