I have some old GE fixtures in my barn I don't know if they are metal halide,mercury vapor, low pressure sodium or what. I have no bulbs. The numbers I have on the fixture are these: C 769N101 400 Watts S517BD 120 V 60 HZ Its pretty heavy about 16 inches across and a dull gray. An optical assembly attaches to it. On the tag its reads General Electric Optical Assembly C777G101A. Can anyone point me in the right direction or know what I have here?