Spectral Effects of Light-emitting Diodes on Plant Growth, Visual Color Quality, and Photosynthetic Photon Efficacy: White versus Blue plus Red Radiation

Arrays of blue (B, 400-500 nm) and red (R, 600-700 nm) light-emitting diodes (LEDs) used for plant growth applications make visual assessment of plants difficult compared to a broad (white, W) spectrum. Although W LEDs are sometimes used in horticultural lighting fixtures, little research has been published using them for sole-source lighting. We grew seedlings of begonia (<i>Begonia </i>×<i>semperflorens</i>)<i>, </i>geranium (<i>Pelargonium </i>×<i>horturum</i>), petunia (<i>Petunia </i>×<i>hybrida</i>), and snapdragon (<i>Antirrhinum majus</i>) at 20 °C under six sole-source LED lighting treatments with a photosynthetic photon flux density (PPFD) of 160 µmol∙m^–2∙s^–1 using B (peak= 447 nm), green (G, peak= 531 nm), R (peak= 660 nm), and/or mint W (MW, peak= 558 nm) LEDs that emitted 15% B, 59% G, and 26% R plus 6 µmol∙m⁻²∙s⁻¹ of far-red radiation. The lighting treatments (with percentage from each LED in subscript) were MW₁₀₀, MW₇₅R₂₅, MW₄₅R₅₅, MW₂₅R₇₅, B₁₅R₈₅, and B₂₀G₄₀R₄₀. At the transplant stage, total leaf area, and fresh and dry weight were similar among treatments in all species. Surprisingly, when petunia seedlings were grown longer (beyond the transplant stage) under sole-source lighting treatments, the primary stem elongated and had flower buds earlier under MW₁₀₀ and MW₇₅R₂₅ compared to under B₁₅R₈₅. The color rendering index of MW₇₅R₂₅ and MW₄₅R₅₅ were 72, and 77, respectively, which was higher than those of other treatments, which were ≤64. While photosynthetic photon efficacy of B₁₅R₈₅ (2.25 µmol∙J^–1) was higher than the W light treatments (1.51-2.13 µmol∙J^–1), the dry weight gain per unit electric energy consumption (in g∙kWh^–1) of B₁₅R₈₅ was similar to those of MW₂₅R₇₅, MW₄₅R₅₅, and MW₇₅R₂₅ in three species. We conclude that compared to B+R radiation, W radiation had generally similar effects on seedling growth at the same PPFD with similar electric energy consumption, and improved the visual color quality of sole-source lighting.

用于植物生长的蓝色（B，400~500 nm）与红色（R，600~700 nm）发光二极管（light-emitting diodes，LED）阵列，相较于宽光谱白光（W），会增加植物视觉评估的难度。尽管园艺照明灯具中有时会采用白光LED，但以其作为单一光源照明的相关研究鲜有发表。
本研究于20 ℃环境下，培育了秋海棠（<i>Begonia</i> × <i>semperflorens</i>）、天竺葵（<i>Pelargonium</i> × <i>horturum</i>）、矮牵牛（<i>Petunia</i> × <i>hybrida</i>）以及金鱼草（<i>Antirrhinum majus</i>）的幼苗，设置6组单一光源LED光照处理，所有处理的光合光子通量密度（photosynthetic photon flux density，PPFD）均为160 µmol·m^–2·s^–1。所用LED包括峰值波长447 nm的蓝光（B）、峰值531 nm的绿光（G）、峰值660 nm的红光（R），以及薄荷型白光（MW，峰值558 nm）LED；其中薄荷型白光LED的光谱组成为15%蓝光、59%绿光、26%红光，外加6 µmol·m⁻²·s⁻¹的远红光辐射。
各光照处理以各LED占比标注脚标，分别为：MW₁₀₀、MW₇₅R₂₅、MW₄₅R₅₅、MW₂₅R₇₅、B₁₅R₈₅与B₂₀G₄₀R₄₀。
在移栽阶段，所有供试物种的总叶面积、鲜重与干重在各处理组间均无显著差异。令人意外的是，当矮牵牛幼苗在单一光源光照处理下继续培育（超出移栽阶段）时，相较于B₁₅R₈₅处理组，MW₁₀₀与MW₇₅R₂₅组的主茎更长，且更早现蕾。
MW₇₅R₂₅与MW₄₅R₅₅的显色指数（color rendering index）分别为72与77，高于其余各处理组（显色指数≤64）。
尽管B₁₅R₈₅的光合光子能效（2.25 µmol·J^–1）高于白光光照处理组（1.51~2.13 µmol·J^–1），但单位电能消耗对应的干重增益（单位：g·kWh^–1）方面，B₁₅R₈₅与MW₂₅R₇₅、MW₄₅R₅₅及MW₇₅R₂₅在三个供试物种中无显著差异。
本研究得出结论：相较于红蓝（B+R）辐射，白光辐射在相同光合光子通量密度与相近电能消耗条件下，对幼苗生长的整体影响相近，且可提升单一光源照明的视觉显色品质。