Yeah this is from the late 50s or 60s, I believe. I've seen this same style 4ft aluminum arm used before, but I've only ever seen it with 100W MV M-250R1s or 50W HPS M-250R2s or 50W HPS AE 113s.
Amazing a radial wave with an exposed lamp survived intact. I wonder if the lighting for this park was salvaged from when the local utilities upgraded their fixtures. I've seen that a number of times with private installations.
This park was never upgraded to HPS. Everything here was MV. The only HPS lights were some floodlights owned by the park itself. I was very surprised that these two radial waves still have their lamps too. Unfortunately all the lights except for the ones I photographed are gone.