pranay

Some interesting info if u want to know about the parabolic and ellipsoidal lamps in 220.

Headlight systems descriptions


What are the names of the 3 different headlight types?


Parabolic: The light source hits a parabolic reflector that will determine the main focus of the beam. Then the front glass will dispurse the ligth more to each side. Ie. Mercedes up until model year 2000.
Free form: Same as parabolic, but front lens is clear. Ie. Volvo V70 below:

Ellipsoidal: Light source hits a parabolic reflector, gets horizontally cut off in the first focal point, then projected back straight again with a curved lens. Ellipsoidals is also known as projector headlights.


What is the difference between a projector and a reflector design?
Efficiency:

Parabolic: 27%
1st Generation Ellipsoidal (found on early 90s BMW): 36%
Free form: 45%
2nd Generation Ellipsoidal (found on late 96+ Audi, late model BMW): 52%

There has been a trend that more and more wehicles go away from the traditional parabolic headlamp. The thick glass that are needed makes it a loser in the game of efficient lighting. It seems like the majority of auto manufacturers select ellipsoidals, but they weren't up to par in the first generation. The lower 180 degrees of the bulb output were practically not getting out of the housing. The second generation is designed with another focal point to increase efficiency.
Beam Cutoff:
Projectors create a much sharper cutoff than reflectors. Although some parabolic reflectors can create pretty decent cutoffs, a projector will always be better. The main advantage of projectors is the fact that they can be aimed higher than reflectors because no stray light (above the cutoff) will exist to cause glare to oncoming drivers. This is especially important with high intensity light sources like HID and the new HIR halogen bulbs.
Universality:
Projectors can be designed to be easily switchable from left drive to right drive beam patterns without loss of light. This usually done by turning the reflector housing in reference to the shield and you get the full 'opposite' beam pattern. UK needs this ability to drive legally on the continental Europe. This is why some cars for the UK market have projectors where the rest of the world do not. With a parabolic reflector, the 'kick up' part of the lens has to be taped up (so you lose the kick up completely).
Versitality:
Projectors are normally not used in combined high/low beam setups, although it iss possible to have a moveable shield and this is just what happens with "bi-xenon projector" setups, but this would be very costly in a economy car with halogen setup. A regular H4 or 9007 application is much more cost effective.
Source: www.hidforum.com


also a wikipedia website:

Headlamp - Wikipedia, the free encyclopedia

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