What did those poles use to carry?

Gullfixtures.

Before the LEDs these arms had HPS GE M400A2s.

do you know what the arms had prior to the GEM400A2's?

and have you see them lit?

Before the M400A2s they had LPS, and before then mercs and stuff. The poles are very old, the truss arms were added onto the poles later.

what kind of arms did the poles have prior to these Trusses?

I think they carried acorns or some other decorative lights plus wires for the trolley system whic is long gone now. Oh no I haven't been there at night, but I saw LEDs installed in other areas of Long Beach as well as nearby Lakewood, all installed by the same contractor. They are daylight, around 6500K but are kinda dim.

Prior to LPS they had stamped OV20s 400w coated MV.In the mid 70s on LB blvd or Pine, they tested 360 Unalux. Then the LPS came.

There are new BetaLED fixtures installed on shaffers crossing and lots of new BetaLED fixtures installed in Colorado Springs, only in intersections and stuff. Colorado Springs is filled with GE M-400 A1 or M-250 A1's, some older Mercs, and lots of newer GE's. An occasional 125 is included but that's it.