High Intensity Discharge or "HID" is the term commonly used to designate four distinct types of lamps that actually have very little in common. They are high pressure sodium, low pressure sodium, metal halide, and mercury vapor. Each requires a few minutes (one to seven) to come up to full output. Also, if power to the lamp is lost or turned off, the arc tube must cool to a given temperature before the arc can be re-struck and light produced. Up to seven minutes (for mercury vapor lamps) may be required.

high pressure sodium

low pressure sodium

mercury vapor

metal halide