Originally Posted by AtlasRider
Sorry, this is a total noob question...
What do stickers have to do with the headlight beam?
Here in the UK, headlamp beams on cars and bikes (almost always) point slightly to the left when dipped. So when we go abroad, the dipped headlamp will dazzle oncoming riders/drivers. The same vice versa for continental riders coming to the UK.
The bending of the beam to left or right is done by a small lenticular lens in the glass of the headlamp. So putting a sticker over it blocks that bit of the dipped beam, which then points straight ahead.
You can just use any piece of sticky tape or duct tape, but the kits, available in shops in Dover and Calais and on the ferries, (and all motor-parts shops) will show you exactly what shape to cut the sticker to (if it needs cutting, sometimes it won't) and where to stick it on the headlamp. Otherwise trial and error can be used. Generally the sticker amounts to about one square inch, plus or minus.
The problem with bikes is that many bike headlamps are not covered in the instructions that come with these kits. (Whereas most modern cars and some older ones actually have a faint etching on the glass to show you where to put the sticker).
As an example, my Honda Dominator here in the UK is a French model, so it's headlamp points to the right when dipped. So it won't pass the annual test here. Luckily I found that the headlamp kits on sale did have instructions that covered the lens of my headlamp so I didn't have to spend time on trial and error.
Some riders when buying a model of bike from the continent for use in the UK go to the trouble of putting a UK headlamp on.
Either way it won't pass the annual test if the light points to the right when dipped.