Optical and Electric Gradients in Photosynthesis

Light‐gradient photovoltage is detected in most of the photosynthetic systems. The effect depends on the intensity, duration and wavelength of short light pulse excitation and on the redox state of the illuminated photosynthetic membrane. In the region of small absorption the polarity of the photovoltage is negative, whereas in the high absorption regions it is positive. The sign depends moreover on the geometrical dimensions of the membrane and on the difference in the refractive indices between the membrane and the surrounding aqueous phase. Light‐gradient photovoltage studies permit a quantitative determination of the membrane birefringence and refractive index anisotropy.