The cell density of Pavlova lutheri was measured during a 17 days-long culture period at the three different-sized culture vessels; a 3l flask, a 20l tank, and a 100l tank. PPFD (Photosynthetical Photon Flux Density) at the center of the 3l flask and the 20l tank under fluoresent lamps was 45mu;molmiddot; m-2middot;s-1, while that at the 100l tank was 300mu;molmiddot;m-2middot;s-1 under high pressure sodium lamps, and 0-1300mu;molmiddot;m-2middot;s-1 under the natural sun light. The cell density was 2.1times;107 cellsmiddot;ml-1 at the 3l flask, 7.4times;107 cellsmiddot;ml-1 at the 20l tank, and 1.6times;107 cellsmiddot;ml-1 at the 100l tank. Differences at the cell density were found in between the 3l flask and the 20l tank, though the same light sources were used for these two systems. The cell densities at the 100ltank were also different when high pressure sodium lamps and natural sun light were used, however no difference at the cell density was found between the 100l tank under high pressure sodium lamps and the 3l flask under fluorescent lamps. Through these results, it can be concluded that a propagation rate of P. lutheri increases under higher PPFD. For higher scaling up of vessels will increase under higher PPFD lighting. It is necessary to examine the much more efficient lighting in order to maximize a propagation rate of the micro algae.
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