Sure, by now we are all aware that LED grow light does wonderful things for plant growth. Plants grow quicker and healthier than under other, traditional lighting methods such as HPS. If the LEDs are good, plants can grow even better than under natural sunlight. But why are they always purple/pink?
All light sources contain a spectrum of colors within it – some light sources contain some of the colors, some contain all. Sunlight contains all spectrum colors and because of that feeds plants with all information they need. Additionally, because of the presence of all spectrum colors, it appears color-free to human eyes.
When constructing an LED lamp, we can decide which color LED chips to place inside. This depends on what kind of response we want to achieve from plants. For instance, if we want plants to grow tall, we will increase the amount of far-red, yellow, orange and green chips inside the luminaire. If we want plants to be compact, we will put more blue or UV colored chips.
Why plants respond in those ways to those particular colors is a broad topic. It is something that we will cover in a separate post. Either way, these responses are encoded in plants’ DNA. So, when designing LED lamps, we can count on plants responding the way nature has designed them to.
We could say that the two most important light colors to place in an LED lamp are: red and blue. Red is the main component that plants need for photosynthesis and stem elongation inhibition. Additionally, it signals to the plants that there are no other plants above it and that it can thus have uninhibited development. Blue stimulates stomatal opening, stem elongation inhibition, leaf expansion, curvature towards light and photoperiodic flowering.
The combination of these two sets of effects will, in simple terms, get the plant from seed to the vegetative stage and eventually to flowering. This however will be much slower than under continuous spectra a.k.a spectra that contain more than just red and blue.
Adding some other spectrum colors such as green, could enhance the leaf expansion rate and stem elongation, which in turn results in higher biomass (yield) accumulation. By adding UV wavelenghts one can affect the accumulation of compounds such as phenolics which could boost the flavor of the end product or its health benefits to humans.
