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How To Aim Headlamps and Auxiliary Lamps
Although an optical beamsetter is the most accurate way to aim lamps, these are not very common in North America. Foglamps, driving lamps, and visually-aimable headlamps do not require a mechanical aimer or other machine in order to achieve correct visual aim. All ECE (E-code) headlamps are visually aimable, and many newer US (DOT) headlamps can be accurately aimed visually. First, you must determine if your headlamps can accurately be aimed visually. If you have ECE (E-code, European-spec) headlamps, you can aim them visually. If your US DOT headlamp lenses are marked VOL, VO or VOR, they can be aimed visually. If your US DOT headlamps are NOT marked VOL, VO or VOR, STOP, they cannot be correctly aimed visually and will require the use of a mechanical aiming device.
To prepare for aiming, the car should have at least 1/2 tank of fuel, weight in the trunk equal to the most frequently carried load (this may be a full trunk, or it may be an empty one, or anything in between), and weight in the driver's seat equivalent to the most frequent driver. All of the tires should be checked when cold to make sure they're at the correct inflation pressure. Jounce each corner of the car firmly (grasp the bumper and push down several times rhythmically) to ensure that the suspension is settled into a normal position.
Locate the car on level ground with the headlamp lenses 25 feet away from a vertical wall. You will be making location reference marks on the wall. Measure the height from the ground to the axis of the headlamp. The "axis" is usually marked with a dot, cross, bulb type designation or name brand, but if not, it is directly in front of the bulb. Now walk up to the wall and measure this same height from the ground, and place a +C mark at that height. Do this for both headlamps.
Next, find the axis (centreline) of the vehicle itself. You can do this by measuring the distance between the axis of the left headlamp and the axis of the right headlamp -- making sure that on multiple-bulb headlamps you're measuring from the axis of the left beam you wish to aim to the axis of the right beam you wish to aim; low to low, high to high, fog to fog, etc. Split this width measurement in half to get the distance from one headlamp to the centre of the vehicle. Walk to the wall and place a oV mark at that distance in from the left or right headlamp. You can walk to the back of the vehicle and sight through the backglass and windshield to check your work and make sure you've marked the center of the vehicle on the wall.
Next, measure downward 3 inches (ECE European-spec headlamps) 2.1 inches (US DOT VOL headlamps) from the left and the right +C marks, and connect these two newly-measured points with a horizontal line we'll call "b-b". After you've done all of this, your wall will be marked thus:
_____+C_________oV________+C______
[this gap is 3" or 2.1", see above]
------b--------------------b------
NOTE The visual aim procedure for US DOT headlamps marked VOR or VO is slightly different. No separate, lower horizontal line is required. Simply connect your +C marks with a horizontal line. After you've done that, your wall will be marked thus:
---------+C-------oV-------+C---------
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.
VERTICAL AIMING
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' on the right side of the beam pattern, and should be lined-up exactly with the horizontal line that connects your +C points.
HORIZONTAL AIMING
These instructions are applicable only to European ECE low beams, because US DOT VOL and VOR headlamps cannot be visually aimed horizontally, and in many cases, cannot be aimed horizontally by any means at all, because no provision for horizontal aim adjustment is provided. [This is because US regulators believe there is no way to define a visual cue, such as a kink in the cutoff, that would allow accurate left-to-right placement of a headlamp beam. Apparently they also believe that cars will not get in fender-benders that will knock the headlamps out of horizontal alignment. For what it's worth, the Europeans have been successfully aiming their headlamps vertically AND horizontally since 1955. -ed.]
European ECE headlamps have a "kink" or "elbow" at the top of the center of the beam pattern, where the cutoff bends upwards. Adjust each headlamp so that the kink lines up (left-to-right) with the +C mark for whichever headlamp you're working on. The tolerance here is +/- 2 inches of point (c). Slight leftward aim (-1") increases seeing distance down the road, but excessive leftward aim increases glare to oncoming traffic.
After adjusting a high/low beam headlamp in the low beam mode, do not attempt to readjust it in high beam mode. All high/low beam headlamps are meant to be adjusted on the low beam setting only--the high beam adjustment is correct when the low beam adjustment is correct. If you are experiencing a problem where setting the low beams correctly places the high beams too high, but setting the high beams correctly places the low beams too low, you are dealing with a poorly-designed headlamp.
DRIVING LAMPS, HIGH-BEAM-ONLY LAMPS IN 4-LAMP SYSTEMS
These instructions apply to ECE high beam headlamps, US DOT high beam headlamps marked "VO", and all driving lamps. These must be adjusted so that the bright, center "hot spot" of the beam is straight ahead of the lamp in both the vertical and horizontal planes. Use the intersection of the horizontal and vertical lines at point +C for each headlamp as "cross-hair sights" to center the high beam hot spot.
Make sure to work on one lamp at a time. It is best to disconnect the power to the headlamp you are not working on, so light from the other lamp's beam pattern doesn't mislead your eyes. Also be sure to disconnect or cover the adjacent high/low beam lamp when you are aiming its high-beam-only neighbour.
FOG LAMPS
Fog lamps are aimed using a procedure very similar to that used for European-spec ECE and US DOT VOL low beam headlamps, but the vertical drop is different. Follow the vehicle-preparation and wall-marking instructions given above for ECE/VOL low beam headlamps, substituting "foglamp" for "headlamp", but with the following changes:
· If the fog lamps are mounted below the bumper, your b-b line should be 1.5" below the fog lamp axis height.
· If the fog lamps are mounted above the bumper, your b-b line should be 4" below the fog lamp axis height.
Fog lamps produce a wide, bar-shaped beam of light. Horizontal aim is much less critical than it is with headlamps. The fog lamps should be pointed straight ahead, not leftward or rightward.
STERN LIGHTING, Daniel J. Stern
Copyright 1998 Daniel J. Stern
No part of this text may be reproduced in any form without express permission of author. Permission to quote is granted for the purposes of communication with the author.