Daniel Stern Lighting Consultancy and Supply
NOTE The visual aim procedure for lamps listed above as "N/A, do not measure downward" does not require the lower B-B horizontal line. Simply connect your +C marks with a horizontal line.
Now draw a vertical line through through the center of each +C point. Do the same with the oV point. These lines make it easier to see the reference marks when you are standing 25 feet away, adjusting the aiming screws on the car. You now have an accurate plot on the wall of the height and separation of the headlamps (but ONLY if your car is level, the ground is level and the wall is vertical!). Note that the "B- B", "C" and "V" designations are for purposes of clarity in this descriptive article. It is not necessary to draw the letters on the wall-- just plot the points. Of course, you may use the letters in your aiming procedure if it will help you.
The low beam pattern of a visually-aimable headlamp has a distinct horizontal cutoff. Below the cutoff is bright light. Above the cutoff is dark. The aim is determined by measuring and adjusting the height of this cutoff relative to the reference marks you plotted on the wall.
For European-spec ECE and US DOT VOL headlamps, the cutoff is at the top of the left half of the beam pattern, and it should be lined-up exactly with the B-B line.
For US DOT VOR headlamps, the cutoff is the squared-off top edge of the 'hot spot' (brightest region of the beam) on the right side of the beam pattern, and should be lined-up exactly with the applicable horizontal line per the table above.
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