Essentially, they have a blanking plate fitted to the bulb to block the light shining downwards, as it's the downward light that reflects back up creating glare.

Don't know about other cars, but I know on the Lexus (because I looked into getting some) the twist lock for the bulb is offset, so when the bulb is twisted in, the blanking part isn't at the bottom, it's off to an angle. So you end up with a small rectangle of light on the road where light isn't being reflected off the reflectors correctly.

The VW Sharan, as I noticed the other day, gets round this by having a blanking "peg" fitted to the actual reflector, directly beneath the bulb itself, which got me thinking maybe I could do something similar with mine, if I can find the part number for this little piece from VW, and try fitting it to my lights.

Then I remember I don't like fucking around with mods, so I didn't bother