Lit square 1969 forms part of the United States group of the 'Ba-O-Ba' series. It is typical of the series in the use of a square glass sheet, though only single-element red-neon tubing defines the edges of the glass in this work. Referring to the 'Ba-O-Ba' series, Sonnier indicated that these pieces were used as sets for video work done in the early 1970s and also became props for performances.¹ Lit square was used as a set for a black and white videotape entitled Mirror Act 1969.² The importance of reflection to this work (and to the series, as noted in the entry for Untitled 1969) can be deducted from the title of the video. The neon element in Lit square is arranged around the perimeter of the glass sheet to maximise the play of neon-generated light and partially lit reflected image. Lit square was first displayed as a discrete work at Sonnier's exhibition at Leo Castelli Gallery in March 1970.

The Australian National Gallery owns one other later neon piece by Sonnier: Expanded sel diptych II 1979.

Michael Lloyd & Michael Desmond European and American Paintings and Sculptures 1870-1970 in the Australian National Gallery 1992 p.398.