Cannabis plants make their own “sunscreen” to protect themselves from UV-A and UV-B rays from the sunYou may be familiar with the term UV-A/UV-B when it comes to protecting your skin outdoors. We use sunscreen to protect our skin from UV rays from the sun in order to prevent skin damage. Too much UV exposure can give you sunburn now, and even carcinoma/melanoma in extreme cases!
When we’re talking about plants, UV-A (315 to 400 nm) and UV-B (280 to 315 nm) are sometimes classified as part of the “blue” light spectrum, though in the last several years, we’ve discovered the UV spectrum has its own unique effects on plants.
Like humans, plants given too high levels of UV light become damaged, and we’ve learned that plants react to UV rays by making chemicals, antioxidants and enzymes to help prevent and repair damage. Basically, they’re making their own “sunscreen!” It’s a little bit like how our body gives us a tan after UV exposure to protect us from further skin damage.
Some growers believe that providing UV-B light to plants may increase the THC levels or some other aspect of potency of cannabis buds. Theoretically, it’s definitely possible since we know that UV-B light does change how plants grow. But what we don’t know is exactly how cannabis responds to UV-B exposure. It’s possible that it increases the levels of THC, but it’s also possible it reduces it, or doesn’t affect THC at all! With what little information we have today, it’s hard to know whether supplementing cannabis with additional UV-B is actually beneficial.
That being said, most grow lights naturally produce some amount of UV rays, though far less than the sun. The exception is LED grow lights with narrow-band spectrums which need UV diodes specifically put in. There are other sources of UV light you can get such as reptile lamps. LED grow lights are also a good choice if you want to supplement above normal levels of UV, but you need to make sure you get one that has been designed to produce UV light since that isn’t standard.
There are new LED grow lights on the market that contain UVB, including this one which also contains light in the infrared spectrum. Although we know that UVB has an effect on cannabis, we don’t know exactly what changes, and whether it’s good, bad or a waste of time!
Blue Light (400 nm – 500nm)
Metal Halide grow lights contain a lot of light in the blue spectrum, and are well-suited to vegetative growth
Blue light is very important. Without at least some amount of blue light, most plants won’t grow normally. The plant has several different ways it measures blue light, and they each have their own effects. For example, when you see a plant growing towards the light, it’s actually only responding to just the blue light. Without any blue, the plant wouldn’t know where to grow!
Blue light also has an effect on how stems and leaves tend to grow. Seedlings and plants given plenty of blue light tend to stay short, with short stems and squat growth. They tend to grow big leaves and spread them out.
It’s often recommended for cannabis growers to use bright white fluorescents or metal halide grow lights during the vegetative stage since the extra levels of blue help keep young plants from growing tall and lanky, and encourages lots of leafy growth.
A bright white fluorescent light (6400k) contains a lot of blue light, which can be a good choice for the vegetative stage.Blue light also works together with red light to help the plant “know” whether it’s day or night time, and help set circadian rhythms. You may notice that cannabis plants start drooping right before the lights go off each day, and they start perking up right when lights come on. This is a way for the plant to save energy while it’s “sleeping.” Since the blue in the light helps it “know” the time schedule, it will prepare as best it can for lights-out and lights-on.
Green Light (500 nm – 600nm)
There has been quite a bit of research on how different spectrums affect plant growth, especially over the last decade by researchers at NASA trying to find a way to grow plants most efficiently in space with LED grow lights.
The green color of these cannabis leaves appears to us because the plant is reflecting back the green contained in sunlight
We have long known that plants need at least red and blue light to grow normally, but recent discoveries have found that green light, while not the most efficient spectrum for photosynthesis, has a significant effect on how plants grow.
Green light has been shown to be involved in seedling and vegetative development, the initiation of the flowering stage, CO2/water usage, stem growth and overall plant height. There’s probably more we don’t know about yet!
But like the other spectrums, plants seem to want just the right amount of green light for the best growth, not too much or not too little. After many experiments with green light, the NASA Biological Sciences research group has reported that light sources consisting of primarily green will cause plants to grow slower. However, combinations of red and blue including up to 24% green actually enhanced growth for some plants over purely red and blue light.
So we’re learning that green is really important! In fact, in one experiment NASA did with lettuce, giving plants only blue/green/red light produced higher yields than full spectrum grow lights!
But cannabis is definitely not the same as lettuce and it doesn’t necessarily mean that adding green light will increase your cannabis yields! Nearly all grow lights provide some amount of green and it seems like adding too much green probably would hurt yields. But getting enhanced growth from green lighting is something to explore, especially for LED growers who often don’t give any green at all!
Note: There’s plenty of evidence that different types of plants respond to green light differently, so make sure you take any light spectrum study with a grain of salt!
In addition to the effects on how a plant grows, green light is what make plants appear natural and green to us. Plants under LED grow lights with just red and blue light tend to look dark or purple similar to how plants look very yellow/gold under a HPS. By adding a little bit of green we can actually see the natural color of leaves, which makes it a lot easier to spot problems!
Leaves appear dark under LEDs that don’t have any green diodes. In the picture below, leaves appear purple except in the front where a little bit of natural light coming from outside the tent. You actually see the leaves’ true green color wherever it’s touched by light that contains green.
Neat fact! Although your plant can respond to green light in some ways, it can’t “see” green when it comes to photoperiods and knowing when it’s day or night. So you can actually use green light to look at your plants in the dark and it won’t interrupt their dark period at all!
Use green light to check on plants in the dark so you don’t disturb their sleep!
Red & Far Red / Infrared Light (660 nm & 730nm)
We can see red light of course, but generally humans can’t see far-red (infrared) light, although we can feel it as heat. Plants, on the other hand, can sense both red and far-red light.
Red light is probably the most important type of light for plants. When it comes to photosynthesis, plants are best able to make energy out of red light. In fact, many plants can actually grow even if they only get pure red light, though they won’t grow as big or as healthy as they do under full spectrum light. Every type of grow light, even ones that are rich in blue like metal halides, provide quite a bit of red light.
However, when it comes to red and far-red light as far as signals (not photosynthesis), it’s not the amount as much as the ratio of red to far-red that’s important to the plant! For the purposes of the plant and its response to light spectrum, red light is ~660nm and far-red light is ~730nm on the light color spectrum.
A germinated seed moves towards red light
After a seed cracks open its shell, but before it makes it to the surface, the root goes down and the seed grows in the direction of greater levels of red light compared to far red. Blue light doesn’t usually make it underground, but the seed can sense red from the surface, and grows in that direction.
Once the seed reaches the surface and gets exposed to blue light, it stops acting like a root and starts acting more like a seedling, opening its leaves and growing towards the closest source of blue light. If it doesn’t get a good amount of blue light at the surface, it continues to grow its main stem longer and longer without making any leaves, acting more like a root than a plant because it still “thinks” it’s underground, or at least hidden from the sun.
Seeds move toward the light, and the leaves inside don’t open up once the plant hits the surface…it’s looking for the right amount of the right color of light!
If a plant doesn’t get access to enough light at the surface, it stays in “root mode” and keeps growing taller without opening up its leaves.
Stems tend to stay shorter when they’re getting more red light compared to far-red
In bright sunlight, a cannabis plant tends to grow short and squat. This is because direct sunlight usually has more red than far-red and the plant reacts to this ratio. So if a plant is getting more 660nm than 730nm light, the stems tend to stay short and the plant grows a lot of nodes with shorter stems.
On the flip side, if a plant is getting a more 730nm light than 660nm, it tends to grow tall and stretchy. This is because, in the wild, when a plant is surrounded by a lot of vegetation, the surrounding leaves absorb a lot of the red light, and so whatever light does filter down to the hidden plant or stem has a much higher ratio of far-red light.
In response to higher levels of far-red light, stems will start to elongate and grow taller, as the plant is “stretching” up towards the light until it gets a ratio with more red and “senses” it’s in direct sunlight again.
If a plant is surrounded by greenery, it starts sensing higher ratios of far-red light, and starts “stretching” upwards to grow past the other vegetation and get access to better quality light.
Plants keep track of days and nights using the ratio of red to far-red light
You’ve seen red light at sunset. The reason you see red when the sun is on the horizon is because red light has the longest wavelengths, which travel the furthest. At sunset the light is fading quickly, and when all other light is too weak to see, you can still see the red coming through the horizon before it disappears too. Infrared light has even longer wavelengths, so it hangs on just a little bit longer. That means for the plant, the highest ratio of far-red light occurs at sunrise and sunset.
The information contained in the light is important to a plant because it needs to be able to “know” whether it’s the beginning or end of the day. A plant can take advantage of the light spectrum information to keep track of day and night by sensing when there’s the highest ratio of far-red light.
A cannabis plant keeps track of the ratio of red and far red light to help it set its internal “clock” Far-red light is the last thing a plant “sees” at sunset, so when there are high far-red levels followed by a period of darkness the plant “knows” that it’s nighttime.
When a plant starts getting higher levels of red light combined with blue from the morning sun, it “knows” that the day has started again. If a plant is exposed to red light during the dark period, it will “wake it up” because it thinks day is happening. Blue light also affects the plant at night by messing up its circadian rhythms, though blue light alone likely won’t stop the plant from flowering.
These processes helps the plant set itself on an internal clock. Keeping track of the length of nights is the main way a cannabis plant knows when to start flowering (making buds). When nights get long, it initiates the flowering response because it “thinks” winter is coming! So growers are able to force the plant to start flowering at any time just by changing the plant’s light schedules!
Note: Even if the plant doesn’t get far-red light before dark, it will eventually “realize” it’s night time, but it starts the clock 1-2 hours later because it didn’t get that far-red “sunset” signal. Because of this, there’s some evidence that if you provide a plant with a burst of far-red light right before it goes to sleep in the flowering stage, you could cut 1-2 hours off your night period and it wouldn’t interrupt the flowering cycle. That being said, it’s always a good idea to give your flowering cannabis plant at least 12 hours of uninterrupted darkness every night to make sure budding goes smoothly! When time schedules get weird, you sometimes end up getting hermies or have your plant revert back to the vegetative stage, which most growers don’t want!
Can I use a thermal imaging camera to watch over cannabis my plants at night?
You can use an infrared camera to “spy” on your plants while they’re sleeping – it won’t interrupt their slumberYes. The way a thermal camera (also called an infrared camera, or thermographic camera) works is it actually absorbs/measures how much infrared light is being given off by objects.
A thermal camera works by showing warmer objects as lighter colors. So for example, the cold ground will appear dark, while a plant is a little warmer and will appear lighter. A human is warmer still and appears almost white on such a camera.
A thermal (infrared) camera doesn’t actually give off any light, it only measures it. So although far-red light does have an effect on plants, it won’t be affected by a camera that doesn’t produce any.
However, if your camera has a screen, the light from the screen is definitely an unwanted source of light!
What if I can only pick one spectrum?
We’ve learned that spectrum can change how a plant grows. So it’s definitely a good idea to try to match the spectrum with your goals, but what do you do when you can only get one light and must choose between one spectrum or the other?
If you have to choose between one or the other, it’s generally recommended to use the flowering light spectrum (more red) for the whole grow. This results in bigger yields watt-for-watt. However, you can successfully grow buds in the blue light spectrum for the whole grow, and many growers do this with excellent results. Some growers even claim they like their quality better under blue lights!
In other words, color spectrum is important, but it won’t make or break your grow.
What are the effects of different bands of spectra on plant growth
UVA / UVB / Ultraviolet Light (280nm-400nm)
Cannabis plants make their own “sunscreen” to protect themselves from UV-A and UV-B rays from the sunYou may be familiar with the term UV-A/UV-B when it comes to protecting your skin outdoors. We use sunscreen to protect our skin from UV rays from the sun in order to prevent skin damage. Too much UV exposure can give you sunburn now, and even carcinoma/melanoma in extreme cases!
When we’re talking about plants, UV-A (315 to 400 nm) and UV-B (280 to 315 nm) are sometimes classified as part of the “blue” light spectrum, though in the last several years, we’ve discovered the UV spectrum has its own unique effects on plants.
Like humans, plants given too high levels of UV light become damaged, and we’ve learned that plants react to UV rays by making chemicals, antioxidants and enzymes to help prevent and repair damage. Basically, they’re making their own “sunscreen!” It’s a little bit like how our body gives us a tan after UV exposure to protect us from further skin damage.
Some growers believe that providing UV-B light to plants may increase the THC levels or some other aspect of potency of cannabis buds. Theoretically, it’s definitely possible since we know that UV-B light does change how plants grow. But what we don’t know is exactly how cannabis responds to UV-B exposure. It’s possible that it increases the levels of THC, but it’s also possible it reduces it, or doesn’t affect THC at all! With what little information we have today, it’s hard to know whether supplementing cannabis with additional UV-B is actually beneficial.
That being said, most grow lights naturally produce some amount of UV rays, though far less than the sun. The exception is LED grow lights with narrow-band spectrums which need UV diodes specifically put in. There are other sources of UV light you can get such as reptile lamps. LED grow lights are also a good choice if you want to supplement above normal levels of UV, but you need to make sure you get one that has been designed to produce UV light since that isn’t standard.
There are new LED grow lights on the market that contain UVB, including this one which also contains light in the infrared spectrum. Although we know that UVB has an effect on cannabis, we don’t know exactly what changes, and whether it’s good, bad or a waste of time!
Blue Light (400 nm – 500nm)
Metal Halide grow lights contain a lot of light in the blue spectrum, and are well-suited to vegetative growth
Blue light is very important. Without at least some amount of blue light, most plants won’t grow normally. The plant has several different ways it measures blue light, and they each have their own effects. For example, when you see a plant growing towards the light, it’s actually only responding to just the blue light. Without any blue, the plant wouldn’t know where to grow!
Blue light also has an effect on how stems and leaves tend to grow. Seedlings and plants given plenty of blue light tend to stay short, with short stems and squat growth. They tend to grow big leaves and spread them out.
It’s often recommended for cannabis growers to use bright white fluorescents or metal halide grow lights during the vegetative stage since the extra levels of blue help keep young plants from growing tall and lanky, and encourages lots of leafy growth.
A bright white fluorescent light (6400k) contains a lot of blue light, which can be a good choice for the vegetative stage.Blue light also works together with red light to help the plant “know” whether it’s day or night time, and help set circadian rhythms. You may notice that cannabis plants start drooping right before the lights go off each day, and they start perking up right when lights come on. This is a way for the plant to save energy while it’s “sleeping.” Since the blue in the light helps it “know” the time schedule, it will prepare as best it can for lights-out and lights-on.
Green Light (500 nm – 600nm)
There has been quite a bit of research on how different spectrums affect plant growth, especially over the last decade by researchers at NASA trying to find a way to grow plants most efficiently in space with LED grow lights.
The green color of these cannabis leaves appears to us because the plant is reflecting back the green contained in sunlight
We have long known that plants need at least red and blue light to grow normally, but recent discoveries have found that green light, while not the most efficient spectrum for photosynthesis, has a significant effect on how plants grow.
Green light has been shown to be involved in seedling and vegetative development, the initiation of the flowering stage, CO2/water usage, stem growth and overall plant height. There’s probably more we don’t know about yet!
But like the other spectrums, plants seem to want just the right amount of green light for the best growth, not too much or not too little. After many experiments with green light, the NASA Biological Sciences research group has reported that light sources consisting of primarily green will cause plants to grow slower. However, combinations of red and blue including up to 24% green actually enhanced growth for some plants over purely red and blue light.
So we’re learning that green is really important! In fact, in one experiment NASA did with lettuce, giving plants only blue/green/red light produced higher yields than full spectrum grow lights!
But cannabis is definitely not the same as lettuce and it doesn’t necessarily mean that adding green light will increase your cannabis yields! Nearly all grow lights provide some amount of green and it seems like adding too much green probably would hurt yields. But getting enhanced growth from green lighting is something to explore, especially for LED growers who often don’t give any green at all!
Note: There’s plenty of evidence that different types of plants respond to green light differently, so make sure you take any light spectrum study with a grain of salt!
In addition to the effects on how a plant grows, green light is what make plants appear natural and green to us. Plants under LED grow lights with just red and blue light tend to look dark or purple similar to how plants look very yellow/gold under a HPS. By adding a little bit of green we can actually see the natural color of leaves, which makes it a lot easier to spot problems!
Leaves appear dark under LEDs that don’t have any green diodes. In the picture below, leaves appear purple except in the front where a little bit of natural light coming from outside the tent. You actually see the leaves’ true green color wherever it’s touched by light that contains green.
Neat fact! Although your plant can respond to green light in some ways, it can’t “see” green when it comes to photoperiods and knowing when it’s day or night. So you can actually use green light to look at your plants in the dark and it won’t interrupt their dark period at all!
Use green light to check on plants in the dark so you don’t disturb their sleep!
Red & Far Red / Infrared Light (660 nm & 730nm)
We can see red light of course, but generally humans can’t see far-red (infrared) light, although we can feel it as heat. Plants, on the other hand, can sense both red and far-red light.
Red light is probably the most important type of light for plants. When it comes to photosynthesis, plants are best able to make energy out of red light. In fact, many plants can actually grow even if they only get pure red light, though they won’t grow as big or as healthy as they do under full spectrum light. Every type of grow light, even ones that are rich in blue like metal halides, provide quite a bit of red light.
However, when it comes to red and far-red light as far as signals (not photosynthesis), it’s not the amount as much as the ratio of red to far-red that’s important to the plant! For the purposes of the plant and its response to light spectrum, red light is ~660nm and far-red light is ~730nm on the light color spectrum.
A germinated seed moves towards red light
After a seed cracks open its shell, but before it makes it to the surface, the root goes down and the seed grows in the direction of greater levels of red light compared to far red. Blue light doesn’t usually make it underground, but the seed can sense red from the surface, and grows in that direction.
Once the seed reaches the surface and gets exposed to blue light, it stops acting like a root and starts acting more like a seedling, opening its leaves and growing towards the closest source of blue light. If it doesn’t get a good amount of blue light at the surface, it continues to grow its main stem longer and longer without making any leaves, acting more like a root than a plant because it still “thinks” it’s underground, or at least hidden from the sun.
Seeds move toward the light, and the leaves inside don’t open up once the plant hits the surface…it’s looking for the right amount of the right color of light!
If a plant doesn’t get access to enough light at the surface, it stays in “root mode” and keeps growing taller without opening up its leaves.
Stems tend to stay shorter when they’re getting more red light compared to far-red
In bright sunlight, a cannabis plant tends to grow short and squat. This is because direct sunlight usually has more red than far-red and the plant reacts to this ratio. So if a plant is getting more 660nm than 730nm light, the stems tend to stay short and the plant grows a lot of nodes with shorter stems.
On the flip side, if a plant is getting a more 730nm light than 660nm, it tends to grow tall and stretchy. This is because, in the wild, when a plant is surrounded by a lot of vegetation, the surrounding leaves absorb a lot of the red light, and so whatever light does filter down to the hidden plant or stem has a much higher ratio of far-red light.
In response to higher levels of far-red light, stems will start to elongate and grow taller, as the plant is “stretching” up towards the light until it gets a ratio with more red and “senses” it’s in direct sunlight again.
If a plant is surrounded by greenery, it starts sensing higher ratios of far-red light, and starts “stretching” upwards to grow past the other vegetation and get access to better quality light.
Plants keep track of days and nights using the ratio of red to far-red light
You’ve seen red light at sunset. The reason you see red when the sun is on the horizon is because red light has the longest wavelengths, which travel the furthest. At sunset the light is fading quickly, and when all other light is too weak to see, you can still see the red coming through the horizon before it disappears too. Infrared light has even longer wavelengths, so it hangs on just a little bit longer. That means for the plant, the highest ratio of far-red light occurs at sunrise and sunset.
The information contained in the light is important to a plant because it needs to be able to “know” whether it’s the beginning or end of the day. A plant can take advantage of the light spectrum information to keep track of day and night by sensing when there’s the highest ratio of far-red light.
A cannabis plant keeps track of the ratio of red and far red light to help it set its internal “clock”
Far-red light is the last thing a plant “sees” at sunset, so when there are high far-red levels followed by a period of darkness the plant “knows” that it’s nighttime.
When a plant starts getting higher levels of red light combined with blue from the morning sun, it “knows” that the day has started again. If a plant is exposed to red light during the dark period, it will “wake it up” because it thinks day is happening. Blue light also affects the plant at night by messing up its circadian rhythms, though blue light alone likely won’t stop the plant from flowering.
These processes helps the plant set itself on an internal clock. Keeping track of the length of nights is the main way a cannabis plant knows when to start flowering (making buds). When nights get long, it initiates the flowering response because it “thinks” winter is coming! So growers are able to force the plant to start flowering at any time just by changing the plant’s light schedules!
Note: Even if the plant doesn’t get far-red light before dark, it will eventually “realize” it’s night time, but it starts the clock 1-2 hours later because it didn’t get that far-red “sunset” signal. Because of this, there’s some evidence that if you provide a plant with a burst of far-red light right before it goes to sleep in the flowering stage, you could cut 1-2 hours off your night period and it wouldn’t interrupt the flowering cycle. That being said, it’s always a good idea to give your flowering cannabis plant at least 12 hours of uninterrupted darkness every night to make sure budding goes smoothly! When time schedules get weird, you sometimes end up getting hermies or have your plant revert back to the vegetative stage, which most growers don’t want!
Can I use a thermal imaging camera to watch over cannabis my plants at night?
You can use an infrared camera to “spy” on your plants while they’re sleeping – it won’t interrupt their slumberYes. The way a thermal camera (also called an infrared camera, or thermographic camera) works is it actually absorbs/measures how much infrared light is being given off by objects.
A thermal camera works by showing warmer objects as lighter colors. So for example, the cold ground will appear dark, while a plant is a little warmer and will appear lighter. A human is warmer still and appears almost white on such a camera.
A thermal (infrared) camera doesn’t actually give off any light, it only measures it. So although far-red light does have an effect on plants, it won’t be affected by a camera that doesn’t produce any.
However, if your camera has a screen, the light from the screen is definitely an unwanted source of light!
What if I can only pick one spectrum?
We’ve learned that spectrum can change how a plant grows. So it’s definitely a good idea to try to match the spectrum with your goals, but what do you do when you can only get one light and must choose between one spectrum or the other?
If you have to choose between one or the other, it’s generally recommended to use the flowering light spectrum (more red) for the whole grow. This results in bigger yields watt-for-watt. However, you can successfully grow buds in the blue light spectrum for the whole grow, and many growers do this with excellent results. Some growers even claim they like their quality better under blue lights!
In other words, color spectrum is important, but it won’t make or break your grow.