Exterior lights are taken care of within the lighting section of the UK MOT. The Road Traffic Act requires all exterior lights to be tested, except front fog lights, some reverse lights and any work lights, used on commercial vehicles, not used for the purpose of driving.
Some Lighting Test Basics
The basic require each light to be able to be switched on and off as required and be the right colour when lit. The front headlights have further requirements, of directional aim.
Sidelights
Starting with the sidelights, which can also be referred to as position lights. These not only show presence of the vehicle, but also its size. Other lights that may give a false profile, ie LED lights in the grille, may end up as a MOT failure.
They must not flicker or go off when tapped, and must either emit a white beam or yellow is allowed if within a front yellow headlamp.
The lens must not be damaged to the point where their ability to beam light is affected. Sometime owners and testers may have a different opinion on this. Cracks, chips and dirty lens can afford a fail.
Registration Plate Lights
Lamps that work with with the side/position lamps are the registration plate lights. The requirements for these are straight forward.
They must be fitted well, be secure, in the correct position, not flicker or go out when tapped and point over the plate, not outwardly showing a white light. Abulb holder that is corroded and does not emit a constant strong beam, may be a fail.
Rear Fog Lights
Clearly the rear fog lights can be very bright when not used in fog.These lights need to be working, emitting a red light, securely fitted, be able to turn on and off and not controlled by any other light.
Light Switches
All light switches should be in good order and obviously work, without any flickering or sparks.
Brake Lights
Vehicles after 1971, must have 2 brake lights, which must emit a steady red light when the drivers foor is on the brake pedal. The lights must be clean, face to the rear and not flicker. Ironocally any extra added brake light, need not be tested.
Indicators
These must be fitted to the 4 quarters of the vehicle, and and can be added to door mirrors etc. These must show an amber colour, not flash too slow or too fast, (60 to 120 times a minute) so can be seen flashing. Must be a clear beam and in good order.
After 1986, all cars must also have hazard lights, which tend to the indicators flashing all 4 sides at once. This process must be able to work, without the ignition switched on
Front Headlamps
A headlamp aligner will used during the MOT test to check if they are correctly aligned and project the correct beam image. which has the following requirements: flat horizontal illumination just below the straight ahead a kick up image rising above the horizontal and away to the left, the point at which the image kicks up must be just to the left of the vertical centre line.
The other variation from the norm is that headlamps are permitted to show either a yellow or substantially white light, anything else will fail.
Having the wrong beam image will class as a fail, but reasonably easy to fix, by any reputable garage. Any damage to the headlamp that affects the image or brightness, may also be a fail then a new headlamp, may be needed.