Sedgley was a professional architect before turning to painting in the early 1960s. He began to explore Op art effects in large paintings of soft-edged concentric circles which appear to pulsate with light and colour. He favoured the circle for its 'anonymity' which allows the sensation of colour rather than the form to command attention.

He made use of contemporary materials, making his own black paint from commercial pigments and resins which were applied with a Devilbliss spray gun. He used masking out to apply the successive layers of colour corresponding to the chromatic scale of the spectrum with white as a neutral spacer. The effect is hypnotic and changes with the movement of the viewer.