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.

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