Light Spectrum and Photoperiod

Marijuana needs light to grow. The light must have the proper spectrum and intensity to ensure rapid growth. Light is comprised of separate bands of colors. Each color in the spectrum sends the plant a separate signal. Each color In the spectrum promotes a different type of growth.

PAR and Light Spectrum

Plants need and use only certain portions of the light spectrum. The most important colors in the spectrum for maximum chlorophyll production and photosynthetic response are in the blue and red range. The main portion of light used by plants is between 400 and 700 nanometers (nm).* This region is called the Photosynthetically Active Radiation (PAR) zone**

"PAR watts" is the measure of the actual amount of specific photons a plant needs to grow. Photons are a measure of light energy. Light energy is radiated and assimilated in photons. Photosynthesis is necessary for plants to grow and is activated by the assimilation of photons. Blue photons are worth more PAR walls than red photons, but scientists have difficulty measuring the exact difference.

Each color of light activates different plant functions. Positive tropism, the plant's ability to orient leaves toward light, is controlled by spec-

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The single humped line in the center of the graph represents the visible light spectrum humans see. The dual humped line represents the spectrum cannabis needs to grow.

Kelvin Scale

Spectrum of A, Photosynthetic response, B. Light spectrum humans use to see,C.Chlorophyll synthesis

This cjraplt shows the exact level at which A. Phototropic response, B. Photosynthetic response, and C. Chlorophyll synthesis take place, trum. Light bulbs deliver only a part oí the necessary light marijuana needs to grow. However, they deliver enough! Most of marijuana's light needs can be met by artificial means.

""One nanometer (ran) — one billionth (10-<!) of a meter. Light is measured in wavelengths; the wavelengths are measured in nanometers.

**5ome scientists still disagree as to the exact PAR zone and make their calculations based on 350 to 750 nanometers. PAR watts measured with this scale will be a little higher.

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