There's a shutter inside the projector that normally blocks part of the light beam. When you go form low to high beam the shutter hides and your light can now illuminate much more of the road. No extra bulb is turned on - just the shutter that normally limits the beam is hidden.

Shutter reaction is much faster then extra high beam bulb being powered, since shutter does not need to be preheated.

More good news - while high beams are on in stock lights you're using 55W on each bulb and there's 4 of them working. That makes 220W. With bi-xenon lenses you use 2x35W on each ballast and few watts more for the shutter. That makes just above 70W.