If you read the last paragraphs of the link you posted (you said you only skimmed that site), you’ll see:
That page seems to be dated 2003, which was quite some time ago. BMW had just switched from a mix of xenon (low beam) and incandescent (high beam) to xenon for both (which they call “bi-xenon”) at the start of the 2003 model year (September 2002), so the technology was still developing back then.
I think the main concern Mr. Stern raises is that aftermarket products are not designed with any specific vehicle application in mind and therefore there’s no testing to see if a particular usage is either safe (in terms of the beam pattern and color that other drivers see) or reliable (won’t melt the fixture, etc).
There’s a name for that kind of person. But I can’t use it here.
Seriously, that wasn’t a (factory) rear fog light. The rear fog lights supplied with vehicles in European markets (where they are required) generally used the same lamp types (what we’d call 1156 or 1157, usually) as the turn / brake lights and were the same brightness. In several cases I’m aware of, the rear fog function actually used the brake light (on one side, generally the driver’s side). Newer cars often have LED lighting, but the rear fog function uses LEDs of similar brightness to the ones used for the brake light.
Unlike front fog lights which serve to illuminate the road so the driver can see better, the rear fog light (singular) is used to warn following drivers that there is a car up there where they can’t see it, not to light up the road.
On my race car, I have a Lifeline rain/fog light, and while you’d definitely know it was on if you viewed it directly, I wouldn’t consider it blinding. It is for a very specific application (vehicles of similar height driving over 100MPH in the rain*) and if you saw it from a different angle, you’d barely think it was lit (the viewing angle is only 12 degrees in any direction).
- Not that you’s want to do that in my car. Even at highway speeds, heavy rain (YouTube video) is extremely unpleasant. As I tell people, “You know why they call 'em bucket seats? Because they fill up with water!” It is worse than a motorcycle, since on a bike you’re sitting on a saddle and water will drain away.