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sunlight plus direct (SL; 90 μmol·m −2 ·s −1 ) or diffuse lighting [photoperiodic lighting (PL); 3 μmol·m −2 ·s −1 ] from high-pressure sodium (HPS) lamps. Lamps were operated when the ambient greenhouse photosynthetic photon flux ( PPF ) was less than 400

collected from D. surculosa ‘Florida Beauty’ stock plants in late spring. The stock plants had grown in a shaded greenhouse for 3 years under a maximum photosynthetic photon flux ( PPF ) density of 300 μmol·m −2 ·s −1 at the University of Florida's Mid

, and red + blue (R + B) LEDs [1:1 photosynthetic photon flux ( PPF )]. The LEDs were purchased from Ryh Dah Inc. (Taiwan). The wavelengths of the LEDs were confirmed using a spectroradiometer (International Light Technologies; ILT900) ( Fig. 1

photosynthetic photon flux density (PPFD) measured (at night) in both high-pressure sodium (HPS) and light-emitting diode (LED) plots. Sunlight-calibrated quantum sensors (SQ-110; Apogee Instruments Inc., Logan, UT), located just above canopy level in the

photosynthesis rates ( A n ) to ( A ) photosynthetic photon flux density ( PPFD ) and ( B ) intercellular CO 2 partial pressures ( C i ), as well as the quantum efficiency of photosynthetic system II (ΦPSII) to ( C ) PPFD and ( D ) C i . Error bars show ± se

:1:1 ratio based on volume. Potted plants were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities ( PPFD ) of 285, 350, and 550 μmol·m −2 ·s −1 , which resulted from the installation of shadecloth with three different

LEDs at two photosynthetic photon fluxes (200 and 500 μmol·m −2 ·s −1 ). z Fig. 2. Spectral distribution of warm, neutral, and cool white LEDs at 200 and 500 μmol·m −2 ·s −1 . Both spectra are shown because overdriving the LEDs to achieve 500 μmol·m −2

. Photosynthetic photon flux ( PPF ) experienced at each canopy position was assessed hourly from 0800 hr to 1800 hr from 18 Feb. [122 d after full bloom (DAFB)] to 31 Mar. 2007 (162 DAFB) with a quantum sensor attached to a light meter (LI-250; LI-COR, Lincoln

light-emitting diode (LED_70) lamps at a photosynthetic photon flux density ( PPFD ) of 70 µmol·m –2 ·s –1 ; supplemental lighting based on an instantaneous threshold (on from 0600 to 2200 hr when outside PPFD was less than ≈440 µmol·m –2 ·s –1

lights on stem elongation of microgreens, especially under different photoperiods, because photoperiod can also affect this plant trait ( Bergstrand, 2017 ). Previous studies indicated that under LED lighting at a photosynthetic photon flux density (PPFD