Green Light: How Can You Use It To Grow Cannabis Plants?

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Added 12 August 2023

One of the biggest investments in your indoor cannabis grow room would be the grow lights, and if you are using high-quality LED grow lights, they might be the biggest investment in your cannabis operation. And due to this, it’s natural for you to pick the best light that produces the right spectrum of light when you need it. 

Generally, you would want your grow lights to produce red and blue spectrums of light since they are required during the different stages of your plant’s growth in different amounts. But did you know that you may be overlooking a potentially important spectrum of light: green?

That’s right. Even though green is not primarily used by your cannabis plants, green light can work wonders in your cannabis grow room if you use it right. It can benefit your plant by improving its photosynthesis and yield to a certain extent, and also protect your eyes from fatigue, and much more. And you’d be surprised to know that your plant does not reflect all of the green light back. 

So, here’s everything you need to know about green light and how it can benefit you as a cannabis grower and your cannabis plants, 

Does Green Light Affect Cannabis Growth?

Does Green Light Affect Cannabis Growth?

For your cannabis plant, light is food and it needs a lot of light to grow well. However, it cannot survive on any random type of light; like any other plant, cannabis requires a specific type of light depending on its growth stage. But generally, it can utilize the following types of lights:

  • UV light, ranging from 100 to 400 nm
  • Blue light, ranging from 400 to 500 nm
  • Red light, ranging from 600 to 700 nm
  • Far-red light, ranging from 700 to 850 nm

All these wavelengths of light can’t be sensed by the human eye, but your plant can sense these lights, especially those falling within the 400 nm to 700 nm range, which is also referred to as photosynthetic active radiation. In other words, your cannabis plant processes photosynthesis the best when it gets PAR light. 

Blue and Red Light for Cannabis Plants 

But before we get into the importance of green light, let’s understand blue and red light for cannabis plants. Green, after all, is a mix of blue and red. As you may already know, young cannabis plants (seedlings and veggies) prefer blue light, ranging between 400 nm to 500 nm, or 4000K to 5500K in the Kelvin range. 

Cannabis uses its cryptochrome photoreceptors to absorb the blue light during its growth stages to produce more mass in the form of branches and leaves. Plus, blue light promotes metabolism by regulating stomata activity, which further leads to better growth and photosynthesis. 

On the other hand, cannabis prefers red to far-red spectrums of light during the flowering stage. This light is warm, between 630 nm to 700 nm, and the plant’s phytochrome photoreceptors absorb these plants. Red light promotes the growth of flowers, which is crucial for cannabis growers. 

Green Light for Cannabis

But unbeknownst to many, the light spectrum that falls between blue and red can also come in handy when growing cannabis plants. Agreed, green does not impact the growth of cannabis plants and their yield as much as other light spectrums, but it can still make a difference. 

Green light can have a noticeable, while not drastic, effect on your cannabis plant’s growth, right from its seedling to bloom stages. You’re probably thinking, don’t plants reflect all the green light since they are so green? You’d be partially right. Plants’ chlorophyll gives the leaves a green color because it reflects green light, but in reality, it only reflects 10% of the green light. The rest of it is still absorbed by the plant. If not, all the plants in the world would be so green it would give us a headache. 

How Does Green Light Affect Cannabis Plants?

How Does Green Light Affect Cannabis Plants?

Sunlight already produces green light, and so do most lamps, even if they are warm or cold temperature. And recent studies have shown that green light can benefit cannabis plants in many ways. Here are some of the benefits of using green light for growing cannabis. 

1. Improves Seedling Stage Development

Your cannabis plant won’t produce a lot of chlorophyll during the seedling stage because it won’t have enough leaves, to begin with. As a result, the photosynthetic process will be slow and inefficient until it puts on a more leafy mass. Here, green light can work as a stand-in light and aid the photosynthetic process. 

Weirdly, cannabis plants can recognize red and blue light but don't really recognize the spectrum that falls between the two ends: green. However, studies show that the plant does realize it’s getting a lot of light when it receives the green light, so it adjusts its development accordingly. 

Essentially, 90% of the green light that a seedling absorbs is used as a bridge that fills the gap between the blue and red ends of the spectrum. So, with green light, the rest of the spectrums are better utilized by the plant, leading to better seedling development. 

2. Supplemental Light

Along the same lines, green light can be used as a supplemental light for your cannabis plant in different growth stages. However, one thing to note here is that a little goes a long way. While a seedling can get away with too much green light, the same isn’t true for a vegetative or a flowering cannabis plant. Too much light can be detrimental once the plant starts vegetative growth as an excess of it can start counteracting the benefits of blue light on the plant. 

As a result, using too much green light in hopes of improving photosynthesis can make your plant’s development slower and even lower the yield in the long run. According to many growers on internet forums, using too much green light can even affect the THC levels in the buds. More on this below.

3. Improves Plant’s Shape and Size 

As mentioned above, green light improves the photosynthetic processes of the cannabis plant, and as a result, the plant produces more energy and grows bigger. Research suggests that green light can make plants grow faster and bigger, and produce a slightly bigger yield than otherwise. 

This is not only true for cannabis plants, but other plants. So, studies conducted on other plants can also give us an insight into how this light can benefit cannabis plants. For example, a study on tomatoes shows that green light leads to an increase in the plant’s size, length of the stem, leaf area, and size of tomatoes. 

Thanks to these studies conducted on not only cannabis but many other plants, there is conclusive evidence that green light can help benefit your plant’s morphology by encouraging it to grow bigger and taller and produce better yields. 

4. Green Light Improves Light Penetration Through the Canopy

Usually, most cannabis growers hang the grow lights on top of the plant. Due to this, the leaves on the top get excellent exposure to light, but the lower leaves of the foliage may not get enough light. This is because light may sometimes fail to penetrate the foliage properly, especially if the beam of light is unidirectional and not of high quality and intensity. 

This imbalance in light exposure can create a few problems for cannabis plants, starting with the lower branches not developing well and slower bud development in the lower branches due to lack of adequate light. The less light that reaches the lower tiers, the lower the photosynthetic rate there. 

So, if you’ve tried everything to fix this issue but your plant’s lower branches still don’t get enough light exposure, you can try supplementing with green light. According to some studies, green light improves light penetration to the lower branches of the canopy. In fact, green light is better than any other spectrum of light at improving light penetration! So, green light can be a valuable tool to have for indoor growers, and this aspect further improves the quality and quantity of your plant’s yields. 

5. Better Flowering Rate 

Your cannabis plant uses photoreceptors like phytochrome and cryptochrome to regulate the flowering stage. Here, phytochrome and cryptochrome receptors are sensitive to the red spectrum and blue spectrum of light, respectively. Still, both photoreceptors absorb green light in slightly lower quantities than their respective spectrums. 

So, if you use green light in your cannabis garden during the flowering stage, you can boost the photoreceptor processes within the two receptors. The green spectrum of light can regulate the flowering processes so the plant can enjoy a longer day without a disturbed night cycle. Plus, there’s always the benefit of better photosynthesis during bloom due to green light, as mentioned above. It’s a win-win situation for a flowering plant. 

6. Makes Other Grow Lights Safer for Your Eyes 

A secondary benefit that’s similar to this is that green light reduces fatigue in your eyes due to single-spectrum lights. You and your team members will be working long hours in the garden on some days, and if you are using a single spectrum of light, especially blue, it can fatigue your eyes and even damage the cornea over long periods of exposure

So, adding a set of green lights in your grow room can also benefit you and your team members by allowing you to see better without getting tired soon or risking damage to the eyes. 

When Should You Use Green Light for Growing Cannabis?

When Should You Use Green Light for Growing Cannabis?

The green light may have many benefits, but it is a niche tool that few growers see the full potential of. It’s not for everyone. So, if you are wondering if you should use green lights for growing cannabis, you can definitely give it a try. It is worth a shot, especially when it can increase your plant’s yield and growth!

However, when you use green light entirely depends on you and what aspect of your cannabis operation you want to improve. Want to increase germination success rates? Want to improve your plant’s photosynthesis? Are your blue-spectrum lights hurting your eyes? In such cases — and more — it makes sense to use green lights. 

But unlike other types of lights, there is no hard and fast rule as to when you can use green lights. It entirely depends on you and your preferences, so the decision lies with you. We suggest that you start using it during the vegetative stage when the risk is low for your plants and see how your plants react to it. 

Figure out what works best for you and from there, experiment with different stages and timings of green light uses, and you’ll quickly learn when you should use green light and when you can get away without it. 

And, when talking green lights, many growers wonder if it's okay to use them during the dark hours to provide uninterrupted darkness to the plants. For example, if your plants are on a 12/12 cycle, they need 12 hours of light and 12 hours of complete darkness to survive and thrive during the flowering stage. In fact, photoperiod plants will start flowering only when you switch to the 12/12 cycle.

The flowering period is a time when the plant is very sensitive, so they will show changes even if there's a small light leak during the dark hours, and the plants may either become hermies or go back to their vegetative stage, known as re-vegging. 

As a grower, you need to do everything to prevent light leaks during this period as all your efforts can go down the drain if you mess up at the last moment. But, there will be times when you want to work on the plants to train or water them, and it's almost impossible to do so during the dark hours as you don't want to be stumbling around in the tent or room.

To explain this clearly, imagine your plants get light from 6 am to 6 pm and the dark period continues from 6 pm to 6 am. This means that you'll have to work on the plants during the light hours when the lights are blazing or you'll have to use a light that won't affect the plants. Many articles suggest that using green lights works great during dark hours as cannabis plants cannot recognize green light without the presence of red and blue spectrums. Some users have also stated that they have used green CFLs successfully and have noticed no changes in the plants. 

However, some sources suggest that you should tread cautiously in this area as cannabis can get affected with even small amounts of green light. This is the same as other lights. While some users say that even a small LED headlamp tucked away in the corner of the room has affected their plants, others say that their plants never had problems. 

So, what should you do? If you really want the answer, you could start with a tiny green light, but it's best not to try it out if you're growing multiple plants. You can experiment with one plant and see how it goes if you're inclined. If not, you can leave things as is and continue working with your plants as you have been doing all this while. 

How Much Green Light to Use for Cannabis?

How Much Green Light to Use for Cannabis?

It’s apparent that your cannabis plant can benefit from green light, but as mentioned above, you shouldn’t use too much green light as it can do more harm than good. 

Excessive green light can affect various natural processes of your cannabis plant, especially those that are enabled by blue light. As a result, too much green light can slow down photosynthesis and eventually reduce the overall yield your plant produces, and sometimes, it can even make the buds less potent. 

According to research, too much green light can also lead to issues in cannabis plants that resemble shade avoidance syndrome or SAS. This syndrome refers to the plant’s response to adapting its growth due to being under the shade of another taller plant. Too much green light can produce similar symptoms in cannabis, which can eventually affect bud development and reduce yield. 

So, depending on the scope of your operation, you should not exceed moderate amounts of green light use. How do you decide that? Essentially the blue and/or red light produced by the primary grow light should not be offset by the green light, and the latter should not produce any negative effects. 

This level varies from plant to plant and set up to set up, so it’s hard to give an exact number. However, it’s better to start low with a small bulb and, with some trial and error, figure out what works best for your cannabis plant. 

Disadvantages of Using Green Lights to Grow Cannabis

Disadvantages of Using Green Lights to Grow Cannabis

1. Restricted Growth 

Since plants are much less receptive to green light to grow well, using it as the primary lighting source can harm your plants and prevent them from growing to their full potential. You may notice elongated stems, reduced branching, and underdeveloped leaves, ultimately leading to low-quality and less yields. 

2. Unidentified Effects on Cannabinoid Production

Cannabis plants respond well to blue and red light which increases the production of cannabinoids. While we haven’t yet understood the effects of green light concerning cannabinoids, you can only use it as a supplemental light along with red and blue lights as relying on it for cannabinoids will not work well for you. 

3. Cost Considerations

Incorporating green light in a setup that’s already expensive may not be very appealing to many growers. Some growers may even think that it’s an unnecessary complication to add to something that’s working pretty fine for them. 

4. Lack of Scientific Consensus

While there is some anecdotal evidence and limited research suggesting the potential benefits of using green light, there isn't yet a comprehensive scientific consensus on its optimal applications for cannabis cultivation. This lack of standardized guidelines can make it challenging for growers to confidently integrate green light into their cultivation practices.

What Type of Green Light Should You Use for Cannabis?

What Type of Green Light Should You Use for Cannabis?

LED grow lights are the most common type of light for cannabis cultivation. They are ultra-efficient, reliable, and customizable. However, they shouldn’t be your first choice when choosing green lights. This is for a couple of reasons, such as the following:

  • Green LED lights are not practical since they are less efficient, both electrically and photosynthetically — it’s an expensive way to produce a light that is supplementary for your cannabis plant 
  • LED grow lights produce green light by using red and blue light diodes, and the result is a light that appears purple, which can result in eye strain for you 

So, what should you use instead? 

If you want to use green light to improve the photosynthesis of your cannabis plant during the vegetative and flowering stages, you can use white LED lights or full-spectrum grow lights. These lights produce the full spectrum of light, including blue, green, and red. 

So, you won’t need different colored lights for your plant’s growth while still ensuring your plant gets the green light it needs. Plus, full-spectrum LEDs produce a more “natural” light and are more energy efficient. 

Search online and you’ll find many options for green grow lights for cannabis plants. If you need nothing more than a regular-sized bulb, you can go for something like the LED Green Hornet which is 3.5w and produces 480 lumens of light. Or you can even go for Agrolite Dark Night, a 100W green night lamp. Green light CFLs will also work. 

For a commercial setup, where you need green light in large quantities, stick to full-spectrum LED lights or pick multiple green grow lights. 

Summary: Green Light: How Can You Use It To Grow Cannabis Plants?

Green light is by no means necessary for growing cannabis. Your cannabis plant grows well enough with blue and red light, with additional UV and far-red lights, during the right growth stages. However, adding a bit of green light can only improve the benefits of blue and red light. 

Green light signals your plant that blue and red light is available, bridging the gap between the two spectrums, and thereby improving your plant's photosynthetic abilities. This can make your plant grow bigger, produce better yields, and increase the germination rates of seedlings. 

So, if you want to take your cannabis cultivation a notch higher, you should consider using the green light. If you are a hobby grower, you don’t need a lot — a simple green grow light bulb can do the trick. In fact, you don’t need any additional light if you already use full-spectrum lights. 


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m0use Green light is not a work light for late at night.
@CannaScience, Dr.Bruce Bugbee vids are all fire. He is legit a cannabis guru, a real one... not like a grow diaries guru & He's also a professor with a doctorate.
@m0use, I read extensively about this and there are conflicting statements but many people have stated that green CFLs have worked for them, so I went with that. Edit - I have added info from the video as well and a word of caution so people can decide. Thanks for letting me know about this video!