The project was conducted in the Heliospectra Plant & Research Lab which is a 80 square meter (861 square feet) temperature and humidity-controlled facility containing 20 individual growth units with reflective curtains. Two cultivars of red-green lettuce were studied: ”Amerikanisher brauner” and ”Galiano”. The lettuce grew under LED light for 23 days in one unit under a selected light spectrum on a Heliospectra LX602C hanging 170 cm (5.6 ft) above the growth table. After 23 days, two thirds of the plants were moved into two different growth units to be treated with different high-light treatments under either the Heliospectra LX602G or E602G. The high-light treatment entailed setting the lamps to provide a light intensity of 440 μmol/m2/s. The last third of the plants were kept as a control group in the unit with the initially selected light spectrum throughout the experiment.
Image analysis was conducted after day one and day two of light treatments.
Both the LX602G and E602G were efficient in inducing red coloration over 1 day of high-light treatment. The red coloring in the lettuce also increased with days of treatment. An additional observation was the LX602G treatment displaying much redder lettuce compared to E602G. Heliospectra believes this is a result of higher concentrations of blue light in the LX60’s “G” type spectrum; however, more research will need to be conducted to verify this. In conclusion, a lighting strategy which entails adjusting both light intensity and spectral quality shortly before harvest appears to have a positive influence on the coloring in lettuce.
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