Flashing light experiments on photosynthesis were performed by

Flashing light experiments on photosynthesis were performed by Emerson and Arnold.
Emerson and William Arnold found that "the yield per flash reached a maximum when just 1 out of 2500 chlorophylls absorbed a quantum".
Next, in 1939, Emerson demonstrated that between 8 and 12 quanta of light were needed to produce one molecule of oxygen.