rx3502007

Ok, I have a new purchase and am a little confused regarding the headlight replacements on an '07 RX350.
From what I can tell, it is a dual purpose headlight. Low beams and high beams from the same bulb. Standing in front, the only thing I can see changing when engaging the high beams is the brightness. No additional bulbs turn on.
Why then, would there be a listing for high beam bulbs and a separate listing for low?
What is the distinction here?
Maybe I'm just thick or missing something.

Thanks

09RX350AWD

There are four bulbs in each headlight housing - low beam (halogen or HID), high beam (halogen), turn signal, and parking lamp. The high beam bulb is the inboard most bulb closest to the grill on each side. The high beam is also used for DRL (daytime running lamps) so if your headlights are off, car is running, and parking brake is off the high beams should be on by themsleves at a lower intensity.

Pg 366 in my 2009 manual shows a picture of the front explaining the location/purpose of each bulb