P700 absorption change signals were measured at 800 nm for plant leaves and plant leaf extracts by illuminating with far-red light. The ratio of the signal amplitudes for the two sample types shows the degree of optical signal intensification. The intensification is due to optical path-length elongation, itself caused by scattering. The intensification was found to be between 6 and 15 for different leaves. For spinach leaves, the intensification varied less than 10% among samples. By replacing the air in the spongy layer of a leaf with an isotonic solution it was shown that nearly half of the intensification is due to the scattering at air-tissue interfaces. The comparison of the P700 signals of a leaf with its extract would seem to be a new technique for determining the optical scattering effects of leaves.