Join Date: Jul 2007
Location: New Zealand
I find that although my cars pass inspection (Warrant Of Fitness) where they use a beamsetter device (trundles across in front of the car), I can usually identify problems and make adjustments later, using the garage door. The problem with the beamsetter is that although it checks the height and beam pattern well, it does not check whether the lights are pointing towards each other (horizontal adjustment). If they are, that limits the 'reach' of the lights and gives a bright area where the beams overlap, darkness at the sides.
By rolling the car towards and away from the garage door, you can see whether the headlight beam centres stay in the same place or whether they move around as the car is rolled further away. The beam should drop by 1-2% with distance, but the two beam centres should stay the same distance apart. Which, naturally enough, should be the distance between the headlights themselves (measured on the car).
A 1% drop in the beam means that the height of the beam centre on the wall is 1cm lower than the centre of the headlight (on the car) for every meter the car is moved away from the wall. 5m from the wall, the beam centre is 5cm lower than the headlight centre.
It can be difficult to identify the centre of modern headlights, but there is sometimes a 'cross hair' on the lens. The centre of the beam pattern is generally taken to be where the diagonal cut-off meets the flat top of the dipped beam.
On my 156, the beam pattern was horribly mis-shaped because the bulb was not fitted correctly (tabs not in slots, bulb at an angle). Strangely, that passed a WOF inspection too but showed up clearly on my garage door. Maybe my local inspectors just don't use the beam-setter machine correctly!
'00 GTV V6, '08 FIAT 500, shell and parts for a '71 FIAT 850 Coupe
Last edited by alexGS; 13-02-10 at 21:55.