# Definition and examples of ellipsoid headlights?



## fahrfrumlosin (Sep 15, 2000)

What is the definition of ellipsoid and how does it work?
Are the golf rallyes considered ellipsoid?


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## PerL (Jan 9, 2001)

*Re: Definition and examples of ellipsoid headlights? (fahrfrumlosin)*

Yes, the rallye golf headlights are ellipsoid, and the Audi RS2 lights are also ellipsiod. I'm sure Cullen got a nice link for some pics and drawings of how they work.


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## PerL (Jan 9, 2001)

*Re: Definition and examples of ellipsoid headlights? (fahrfrumlosin)*

Basically the ellipsoid lights are all that has a thick lense. They are also known as projector lights. Rallye Golf, Audi RS2, BMW, Audi A4 and A6, G/J 4 with HIDs has ellipsoids, as do the new Passat, Honda NSX etc etc.


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## EuroStyle (Jun 24, 2000)

*Re: Definition and examples of ellipsoid headlights? (PerL)*

Also the Hella and Pzwo dual rounds for the Mk3 use a projector, and M3 lights use them as well.....
Sean


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## [email protected] (Aug 25, 2001)

*Re: Definition and examples of ellipsoid headlights? (EuroStyle)*

actually, in the BMW world, the European Ellipsoids for the E30/E34/E36 (i am sure its for others too) its a projector SURROUNDED by a reflector.... so the projector focus' the light to the cutoff point, and for distance, and the reflector shines light on the "nearer" objects


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## Cullen (Apr 5, 1999)

*Re: Definition and examples of ellipsoid headlights? (Anand20v)*


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## Cullen (Apr 5, 1999)

*Re: Definition and examples of ellipsoid headlights? (PerL)*

quote:[HR][/HR]Basically the ellipsoid lights are all that has a thick lense. They are also known as projector lights. Rallye Golf, Audi RS2, BMW, Audi A4 and A6, G/J 4 with HIDs has ellipsoids, as do the new Passat, Honda NSX etc etc.[HR][/HR]​100% ALL VAG cars with HIDs!


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## PerL (Jan 9, 2001)

*Re: Definition and examples of ellipsoid headlights? (Cullen)*

quote:[HR][/HR]100% ALL VAG cars with HIDs![HR][/HR]​Not the A8 with Bi-xenon? If so, that is one huge lense


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## Cullen (Apr 5, 1999)

*Re: Definition and examples of ellipsoid headlights? (PerL)*

quote:[HR][/HR]100% ALL VAG cars with HIDs!
Not the A8 with Bi-xenon? If so, that is one huge lense







[HR][/HR]​Ok was that so...? Ok then 99%










[Modified by Cullen, 10:35 PM 11-8-2001]


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## 16v (Aug 4, 1999)

*Re: Definition and examples of ellipsoid headlights? (fahrfrumlosin)*

the ellipsoids are easy to see here:


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## Jetta4Life (Sep 5, 2001)

*Re: Definition and examples of ellipsoid headlights? (16v)*

what models are these headlights for? A2 or A3?


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## 16v (Aug 4, 1999)

*Re: Definition and examples of ellipsoid headlights? (Jetta4Life)*

quote:[HR][/HR]what models are these headlights for? A2 or A3?[HR][/HR]​


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## Jetta4Life (Sep 5, 2001)

*Re: Definition and examples of ellipsoid headlights? (16v)*

Those are MONEY! I used to have an 87 Golf GL, I almost wished I still had that car!


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## ilja (Jul 25, 2001)

*Let's shed some light on this subject!*

There are some incomplete answers here. Lens thickness is not the issue; it's lens shape that matters. Even then, ellipsoidal reflectors and lenses work together -- or not at all. 
As far as the original question on how the headlights work... let's start at the beginning. I'm no physicist, but as I understand it light works like this: photons travel along light waves, which literally bump into other particles (some just floating in the air, others such as comprise trees and guardrails tend to stay put) and go whichever way they will. Some off these light waves reflect back into your eye and convey information about whatever they bounced off of... that is, each object reflects only some part of the light - of the color of the light - that shone on it. 
Since you only see stuff that light is bouncing off of, and even then only what reflected light makes it all the way back into your eye... any generated light from a headlight that isn't reflected back into your eye is wasted, and inefficient. Since there's not much we can do to change, to improve how, the bits and pieces of the world around us reflect light (though reflective signs and road markings do just that) headlight designers have to try to make more light from your headlights GO WHERE THEY WANT IT TO GO, in the hope that more light, more information, will get back to your brain rather than just scaterring willy nilly. 
Even bad headlights throw a lot of light -- just stand in front of them! Good headlights are good because they make more light reflect off what is in front of them, back into your eyes. Bad headlights can have the same power (potential?) but they are bad because scatter light every which way. This scattering light is seen as flare, and in practice, is the principle reasons why older the beams of older headlights dim over distance. (The other big reason is lamp technology, but that's another subject.) Basically, there's just not enough light getting to the target, and back -- which sucks when you're going 70mph and will be at that target (whatever it is) in less than a second. Ok, that's obvious, but establishing the basics are important.
You can see in the simple diagram above, the light waves leaving a parabolic (of or pertaining to a parabolic, i.e. non-ellipsoidal conic section) reflector travel along (roughly) parallel lines, and are for that reason alone more prone to dispersal over distance. In contrast to conventional reflector lamps, an ellipsodial lamp (meaning: reflector/lens combo, ignoring the differences in the lamp elements themselves) focuses the various light waves back in on themselves, into a smaller area. This makes more light bounce off the target (read: road) and so more light gets back to your eyes.

An interesting side note here (perhaps I kid myself) is that this technique - of using a trick lens to focus light - is one of the oldest ideas in the book; the Fresnel lens developed by an eminent frenchie of the same name introduced the idea of using compound lenses to narrow, focus, or otherwise manipulate light waves... about 200 years ago. Fresnel lenses are still used in lighthouses all over the world, and in most theaters. 
So... the idea here is that if you focus the unruly mass of reflected light waves bouncing off the refletor into say, a handy conic pattern (perhaps with point of cone pointing out, or vice versa -- they sell both) the same amount of candlepower (lumens, brightness, whatever) can be put contained in a smaller area. Which makes the light seem (be?) brighter, even through it's the same poor filament doing the same work. 
Another benefit of using this ellipsoidal reflector/compound lens duo is the light can be - needs to be - aimed. Usally designers pick out a spot some fair distance from the car -- and for this reason ellipsoidal headlights often light the road better 50' from the bumper than right in front of it. To oversimplify things to the point of innacuracy, ellipsoidal lamps (can) aim a cone of light at a specific target, while a traditional parabolic lamp produces a cylinder of light that can basically only be pointed in a certain direction, not aimed at a specific place. (An earlier post correctly notes the direct beam from the lamp, or the "projector light", goes further down the road... while the reflected light fills in the near distance.) Note while all of this light is being focused by the lens, the light coming off the reflector is passing through more of the lens, and at a greater angle. This often produces a prismatic effect which changes the color of the light, or creates the multicolor headlights you see on nice cars. You can see it on the road, too; these lights have a clear hot spot surrounded by a less-intense (but still defined) wash.
Hope that helps, 
Isaac in Cambridge
[email protected]


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