Light spectrum influence on plant growth

Light spectrum influence on plant growth

From the report «We are all somewhere on a Spectrum – Urban Ag News», of Janet Colston PhD, published in Yesafricabiz.

The light exerts a powerful influence on plant growth. These effects can range anywhere from seed germination to leaf expansion and from flowering to fruiting.

Deeper in the chloroplast a wide range of photoreceptors exist, including phytochromes, cryptochromes, phototropins and ultraviolet-B receptors help plants discriminate light signals from ultraviolet to visible to far red wavelengths. Essentially the plant has a control mechanism that distinguishes wavelengths through these photoreceptors and a metabolic switch to biological reactions.


In general plants exposed to blue light encourage vegetative leaf growth, stem elongation and rooting whereas red light, when combined with blue, switches on genes for plants to flower and fruit. This is not surprising when experiments show an increase in chlorophyll content in the PAR range of the spectrum. Green wavelengths reflect most light (hence why we see them as green) but this specific wavelength is known to be responsible for deeper canopy penetration and absorption balance of excess energy in some plants. The latter is an important physiological step, often overlooked as not all energy is used in photosynthesis (remember it’s rate limiting) and excess energy must be dissipated safely as heat.