How Much Daily Light Integral (DLI) Does Cannabis Require?

by Morgan

March 22, 2021

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Numerous factors determine how well your indoor harvest will be, the same as in other plants. One of the most important points growers need to consider is the daily light integral (DLI).

And with this tell-all post, you’ll max out the lighting for a better harvest.

What Daily Light Integral Does Cannabis Require?

Marijuana usually requires a daily light integral of around 40 to 51 units to grow as expected. Other factors determine how much light levels cannabis can tolerate. Some reports show marijuana could tolerate much higher daily light integral.

For the daily light integral to have desired effects on plants, several elements are involved. Chief among these elements are light intensity, lighting source, hours of light, and lumen spread.

What is DLI?

Daily light integral (DLI) refers to a value that describes the photosynthetically active radiation (PAR) over a space every day. In simpler terms, the daily light integral is a description of how much light your plant has access to each day.

How to Measure DLI

Accurate DLI measurement will be incomplete without mentioning two terms – micromole (μmol) and photosynthetic photon flux density (PPFD).

So, we’ll be looking at these terms sequentially:

μmol: is the measurement unit for PPFD. The unit measures readings over a sq. meter each second.

PPFD: refers to the light intensity your plants receive. It is measured in micromoles/sq. meter /second. The PPFD parameters are usually much stronger when measured close to your grow light.

PPFD values will drop with an increased distance from your LED grow light. PPFD values usually drop as light naturally loses its strength from source to transmission end path. Grow intensity charts usually show how much PPFD you should expect your plants to get.

For example, let’s say you have your grow light set at a specified height (usually 30”) in your grow tent. Let’s also assume that the PPFD is 750µmols/m2/sec. You’ll refer to this value as “750 micromoles per square meter per second”.

DLI: is the PPFD throughout the day. It is measured in moles/sq. meter/day, or mol/m2/day.

DLI outdoors usually ranges from 4 – 60+ mol/m2/day. Greenhouse DLI values rarely top 25mols/m2/day.

Disparities between both DLI indices stem from several obstructions present in greenhouses. If you’re targeting improved illumination for your plant, supplemental lighting usually works best, especially in poorly lit environments.

Why is it Important to Measure DLI Required for Vegetable Cultivation?

An optimal yield is what cannabis growers desire, particularly newbies to indoor marijuana soil planting. At every level of crop planting through to flowering and seeding, every factor plays a major role.

With the right lighting, several canna strains can easily flower in less than specified lighting times. And with the extra illumination, these crops could surpass expectations. Budding, vegetation, and other stages get direct boosts from proper lighting.

Measuring how much light your crops need to grow makes it a lot easier to streamline your grow effort. Since you have an idea of what’s needed for better lighting, getting a bigger ROI becomes easier.

Levels of DLI Needed by Marijuana Through Different Stages of Cultivation

Cannabis requires a growing spectrum of light throughout its cultivation stages. And cultivators need to apply a different level of lighting throughout the cropping period. To assure optimal yield, monitoring DLI levels is important in three phases of the cycle – infancy, vegetation, and flowering.

First three weeks:

The marijuana crop’s first stage is also its most important. Cultivators should ensure their first-stage canna plants get DLI from 13 – 19 units each day. That’s at a rate of 200 – 300 PPFD for eighteen hours.

At this range, there’s a chance of better yields when your plant crosses to the vegetation stage.

Vegetative stage:

At the veg phase, your plant has to receive upwards of 20 moles of light each day. But the DLI isn’t expected to exceed 35 units at this period. Because this is a make-or-break stage, growers are mostly at odds on numerous fronts.

During the veg phase, canna plants usually require more energy to boost growth potential. Some growers could flat-out disregard recommendations and double the required DLI for increased vegetation.

Several elements, like hours of light, light intensity, and grow light spread could impact growth at this stage.

Flowering stage:

Optimal flowering may require around 38 – 65 DLI units each day. If your marijuana flowers as it should, you can expect a good harvest.

Why is Lighting a Facilitating Element for Horticulture?

The electromagnetic radiation emitted from light sources is what several plants need to grow. How much light your plant has access to every day could determine the resulting harvest. As expected, light levels differ.

Exposing certain plants to low or excess light levels could impede growth potential. Active radiation from the sun is a superior source of lighting most plants grow under. But under some conditions, harsh sun rays could damage crops, especially in arid regions.

Similar effects are common in indoor growing, particularly when you’re growing marijuana and other high-light intensity plants. If you are targeting a big indoor harvest, getting the right light spread your crops need is not negotiable

How Is Cannabis Different From Other Greenhouse Plants?

Cannabis has a composition much unlike other notable greenhouse crops. Growers have noticed wider disparities in the photoperiod of a marijuana greenhouse than most flowering plants.

In a nutshell, cannabis takes on much more light than any regular greenhouse plant. A close look at marijuana’s photosynthetic photon flux density (PPFD) rating shows, it possesses a superior light absorption potential.

Metabolite Production in Cannabis – What Role Does Lighting Play in Producing Industry-Specific Variants?

Marijuana is largely used for recreational or medicinal purposes. THC is widely known as the major psychoactive component in marijuana, responsible for the ‘high’ users experience. And on the other hand, medical marijuana usually isolates cannabidiol, or CBD, due to its beneficial properties.

All marijuana plants produce THC and CBD in different amounts, regardless of their strain. But most growers are keen to know how the daily light integral affects metabolite production.

12-hour, 18-hour, or 24-hour Lighting – Which is Better for Marijuana?

Marijuana has a high photoperiodicity coefficient (meaning it reacts to how much light it receives). The plant has a steady shift in responses to hours of light it receives over a 24-hour period. Foliage continues to form in the plant’s vegetative state when lighting follows a 12hr/day format.

Some growers debunk the 12hour/day suggestion, claiming 16-18hrs/day is much better for canna growth. Others believe 24hrs lighting greatly influences marijuana throughout cultivation.

If you’re targeting optimal yields, which statement holds true? None, quite frankly!

Flat-out lighting suggestions rarely do any good to your harvest. And if you plan to consistently get great returns from marijuana growing, blanket plant lighting isn’t ideal. It’s essential to know that the photoperiod rating of marijuana means it needs a dynamic level lighting program.

Auto-flowering Weed Plant – How Much Lighting is Necessary?

Auto-flowering weed usually has to remain under light intensity for most parts of its life cycle. Since that’s the case, proper lighting becomes indispensable. A light intensity range of 300 – 620 micromoles is needed to maintain auto-flowers throughout their life cycle.

Since most of these plants need up to 18hrs light per day, precise lighting is important to prevent plant burning.

How to Increase DLI for Canna Growers

Obstruction removal

Letting your plants bear the sun’s full force is never a great idea, particularly for in-house canna grows. But it could be ideal to remove certain obstructions to the sun’s rays to get better lighting.

Leveraging lighting

If the sun doesn’t get to where your crops are, it’s best you increase lighting around your plants. Increasing grow lights around your cropping area is one way to ramp up the required illumination marijuana needs to flower.

Several elements go into proper use of indoor grow lights, so it’s best to check them out before installing these lamps.

Using grow lights with stronger PPFD concentration

When it comes to purchasing the best LED grow lights, it’s best you go big or go home. Cheap lights may not offer the illumination your plants need. So, putting in some more dollars for increased quality shouldn’t hurt.

Recommended Strains for DLI Increase

Equator strains, haze, and Sativa canna variants:

If you’re targeting a bountiful yield, you need strains with the right makeup to support your effort. Sativa, haze, and equator strains are ideal fits for increasing your marijuana DLI.

Indo-Aryan variants:

Variants from the Indo-Aryan areas are popular for their strong lighting absorption credentials. If you plan to get more light onto your preferred crop, these could be ideal variants to try out.

Hybrids:

Extensive cross-pollination techniques over the years have created some badass, hybrid canna variants. Many of these hybrids can withstand lighting some other variants can’t handle.

What Does PAR Mean?

Photosynthetically active radiation (PAR) refers to the light wavelength range that supports plant photosynthesis. PAR is measured in nanometers and ranges from 400nm to 700nm. Several PAR meters are available for getting accurate readings across your grow tent.

FAQs

How Much PPFD Do Seedlings Need?

Seedlings should receive from 500 µmol per square meter and not more than a thousand µmol per square meter. Anything higher or lower than this range (for PAR light) may impede growth.

How Do You Calculate Daily Light Integral?

DLI is a function of instantaneous light intensity expressed as moles per day.

How Much PAR Do I Need For Veg?

PAR intensity for vegetable growth should not be lower than 300 µmols/m2/sec and not more than 400 µmols/m2/sec.

When Should I Harvest My Marijuana Seeds?

Harvesting marijuana seeds depends on your chosen variant. Marijuana variants with seedlings take much longer to grow than seedless variants.

Proper DLI Exposure is Crucial to Your Marijuana Harvest

Light plays a major role in successful grows and bountiful harvests, whether you’re an indoor or outdoor grower. Without light, even at a minimum intensity, photosynthesis cannot happen. Proper light supply for your plants provides the necessary photons required for growth.

Some requirements may be negotiable. But the right lighting has to be delivered to your crop for a better yield.

And if you’re a marijuana grower, the debate on how much daily light integral (DLI) your plants need is indispensable. Ensure you create a perfect environment for your marijuana plant to get the right DLI. Maximizing your harvest requires vetted information and the right input.

Better harvests largely depend on maintaining uniformity across your marijuana grow area. When you’ve fully grasped what the daily light integral (DLI) means for your crop growth, better lighting is less hassle.

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About the author 

Morgan

I discovered the benefits of Cannabis at a young age in 2002, with years of trial and error, my knowledge grew just like my plants. As my love for cannabis unfolded I began to teach and learn, trying to gain as much information and practical growing experience.

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