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Does anyone know what the difference is between a D2S HID bulb and a D4S bulb, I have been trying to find out and have not had any luck. I am trying to decide what bulb to go with in my new 08 IS350
D2 bulbs are Mercury filled. The new D4 bulbs which the 2IS uses is Mercury free. You CANNOT use a D2S bulb inside the 2IS because it will not ignite, or rather, it will not stay lit. You MUST use D4S.