Grow lights are a major investment for growers. For new entrants, it is a key investment they will make in creating quality products and satisfactory yields.
Current market dynamics in the medical and recreational cannabis industry are placing ever increasing pressure on growers. The push is on and will continue for growers to consistently deliver the most marketable and high-quality products possible — and push their plants harder than they ever have before for maximum yields.
With literally hundreds of lights currently on the DesignLights Consortium (DLC) horticulture qualified products list (QPL) and all the marketing hyperbole surrounding LED lighting, how can growers decide? We strongly suggest you follow the science on DLC and not marketing claims from Chinese manufacturers and their U.S. import partners.
Follow The Science of The Plant Based on Published Research
It is easy for growers today to follow leading scientists on plant morphology to decide on lighting features and functions. We use YouTube as a main source as learning from audio and visual is much better for us. We follow leading plant and light scientists including Dr. Bruce Bugbee of Utah State University and Dr. Erik Runkle of Michigan State University. We strongly suggest you follow them as well!
The science for Neocision® LED grow lights is based on studies on the cannabis plant. Different types of plants will react differently to both intensity and spectrum. In the study of cannabis, it is important to know that cannabis is a short-day plant.
A plant that requires a long period of darkness is termed a “short-day” (long-night) plant. Short-day plants form flowers only when day length is less than 12 hours. Many spring and fall-flowering plants are short-day plants, including chrysanthemums, poinsettias, and Christmas cactus – just like cannabis. If these plants are exposed to more than 12 hours of light per day, bloom formation does not occur.
Other plants require only a short-night to flower. These are termed “long-day” plants. These bloom only when they receive more than 12 hours of light. Many of our summer-blooming flowers and garden vegetables are long-day plants, such as asters, coneflowers, California poppies, lettuce, spinach, and potatoes. These all bloom when the days are long, during our summers.
Cannabis And Nine Cardinal Parameters
The environment can be divided into the nine cardinal parameters: CO2, temperature, humidity, light, wind, oxygen in the roots system, nutrients, water, and root-zone temperature. If only one is neglected, it can have a huge impact on plant health.
If there is one question that cannabis growers lose sleep over for lighting, it is — are my plants getting enough light? Rarely will a grower question – are my plants getting the right spectrum mix of blue, green, and red?
Years of science and growing cannabis in different environments have demonstrated it is full spectrum photons received (like the light from the sun) that drives photosynthesis, plant morphology and yields when the nine cardinal parameters are coordinated for optimal growth.
Increasing photosynthetic photons demands increases in watering rates. More water will increase demand on dehumidification systems as the plant transpires the added water into your cultivation rooms. To offset this increase in relative humidity (RH), you will also need to adjust your temperatures for a balanced vapor-pressure deficit (VPD) that will maximize growth and yields.
Adding dehumidification requires an increase in cooling capacity. Dehumidifiers create heat which adds to your sensible loads which, in a cultivation environment, are primarily driven by the heat dissipated from your LED lights. Increasing light intensity alone has significant limits on the end results and may cause an unnecessary increase in operating costs.
It is important, at the planning stages of your grow facility, to weigh your increased capital acquisition costs and higher electric bills that added HVACD and lighting costs can create when calculating your return on investment (ROI).
What is DLI and Why is it Important for Cannabis Growers?
Daily light integral (DLI) describes the number of photosynthetically active photons (individual particles of light in the 400-700 nm range) that are delivered to a specific area over a 24-hour period. This variable is particularly useful to describe the light environment of plants. DLI is a unit of measurement of light. DLI is measured by plant scientists in moles of light per square meter per day or mol/m2 per day (moles per square meter per day).
Properly increasing your DLI is an effective way to increase yields. A higher DLI increases total photosynthesis and drives cannabis plants to produce big buds in the flowering stage.
Healthy mature cannabis plants can thrive indoors with 35-45 DLI. Outside, in the summer, 60 DLI is common on long summer days. That is incredible DLI and demonstrates that cannabis can accept and thrive under high light levels that are full spectrum. Here we rely on quality information from scientists on light intensity including this excellent video from Dr. Bruce Bugbee – Cannabis Grow Lighting Myths and FAQs with Dr. Bruce Bugbee.
If DLI is so important, why do lighting manufacturers always talk about photosynthetic photon flux density (PPFD) and what is it?
Understanding Key Measurements of LED Grow Lights
These terms are used in the measurements of LED grow lights:
- Photosynthetic Active Radiation (PAR) describes the wavelengths of light that sit within the visible range of 400-700 nm. It was originally defined by research undertaken by Dr Keith McCree in the early 1970s, and it is described as the type of light required for photosynthesis.
- Photosynthetic Photon Flux (PPF) measures the total amount of PAR that is produced by a lighting system each second. This measurement is taken using a specialized instrument called an integrating sphere that captures and measures all photons emitted by a lighting system.
- Photosynthetic Photon Flux Density (PPFD) is the amount of light that reaches your plants within the PAR region of 400 nm to 700 nm or the number of photosynthetically active photons that fall on a given surface each second. The PPFD is expressed in μmol/m²/second, or micromoles per square meter per second. In contrast, DLI is the amount of moles of light reaching the plant per square meter per day.
Once you know the average PPFD, you can calculate average DLI your plants are receiving.
DLI=PPFD∗LFD∗(3600/1,000,000)
- Where DLI is the daily light integral (mol/m2/day)
- PPFD is the photosynthetic photon flux density (μmol /m2/second)
- LFD is the light hours per day.
Quality lighting manufacturers will provide you with LED grow light layouts that calculate the average PPFD on your plant canopy, as well as minimums and maximums.
To obtain these calculations, you need to use specialized software to calculate PPFD at any given point in your canopy along with the average, minimum, maximum and uniformity of light delivered to your plant canopy at any distance between the bottom of the fixture and the top of your plants.
Lighting Analysts is the only software that has a horticultural mode specific for calculation of PPFD. Their specialized program, ElumTools, supports a separate and specific mode for horticultural lighting calculations. When the software is set in horticulture mode, grow lights (luminaires) can be assigned output in terms of PPF, or by PPF Factor (µmol/s/kilolumen) which can be computed from the spectral power distribution of the light source.
The manufacturer needs to provide a standardized data file which expresses the light output of a luminaire as luminous intensity versus angle along with sufficient descriptive and documentary test information. The term IES is derived from the acronym for the Illuminating Engineering Society of North America (IESNA). IES files are assigned the file extension “.ies“. IES files are used by lighting designers to model the illumination performance of a lighting scheme using commercial lighting design programs. An IES file is commonly referred to as “photometric data” for a luminaire.
Crop Yield Increases with Added Light Intensity
In studies conducted at the University of Mississippi, the scientists concluded:
“In view of our results, it is concluded that C. sativa can utilize a fairly high level of PPFD and temperature for its gas and water exchange processes, and can perform much better if grown at ~1500 μmol m-2 s-1 PPFD and around 25 to 30°C temperature conditions.”
Mitch Westmoreland, Ph.D. candidate and Research Associate at Utah State University’s Crop Physiology Lab, is studying the effects of added light intensity on cannabis yields.
In Westmoreland’s experience, he found many cannabis growers are happy to hit 700 to 1000 PPFD. This is enough light for growing quality cannabis; however, it is not close to maximizing yields. For perspective, peak outdoor light intensity on a midsummer day is around 2000 PPFD.
Texas Original Compassionate Cultivation (TOCC), estimates the average cannabis facility grows at 900 to 1000 PPFD during the flower stage. The TOCC studies show the best value was around that 1800 micromole level for cannabis. Yield increases started to diminish from 1800 to 2500. While yields continue to increase up to 2500 PPFD, it was more bell curve than linear beyond 1800 PPFD.
This increase in yield is measured in this chart from numerous studies performed by Fluence Science including the TOCC study:
Tests have not shown that there are any changes in the plant production of cannabinoids, terpenes, or other measurable secondary metabolite levels in percentage of the total yield from increased intensity.
There Is No Magic Spectrum Mix
Spectrum has a definite effect on photosynthesis and plant shape. For ideal shape to eliminate stretch and reduce height, Bruce Bugbee recommends 20% blue. His studies also show there is no statistically defined increase in cannabinoids once the blue percentage goes over 20%.
It is important to understand these key points:
- Blue Photons – Inhibit cell expansion. Good for controlling plant heigh, blue photos are highly photosynthetically active. Blue (450–485 nm) is the wavelength with the greatest effect on plant quality factors such as secondary metabolite expression. Blue light also can influence pigmentation and chemical content of shoots, leaves, and flowers including terpene production. Research is continuing to determine which terpenes are most influenced by blue light. Source: Cannabis Science Tech
- Green Photons – Facilitate human vision. Green is also photosynthetically active and will penetrate the canopy better. Source: Dr. Erik Runkle Michigan State University
- Red Photons – 15% more efficient photosynthesis than blue. You can grow and flower plants just with red photons. Source: Dr. Bruce Bugbee Optimal Spectrum
- Far-red Photons – enhance cell expansion with the highest leaf penetration. Excellent for leafy green plants like lettuce. Not good for short-day plants (such as cannabis) as it will create taller plants and weaken the plant. There MAY be value to add some far-red at the end of the cannabis plant cycle. There is no tested and proven formula done in proper, controlled study for the grower to use that defines how much far-red to use, when to start it, or how long it should be on each day. Source: Dr. Bruce Bugbee The New 400-750 nm ePAR Range
You can use the Design Lights Consortium (DLC) Horticulture Qualified Products List (QPL) for proper validation of all fixture outputs.
Our Conclusion
- The most important aspect for cultivators to focus on is maximizing the average PPFD they can afford to invest in. It must be a balance of all costs including additional costs for HVACD. HVACD costs increase as added wattage and/or light intensity will create the need for additional heat and humidity removal. A reasonable goal should be between 1200 PPFD for racks where height is limited and 1500 PPFD (exceeds full sunlight in summer) when there are no height restrictions.
- Focus on lighting that provides a full spectrum for flowering with high levels of blue and red for maximum photosynthesis while controlling plant shape. Blue maintains plant height, red is essential for flowering and maximizing yields. Blue also assists with terpene production.
- Spectrum tuning is not necessary and will add little to no value if it results in lower average PPFD. It is far easier and less costly to start with the highest PPFD you can obtain, and then simply dim a fixture that has a proper balanced spectrum if you wish lower intensities for starting and finishing your crop.
- We strongly recommend that you use fixtures for flowering with a minimum efficiency of 2.75 umols/j (umols per joule), this is also expressed as 2.75 PPE (Photosynthetic Photon Efficacy).
