Catalyzes the decarboxylation of free fatty acids to n-alkanes or n-alkenes in response to blue light (PubMed:28860382, PubMed:30144559). Substrate preference is toward fatty acids with C17 or C18 chains (PubMed:28860382, PubMed:30144559). Saturated fatty acids are converted to alkanes, not alkenes (PubMed:28860382, PubMed:30144559). The decarboxylation is initiated through electron abstraction from the fatty acid by the photo-excited FAD (By similarity). a long-chain fatty acid + H(+) + hnu = a long-chain alkane + CO2 H(+) + hexadecanoate + hnu = CO2 + pentadecane Binds 1 FAD per subunit. Activated by blue light and repressed by red light. Optimum pH is 8.5 (with palmitate as substrate). May be used in light-driven, bio-based production of hydrocarbons. Belongs to the GMC oxidoreductase family.