Light-emitting reaction in luminous bacteria. The specific role of the beta subunit is unknown, but it is absolutely required for bioluminescence activity. a long-chain fatty aldehyde + FMNH2 + O2 = a long-chain fatty acid + FMN + 2 H(+) + H2O + hnu Heterodimer of an alpha and a beta chain. Belongs to the bacterial luciferase oxidoreductase family.