Explanation

Emerson et al, (1957) discovered that far red light (above 680 nm), which is Photosynthetically inefficient can be made efficient by supplementing it with a beam of shorter wavelength (red beam below 680 nm). Further the quantum yield in combined beam (far red+red) is more than sum total of quantum yields in two separate beam. This enhancement in quantum yield by supplementing far red light with red light is called Emerson enhancement effect.