As previously said, the RX's headlights come in 3 configurations:
1)Halogen:

2)BiXenon

3)LED


To clarify, The Rx350's BiXenon headlamps do in fact use a shutter to differentiate between low and high beam output. Also, as said before, the design of the bixenon system in the Rx is one of the best out there. Its bowl efficiently directs light wide, yet far to provide a wide field of vision. There's also a section of the bowl that diffuses light to allow your eyes to focus easier in the distance. The lower side of the step, that encounters oncoming traffic, is also lowered further to decrease the risk of blinding opposite traffic. Combined with its AFS ability, these are one of the most intelligently designed units out there.





more pictures of the units internals as well as various output shots of OEM vs. modified can be found here on pages 1,4,7,8,10-12

linky click click

 

One more thing, The Lexus IS does have BiXenon headlamps but in highbeam mode, both the shutter is lowered in the HID projector as well as the activation of the auxiliary halogen highbeams. I feel that its nice to have since the highbeam from the HID will work in conjunction with the AFS since halogen reflectors only point directly ahead of you. It's a whole lot of light being cast in the dark.

*Edit*
One more thing for you Rx owners, are you able to pull the left stalk (light control and turn indicators) toward you? does this activate a flash from your HID's or Halogen DRL's?

I'm asking because my on my 2006 e90 330i, pulling back on the stalk activates my halogen drl to "flash," aside of pushing it forward, which activates my shutter for my BiXenon highbeam. This setup saves your HID's from suicide lol.

 

Interesting.