Robert Emerson (November 4, 1903 – February 4, 1959) was an American scientist noted for his discovery that plants have two distinct photosynthetic reaction centres.

[3][1] Thomas Hunt Morgan invited him to join the Biology Division at the California Institute of Technology where he worked from 1930 to 1937, and again for a year in 1941 and 1945.

[1][5] Emerson and William Arnold found that "the yield per flash reached a maximum when just 1 out of 2500 chlorophylls absorbed a quantum".

[3] This dispute was settled after the death of both men, and it is now agreed that Emerson was correct, and the accepted modern value is 8 – 10 quanta.

[2][9] These results were later shown to be the first experimental demonstration that there are two photosynthetic reaction centres in plants.