The information provided here is to the best of my knowledge and experience and may contain my personal opinion.

Headlight alignment is also critical to performance. Dull high and low beams are often the result of them actually pointing too high so the light just doesn’t land on the road, not to mention the hazard they create to on-coming traffic. The fall of the light beam is often printed onto the headlight in a percentage value and can be adjusted by anyone with a bit of mechanical aptitude.

If no figure is provided then a good rule of thumb for up and down alignment is 1centimetre of fall over 1 metre of distance, or 1 inch over 8 feet. This could also be called 1%. My Colorado has an alignment value of 1.2%, close to my figures above. It may be slightly higher to factor varying loads as it is a commercial vehicle.

To align headlights park on a level surface facing square on to a wall or roller door. Ideally the front of the car should be about 3 metres from the wall. Too close and it will be hard to be accurate, too far and the centre spot of light will spread too much to actually see where it is. Measure height of globe centre from ground and mark this on the wall then measure down 1 centimetre for every metre distance from wall (3cm for 3m or 2cm for 2m) and place another mark. With headlights on high beam align the centre of the hot spot of light on this line.

Spot lights are generally adjusted with no or only a very small amount of fall.

For left and right adjustment find the centre line of the car and measure out to high beam globe centres. Mark this measurement on your wall and adjust lights so the centre of the hot spot is on this line.

It is worth remembering that in a standard 55/60 watt high low headlight system that the low beam (55 watt) is only producing slightly less candlepower than the high beam, however due to a reflector on the globe all of this light is directed to the top half of the headlight reflector causing it to shine downwards rather than straight forward. So really that beam will have a much higher lux measurement than it would if it was in a high beam application. This is why misaligned headlights due to heavy rear loads, towing or poor adjustment seem as bright or brighter on low beam than they would on high.

Choosing Lights Part 4 – Headlight alignment.