Demystifying Light Spectrum for Cannabis Growing

We use science to study cannabis growing and we're passionate about helping  growers to maximize yield and potency while reducing their energy costs. We have fun doing it too. 

We’ve spent years in partnership with hundreds of cannabis growers, studying how marijuana plants grow and flourish under different lighting conditions. Many growers expressed their lack of confidence in alternative light spectrum and in particular LED. They felt more comfortable with the tried-and-true light spectrum from high pressure sodium and ceramic metal halide lamps.

At the same time, outdoor cultivators strongly believe the sun is the best source of light for marijuana growing.

We wanted to make sure we understood how cannabis grows under both artificial indoor grow-lighting and also the sun.

Then we focused our attention on traditional technology such as HPS, CMH, and fluorescent lamps. We compared top brands such as Gavita and Nanolux against each other, and against various brands of LED lamps, in flower.  We also compared a broad range of fluorescent tubes used in clone and veg.

Using photo spectrometers to collect hundreds of spectral readings, we grouped the lamps that work well in cannabis together, and separated the ones that didn’t. 

The results? We found what has been proven to be the correct spectrums for  cannabis growing. As all growers know, cannabis plants prefer different light spectrums as they transition from clone to veg to flower. We identified which spectral mixes worked for each phase and engineered that in to the line of FGI LED lamps.

Our lamps include the spectrum grower like from HPS lamps like Gavita or Nanolux for flowering. For plants in the later veg phase we included spectrum from CMH lamps made by Gavita and others. In early veg and clone phases we include the spectrum found in florescent lighting. But in all cases we added light spectrum found in outdoor growing under the sun, because we believe it is true that our sun is the ultimate grow lamp.

Below are side-by-side spectral charts showing how each of these lighting types perform in terms of output of photosynthetic light, or PAR (photosynthetic active radiation is a measurement of the total amount of photosynthetic light each lamp produces, measured in µ/m²/s).

Figure A below represents total PAR from the sun. The white line on the graph indicates the McCree Action Curve which demonstrates which wavelengths of light plants use to make photosynthesis and grow.

Figure A; The sun and McCree Action Curve

Figures B below represent the PAR output of a Gavita double-ended HPS lamp as compared to the PAR output of the FGI Lightpanel 500 and 700. The white line indicates the McCree Action curve and shows how close each light is to replicating necessary light distribution of the sun.

Figure B; Gavita DE HPS lamp versus FGI LED Lightpanel 500/700 flower lamps

Figure C, below, represents the PAR output of a Gavita CMH lamp as compared to the PAR output of the  FGI Lightpanel 500 and 700. The white line indicates the McCree Action curve and shows how close each light is to replicating necessary light distribution of the sun.

Figure C; Gavita CMH  lamp versus FGI LED Lightpanel 500/700 veg mode  lamps

Figures D, below, represents the PAR output of a typical T5HO fluorescent lamp as compared to the PAR output of the FGI Lightbar 100 and 185. The white line indicates the McCree Action curve and shows how close each light is to replicating necessary light distribution of the sun.

Figure D; Fluorescent T5HO lamp versus FGI LED Lightbar 100 / 185 veg lamps

In comparison to the sun, the FGI lamps have more preferred PAR output than HPS, CMH, or T5HO fluorescent lamps. The proof is in how the plants have responded. Healthier clone starts which receive the preferred blue light from the sun but also green, yellow, and red which are lacking in T5HO fixtures. Robust veg and  mother plants which receive the full range of light spectrum of our sun, which is lacking in CMH lamps. And most important, big healthy flowers which tipping  the scales increased dry weights than those produced under the more narrow HPS spectrum.


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