Headlamps:

Headlamps must be a matched pair, same shape and size and emit the same intensity and colour and must be sufficient to illuminate the road ahead. Headlamps can be any colour but must give an acceptable beam pattern on the headlamp aim test.

Dip switches must extinguish all main beam headlamps and leave on at least one pair of dip beam headlamps.

Headlamps must each be the same colour and size and must be symmetrical to one another.

Headlamps must operate immediately when switched to main or dip beam.

A main beam warning light is not part of the test.

Masks or kits to convert left hand drive to right hand drive are acceptable providing the device is secure and doesn't reduce the light output unduly.

Damage to a headlamp lens must affect the beam pattern adversely or reduce the light output well below that required to illuminate the road ahead, before it fails. Parts of a broken lens etc which might cause injury to persons walking by the vehicle could fail under body condition requirements.  

Checking the headlamp aim needs special equipment but the object is to ensure the dipped light does not cause dazzle to oncoming traffic.  This means the aim must be below the horizontal (e.g taken from the centre of the headlamp unit).  

Some headlights, e.g European 'E' beam, are tested on dip beam whereas others, e.g 7 inch round British American, are tested on main beam.

Vehicles with complex headlamps may need to be moved closer to the beamsetting equipment to provide a "readable" pattern. The Ford Mondeo is one example.

Interior adjustment devices will not be touched unless the lamp is set too low.  In this case the tester will re-set the adjuster to its highest position to see if that cures the problem.