Blue light is the portion of the visible light spectrum with wavelengths of approximately 400 to 500 nanometres (nm). It is strongly absorbed by chlorophyll and other plant pigments, making it an important driver of photosynthesis. Blue light also provides key signals that regulate plant development through photoreceptors such as cryptochromes and phototropins.
Plants use blue light to control processes including stomatal opening, phototropism (growth toward light), leaf expansion, chloroplast movement, and stem elongation. Adequate blue light generally produces more compact growth with shorter internodes and thicker leaves, while very low proportions of blue light can contribute to elongated, stretched growth. Because blue light is only one part of the spectrum, plant performance depends on the overall light spectrum, PPFD, and Daily Light Integral (DLI), not blue light alone.
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