Kia Optimas with HID headlights use D3S HID bulbsfor the low beam.
How to replace low beam light bulb Kia Optima
Step 1: Open Hood
Pull on the hood release to open the hood.
Step 2: Remove old light bulb
Locate the back of the headlight assembly. In the following picture, you can see the location of the right low beam bulb on the passenger side. First, you need to remove the light bulb cover. To remove this cover twist it counterclockwise and remove it. Next, you need to remove the low beam bulb. Remove the bulb socket from the headlamp by turning it counterclockwise.
Step 3: Install new low beam light bulb
Remove the old bulb from the socket by pulling it. Press the new bulb into the socket. Align the tabs on the socket with the slots in the headlamp assembly and twist the socket to lock in in place.
Step 4: Replace the headlight bulb cover
As a last step install the headlamp cover by twisting it clockwise.