How to Use Supplemental Lighting for Cannabis Greenhouse

Imagine this: you’re growing your cannabis plant in a greenhouse but it isn’t growing as well as you’d hoped for. One of the common reasons for this could be improper lighting conditions.

But wait, isn’t the sun the best light source for cannabis plants? It is, but there are a lot of variables that exist between the sun and your cannabis plant. We’re talking about everything from dust to the earth’s atmosphere. 

So, how do you fix that? With supplemental lighting. In this article, learn how to use supplemental lighting for your cannabis plant along with the best tips on doing so. Read on to know more. 

Why Should You Use Supplemental Lighting in Cannabis Greenhouses?

Greenhouses are awesome — they allow you to get the benefits of natural cultivation while protecting your cannabis plant. Sometimes, however, things may seem a bit cloudy — literally — if the natural light is not enough. That’s exactly what supplemental lighting is. 

Supplemental lighting helps you give your plant the extra light kick it needs to keep thriving. This can come in handy for a variety of situations, which is why it is recommended that greenhouses have supplemental lighting. 

So, how can these extra lights benefit your plants? Let's explore some of the benefits.

1. No More Short Growing Seasons 

When cannabis thrives outdoors, but with supplemental lighting, you become the master of your plant’s growth stages. Facing a short growing season? No sweat! Give your seedlings a headstart in early spring by mimicking longer summer days with extra light. Similarly, you can also extend your harvest well into fall, maximizing your potential yield.

2. Compensate for Greenhouse Glazing

Greenhouse glazing can sometimes be a bit like sunglasses — it blocks out some of the good stuff. Dirt, material thickness, or even the type of glazing itself can affect how much light reaches your plants. Supplemental lighting steps in as your knight in shining armor, ensuring your cannabis plants get the optimal light intensity they need to thrive.

3. Much Better Yields

Light is like plant food, and cannabis thrives with a good amount of it. Supplemental lighting helps you provide that extra boost, leading to potentially bigger, better harvests. 

Remember, it's all about balance — we're not talking about replacing natural light entirely, just complementing it. Think of it as that extra growing power that translates into more potent, visually appealing buds.

4. Faster Harvest Cycles

The faster you can get your cannabis plants through their growth cycle, the sooner you can enjoy the rewards of your hard work. With natural sunlight alone, you're at the mercy of the seasons. But by adding supplemental lighting, you gain more control. 

High-quality lighting systems offer incredible flexibility, allowing you to mimic natural light patterns for optimal growth while still accelerating your harvest cycle compared to relying solely on the sun.

This translates to potentially more harvests per year, even in areas with less sunlight or during winter months. It's like having your own personal sunshine machine, all within the comfort of your greenhouse!

Why You Shouldn’t Use Supplemental Lighting in Cannabis Greenhouses?

While supplemental lighting offers incredible benefits for cannabis greenhouses, it's important to weigh both the advantages and disadvantages before making a decision. So, let’s dive into some reasons why supplemental lighting may not make sense for some growers. 

• They Can Be Expensive Upfront 

Adding supplemental lighting requires an initial investment in the fixtures themselves and the ongoing cost of electricity to power them. For many hobby growers, this may not always be worth it. 

Sure, the benefits of such lighting are awesome, but it’s not like greenhouses aren’t capable of growing healthy plants. But if you must use supplemental lighting, you can still offset the cost in a couple of days. 

The first way is to apply for rebates. Many government and utility programs offer generous rebates and incentives for growers who choose energy-efficient lighting solutions. These can significantly lower the upfront cost and make the switch from traditional lighting more attractive. 

Research what programs are available in your area — you might be surprised by the savings! Remember, you’re growing a plant that was restricted not long ago, so don’t be surprised if your application gets rejected. It happens. We would strongly advise against lying about the plant you’re growing, though. That can backfire. 

Then, you can use LED lights. These lights, the most popular choice for plant growth, are known for their energy efficiency. They use less power than traditional options to deliver similar or even higher light intensity levels, leading to immense energy savings. 

Additionally, LEDs generate minimal heat, reducing the need for extra ventilation or cooling systems. They also impact plant transpiration, requiring less dehumidification. These combined factors can significantly reduce overall operational costs. We’ll get into the best lighting options later in the article. 

• Additional Things You Need to Take Care Of

Unlike natural sunlight, supplemental lighting requires some maintenance. While LEDs boast impressive lifespans exceeding a decade, other options typically last for a shorter period and can lose effectiveness within a year (sometimes half of that, even). 

Additionally, you’ll need to keep them clean. LEDs often require minimal cleaning compared to other lighting options. Some models even have special features like IP67 ratings, allowing them to be quickly hosed down for easy maintenance. Other lighting systems might require more regular and careful cleaning. 

Some light panels like HIDs, HPS, and MH lights require consumables. These include bulbs, ballasts, or driver replacements, which need to be replaced over and over again. These can build up your costs over time — it’s usually never fire-and-forget when it comes to grow lights. 

Remember, while there is an initial investment and ongoing costs associated with supplemental lighting, the potential benefits in terms of increased yields, faster growth cycles, and energy savings can be substantial. 

Types of Supplemental Grow Lights 

Let’s be honest, natural light, as good as it is, can be unpredictable. And now that you know the pros and cons of supplemental lighting, it’s time to fix that issue. To do so, you have a few options available in the market right now. 

Each option comes with its own pros and cons, so you must decide which one works best for your cannabis greenhouse and suits your plants. Here are the most popular types of supplemental grow lights.

Spoiler alert: the details more or less are similar to indoor grow rooms. 

1. CFLs

The most basic kind of supplemental light you can use for your greenhouse is CFLs. They are super affordable and readily available (you might even have some spare bulbs lying around!) These lights are perfect for beginners or those on a tighter budget. 

They're gentle on the heat front and energy-efficient, making them ideal for nurturing seedlings or leafy greens that don't require super intense light. However, their light output might not be enough for some high-maintenance cannabis strains. 

2. HIDs or High-Intensity Lights

HIDs are tried and tested lights that are the workhorses of the grow light industry. They are easy to set up and relatively affordable. These lights, including metal halide (MH) and high-pressure sodium (HPS), pack a serious punch in the light department.

They can easily meet the DLI needs of most cannabis plants throughout their lifecycle, ensuring they get all the light they crave to flourish. Plus, they're known for their reliability and consistent light output. 

But there's a catch — these grow lights can get a bit hot, so careful positioning is key to avoid scorching your plant friends. They also use a reflector and ballast, which can add to the costs. Lastly, they aren’t the most eco-friendly.

3. LEDs

LED lights are all about energy efficiency, customization, and a long life. 

To start with, LED lights offer a spectrum of light options — sometimes, 16 million colors! So, you can customize them as you want to suit your plant’s needs or mimic the sun’s light during specific times of the year. 

They also last a long time. As mentioned earlier, most high-quality LED lights have a life of upwards of 11 years. That’s a long time. And they are super energy efficient, too. While the initial investment may be high, they are significantly cheaper to run in the long run. 

These lights also don’t generate a lot of heat. So, you don’t have to worry about compensating for the extra heat or your plant burning under them. They haven’t quite reached the light output of HIDs just yet, but give it some time — the gap is narrowing as we type. 

4. Ceramic Metal Halide (CMH) Lights

CMH lights are very popular, especially among cannabis growers nowadays due to their ability to provide a balanced spectrum of light that closely imitates natural sunlight. Unlike HID (High-Intensity Discharge) lights that rely on quartz or fused quartz arc tubes, CMH lights feature ceramic arc tubes offering several advantages.

A standout characteristic of CMH lights is their capacity to generate a light spectrum that closely mimics sunlight. In fact, these lights are the closest you can get to natural sunlight. This comprehensive spectrum encompasses wavelengths across the spectrum along with segments of ultraviolet (UV). Infrared (IR) spectra. This ranging spectrum equips plants with the range of light necessary for optimal growth and development.

CMH lights emit a blend of red light wavelengths crucial for fostering plant growth and supporting various growth stages. Blue light proves beneficial during the growing phase as it boosts the development of leaves, enhances root development, and regulates plant structure. On the other hand, red light is important during the flowering stage as it promotes flowering or bud production and enhances the quality of yields. By delivering the ideal light spectrum, CMH lights support the production of oils, terpenes, and cannabinoids resulting in potent cannabis flowers with enhanced flavor profiles. What’s more, their versatility throughout all stages of cannabis plant growth helps whether it's during the seedling, vegetative, flowering, or for propagation purposes.

Also, the balanced spectrum emitted by CMH lights ensures that plants receive light across various wavelengths enhancing the efficiency of photosynthesis. This results in improved rates of photosynthesis leading to plants with increased yields. In short, CMH lights offer consistent and dependable light output to help growers maintain ideal growing conditions consistently.

Recognized for their high efficiency compared to traditional HID lights like HPS (High-Pressure Sodium) lamps, CMH lights produce more light per watt consumed, leading to cost savings on energy consumption in the long run.

Whenever you purchase grow lights, one of the first things you look for is durability. After all, what good is a grow light if it doesn't last for years? CMH lights tick the checkbox even in this aspect as they offer a longer lifespan compared to several other lighting options. This reduces the need for frequent bulb replacements and maintenance costs. In general, CMH lights are a perfect choice for cannabis growers looking for a versatile and high-yield lighting solution. By providing a balanced spectrum of light that closely replicates sunlight, CMH lights create ideal growing conditions for healthy cannabis plants at every stage of growth.

5. Plasma Lights

Several growers, especially commercial operators, are using Plasma lights to grow cannabis. These lights use a gas discharge process to produce light and offer advantages over other lighting sources.

Like CMH lights, Plasma lights also produce a spectrum of light that closely mimics sunlight. Unlike some types of lighting that focus only on specific wavelengths, plasma lights emit light across the entire spectrum, including ultraviolet (UV) visible and infrared (IR) wavelengths. This comprehensive spectrum provides plants with all the light for photosynthesis and overall growth.

Also, plasma lights are highly effective in converting electric energy into light. They are popular for their brightness and energy efficiency using electricity than other lighting options. This efficiency not only cuts down on energy bills but also helps reduce the environmental impact, so you can grow cannabis without disrupting the environment. 

One key advantage of plasma lights is their lifespan compared to HID lights like HPS and MH bulbs. With care, these lights can last for tens of thousands of hours minimizing the need for replacements and lowering maintenance costs.

Another benefit is their heat emission, which is much lower than traditional HID lights. This feature allows growers to place the lights closer to plants without causing heat-related issues. It also eliminates the need for cooling systems in the grow area leading to energy savings and simplified control.

Plasma lights are versatile and suitable for all stages of growth, from seedling to flowering, offering flexibility throughout the plant's life cycle. Plasma lights emit a range of light that's essential for the healthy growth of plants especially during vegetative stages and flowering. Whether used alone or alongside sunlight or other lighting options, these lights create optimal conditions for growing cannabis.

The diverse light spectrum from plasma lights supports excellent plant growth resulting in plants with better yields and quality. By providing a mix of wavelengths, these lights stimulate photosynthesis, promote root systems and enhance the production of vital terpenes and cannabinoids in cannabis plants.

Remember, there’s no one-size-fits-all when it comes to grow lights. You need to consider your needs and priorities, along with your budget, before choosing the right grow light type for you. How do you do that? Keep reading. 

Tips for Using Supplemental Grow Lights for Greenhouses 

Now that you know the basics, let’s get into the nitty-gritty. In this section, you will learn how to properly use supplemental grow lights while avoiding common mistakes that many growers make. Here are the tips you need to follow. 

1. Calculate the Available Light First

The first step should always be to asses the current natural light situation in your greenhouse. Otherwise, you may be fixing an issue that doesn’t exist or climbing up the wrong mountain, so to speak. Everything that follows rests on this step. 

First, understand the light fluctuations in your greenhouse. Sunlight varies throughout the year; it is weak during the beginning and end of the growing season and, in some seasons, the sunlight hours may also be fewer. Some regions also experience frequent cloudy periods. 

Your cannabis plant needs 18 hours of light during the growth stage and 12 hours during bloom. So, figure out how much light your plant needs during each of its growth stages and where sunlight might be lacking. 

For example, your plant may require 12 hours during bloom but sunlight is only present for five hours. So, your plant requires seven additional hours of supplemental sunlight to bridge the gap.

Measure the Natural Light Available 

To help you along the way, it’s ideal to measure the natural sunlight available in your greenhouse. Generally, greenhouses have many obstructions that may limit sunlight. For example, glazing restricts sunlight from 67% to 92% percent, depending on whether it is made of plastic or glass. Other obstructions include fans, fixtures, lights, struts, pipes, etc. Finally, there is dirt to make matters worse. 

Such obstructions can lead to the greenhouse only getting 50% to 70% of the natural sunlight. You must account for this and your supplemental lighting should offset this. But how do you measure the natural light? 

Start with understanding the glazing specifications of your greenhouse covering. They usually mention visible transmittance. You can also move equipment around strategically to ensure maximum sunlight penetration in the greenhouse. 

Understand the DLI 

DLI or Daily Light Integral refers to the amount of light (photons) usable by plants (PAR) that reaches them over 24 hours. DLI is measured in moles (mol/m²/day). Understanding DLI is crucial for determining the amount of supplemental light required, especially when natural sunlight is inadequate. 

Many online resources provide information on DLI ranges for specific locations in Europe and America. Make a note of the lowest and highest DLI for each month in your region. This data will be valuable in planning your supplemental lighting strategy.

2. Understand Your Plant’s Lighting Needs

Now that you've grasped the importance of natural light and DLI in your greenhouse, let's explore how to use this information to tailor your supplemental lighting specifically for your plant babies.

Different plants have varying light needs throughout their life cycles. Cannabis, for example, requires progressively more light as it matures. This is your plant’s DLI requirement, which is as follows:

• Seedling/Clone Stage: 15-20 mol/m²/day
• Growth Stage: 20-40 mol/m²/day
• Bloom: 25-50 mol/m²/day

Now, you have three readings at your hand: local DLI, greenhouse light transmission (VT), and required DLI for the plant. The next step is to figure out how much light your plant needs. 

Use the following formula to calculate the amount of supplemental DLI needed:

• Supplemental DLI = Target DLI - (Natural DLI x Greenhouse VT rating)

Example: Your region has the lowest DLI of 25 mol/m²/day in December. Your greenhouse glazing has a VT rating of 70%. You're growing cannabis in the flowering stage, targeting a DLI of 40 mol/m²/day.

• Supplemental DLI = 40 mol/m²/day - (25 mol/m²/day x 0.70) = 40 - 17.5 = 22.5 mol/m²/day

Knowing the supplemental DLI requirement helps you choose appropriate grow lights. Then comes PPFD or photosynthetic photon flux density. This is essentially the amount of photosynthetically active radiation (PAR) light falling on a specific surface for a second.

You can use online calculators to convert DLI to PPFD for your target light levels and desired photoperiod (light hours per day).

Alternatively, use a PPFD meter to measure light intensity at various points within your greenhouse canopy. This helps ensure your plants receive adequate light for optimal growth.

Ideally, cannabis plants need the following PPDF levels:

• 308 to 617 μmol for 18 hours during growth stage 
• 462 to 926 μmol for 12 hours during bloom 

By following these steps and using the right tools, you can create a customized lighting environment that caters to the specific needs of your plants, ensuring they thrive in your flourishing indoor greenhouse!

3. Planning Out the Logistics of Supplemental Lights

Now that you've figured out your plant’s light requirements, let's dive into the practicalities of planning your supplemental lighting system for your greenhouse. 

Understanding Light Spectrum

Sunlight provides a full spectrum of light, containing various wavelengths that influence plant growth differently.  When using artificial grow lights, it's crucial to choose those lights that emit the ideal spectrum for your cannabis plant. 

Here is a short guide on the best light spectrums for cannabis plants:

• Seedling Stage: Blue-dominant light is ideal for promoting strong root development and compact growth in young plants.
• Vegetative Stage: Blue light continues to be beneficial during this stage, encouraging vigorous branching and foliage development.
• Flowering Stage: Red and far-red light wavelengths play a key role in flower and bud production. Opt for lights with a red-dominant spectrum during this stage.

Next, you need to figure out which lights work best for you. Use the above-mentioned information on the best types of grow lights for your cannabis plants. 

Lighting Scheduling

Creating a lighting schedule for cannabis in a greenhouse is more nuanced than a strictly indoor setup. This is for three reasons.

One, unlike controlled indoor environments, greenhouses experience natural light variations due to weather and daylight hours. There's no one-size-fits-all solution.

Two, to determine your supplemental lighting needs, you must consider factors like natural DLI, greenhouse light transmission (VT), and desired PPFD levels (remember the conversion from DLI). Daylight hours also play a role.

Three, these calculations will give you a baseline for how long your supplemental lights need to operate each day. It could be a few hours at dusk or split between dawn and dusk, depending on your specific situation.

Positioning Supplemental Lights

Since sunlight remains the primary light source in a greenhouse, positioning supplemental lights strategically is crucial. Here are some tips regarding light positioning:

• Unlike indoor setups requiring numerous lights, greenhouses typically use fewer lights spaced further apart.
• Aim to position lights in a way that minimizes disruption to the natural light reaching your plants.
• Choose smaller, yet powerful lights that provide adequate supplemental light without blocking natural light. 
• It’s always a good idea to research and discuss options with other growers to find the optimal size, shape, and height for your specific setup. 

Optimizing these factors ensures your plants receive sufficient light while minimizing light shadows. By following these tips and strategically planning your supplemental lighting system, you can create the perfect light environment to nurture your plants and transform your greenhouse into a thriving indoor garden!

4. Avoid Common Mistakes 

Even if you have everything figured out, you can still make mistakes. So, here are some common mistakes that new growers make, so that you know what to avoid when you get started. 

Incorrect Calculations

If you’re anything like us, you hate math and are bound to make mistakes. In such cases, it’s always best to double-check your answers. If only we were as good with numbers as we are with cannabis plants, right? 

Seriously, avoid making this mistake. It can either end up burning your plant or causing light depreciation. If not, it would at least create a dent in your wallet.

So, understand your plant's light needs at each stage. Use reliable measurement tools like PPFD meters to assess actual light levels within your greenhouse. Double-check your calculations to ensure accuracy.

Uneven Light Exposure

Improper arrangement and distribution of lights can result in uneven light exposure across your plant canopy. Some plants may thrive in optimal light, while others languish in shadows.

Design your lighting system strategically to ensure even light distribution. Consider the greenhouse layout, plant height, and canopy density. As plants grow and the canopy thickens, adjust lighting positions to maintain light penetration to lower leaves.

Setting and Forgetting It

Monitor Your Plants, always. Pay close attention to your plant's overall health and growth patterns. Are they stretching excessively? Are leaves showing signs of light stress? Adjust your lighting accordingly.

Summary: How to Use Supplemental Lighting for Cannabis Greenhouse

There you have it — a detailed guide on supplemental lighting for cannabis greenhouses. So, what are you waiting for? Let’s start fixing the lighting in your greenhouse so your cannabis plants can flourish. 

Here’s a summary of everything we mentioned above:

• Supplemental lighting brings benefits like better yield, fewer light fluctuations, and faster harvest cycles 
• Although, they can be expensive and require some maintenance 
• Start by choosing the type of grow light you’d like to have 
• Figure out your plant’s DLI and PPFD requirements using the formula we mentioned 
• Understanding your plant’s light spectrum and intensity requirements 
• Plan out everything before you start drilling holes in your greenhouse — metaphorically speaking 
• Be wary of common mistakes

Keep these things in mind and your green beauties will grow better than ever!