ISHS Acta Horticulturae 440: International Symposium on Plant Production in Closed Ecosystems
QUANTIFICATION OF LIGHTING SPECTRAL QUALITY EFFECT ON LETTUCE DEVELOPMENT USING MACHINE VISION |
| Authors: | S. Sase, P.P. Ling |
| Keywords: | artificial lighting, lettuce development, light spectral quality, machine vision |
| Abstract:
The effect of spectral quality on the growth and development in lettuce was evaluated by machine vision. Lettuce plants (Lactuca sativa L. cv. Okayama Saradana) were transplanted at 10 d after seeding. Immediately after transplanting, the plants were transferred to controlled environment compartments and grown hydroponically under four different spectral qualities (white, blue, green, and yellow light) at an equal photosynthetic photon flux density (PPFD, 400–700 nm) of 250 μmol m-2 s-1 using specially designed HID lamps. The spectral photon distribution of the blue light had peaks at 410 and 450 nm, and the photon flux density in the 400–450 nm region was 53% of the PPFD. The green light peaking at 540 nm provided 64% in the 500–550 nm region, and the yellow light peaking at 570 and 590 nm provided 81% in the 550–600 nm region. Top view projected images of the plants were captured using a portable image acquisition chamber. The images were recorded by a video recorder and analyzed using a commercial machine vision station. Morphological features such as top projected canopy area, perimeter, roundness, and aspect ratio were evaluated. The results showed that the top projected canopy area and the perimeter were affected by spectral quality and reduced by blue light. Actual leaf area measured on the harvested plants showed the similar tendency. Leaf number in yellow light was significantly increased. No significant differences in top dry weight were found in the treatments. Roundness of entire plants was slightly reduced by yellow and blue light. No significant differences in canopy aspect ratio were found. Evaluation of individual leaves in the early growth stage showed that leaf elongation was inhibited by blue light. The growth rates in leaf length and width in blue light were the least, compared with those in other treatments. Aspect ratio of individual leaves was increased by blue and yellow light. | |
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