Electricity is magic so I won’t explain the energy that brings the light but headlamps are a rather complex arrangement of lens and reflector. Until the advancement of computer modelling enabled engineers to design differing types of reflectors most headlamps before the 1970’s were fairly similar and simple. In essence they have a bulb which shines light onto a parabolic reflector and then through the lens into the area in front of the car. The parabolic reflector takes the light from the bulb and directs it parallel to the bulb’s axis in straight lines which means that the light is therefore organised (like a torch) and more useful than the scattered light of say a candle flame. The filament of the bulb will be positioned at the focus of the parabola making full use of the reflector to give the greatest light quantity. The parabola has makes all the light waves nice and straight and organised and the lens can do its work to direct the light. The reason why these early cars had round headlamps was that it is the resulting shape for a parabolic reflector. The ribs on these headlamps’ lens’ aren’t for your pleasure they are called flutes, and it is their job to direct the light into the required direction. Nominally downward away from an oncoming driver’s eyes and to the off driver’s side direction.