Theme : Headlamps – See the Light?

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.

Headlight_lens_optics_schematic

Moving beyond the simple parabolic shape described above are headlamps that have non-uniform reflectors that combine the work of the flutes with that of the reflector within the reflector itself. This allows the designer greater freedom in what shape the headlamp can be and the reflector and a fluted lens can be paired to give a greater balance between the need to see and the desire to be noticed. They are more complicated to design in principle but can relieve the manufacturer the need to make a fluted lens, instead using a simple, strong polycarbonate cover whilst having the cheaper to produce reflector light the way (ahem). Most modern cars utilise this type of headlamp.

Headlight_reflector_optics_schematic

More commonly headlamps are now moving toward a projector style arrangement as they offer the ability to make the unit much smaller in diameter. The main difference to the reflective type lamps above is the incorporation of another lens (condenser lens), shutter and the use of an ellipsoidal reflector rather than the parabolic or modified parabolic explained above.

Headlight_projector_schematic

This is a very basic description of headlamp arrangements, there are other complexities obviously and I encourage you to ask any questions you may have or indeed conduct your own research and help others understand more. (All pictures gratefully and perpetually on loan from wikipedia)

One thought on “Theme : Headlamps – See the Light?”

  1. Firstly Mark, a word of thanks for illuminating a hitherto dark corner of my automotive knowledge. Even as a shallow, braying youth studying automobile engineering, I found automotive electrics to be some form of arcane and disturbing art, practised by furtive, light-averse oddballs – although upon reflection that may just have been my college lecturer. I really should have paid better attention – had I done so, I would have had the knowledge to post something that displayed some fleeting grasp of the technicalities, rather than what Mr. Kearne rather witheringly described as the ‘half-baked ramblings of a befuddled intellect’. Mind you, the hand written note upon which these words were branded was littered with sherry stains and the occasional typo, and was addressed to someone called Terry, so I’m not really sure for whom it was intended…

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