We have to know that the spectrum shows the portion of different wavelength. If we only turn on far red the spectrum would look like this.
The FR is relatively weaker than the other so the shape becomes shorter and wider on a full reference graph.
The FR is relatively weaker than the other so the shape becomes shorter and wider on a full reference graph.
3 Likes
This may help illustrate the UVB. As you know the UVB is not visible so when turned on you can barely see the excitement glow on the surface chip but not see anything in the environment. 5 chips are UVB.
3 Likes
What is the μmol PPF output of the UVB LEDs you are using, and for how many hours per LM80 are these LEDs be able to deliver this output? In our experience the yield results as measured through potency and terpene testing will really depend on the PPF fraction in this spectrum delivered to the crop.
Our customers have been experimenting with very high levels of shortwave blue LED light (>350 μmol/m2/s 400-475nm out of an aggregate 900μmol/m2/s over 400-700nm), and we provide a 90%, 50K hour output guarantee on these LEDs. We can do this because blue LEDs are well developed and very cost effective. UVA LEDs on the other hand cost lighting manufacturers around $0.20 or more per μmol PPF, with UVB LEDs coming in at a far higher cost (and lower associated lifetime) than this.
Absent doing an integrating sphere measurement in the UVB range since your instrumentation does not go that low, what is the theoretical UVB PPF output of the three UVB emitters you are showing in the fixture above?
2 Likes
I am having the engineers put a report together on this for theoretical PPF of the UVB. The chips are 5W. But, I do not think a PPF value is truly a valid measure as the UVBs purpose in our case is not to effect Photosynthesis, but to purposefully cause damage at a cellular level to induce the natural defense mechanism of creating oils to protect the flower. We know that high mountain outdoor grown cannabis is more potent due to much higher UVA and UVB levels at high altitude, what we don’t fully understand; is this because of the photosynthetic process or the damage to the plant caused by UV?
In the comparisons we have tested of the flowers of the same genetics, same spectrum, nutrients, etc. The plants (flowers) we exposed to the UVB were visibly denser in mass and trichomes, darker in color and much more pungent in smell and flavor.
Does the short wave blue LED cause cellular damage or is it for photosynthetic value?
3 Likes
Hi Tim-
According to ASABE S640, UVA / UVB radiation can be expressed in radiant watts or photonic units (PPF, etc):
The ultraviolet radiant flux ( Φ uv) is measured or calculated without weighting factors across the wavelength interval of 280 nm to 400 nm. The unit of Φ uv is expressed in watts (Wr).
The ultraviolet photon flux ( Φ p,uv) is measured or calculated without weighting factors across the wavelength interval of 280 nm to 400 nm. The unit of Φ p,uv is micromoles per second (μmol × s-1).
If we are talking about UVA/UVB light in relation to pathogen mitigation and sanitation, most of the published papers are using mW/cm2. If we are thinking about the UVA/UVB spectrum in relation to the photon density on the canopy or the photon fraction of a light fixture, there are times where photonic units are useful.
We see similar differences in our treatment groups grown with a high blue light fraction; the key is keeping the PAR levels high (800μmol/m2/s+). We don’t believe 450nm is causing cellular damage. But we also see massive differences in potency, pigment development, and trichome development when we have groups cultivated under different vapor pressure deficit (VPD) levels. Spectrum manipulations are only scratching the surface when it comes to manipulating this crop.
3 Likes