How does the Nissan Sentra use one bulb for high and low beams?

I have a 2006 Nissan Sentra 1.8 Special Edition.


Also do you know how good the sylvania silverstar headlights are?


Thanks|||there are two seprate filaments one for loe, the other for high. Sylvania silverstars are reallly nice, I have them in my car. The light they produce is ultra white, there is no yellowish hue in the light like regular bulbs.|||There are two elements enclosed in it.