Much of his acousmatic music displays an interest in the abstraction of unseen and unrecognisable sounds, an approach particularly strongly evident in earlier works such as Arrivals (1987) and Time and Fire (1991).
However, with the composition of Scherzo (1992) a parallel concern with the anecdotal and pictorial possibilities of recognisable sounds began to emerge, and much of his subsequent work plays on the tensions between these two approaches.
Ascent (1994) evokes the wildness of the mountain landscape of Snowdonia, which was awarded a ‘Euphonie d’Or’ by the Bourges electroacoustic music competition, as one of the most notable former prizewinning works between 1975 and 2005.
The cycle of works Four Anglesey Beaches (Penmon Point; Cable Bay; Benllech Shells; Llanddwyn Skies) (1999-2003) takes as its inspiration the seascapes and coastal locations of the area.
Lewis's more recent work includes more music for orchestras and ensembles, though an acousmatic concern with the materiality of sound remains: Eclipse (orchestra, 2004) was premiered under Elgar Howarth, while in the same year Tempo Reale (string quartet, 2004) was chosen by Sir Peter Maxwell Davies for a performance in London's Wigmore Hall.