Abstract
Leaf lettuce crops (Lactuca sativa L. cv. “Greenwave”) were grown in a plant production system using a Mirror Duct which intensified sunlight and transferred it to the inside of buildings. This system was expected to reduce the operational energy and lighting cost. The experiments were conducted under four photosynthetic photon flux densities (PPF) of 140, 160, 180, and 200 μmol m-2s-1, in two light conditions, fluorescent light only and fluorescent light plus sunlight transferred with the Mirror Duct, and were repeated five times in total from August 2002 to July 2003. Five different solution temperatures were finally obtained through all the experiments due to temperature changes inside the experiment facility. Variance was analyzed to estimate the effect of these environmental factors on the growth of leaf lettuce. It was found that the fresh weight of leaf lettuce increased as PPF increased and the rate of increase of weight was 0.6 to 1.0 g per unit PPF in both 17.4°C and 23.5°C solution temperatures; the solution temperature had a significant effect upon the fresh weight; and a difference in fresh weight at harvest of between 40 and 60 g was observed between 17.4°C and 23.5°C solution temperatures. The light containing 10% sunlight was not effective for increasing fresh weight at harvest compared to the fluorescent lamp.
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