We present experimental results demonstrating that, relative to continuous illumination, an increase of a factor of 3-10 in the photon efficiency of algal photo-synthesis is attainable via the judicious application of pulsed light for light intensities of practical interest (e.g., average-to-peak solar photon flux). We also propose a simple model that can account for all the measurements. The model (1) reflects the essential rate-limiting elements in bio-productivity, (2) incorporates the impact of photon arrival-time statistics and (3) accounts for how the enhancement in photon efficiency depends on the timescales of light pulsing and photon flux density. The key is avoiding clogging of the photosynthetic pathway by properly timing the light-dark cycles experienced by algal cells. We show how this can be realized with pulsed light sources, or by producing pulsed-light effects from continuous illumination via turbulent mixing in dense algal cultures in thin photo-bioreactors.
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