DIYbanter - View Single Post

In article ,
says...

They need a ballast (big transformer), and a capacitor. They take
thousands of volts to ignite, and thus require special HV socket and
wiring from ballast to socket. The ballast will require cooling (fan of)
it's own.

About that part about the especially high voltage:

MH fixtures include the ballast, socket and wiring in between -
problem solved.
Also, the high voltage starting is for the "pulse start" types, which
most 175 and 400 watt MH are not.

Pulse start has an advantage - it allows an arc tube lacking a starting
probe, and a "simpler cleaner" arc tube makes those are slightly more
efficient and have slightly better lumen maintenance - maybe a little
significantly better.
Ones with ceramic arc tubes have better color rendering and those are
pulse start - but I believe are mainly lower wattages.

- Don Klipstein )