Drivers from the UK who intend taking their cars to the continent will need to prevent the headlamp beam from pointing towards oncoming motorists.

This small modification must be carried out even if you only intend driving during daylight hours as it is compulsory to use dipped headlights during heavy rain or poor visibility.

The headlamp comes in many shapes and sizes and is the largest (and the most expensive) out of all the lights on your car. It is white when illuminated and more often than not can be found at the front of the car. There is one pictured on the right, but don't be misled by this drawing as most cars have at least two of them.

Next time you go up the pub in the car, try and park it by a wall and when you come out again at closing time turn on the headlights and see if the pattern looks anything like this one on the right.
If it doesn't then your car is probably facing the wrong way. If you can't find the light switch then you are probably in the wrong car.

Contrary to popular belief, headlights do not dip down and to the left. They dip down but with a portion of the beam going up to the left as can be seen in the simulation above. This portion of the beam is about 15° above the centre line of the lights (the horizontal red line on the pub wall, if there is no red line have a word with the landlord).
The prism section on the lens (orange in the drawing) causes this and the result is us being able to see the footpath, the kerb, the drunk further up the road than would otherwise be possible.

The Problem

The problem is that when we drive on the continent (on the right hand side of the road remember) this light will shine 15° above the headlights of oncoming cars, therefore into the eyes of the unfortunate driver, not le footpath, das kerb, ein drunk which / who is now on our right. Or should be.

The Solution

We have several options here:

• Buy and fit a pair of headlights made specifically for left hand drive cars (not recommended)
• Ignore the problem and drive illegally (not recommended)
• Buy some of those neat stick on `Beam Deflectors´ available from all good motorists shops
• Follow the simplest and cheapest method below

The Simplest and Cheapest Method

Tools required:

• Dry clean cloth
• Glass cleaner (if not available, alcohol is a good substitute, get some while at the pub experiment)
• Scissors
• Roll of black insulation tape

Using the cloth and glass cleaner thoroughly clean the whole lens removing all those dead flies that you couldn't be bothered to remove the last few times you washed the car and that have now baked on.
Now stick tape onto the area that resembles the orange part in the previous drawing. This area is called the side flare prism by the way.
Finally remove the tape because you really should do it while you are waiting to board your ferry not while the car is on your drive.

A word of caution here, some headlamp outer glass may be made of a plastic derivative. Alcohol, petrol or any other corrosive liquid will have a disastrous effect if brought into contact with this material. If in doubt, use clean water and mild detergent.

Additional Notes

On cars with a four headlight system it is usually only the outer headlights that require the modification
It is no longer necessary to have the headlights tinted yellow.
Disregard anyone that suggests tape on the headlamp will make the light too hot. The difference is negligible. Car headlamps are designed to be cooled as the vehicle is in motion, another reason to turn off your headlights when stationary/parked (Highway Code Rule 137).

Many thanks to Barry Page for the following information on projector lamps.

The focal plane of HID and projector lamps is within the light assembly itself and it is not possible to control the light pattern successfully by adding a mask to the outer cover (which is the focal plane for old style lamps). All projector lamps that I know of have a switchable shutter inside the lamp asy which is accessed by removing the rear cover (usually a substantial rubber moulding) and inserting a small screw driver to flick the shutter control in the appropriate direction and there may be some with external control. HID systems (the very bright blue/white lamps) usually have a rotating switch external to the light asy to switch the shutter which has a positve 'click' sound and feel to confirm that it has locked in position.