Overview of Spectrum Effects on Cannabis Production
Professor DeBacco



Summary
This provides a quick visual and textual summary of the major classifications of spectrums

In addition the main impact on a plant is also provided.
McCree Curve developed in the Late 1960’s – early 1970’s was attempt to understand how plants use light
Interpret with caution as this study was done with multiple points in time data points that was then put into the curve graph
Plants can adjust to their environments, and plants will make the most of the light available to them, which may result in changes in morphology


UV Light (100-400nm) Basics
UV radiation spectrum is divided into three regions called UVA, UVB and UVC.
As sunlight passes through the atmosphere, all UVC and most UVB is absorbed by ozone, water vapor, oxygen and carbon dioxide.
UVA is not filtered as significantly by the atmosphere.
The UV region covers the wavelength range 100-400 nm and is divided into three bands:
UVA (315-400 nm)
UVB (280-315 nm)

UVC (100-280 nm)


The relatively long-wavelength UVA accounts for approximately 95 per cent of the UV radiation reaching the Earth's surface.
With increasing altitude less atmosphere is available to absorb UV radiation. With every 1000 m in altitude, UV levels increase by approximately 10 per cent.


UV Light and Plants Response
UV light responses in plants is similar to blue light
UV light does drive photosynthesis and can also trigger cannabinoid synthesis and potentially reduce disease
UV light does cause some stress to the plants so they may develop thicker leaves and/or protective compounds (ex. Pigmentation such as anthocyanins)

New Look at Old Data
Dr. Bugbee’s lab at Utah State University investigated physicist Keith McCree’s data from the 1970’s in relative photosynthetic efficiency.
Looking at the data the error bars represent the range of plant species from the paper showing small variations among species when grown in the field.
The growth chamber grown plants indicate larger variability.
Is it possible that the field grown plants synthesized compounds to block UV for protection light reducing the effectiveness of those wave lengths?



Blue Photons (430-450nm) and Plant Response
Blue photons reduces cell expansion
Blue photons as a result keep plants shorter and reduce leaf expansion
Notice the morphology difference from growing a cannabis plant under 5% blue vs 20% blue light…



Green Light (500-600nm) Related to Plants
While plants are green indicating there are green wavelengths reflected by the plants this does not mean these are wasted wavelengths.
Green wavelengths of light penetrate deep in the leaf and are absorbed by certain plant pigments which are of benefit to the plant.
Chlorophyll may have reduced absorbance of green wavelengths but this is not the only plant pigment.

Green Photons and Plant Diagnosis
Green photons, as part of white light allows growers to see the plants and better diagnose potential problems

Red Photons (640-700nm) and Plant Response
Red LED’s are among the most efficient at converting electricity into photosynthetic photons and are relatively inexpensive.
Chlorophyll strongly absorbs red light, thus it is effective at photosynthesis.
Many plants grown under only red light (no blue) will have…
A stretched/tall appearance
Thin large leaves large
Far-red (700-800nm) Basics
Far-red light is a range of light at the extreme red end of the visible spectrum, just before infra-red light.
Usually regarded as the region between 700 and 800 nm wavelength, it is dimly visible to human eyes.



Far-Red Light and Plant Response
Far Red is a critical spectrum for plants as it is utilized in the photosynthetic process and can cause an impact on a plants shape
Far-Red is also perceived by the plant photoreceptor phytochrome which is important for light detection (and timing flowing in some plants).

Light Penetration Into Leaf
Notice the difference across the different colors…



Blue vs Far red
Far Red will enhance cell expansion which is essentially the opposite of blue photons
Plants grown indoors with 80 to 90 percent red light and 10 to 20 percent blue light are quite compact, with smaller leaves and shorter stems.
White vs +10% far red
Very important with lettuce with other plants it will cause plants to grow very tall

Summary of Colored Photon Effects


Special Thanks To…
Combination of research data from…
Dr. Bruce Bugbee of Utah State University and Founder of Apogee Instruments Inc.
Shane Torpey MICRO founder

Professor Erik Runkle of Michigan State University




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