Headlight adjustments

[hagis]

What are the rules regarding headlight adjustments? I know it's checked on MOTs, but what specifically are they looking for.

I accidentally adjusted one of mine when I was changing the bulb last weekend but I've a suspicion that they're both out of alignment are might be too high.

[audipersempre]

Headlamp Alignment Testing Criteria



The most common type of headlamps fitted to vehicles are those known as European type headlamps which are checked for aim on the dip beam.

These headlamps have an asymmetric dipped beam pattern with a distinctive horizontal cut-off on the right, and a 15 degree wedge of light above the horizontal (the 'Kick up') towards the left.

Any of the following points will result in the vehicle being refused a certificate:

• The beam pattern blurred and does not show a distinctive cut-off point.
• The beam 'kick-up' is to the offside, i.e. The headlamp dips to the right.
• The image break point is not between the vertical -2.0% line (blue vertical line) and the vertical 0% line (black vertical line).
• Headlamp centres not more than 850mm above the ground. The beam horizontal cut-off line (pitch) is not between -0.5% and -2% line (red lines).

OR

• Headlamp centres more than 850mm above the ground. The beam horizontal cut-off line (pitch) is not between -1.25% and -2.75% line (green lines).

NOTE: There will be no opportunity to adjust headlamp alignment during the test. Levelling devices should be set for unladen condition, normally located on vehicle dash.

Example of computer screen showing the Light Beam Test readings

[gavinl1967]

I too would like to check my headlight adjustment, as I've just fitted a set of HIDs to my A4. Is there any kind of "ball park" test that you can carry out yourself, ie, park the car 'x' distance from a wall, then adjust the beam pattern to 'y' height on the wall?

Or is that just too simple...................

[NickPicks]

Well, if you park 20m away from the wall, then you can work out how much the lights should drop:

Using the rule of 0.5% to 2%, the image break point should be between 100 and 400mm below the centreline of the headlights. (assuming that % slope means drop as percentage of distance - I usually work in degrees)

This only becomes too simple in that finding a dead flat piece of ground is virtually impossible: The ground needs to be horizontal between the front of the car and he wall (otherwise you're not measuring upto the centreline of the headlights well enough), and the ground needs to be flat between the front and rear wheels (if the front wheels are half an inch higher than the rear ones, then that's 0.5% slope).

I'm a civil engineer, and do quite a bit of measuring of relative heights. You could use a spirit level with a laser beam attached to measure the relative heights of the front and rear wheels, and then use the laser to project the headlight centreline to the wall, and work out the correct drop from those measurements.

[gavinl1967]

Well, if you park 20m away from the wall, then you can work out how much the lights should drop:

Using the rule of 0.5% to 2%, the image break point should be between 100 and 400mm below the centreline of the headlights. (assuming that % slope means drop as percentage of distance - I usually work in degrees)

This only becomes too simple in that finding a dead flat piece of ground is virtually impossible: The ground needs to be horizontal between the front of the car and he wall (otherwise you're not measuring upto the centreline of the headlights well enough), and the ground needs to be flat between the front and rear wheels (if the front wheels are half an inch higher than the rear ones, then that's 0.5% slope).

I'm a civil engineer, and do quite a bit of measuring of relative heights. You could use a spirit level with a laser beam attached to measure the relative heights of the front and rear wheels, and then use the laser to project the headlight centreline to the wall, and work out the correct drop from those measurements.

Thanks for that ......................perhaps I'll just go ask a local garage to align them..........

[hagis]

I'm more confused than I was before (though thanks for posting the details!). I think mine are too high so I've used the headlight adjustment on the dashboard for now.