There are a few different factors to consider when choosing what spectrum you will need; the species of plant, the growing environment and the desired qualities of the plant all affect lighting requirements. This guide looks at the spectra developed by GN and focuses on how plants utilise different wavelengths of light, dispelling some myths about spectrum. For the purpose of this guide we will refer to blue light as wavelengths in the 400-500nm range, green light as 500-600nm, red light as 600-700nm and far red light as 700-740nm.
At GN we have developed two spectra for our grow lights: one for indoor growing and one for growing in greenhouses. Both are full spectrum meaning they emit all wavelengths of light in the 400-700nm PAR range. The indoor spectrum has been carefully balanced to drive photosynthesis while ensuring other pigments are not compromised. The greenhouse spectrum has been designed with more blue light than the indoor spectrum to off-set plant stretching which ofen occurs in greenhouses due to high levels of far red light. If you are interested in purchasing a light with our greenhouse spectrum, please contact us
Many companies focus their spectrum on delivering the optimal light for photosynthesis. Traditionally this meant using light soley from the blue and red part of the spectrum as studies showed that these are the wavelengths most absorbed by chlorophyll A and B and therefore are drivers of photosynthesis. But chlorophyll A and B absorbtion is not the only factor in photosynthesis
You may hear it a lot that green light is reflected by plants, giving them their green colour, therefore plants do not use green light and it is wasteful to include green light in your spectrum. This is not the case.
A paper published in the 70s by K. J. McCree shows us that green light is not only used by plants for photosynthesis but it is almost as effective as blue light in some plant species. The McCree Curve shows the relative effectiveness of individual wavelengths on photosynthesis. It is thought that this use of green light is down to pigments such as carotenoids that absorb green light and transfer the engery to chlorophyll for photosynthesis.
Many lighting companies misuse the McCree curve viewing it as a blueprint for ideal spectral power distribution. This is not correct for a few reasons. The McCree curve was produced from experiments using individual wavelengths of light to measure photosynthetic response and doesn't indicate the response to a full spectrum of light. Also, these experiments were conducted using small leaf samples of 22 food crop plant species and therefore do not reflect the response of a whole plant or of all plant species. Finally the curve represents photons that have been absorbed, not photons emitted from a light source.
While little is known about the potential role green light plays in photomorphogenesis there are other benefits to having green light in your spectrum. Studies show that green light is efficient at penetrating through canopies, increasing photosynthesis beneath the canopy and increasing yields. Adding green light to grow light spectra will also increase the colour rendering index of the light, providing a more natural white light which will make it easier to inspect crops.
Photomorphogenesis is plant development that is triggered by light, such as seed germination, seedling development and flowering in photoperiod crops. This development is triggered photoreceptors in the plant that respond to absorbing certain wavelengths of light. Typically plants contain phytochromes, which are photoreceptors that respond to red and far red light, and cryptochromes that respond to blue light.
Red and far red light trigger many developmental processes in plants. Phytochromes are responsible for processes such as flowering in short and long day plants, stem elongation in response to shade and the production of flavinoids such as anthocyanin (blue-purple plant pigment). There are two forms of phytochromes; red light absorbing, Pr and far red light absorbing, Pfr. Pr converts into Pfr after absorbing red light and Pfr converts into Pr after absorbing far red light. Red light is generally available to plants during the daytime, and far red light available in the shade and during the night, therefore plants use Pfr and Pr levels to determine when there are changes in the length of daylight and when they are in the shade.
Blue light is responsible for similar processes to red and far red light. One of the differences is that cryptochromes (which absorb blue light) can inhibit stem elongation. This means that adding more blue light to a spectrum could be ideal for those looking to offset the stretch that can be caused by far red light (shade response). This often occurs in greenhouses where there is an abundance of far red light. Blue light is also the trigger for phototropism where plants move and grow towards the light.