HID Lamps:
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Mercury lamps have been used since the 1930's. They emit a bluish white light. Often the bulbs are coated with a white phosphor and you cannot really see the arc tube.

High Pressure Sodium (GE name: LUCALOX®) emit a yellowish white light and are commonly used today in street lighting. They were invented by GE in the early 1960's

Metal Halide (GE name: MULTIVAPOR®) were invented by GE and introduced at the New York World's Fair in 1962

Each HID lamp has its own dedicated ballast type. You also must be sure that the correct ballast for operating the lamp is in the fixture.