The difference between the D2S and D4S HID replacement bulb is that the D4S is the Mercury-free version of the D2S. This is the same for the D1S and D3S HID replacement bulbs as well.

D2S bulbs are commonly on vehicles such as (but not limited to) the Acura TSX, TL, MDX, etc. and Nissan/Infiniti G35, G37, 350z, etc. The D2S bulb is the common OEM HID bulb replacement for most Japanese vehicles.

D4S bulbs are commonly used for Lexus/Toyota vehicles such as (but not limited to) the IS250, IS350, IS-F, GS350, LS460, and Prius. It is also used on the Honda CR-Z.

D1S and D3S bulbs are commonly used on European vehicles such as (but not limited to) BMW, Mercedes-Benz, and Audi.

The OEM HID Bulb Replacements we carry are based as a D1C/D2C/D3C/D4c bulb. These bulbs are a hybrid version of both DXR/DXS type bulbs and will function just like how your stock bulbs do.