Which lights are you looking to upgrade? Our 2007 Lexus GST350 Lighting Guide shows the Low Beams are D4S (factory HID), so even if you could find a conversion for that you would be looking at a lighting downgrade - HIDs are still the king as far as output goes. If you need some new D4S HID Bulbs there are lots of options to choose from. The stock bulb is usually rated 4300K, so the Philips D4S 4300K are a nice replacement if you don't want anything different.

If you wanted to change your High Beams (9005 bulbs) or Fog Lights (9006 bulbs), LEDs could be a good way to go there, however.

~Robert