I am curious why do you like specific GE form 109? Why not else GE M250, M400 and etc? Because of V shape cast glass bowl?
That's one reason why. But in a nutshell, because it's a weird one
I am not the most knowledgeable when it comes to 1940s streetlighting, but I think the Form 109 was GE's first steps into high-power mercury lighting. It looks like it started as, or reused parts from an existing incandescent luminaire design. The clip-on refractor-reflector assembly was common on older designs. Later models are closer to what we're used to nowadays. It really is a unique design!