Complex sentence: Like other HID lamps, they operate under high pressure (4 to 20 atmospheres) and require special fixtures to operate safely, as well as an electrical ballast, and require a warm-up period of several minutes to reach full light output.
Split into simpler sentences: Like other HID lamps, they operate under high pressure (4 to 20 atmospheres) and require special fixtures to operate safely, as well as an electrical ballast. They also require a warm-up period of several minutes to reach full light output.