Hello -- I'm adding some fluorescent strips to the walls of a small
home office, to give me some indirect lighting. My plan was to use
standard "portable" lumiares (i.e. with cord and plug, no junction box
in the unit), and put a wall outlet behind the valance.

Now, as I lay it out on the wall I find that the outlet peeks out below
the lower edge of the valance. Is it acceptable to rotate a box 90
degrees, so it's horizontal instead of vertical in the wall? That would
make it short enough to be hidden. Are there any other options?