THE SCIENCE

The research team behind the Photon LED™ firmly believe that to create the best possible LED grow light fixture, two key factors need to be addressed - quality of spectrum and intensity.

Photon LED’s FullPhotoSpec™ Spectrum

Photon FullPhotoSpec Spectrum Chart

Figure. A

Photon LED’s FullPhotoSpec™ light spectrum(fig. A) is the result of multiple years of research into optimum light spectrums for plant growth. The result of this extensive research has led us to develop a full spectrum light with a spectrum which closely mimics the McCree Curve.

Designed in the 1970s by Dr McCree, The McCree curve outlines the plant’s average response to different wavelengths and each wavelength’s importance to plant growth. Photosynthesis was found to largely occur between wavelengths of 400nm (deep blue) to 700nm (far red), which is commonly known as the photosynthetically active radiation (PAR). Therefore, it is widely accepted that a grow light emitting a spectrum closest to the McCree curve will show a higher rate of photosynthesis than one that does not; this translates to a larger, faster growing plant and an increase in yield.

PHOTON LED™ LIGHT INTENSITY

Photo LED 7 way v1 and v2 PPFD readings

PPF (Photosynthetic photon flux) is a measurement of the number of Photons in the 400-700nm PAR range emitted from a light source. In other words, light intensity. Photon LED™ modules have been designed to output maximum light intensity to drive higher levels of photosynthesis. Each Photon LED™ module contains 144 individual 1W LEDs which collectively drive a whopping PPF of 125 umol/s or 2.02 umol/J. 

PPFD (Photosynthetic photon flux density) is the number of photons that land on a given surface area from a stated height. When comparing PPFD values  of different lights, it's  essential  to  look  at 

Figure. B 

multiple measurements of each light rather than just one. Manufacturers can easily create lights which band together LED chips producing huge PPFD figures, you’ll notice however that these lights soon have diminishing PPFD values when measurements are taken outside of this small centralised footprint. PAR intensity maps (fig. B) allow us to compare PPFD values over a footprint of 1.2m2 , we have provided these charts for each of our Photon configurations in our technical specification sheets (which can be found on the 'which photon?' page) to allow you to make an educated decision when acquiring your new grow light.

GREEN LIGHT MYTH

There has been a longstanding assumption that because Chlorophyll pigments are the main light absorbing component in plants, a grow light that follows this absorption trend will be the best light.

In reality any grow light that omits other wavelengths (such as green and yellow) tend to fall behind in side by side growth comparisons with full spectrum lights. Figure C is a graph showing the absorption rates of Chlorophylls a & b, as well as Carotenoids; you can clearly see distinct peaks around 450nm and 640nm (relating to the blue and red spectrum respectively). A study in 2016 by T. Ouzounis(1) showed that for multiple plant species the combination of both blue and red causes greater growth and yield than if a plant was solely given red or blue light. This gives weight to the idea that a solely red-blue grow light is best for plant growth, however we believe that by adhering to just the spectral peaks of Chlorophyll a & b essential plant functions are being irrationally dismissed.

 

Figure C.

Various studies in the past have shown that the addition of supplemental green light to a red-blue spectrum enhances photosynthetic activity and increases plant growth. NASA conducted a study in 2006(2) which showed that the supplemental addition of just 24% green light to red and blue LED's greatly increased yield. A later study(6) also concluded that green light penetrated deeper into leaf tissue, and further drives photosynthetic activity when in the presence of a strong white light; highlighting the fact a full spectrum light drives photosynthesis more efficiently than heavy red-blue spectrum's, (2)(5)(6)(7).

In addition, the majority of red/blue wavelengths are absorbed by the upper reaches of the plant. Conversely  green and far red wavelengths penetrate to the lower parts of the plant; signalling to the plant that these regions are being shaded, inducing rapid growth for the lower regions to catch up. This leads to a fuller, more even canopy which in turn creates better light spread across, the now larger, surface area. To summarise, without a full spectrum light, this isn't possible and only the tops would continue to grow, further cause for a decrease in potential yield.

To summarise, 95% of green light is actually absorbed or diffused by the plants. Therefore, here at Photon LED™ we firmly believe that full spectrum grow lights inclusive of all light within the PAR range are the future of horticultural lighting systems.

For a list of references please click here.

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Photon LED 7 Way Module PPFD Chart