Robert Emerson described the eponymous effect in 1957. In his paper he observed that:
# When plants are exposed to light having wavelength greater than 680 nm, then only one photosystem is activated; i.e. PS700 resulting in formation of ATP only.
# When plants are exposed to light having wavelength less than 680 nm, the rate of photosynthesis was very low.
# On giving both shorter and higher wavelengths of light, the efficiency of the process increased, because both photosystems were working together at the same time, resulting in higher yield.