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The paper describes work carried out to determine the feasibility of using a SPICE circuit simulator to predict harmonic current levels, and conducted interference (9 kHz to 30 MHz) produced by a phase controlled lamp dimmer and flyback converter switched-mode power supply (SMPS). The SPICE models are constructed using realistic models for the passive components and approximate models for the switching and control circuitry so that switching rates and duty cycles can be precisely controlled. The SPICE time-domain data was processed to predict the harmonic current and average and peak conducted interference values. The models are compared with measured results. Whilst the harmonic currents can be predicted accurately, there are still significant problems with the accurate prediction of conducted interference. However, the SPICE model predictions follow the measured data with changing load.