Effect of Supplementary Cyan Light to Deep Red and Royal Blue Range Wavelengths on the Growth of Iceberg Lettuces

Abstract

This article investigates the effect of cyan (≈500 nm) light on the plant growth as a supplementary light source to common deep red (≈660 nm) and royal blue (≈440) lights. For this purpose, a 3-floor shelf is prepared containing Vernalia type iceberg lettuce seeds. Carbon dioxide content of air, soil and air humidity, environment temperature, water, fertilizer and nutrient contents controlled at desired values; being same for the whole system. First and second floors are lighted 18 hours a day, with the same photosynthetic photon flux density (PPFD) of 360 μmol m-2 s-1. First floor’s lighting was composed of 65% deep red and 35% royal blue lights. Second floor’s lighting was composed of 55% deep red, 25% royal blue and 20% cyan lights. Third floor is lighted with sunlight, in order to make a comparison with natural lighting. The experiment lasted for 30 days. The experiment results showed that, addition of cyan light allowed the plant to grow 10% by dry mass relative to common red and blue grow lightings. Most of the growth difference is occurred during the seedling period, and nearly stayed constant during the vegetative period. Besides, red and blue grow lights increased plant dry mass 15% with respect to natural sunlight, meaning that tailor made cyan light addition to red and blue grow lights could boost 26.5% natural plant growth involving only sunlight.