Accessory lights defined.
Fog/Cornering lights: Usually mounted low for best results w/a wide flat beam. Often yellow in color to help the driver see in foggy conditions, but when used as a cornering lamp, may be white in color and/or mounted up higher. Used only w/low beams.
e.g. I used a set of white fogs, mounted on top of the bumper, as cornering lights, and a set of yellow fogs underneath for poor conditions when I used to run street rally's w/my Volvo sedan.
Driving lights: Mounted @ the same level as the high beams whenever space allows and used in conjunction with them, they're nearly always white in color (some pro-racing series use yellow DL's to distiguish different classes running in the same race at the same time) and throw a long beam that is more focused (narrower) than std high beams, but more diverse than pencil/spot beams.
Combination beams: When mounting space is limited. W/dual lenses and sometimes dual bulbs these carry both a fog lens for a wide pattern and a driving lens for a more direct, focused pattern. Mounting should be between low and high as they are a compromise, and in my opinion should be avoided, especially if sharing a bulb for both functions.
Passing lights: I had a set on two different cars I owned and LOVED them, but they are hard to find in this country. These throw a narrower, longer beam than driving lights, but not as narrow as a pencil/spot beam. They always have a white lens and should be mounted and connected as driving lights would be (high beams only.) From my experience, they fill in that "hole" caused by std high beams that reflect light from the sides but seem to dissappear on blacktop. The effect of passing lights from the drivers seat is one of a completely lighted oval pattern. As I'd said, I loved mine a lot.
Pencil/spot beam: Always white and mounted wherever additional light is needed, but usually high, as near the high beams as possible. These throw a very long, narrow (focused) pattern and should only be used w/high beam headlights.
Also, remember that any light will make the most of it's available output if mounted in a round (parabolic) reflector/round lens, and in this case bigger is better. That's one reason I am not a fan of the new Mazda fogs.
I hope this helps define accessory lights.
