Headlamp types

I have a low beam in my '06 so eventually I'll be dealing with it. I keep reading various re-lamping threads where folks are mentioning LED & HID lamps. Are these owner-installed options or are their different builds? I assumed they were H19 or similar, but since you really can't see anything until ya remove the bumper cover...
The high & low beams both have lenses similar to half a clear billiard ball, would that be the same regardless of lamp type? I figure I 'll just change all four headlamps plus the little clear running lamps since I have no idea how long anything's been in the car and I can't see doing this more than once. At 135k miles, I'll assume the new rpl. lamps will outlast the car anyway. Thanks!