Abstract
Several physiological and yield parameters were evaluated in lettuce plants, cv. ‘Trocadero’, while growing at four different photosynthetic photon flux (PPF) (70, 120, 250 and 400 ± 10 µmol m-2 s-1), under four light spectra, white (W), red (R) and blue (B) Light-Emitting Diode (LED) lamps and cool white fluorescent tubes (FL). Yield parameters were also evaluated on spinach, turnip and radish, growing under identical light spectra but using a single PPF (340 ± 10 µmol m-2 s-1). Lettuce development was impaired at PPFs below 250 µmol m-2 s-1 for all tested spectra. At higher PPFs (250 and 400 ± 10 µmol m-2 s-1), for the two broad spectra tested (W LEDs and FL light), no significant differences were registered on all physiological and yield parameters evaluated. On all situations W LEDs performed, at least, as good as the FL light, indicating that actual W LEDs can efficiently replace traditional light sources, with all the inherent benefits, which include significant lower power consumption. For all species, narrow light spectra (R and B LEDs) proved not being able to provide normal plant development. Plants under R LEDs, although presenting, in some situations, a fresh weight higher than those achieved with the broad light spectra, always led to abnormal plant morphology, characterized by expanded petioles and leaf curling. B LEDs, in spite of promoting plant growth with normal morphology, frequently led to a lower number of leaves and consequently to a lower fresh weight.
Highlights
Light-Emitting Diode (LED) light is known since 1920, a practical visible-light version, usable only as indicator lamps due to its very low power, was only developed in the early 1960s
From the results of yield parameters presented in table 1, it is possible to observe that photosynthetic photon flux (PPF) significantly affected all variables under evaluation, being the best values achieved when the highest PPFs (250 and 400 μmol m-2 s-1) were used
LED light opened a new array of possibilities in order to understand plant growth behaviour under narrow band wavelengths, and, most researchers, are still looking for the best combination of R/B/G LED light in order to optimize production
Summary
LED light is known since 1920, a practical visible-light version (red), usable only as indicator lamps due to its very low power, was only developed in the early 1960s. As stated by Brandon et al (2016), LED light present several advantages when compared with traditional light sources; - Lower consumption and longer lamp life; - Light intensity adjustment 0-100% (dimming); - Lower heat emission, allowing its installation near the plant canopy. The knowledge of these advantages, combined with the possibility of using specific wavelengths, have driven the interest of plant producers on the use of LED light, either as a supplement, in conditions where the natural light is not enough, or for plant production under 100% artificial light conditions
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