Impact of sun-simulated white light and varied blue:red spectrums on the growth, morphology, development, and phytochemical content of green- and red-leaf lettuce at different growth stages

•Plants grown under a LED-SUN spectrum had stem length 2.1–4.4 times longer than all treatments, indicating bolting.•Plants grown under a LED sun simulated spectrum have higher fresh mass per dry mass ratio.•Plants grown under a LED sun simulated and 100B spectra had greater leaf area than common B:R treatments.•Phytochemical content was lower in plants under SUN and 100B LED spectra.•The impact of light spectrum on plant growth was differed by plant growth stage (transplant, baby-leaf, head lettuce). Light drives photosynthesis and regulates plant morphology, physiology, and phytochemical content. Using light emitting diodes (LEDs), customized spectra can be created, including spectrum that simulates solar light. The aim of this study was to assess the growth, development, and phytochemical content at three marketable stages of lettuce (transplant, baby-leaf, and head-lettuce) under a sun-simulated spectrum and common light spectra used in indoor growing systems. Oakleaf red (Salanova® ‘Red Oakleaf’) and green (Salanova® ‘Green Oakleaf’) lettuce were grown under seven spectra. A sun-simulated light treatment (SUN) was created with 5 % ultraviolet-A (UV-A), 20 % blue (B), 26 % green (G), 26 % red (R), and 23 % far-red (FR) light as percent photon flux density (PFD). In addition, five treatments of differing blue:red (B:R) ratios were evaluated: 0B:100R (100R), 20B:80R, 50B:50R, 80B:20R, and 100B:0R (100B) and fluorescent white light was used as a control (6500 K). Plants were provided with 200 ± 0.7 μmol·m−2·s−1 biologically active radiation (300–800 nm) for 18 h and grown at 20.0 ± 0.2 °C temperature. Fresh mass of lettuce in the SUN treatment was not significantly different when compared to B:R light treatments in all harvest dates despite the 36 % greater photosynthetic photon flux density (PPFD) in B:R treatments. Plant dry mass on day 17 of’ Green Oakleaf’ and ‘Red Oakleaf’ grown under 20B:80R was 15–39 % greater than those grown in 100B and SUN. When calculating total dry mass accumulation to cumulative yield photon flux density (YPFD), plants in SUN treatment accumulated the same dry mass per YPFD input (mg mol−1). Leaf area at day 42 of plants in 100B, SUN, and FL was 39–78 % greater than plants in B:R treatments. At final harvest (day 42), plant stem length in SUN was 2.1–4.4 times longer than in all other treatments, indicating bolting and flowering initiation. Both total phenolic and anthocyanin concentrations were greater in the B:R treatments