Catalyzes the reduction of FMN, and to a lesser extent, FAD, using NADH as an electron donor. Is able to provide the FMNH(2) required for the Baeyer-Villiger oxidations catalyzed by 2,5-diketocamphane monooxygenases and 3,6-diketocamphane monooxygenase. NADPH acts as a very poor cosubstrate. FMNH2 + NAD(+) = FMN + 2 H(+) + NADH FADH2 + NAD(+) = FAD + 2 H(+) + NADH kcat is 283 sec(-1) for the reduction of FMN. kcat is 128 sec(-1) for the reduction of FAD. Optimum pH is 7.5 in Tris/HCl buffer. Optimum temperature is 30-35 degrees Celsius. Has a half-life of about 80 minutes at 25 degrees Celsius. Homodimer. Likely forms a loose transient complex with monooxygenases for which it provides FMNH(2). By (+)-camphor. Belongs to the non-flavoprotein flavin reductase family.