[mcrews]

Originally Posted by topcat

First off, I have an MSc in optics - but I don't work in auto headlight industry. While there are good and bad HID kits (I have had both), I have to take issue with quite a lot of the information on the Daniel Stern website. This makes me wonder that there may be some bias because of some vested interest of the author.

First off, I don't have a degree in optics but I can read charts and graphs

Originally Posted by topcat

Firstly and fundamentally, the diagram here comparing arc and filament:- http://dastern.torque.net/Photometry/filamentarc.jpg

Assuming the arc and the filament are the same or similar lengths, in the same position, on the same axis, then it seems to me that the arc shown will be a fine replacement for the filament (in a projector style headlamp). The 10,000 cd/cm2 bright spots on the ends of the arc are such a small volume of the rest of the 6,000 cd/cm2 arc they should not cause great concern.

You, personally, can discount it if you like, but the FACT (not 'it seems to me'), is that the HID is at least 10x brighter.
(see chart AGAIN)

Originally Posted by topcat

next, I quote from Daniel Stern: "This article will never go out of date, because the problems with HID kits are conceptual problems, not problems of implementation. Therefore, they cannot be overcome by additional research and development". I disagree with this also. I repeat, if the arc is the same dimensions as the filament in the same place as the filament, then in a "projector" style headlamp the arc will project in a similar way to the filament. Hell, the lumps and bumps in illumination in a modern filament headlight are still obvious, and the filament has all those gaps betwen the wires.

THE FACT that the HID is brighter cannot be disputed. Kinda like the laws of physics or gravity. That is what Stern is referring to. FACTS, LAWS of SCIENCE. (surely you can refer to some course work in your degree that validates your 'feelings'?
"being in the 'same place' does not overcome the significant brightness that is NOT in the halogen bulb.

Originally Posted by topcat

Also, I quote: "Probably the biggest issue is HID headlamps' significantly worse color rendering index (CRI), which is in the high-60s to low-70s range. Halogen headlamps' CRI tends to be around 90 to 97 or so."
That 60-70 CRI doesn't fit with the info I can find. HID, being an arc lamp, can give a much flatter spectrum of illumination than a filament. From wikipedia: "The output of a pure xenon short-arc lamp offers fairly continuous spectral power distribution with a color temperature of about 6200K and color rendering index close to 100." EDIT: Turns out automotive HID uses metal halide arc lamps which have a more spiky spectrum- so the CRI could be worse.

Originally Posted by topcat

I would add that my own experience of a cheap HID kit shows that there are some bad kits out there, and it's not as easy to get it right as the vendors would have you believe. The most important thing is that HID conversion should be done in a projector style lamp, not a reflector style, because the metalised end of the filament contributes to the shutoff in a reflector lamp. But there's no fundamental reason (I can see) which would stop an arc replacing a filament in a projector lamp, if an arc of the same size is situated where the filament would have been (and on the same axis as the filament).

So in the last paragraph, you say "IF" the arc is the same as the halogen"

SO help me with some book learning because the FACT is:
Halogen and HID are two different bulbs.

Let me pose this thought:
If all the bad light and glare that is FACTUALLY proven in the HID in halogen lamps really exists(at least 10x brighter causing the fail)
Where does all that excessive light go in a halogen projector lamp?
As Stern so clearly stated the problem begins BEFORE all of your 'ifs'.

Finally, a halogen projector lamp does not have a shield for a cut off. How do you provide the required by law cut off when an hid bulb is in a halogen projector?