The UK – a (shining) example to us all? I daresay many continental Europeans would beg to differ. But in fact, when it comes to automotive lighting, this is indisputably the case: unlike their French, German or Italian cousins, British motorists know precisely what to do when they cross the channel and take their right-hand drive cars onto the left-hand-drive continent. They either adjust their headlamps or tape them up correctly.
This is because dimmed headlamps always illuminate the road asymmetrically: the edge of the roadway is illuminated more than the center. This avoids dazzling oncoming traffic and improves the visibility of distant road signs. It also ensures that pedestrians, cyclists or wild animals on the edge of the road can be spotted sooner. Cars designed for driving on the right hence illuminate the right-hand side of the road more while cars designed for left-hand traffic cast more light on the left.
This is achieved by different technical means. In older vehicles, the headlamp diffuser has a special pattern and the reflector is correspondingly shaped. Modern vehicles, on the other hand, have appropriately shaped free-form reflectors, which harmonize with clear glass headlamps. And in “projection systems” – the third category – lenses and shades ensure the correct light distribution. In the latter case, the asymmetrical part of the beam can simply be switched off by technical means (see instructions).
But let’s get back to the topic of reflector headlamps: models for the UK (and also for example Irish, Maltese, Australian and Indian) market can often be switched from the position for left-hand traffic to the position for right-hand traffic in one swift move. Here on the continent, most carmakers dispense with this function for cost reasons. In this case, the headlamps need to be taped up, i.e. covering the part of the glass that directs the beam to the right.
If you have older headlamps (without clear glass), it is best to imagine them as cakes which are divided into twelve slices at the positions of the numbers on a clock: it’s usually the “3 ‘o clock slice” you need to deal with. A cheap option is to cover it with black adhesive tape (but do be sure to buy a good quality tape that can withstand heat and moisture). Sometimes it can be worthwhile to pop round to a specialist store or your local mechanic and ask for help: they might supply you with ready-made strips and templates that fit your model. You can work more precisely with these than with adhesive tape.
If you have clear glass headlamps, there is no pithy rule-of-thumb. You will have to ask at your workshop. Or look through the instruction manual. Instructions on taping headlamps are obligatory in the manuals of cars built from around 2005 onwards.
Incidentally, be careful with headlamp cleaning systems: if they do their job too well, films and tapes can become detached and your headlamp will dazzle oncoming traffic again. Be sure to conduct regular checks to prevent this!
Just to round off, here comes a safety tip: just because you have taped up a headlamp with a right-hand bias, this doesn’t mean you have converted into a headlamp with a left-hand bias. Instead, you’ve made a symmetrical light with a reduced range. This will reduce the visibility of the roadway.