1FlexedLex

whats up forum. pretty new member here, been lurking and searching this forum for a while now. trying to get use to it. i am new owner to lexus and this is my first luxury car. i have a 07 is250. I bought it used back in april of 2013. the passenger side headlight went out and there's condensation all over the lens and now the headlamp is turning yellow. im planing to get a new headlamp. my question is, since my car comes equipped with factory HID can i install a D4S aftermarket HID kit? or do i have to get a new OEM ballast, OEM bulb. i want to change both sides at once. so i assume a aftermarket kit would be easier to maintain and install. i have no warranty on the car and i will be changing these lights myself. pics coming soon any help and info or a direction to go in would be appreciated.