RE: PIAA Whites

[Michael Gambini <gambini@xxxxxxxxxxxxxxxx>]

This is an interesting theory, but I doubt that it is right. The reflector 
on the back of the headlamp would normally be designed to send out a 
collimated(parallel rays of light) light pattern. The reflector would not 
focus the light back unto the filament. I would guess that the reason they 
claim higher efficiency and bluer light is that they are raising the 
pressure or changing the chemical content of the gas surrounding the 
filament. This may allow them to raise the temperature of the filament, 
which will then give off "bluer" light. Also, the reason that the dichroic 
lights look different color off axis is that the dichroic coating is an 
interference film that is deposited in increments of thickness so as to 
cause destructive or constructive interference at selected 
wavelengths(color). When you look off axis, you are looking through the 
film at an angle, which makes it optically thicker( remember those sines 
and cosines!!), so the constructive/destructive interference wavelength 
changes, and the color content is affected.

Mike G
1996 VFR750
1993 BMW 325i, Bilsteins,JC Chip

On Monday, February 01, 1999 4:26 PM, tedcrum@domain.elided 
[SMTP:tedcrum@domain.elided] wrote:
> PIAA bulbs use a dichroic reflector system that reflects undesired light
> (blue and IR in the case of the foglights, IR for driving lights) back
> into the bulb where it heats the filiament, resulting in greater
> efficiency. This is the reason for the blue tinge off-axis that made 
these
> so fashionable. Many urban-custom foglamps use a "cold mirror" bulb with 
a
> dichroic reflector that just dumps IR out the back. These were developed 
to
> keep film and people cooler when under lights, but they are no more
> efficient. They do change color with angle a bit, so people with simple
> taste like them.
>
> -Ted Crum
>
> -----
> Ted Crum
> tedcrum@domain.elided

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