The LH-50A and what I think is the BH2-MLSH45/50 look very similar. The main difference is the illuminator diameter which is much larger on the LH-50A. The LH-50A actually says LH-50A on it (upper left on second picture, hard to see above) and the other has no model listed on it.
- BH2-HLSH45/100 ("100W Halogen Lamp Housing"): much larger and white
- BH2-LSRF ("Fluoresence Lamp Housing"): requires BH3-UET8 extension tube designed for BH3-MJL bulb holder
- BH3-MJLT: different construction than others. Requires "BHS-LSH50 for 8" arm and the BH3-LSH50-10 for for 10" arm"
I've also seen reference to BH2-ULSH80