MOT - Headlamp beam image incorrect

[Deleted User]

What on earth is this? Surely if headlamps work its fine?

Its an old 1989 mini. Never headlamp units needed?

rich13348

The light has patterns on the lens and shaped reflectors that produces a specific shape which stops light blinding oncoming cars and lights up signs on the left hand side of the road.

Probably moisture on the inside of the lens or the reflector at the back causing an unusual pattern.
If this image is wrong the correct parts of the road may not be lit up.

Ask your MOT tester for an explanation if you don't understand anything on your MOT failure or advisories.

pompeyrich

[quote=[Deleted User];discussion/5463446]What on earth is this? Surely if headlamps work its fine?

Its an old 1989 mini. Never headlamp units needed?[/QUOTE]

Taken from the MOT testers guide, it states as "reason for rejection";

1.
A headlamp which does not conform to diagrams 1, 2 or 3 that has a beam image which is aimed so that it dazzles other road users.

2.
Projected beam image obviously incorrect, e.g. where the headlamp bulb is incorrectly fitted or the reflector is seriously corroded.

Might not be too serious, mine failed because I had somehow fitted the bulb upside down in the holder, which seems impossible given the bulb has a lug that fits into the headlights slot!

Joe_Horner

Further to the first two answers. if you shine your low-beam headlights against a wall at night you should see a pattern of light similar to this:



There are some alternative patterns available, but that should be good for a Mini of your age. Note that the above shows the pattern for a single headlamp - with two you get a double image which should have the two cut-offs at the same height and two kick-ups which are separated by about the distance between your headlight centres.

The pattern has 3 important parts parts:

A flat-topped part to the right, which should be aimed so that the cut-off between light & dark is pointing very slightly downwards towards the road. That's what prevents yoru low beam from dazzling drivers coming towards you.

The inflection point, where it "kicks up" from flat to angled up. That should be aimed very slightly to the left.

The kick-up to the left. That's there to throw useful light to the side, helping you to see verges, road signs, pavements etc.

Headlamp aim for the MOT checks the height of the right-hand cut-off and the inflection point to prevent dazzle but it doesn't check the shape of the beam.

So they also visually check that the beam shape more or less follows the above pattern - if it doesn't then you can still dazzle people even with "good" aim and - if it's too far out - then it might be impossible to check the aim at all because of a lack of clear cut-off or inflection point.

The usual reasons for bad pattern (assuming it's not had the light units changed recently) are:

Dirt or moisture on the lens (inside or outside). The reflector has little effect on older style lights but the lens is critical because all those steps in the glass that shape the beam (apart from the basic cut-off).

A poorly fitted (or worked loose) bulb - you can completely reverse a headlight from LHD to RHD by rotating the bulb about 15 degrees. For a while in the 70s some headlight units even came with a lever to do just that for your foreign holidays!

A faulty bulb. The position of the filament and the metal shield inside the bulb are also part of the beam shaping system so if they've moved from age or damage the beam can be thrown way out!

Occasionally (but shouldn't apply unless the light unit's been changed since the last MOT), an incorrect light unit - typically a LHD version which will kick-up to the right instead of the left.

First thing to do is to check that they're visually clean and that the bulbs are properly fitted. If need be you can clean inside by removing them, removing the bulb, and rinsing out with warm soapy water followed by plenty of cold water to remove any soap residue.

If both those are ok then it's worth finding a wall at night to see exactly what pattern IS being produced before randomly replacing parts, which can get expensive.

AdrianC

On an old Mini, there's three possible causes.

The reflector's manky and different bits are reflecting better or worse than others, so the beam's not what it should be.

The bulb's been put in rotated.

The whole light unit's been put in rotated.

None of 'em should be expensive to sort.

JJ_Egan

Headlamp beams is one of those check before MOT items .

EdGasket

JJ_Egan wrote: »

Headlamp beams is one of those check before MOT items .

Well you can check it lights up but can you really check 'beam image' ??

AdrianC

EdGasket wrote: »

Well you can check it lights up but can you really check 'beam image' ??

Yep. And alignment.

All you need is some level ground and a wall.

arcon5

JJ_Egan wrote: »

Headlamp beams is one of those check before MOT items .

lol ye!! right after you've stuck your nose in the exhaust pipe to check for excessive carbon monoxide!

Joe_Horner

arcon5 wrote: »

lol ye!! right after you've stuck your nose in the exhaust pipe to check for excessive carbon monoxide!

As Adrian said, all you need is a wall at night. For basic pattern check you don't even need flat ground.

In fact, you quite often don't even need a wall - the tailgate of the car in front is usually enough to see you've got a flat cut-off and, if you're lighting up road signs on low beam, you've also got a kick-up to the left. Got both of those - which you can check at 70mph on a motorway - and the beam pattern's not far out, although alignment may be

Strider590

Beam patterns, the reason why I get quite frustrated with people who stop illegally facing oncoming traffic an night.