Reduces FMNH(2) to FMN, with NADH or NADPH as reductant. It also reduces nitroaromatic compounds, quinones, chromates and azo dyes. It could supply the reduced form of FMN to luciferase-like protein and contribute to the degradation of aromatic compounds. FMNH2 + NADP(+) = FMN + 2 H(+) + NADPH FMNH2 + NAD(+) = FMN + 2 H(+) + NADH FMN is a competitive inhibitor of NADH, and therefore leads to the preferential utilization of NADPH. Homodimer. Strongly induced by stress due to exposure to 6-brom-2-vinyl-chroman-4-on (chromanon) and less strongly induced after exposure to 2-methylhydroquinone (2-MHQ) or catechol stress. Catalysis proceeds by a classical ping-pong bi-bi reaction mechanism. The reduction of nitro-organic compounds and inorganic chromate occur in the absence of external FMN and are therefore believed to require binding of these substrates in the active site. In contrast to these reduction processes, azo dyes are reduced only in the presence of external FMN, indicating that azo dye reduction occurs outside the active site of the enzyme. Belongs to the flavin oxidoreductase frp family.