I have a light base like that. Its actually just a cover to shield the actual bolted hold down plate. You have to place this cap onto the light pole before you attaché the light fixture up on top.
So, you have a pole with a flat ~3/4" plate on the bottom. You put 4 bolts into a wet cement foundation with in your pillar (Use a plywood template to hold the studs in perfect alignment and orientation). When the cement is dry, install the pole and level it with two sets of nuts on each stud. Then slide the cover over the base plate, capping the actual nuts. Load the power wire at one of these stages, too. Install the light bar and wait for darkness. I use proximity sensors that run 25% output at dusk to dawn. When a warm object comes close, they turn on 100%.
This presumes your light base is a cover. If its an actual mounting plate, consider using it just as a cover. That doesn't look strong enough to hold up a serious light pole...
