Emerson and his colleagues, while studying the productivity of photosynthesis with different light wavelengths, found that there is a sudden decline in the rate of photosynthesis at 680 nm (far-red light), the far red end of the spectrum. This was called the Red drop. Emerson also observed in the experiment that after the decline in photosynthesis at 680 nm of the red end of the spectrum, if 650 nm (red light) waves are also provided at the same time, then photosynthesis can occur again at full capacity, that is, by giving two lights simultaneously of different wavelengths, not only the rate of photosynthesis improves but its total quantity is also more than the sum of the separate quantities received by both the wavelengths. Therefore, the increased activity of photosynthesis by simultaneous use of light beams with different wavelengths is called Emerson effect.