Discussion of recent posts

[quk@sievers.com (Phil Payne)]

In message <199701200601.WAA30945@cosmoslink.net> "Meron" writes:

>> The difference is that in my car, the light output is carefully focused where
>> we want it to go.

> Not true, think about it this way:

I think it's pretty arrogant to say something like that without having seen the 
setup in question.

> a prism is designed (for a headlight ) to take advantage of a bulb, meaning
> it will project the light to a cretin distance, your headlight is aimed to
> provide you with light from point A to point B  (say for the purpose of
> discussion 100 feet).

There are no distance limitations on light.  If you go over a hump-back bridge 
with your mains on, that light will eventually reach the stars.

Moreover, the apparent luminosity of an object - whether radiating of itsself 
or reflecting incident light, is independent of distance from the observer.
 
Simple geometry - if you're twice as far from an object, it appears half the 
size and therefore one quarter of the area.  According to the inverse square 
law, though, only one fourth as much light reaches you.  This is why main beams 
are just as blinding a mile away as half a mile away, allowing for absorption 
losses.
 
Light leaving your headlights is going to travel for ever.  The prisms cannot 
affect how far it goes, only in which direction.  Euro lights are designed such 
that _very_ _little_ goes in the direction of an oncoming vehicle - most goes 
into the lower quadrant on the nearside, with controlled leakage to the upper 
quadrant.  On my lights, this leakage is more pronounced on the nearside light 
than on the offside, because upper quadrant leakage on the offside light would 
pass through the space in front of the driver and cause a nuisance in fog.
  
> If you use a different bulb (positioned in a different location in the
> prism) you are tempering with the original design, consequently diminished
> performance), just an example I don't know if that is what you did.

Now that's true.  However, the manufacturers of the 170/100 watt bulbs are 
aware of this and position the filament _EXACTLY_ where the filament of the 
65/55 watt bulbs lands up.  The beam pattern is exactly the same as with the 
stock bulbs.

> If you are changing the wattage of the bulb (which you did) you are still
> using the same prism with more light intensity, most of the time IT IS FAR
> MORE IMPORTANT TO HAVE AN EFFICIENT PRISM than more wattage (sorry for
> shouting).

Yes, but it isn't the prism with which you appear to be familiar.  Many have 
posted about the clear superiority of the Euro prism mouldings over US stock 
lights, even with stock bulbs.

> Most of the time if your prism is not designed to handle the added wattage
> read bigger, you are getting a very small advantage!!!

There you go again.  You haven't seen this setup, and you have the arrogance to 
tell us we are getting a "very small advantage".   

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club