Page 19 - Griffin Gazette Issue 2 - 2021

Sole-source applications should employ broad- CANNABIS & HEMP
spectrum lights, such as high-pressure sodium (HPS) 2
or LEDs that incorporate white diodes. These will be PPFD: 300-400 µmol/m /s
range for young plant; 800-1200
your only source of light, so knowing the full lighting µmol/m /s range for production
2
requirements of the crop is a must as well. Nighttime
interruption or daylength extension lights require lower DLI: 27 mol+
intensities to achieve desired effects – the light fixtures Photoperiod: Short-day crop.
required for this can be smaller and lower-powered. Vegetative growth occurs
under long photoperiods (16-18
Second, decide what type of spectrum needs to be hours), with flowering occurring
provided. As previously mentioned, broad spectrum light under short days (12 hour)
is best for sole source. This means choosing a light that Special Considerations?
provides photons across the photosynthetically active The upper limit for cannabis
radiation (PAR) range. While typically considered less light tolerance has not truly
electrically efficient, providing a broad spectrum ensures been ascertained. The rule of
that no unexpected or undesirable growth effects occur 1% light increase leading to 1%
due to light color. Single-color or two-color LEDs, yield increase seems to hold
typically red and blue, are best used as supplemental true to at least 35 mols when
lights where sunlight is the main light source. Boosting environmental conditions are
levels of single colors can affect qualities such as plant properly controlled.
height and leaf expansion. Day length extension and
nighttime interruption often employ red or far-red light in
newer LEDs, HPS, or incandescent bulbs. Using a broad
spectrum or single-color fixture meant for supplemental STRAWBERRIES
or sole-source lighting provides light in excess of what is PPFD: 400-600 µmol/m /s
2
required for photoperiodic lighting. range
Third, make sure your chosen fixtures can supply the DLI: 12 mol minimum; 20-25
amount of light needed for your specific application. mols/day ideal
As mentioned, photoperiodic lighting calls for low light Photoperiod: Variable
intensity. Sole-source lighting needs require all light to Special Considerations?
come from artificial sources; these would be high light Strawberry varieties come in
intensity needs, depending on the crop. Supplemental June-bearing (short-day) and
lighting needs are often somewhere in between, and Ever-bearing (day-neutral)
depend on seasonality and geographic location, along varieties. Be aware of the
with crop requirements. photoperiodic requirements of
the variety you have chosen.
Finally, many fixtures provide added features such as
dimmability or spectrum control. These extra features
can offer flexibility in specific applications but are not
required for successful lighting. Additionally, reputable
lighting manufacturers will provide well-known
certifications for their products. Some examples of TOMATOES
these certifications are UL Listed, RoHS Compliant, ETL PPFD:400-600 µmol/m /s
2
Listed, DLC Listed, and FCC Listed. These certifications range
ensure that products are well tested, safe to use, and DLI: 20 mol minimum; 25-30
certified by various non-profit organizations. mols/day ideal
Not all lights are created equal. Some perform best in Photoperiod: 14 hours
sole-source (no sunlight) situations, where others excel as Special Considerations?
supplemental lights in greenhouses. Our understanding Tomatoes do not have a
of the effects light has on plants is also constantly photoperiodic flowering
evolving. In the fast-moving field of horticultural lighting, response; they begin flowering
understanding these important terms will help growers when temperatures, light
make sense of equipment specifications, and choose levels, nutrition, and age are
products appropriate for their facilities. appropriate.

GRIFFIN GAZETTE 2021 | 19