Page 14 - Griffin Gazette Fall 2015

Bonus

Digital Content

Lighting

Young Plants

By Tami Van Gaal, GGSPro Technical Specialist

What is light quality and why is it important? level and reporting the reading as micro-moles of light per unit area
Light quality refers to the wavelength of light. In the visible spectrum per unit time, generally reported as umol/m2/s. A PAR reading would
(the range of wavelengths we can see), different wavelengths of light tell a grower if there was adequate light to manipulate photoperiod,
are different colors. This spectrum ranges from red at 700 nm to but would not necessarily tell a grower if there was adequate light
violet at 400 nm. Plants use light in this same general range, with over the course of a day to support plant growth.
different wavelengths impacting growth in different ways. Light in
the violet/blue and orange/red wavelengths are more important for What is DLI?
photosynthesis. Plants reflect most green light (approximately 510 When we want to understand the total light reaching a crop over the
nm), which is why we perceive the leaves to be green in color. Red course of a day, we turn to the daily light integral (DLI). DLI measures
and far-red light impact plant recognition of photoperiod and seed accumulated light over the course of a day and is reported as mol/
germination. Higher ratios of blue light can result in shorter plants. m2/d. DLI is best measured at crop level with a meter intended for this
Likewise, high amounts of far-red light will increase cell elongation, purpose, though some extrapolation could be made using existing
which is why we avoid shading crops with hanging baskets. greenhouse monitoring equipment.

What is PAR? Ambient DLI varies widely across the country throughout the year.
Photosynthetically active radiation (PAR) includes light with Jim Faust at Clemson University led work to create national DLI
wavelengths between 400 and 700 nm, which is the range of light maps, which can help growers understand the ambient DLI before
used by plants. Measurements of PAR indicate instantaneous light entering the greenhouse. Remember that greenhouse coverings
intensity in this specific range, essentially answering the question, and structures will reduce the light entering the greenhouse, so
"How much usable light is hitting the crop at this second in time?” the Outdoor DLI Maps on the next page should not be used as an
The most correct way to measure PAR is by using a meter at crop indicator of bench level DLI.

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Lighting Products from Griffin – 3
Germination Chambers
Lighting Products from Griffin –
LEDs are an option for germination chambers, Photoperiod Control
including the HortiLED from
P.L. Light Systems. (Image 1) Choose a Beamflicker product from Parsource for efficient, effective
photoperiod lighting of a large area. (Image 2 & 3)
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