Introductory Crop Physiology

Red drop and Emerson’s enhancement effect

• Robert Emerson noticed a sharp decrease in quantum yield at wavelength greater than 680 nm, while determining the quantum yield of photosynthesis in chlorella using monochromatic light of different wavelengths.
• Since this decrease in quantum yield took place in the red part of the spectrum, the phenomenon was called as red drop.
• Later, they found that the inefficient far-red light beyond 680 nm could be made fully efficient if supplemented with light of shorter wavelength (blue light).
• The quantum yield from the two combined beams of light was found to be greater than the sum effects of both beams used separately.
• This enhancement of photosynthesis is called as Emerson’s Enhancement.

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