Diatoms are one of the most promising feed-stocks for producing feed supplements, bioactive pharmaceuticals and biofuels in a bio-based economy. The marine pennate diatom Phaeodactylum tricornutum is able to accumulate large amounts of specialty carotenoids. Among the valuable carotenoids present in diatoms, fucoxanthin has health promoting effects in humans, including anti-cancer, anti-obesity, and anti-diabetic effects as well as anti-malarial activity and it has been found that fucoxanthin was more potent than β-carotene and astaxanthin in terms of anti-obesity and anti-proliferative effects on adult T-cell leukemia cells. The demand for fucoxanthin in the global market has been increasing dramatically. In this study, we characterized the biomass productivity and biomass yield on light energy of P. tricornutum with light emitting diode (LED) based photobioreactors. Under red LED illumination, increasing the photon flux from 85 to 255 µE/m²/s caused photoinhibition on Phaeodactylum cells regardless of 3.0 mM or 0.3 mM of metasilicate in the medium. In contrast, combined red and blue (50%) LED illumination gained higher biomass yield and growth rate. Fucoxanthin accumulated up to 2% of dry biomass in batch culture and exceeded chlorophyll a in content under combined red and blue LED condition. These results demonstrated the feasibility of fucoxanthin production in P. tricornutum and one biosynthetic pathway was proposed to facilitate its development.