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representation of middle
                                                                            wavelengths (green, yellow)
                                                                            and red/far red light. This light
                                                                            appears yellowish in color.
                                                                            Metal halide (MH) fixtures
                                                                            also provide full-spectrum
                                                                            light, but with more blue and
                                                                            less red and far red than
                                                                            HPS. This heavier percentage
                                                                            of blue light tends to reduce
                                                                            stem elongation and impacts
                                                                            production of secondary            Infinity light bar from Transcend
                                                                            compounds (e.g., improved          Lighting

                                                                            anthocyanin production for
                                                                            leaf color). Light from MH fixtures does appear bluer in color.
                                                                            Light-emitting diode (LED) fixtures can provide true white light, full-
                                                                            spectrum light or very narrow-spectrum light, depending on the
                                                                            diodes used. Recipe-specific standard options typically include
                                                                            white, blue, red and far red light in varied proportions. Some LEDs
                                                                            are easily recognized by their pinkish light, but remember that the
                                                                            human-perceived color can differ greatly depending on diode use.

Grow Better                                                                 Light intensity is the energy, or strength, of light. Our industry
CEA Crops                                                                   describes light intensity in several ways, which can lead to
with Smart                                                                  some confusion. First, the standard unit of measurement for
Lighting Choices                                                            light energy (intensity) is the micromole (µmol). Next, some
                                                                            descriptors of intensity refer to light generated by the fixture, while
                            By Tami Van Gaal,                               other descriptors refer to the intensity of light striking a surface.
                            CEA Division Leader                             Photosynthetic photon flux (PPF), measured as µmol/s (s=second),
                            Lighting plays an important role for both       describes an instantaneous measure of light intensity produced by
                            ornamental growers and Controlled               a fixture. However, fixtures vary greatly in how this light is directed.
                            Environment Agriculture (CEA) growers. For      Some fixtures have a more focused dispersal pattern and some
                            ornamental crops, photoperiodic lighting        have a wider dispersal pattern. The photosynthetic photon flux
                            controls flowering, while supplemental          density (PPFD) considers both fixture output and dispersal. PPFD
                            lighting increases light intensity to reduce    describes light intensity delivered to a surface and is measured
                            crop time and improve crop quality. For         as µmol/m2/s (micromoles of light hitting a square meter in one
                            CEA growers, lighting is critical to achieving  second). PPFD is also an instantaneous measure of light intensity.
consistent yield and product quality for year-round production.             Remember that the PPFD reported for a fixture is specific to the
While some lighting products bring flexibility for use in several           distance at which the measurement is taken.
different CEA applications, the best solution will be tailored to
the production scenario. This article describes some common                 Instantaneous intensity measures like PPF and PPFD help us to
production scenarios and top choices for these situations. Before           compare fixtures, but when we reference crop needs, we need to
we get to specifics, it’s important to understand some basic terms          consider the cumulative light delivered to the crop over the entire
and concepts.                                                               light period. Enter the daily light integral (DLI). DLI is measured as
Light quality refers to the color, or wavelength, of light. Wavelength      mol/m2/day (1 mol = 1,000,000 µmol). Fixtures with different PPFD
is described in nanometers (nm). All horticultural fixtures focus on        can be used to achieve the same DLI by adjusting the distance
photosynthetically active radiation (PAR), or light in the 400-700          from the crop and the duration of fixture operation.
nm range. Light quality varies with fixture type. High-pressure
sodium (HPS) fixtures provide full-spectrum light, with heavier             Growers should also consider efficiency in fixture operation: How
                                                                            much light does a fixture create for each unit of energy consumed?
                                                                            In this case, the unit of energy most often used for comparison
                                                                            is the joule, with the efficiency rating reported as µmol/J (if you
                                                                            think in terms of power, i.e. watts, 1 W = 1 J/s). Remember that

                                                                            HortiLED lighting from P.L. Light Systems

16 Griffin Gazette winter 2017
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