Joshua Putnam wrote:

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.

My 400W MH fixtures don't have fans for cooling, just the back of the
ballast exposed to air. A lot of warehouse and parking-lot lights
use 400W MH without cooling fans.

The point I'm trying to make is that heat is a problem that needs to be
addressed, and that it will be a problem if you try and build fixtures
in, and not leave them out in the free air.

A small muffin fan is an easy DIY to do cooling, when one doesn't have
ability to design and test a better enclosure.