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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
