An evaluation was conducted of a mechanical beam switching system that may be appropriate for use with HID lamps. Subjects rated the adequacy of beam change time at several rates, compared with an electrical beam changing system.The results indicate that the subjects rated the mechanical and electrical systems the same, at the shortest change time for the former. Longer change times elicited poorer ratings for the mechanical system. The change from low to high beam was rated better than the change from high to low beam in the mechanical system. This difference was statistically significant at the two slower change rates investigated.