A physical method for maintaining the freshness of vegetables and fruits via the technology of the optical signal and optical signal generator are disclosed. By adopting the computer programmable pulsed scanning signal generator, it controls the light-emitting device mounted with red, green and blue light sources group to generate optical signal with pulsed or pulsed periodical scanning combined spectrum. The optical signal irradiates the fresh-cut fruits and vegetables preserved in the storage assembly at room temperature or at controlled temperature and humidity. By regulating the optical signal with periodical pulsed spectrum or pulsed scanning spectrum or periodical pulsed scanning combined spectrum, the irradiated vegetables and fruits obtain photon energy needed in light reactions of photosynthesis from the lighting environment of artificial optical signal which is in bright and dark periodic variation. The metabolism of the cellular tissue is recovered and maintained, and the growth inertia is kept at
