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

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 ( Begonia × semperflorens ) , geranium ( Pelargonium × horturum ), petunia ( Petunia × hybrida ), and snapdragon ( Antirrhinum majus ) 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 MW 100 , MW 75 R 25 , MW 45 R 55 , MW 25 R 75 , B 15 R 85 , and B 20 G 40 R 40 . 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 MW 100 and MW 75 R 25 compared to under B 15 R 85 .