Effects of light quality, daylength and periodic temperature variation on the growth of lettuce [Lactuca sativa] and radish [Raphanus sativus] plants

Effects of light qualities under continuous lighting, daylengths at a constant temperature, and periodic temperature variations under continuous lighting on the vegetative growth of lettuce and radish plants were studied to find the suitable environmental conditions for plant production in controlled environment rooms. Among the four light qualities, most growth parameters increased with increasing photon flux of the red component and the red/blue ratio in the light spectra, except when the red/farred ratio was extremely high. The plant growth was promoted with the increase of daylength up to 24 h, whereas the lighting effiency in terms of dry-matter production per lighting duration was greatest in 20 h daylength. Daily periodic temperature variations showed some effects on the plant growth and the greatest effect was found in temperature regimes of 16 H/8 L for lettuce and 20 H/4 L or 16 H/8 L for radish. The increased dry matter was distributed to both the top and roots in lettuce, but exclusively to the storage root in radish.