Pre and early post war cars were fitted with one plain and one solenoid operated mechanical dipping reflector.  When headlamp dipping was applied, the plain lamp would turn off, and the solenoid would physically dip the reflector away from the main beam position. Both bulbs would be single filament as this was all that was required.  However, nowadays both reflectors can be fitted with twin filament bulb holders and bulbs to achieve modern style dipping.  The solenoid is redundant, but the original reflector can still be used.