A novel hydroponic photobioreactor is proposed for high-density cultivation of plants. This cultivation can be achieved by growing plants on a floatable platform, allowing the roots to directly contact a continuously aerated nutrient solution. Plant growth of Mentha x piperita (peppermint) can be shown to strongly correlate with the light intensity at incident light intensities between 0 and 650 mu mol m(-2) s(-1). For a constant incident light intensity (I-0 = 420 mu mol m(-2) s(-1)), the overall specific growth rates of these plants are found to be strongly dependent on the plant density. They range from 0.023 to 0.075 d(-1) for plants grown at a density range from 16 to 256 plants m(-2). A simple mathematical model is presented that allows one to predict these effects of light intensity and plant density on peppermint growth. Light delivery is derived from the modification of Beer-Lambert＇s law. From this, the relationship between the light extinction coefficient and plant density can be experimentally determined. The light transport can then be coupled with plant growth kinetics under light-limiting conditions. The predicted growth results agree reasonably well with most experimental results from a growth period of 17-20 days. On the basis of these simulation results, we suggest that a more efficient way of delivering light to this photobioreactor can be attained by supplying light from both the top and the bottom of the plant shoots. The proposed design takes advantage of the small size and low weight of light emitting diodes, which allow them to be mounted on platforms for delivering light closer to the plants.