In our 1960
Pacer all the interior lights (three) were 120 V except for the light fixture in the middle of the ceiling, which had sockets for both 120 V and 12 V bulbs. (That was the only 12 V device in the trailer; the '60 Pacer did not originally have a coach battery, just a connection to the tow vehicle battery.)
One option is to put in a small inverter to give you enough 120 V to run the lights from the 12 V battery. We did that and it worked pretty well with compact fluorescent bulbs in the 120 V sockets. (We also added a coach battery.)
Alternatively, you could run a 12 V wire to the fixture and put one or two LED lamps inside the fixture to provide 12 V lighting when boondocking.