Abstract: The invention relates to a light diffuser, consisting of a holding mechanism and, releasably connected thereto, an inflatable sack that is at least partially translucent, wherein the holding mechanism comprises an adapter ring that at one end serves for attachment to a spotlight and at the other end as a receptable of the sack, and furthermore the adapter ring is closed off at the attachment end so as to be translucent and pressure sealed, and at the holding mechanism means are provided for supply of a gaseous filling medium. In accordance with the invention there are arranged at the adapter ring a compressed-gas connection as well as an electronically actuatable valve for the gas supply, such that a first pressure sensor determines the increasing of pressure within the sack fixed to the ring and sends a switch-off signal to the valve when a preset maximal pressure value has been reached, in order to terminate or interrupt filling automatically.