This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is chlorophyllide-a:NADP+ 7,8-oxidoreductase. Other names in common use include NADPH2-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide reductase, protochlorophyllide oxidoreductase, and protochlorophyllide photooxidoreductase. This enzyme participates in porphyrin and chlorophyll metabolism.
There are two structurally unrelated proteins with this activity, referred to as light-dependent and the dark-operative. The light-dependent reductase needs light to function, while the dark-operative version is a completely different protein, consisting of three subunits that exhibit significant sequence similarity to the three subunits of nitrogenase. This enzyme might be evolutionary older but (being similar to nitrogenase) is highly sensitive to free oxygen and does not work if its concentration exceeds about 3%. Hence the alternative, light dependent version needed to evolve.
^Yuichi FujitaDagger and Carl E. Bauer (2000). Reconstitution of Light-independent Protochlorophyllide Reductase from Purified Bchl and BchN-BchB Subunits. J. Biol. Chem., Vol. 275, Issue 31, 23583-23588. 
^S.Yamazaki, J.Nomata, Y.Fujita (2006) Differential operation of dual protochlorophyllide reductases for chlorophyll biosynthesis in response to environmental oxygen levels in the cyanobacterium Leptolyngbya boryana. Plant Physiology, 2006, 142, 911-922 
Apel K, Santel HJ, Redlinger TE, Falk H (1980). "The protochlorophyllide holochrome of barley (Hordeum vulgare L.) Isolation and characterization of the NADPH:protochlorophyllide oxidoreductase". Eur. J. Biochem. 111 (1): 251–8. doi:10.1111/j.1432-1033.1980.tb06100.x. PMID7439188.