The lamp post we purchased did not have instructions. So after doing research there are many conflicting methods...use concrete, do not use concrete. Well, our plan is to install a 22 inch hole filled with gravel on the bottom and then filled with concrete to secure the post. In regards to the electric, we plan on using # 14 outdoor direct buried wiring because the wiring for the light (switch and wall wiring is # 14). The run is about 75 feet in total. We plan on drilling a hole between the joists to get outside. And then use that grey conduit you find in the home stores and install all the way to the post and make a 90 degree bend up into the bottom of the post. We are thinking use direct buried wire for added protection, does this make sense?

Now, in regards to the lawn, we can rent a 3" trench machine for 4 hours for $75 and make the trench. We can either go across the lawn or under a paver walkway from the post to the basement. Is under paver walkway a bad idea? It would avoid the grass damage issue. I was thinking pull up the center pavers, trench, backfill, and replace the paver. How did would you go?

You could direct-bury the UF without conduit (except for protection where it emerges from the ground), but you'd need to provide GFI protection at the house.

I routinely use rigid conduit so that the depth only needs to be 6 inches.

A good labor savings for trenching, even with a ditch witch.

Can the 6" depth also include the paver bed materials? I believe it is sand. Or do I need to go below that setting material into the actual "dirt?"

When you say rigid conduit, you are talking the shiny stainless steel conduit, correct?

We installed the lamp post yesterday and used the plastic grey conduit and stubbed it out outside the concrete pouring (in the hole we made). Can I connect the metal to the plastic? The plastic is 3/4", but I think we may have oversized it from reading other posts. Can we connect 3/4" plasic to 1/2" metal? Is all the metal piping waterproof like the plastic which gets glued?

I think we will go with the 6" over the 18".

According other other poster, we will need to return the UF wire and get THWN.

Underground is a wet location by definition.

I think you are thing if EMT (Electrical Metallic Tubing) and not rigid metal conduit.

Rigid metal conduit goes together with pipe threads.
It is about as tight as you will get.

The steel is thick enough and zinc plated so that only very corrosive locations are an issue.

"Can the 6" depth also include the paver bed materials?"

Yes, and your AHJ may even allow the pavers themselves.

$12.19 for 1/2"
$13.76 for 3/4"

It is not cheap when you compare it to a section of plastic a tad over a buck.

Plus you need a pipe bender and threader and couplings. There are fittings for plastic that will give you male thread you can install the rigid too, but no clue if this is code approved. There are numerous fittings you get get any configuration you essentially need. I would guess the plastic is a ton easier to use and install plus it appears very forgiving (would bend on a straight away).

I am not sure if you can install UF inside conduit. I am sure it will work fine, but I think it gets derated?

Rigid is bent with power equipment, you are not going to bend it with a typical EMT hickey.

Pre-formed 90 degree bends are easily available.

You can even escape threading with mechanical connectors (though it uses the same threads as plumbing pipe).