Catalyzes the dehydrogenation of (R)-lactate (D-lactate) to pyruvate. Active in vitro with the artificial electron acceptor 2,6-dichlorophenolindophenol (DCPIP), but not with NAD, NADP, or cytochrome c. Also displays a very low oxidase activity in vitro on D-lactate and L-lactate with O2 as the electron acceptor, but this activity is most likely not physiological. (R)-lactate + A = AH2 + pyruvate Binds 1 FAD non-covalently per subunit. Binds 1 Zn(2+) ion per subunit. kcat is 5.2 sec(-1) with DCPIP as electron acceptor (at pH 7.4 and 25 degrees Celsius). Belongs to the FAD-binding oxidoreductase/transferase type 4 family.