  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.
