Xenon headlamps were introduced in 1991 as an option on the BMW 7-series. This first system used an unshielded, non-replaceable burner designated D1 — a designation that would be recycled years later for a wholly different type of burner. The AC ballast was about the size of a building brick. The first American-made effort at HID headlamps was on the 1996-98 Lincoln Mark VIII, which used reflector headlamps with an unmasked, integral-ignitor burner made by Sylvania and designated Type 9500. This was the only system to operate on DC; reliability proved inferior to the AC systems. The Type 9500 system was not used on any other models, and was discontinued after Osram's takeover of Sylvania. All HID headlamps worldwide presently use the standardised AC-operated bulbs and ballasts.