When it comes to measuring how “good” a grow light is, or how much light it’s producing for your plants, it can get confusing because a lot of terms get thrown around willy-nilly.
The truth is that there is no one best way to measure light, but there are several ways and each has their own strengths and weaknesses.
Lumens
One of the most common ways you’ll see light measured is with lumens. Lumens measure “luminous flux” which is a fancy way of saying that it’s how much light you can see as a person. It measures how “bright” something is to human eyes, and it’s weighted so that light we see counts more than the light we don’t see as well. The amount of light received at a particular point in space is known as lux, or lumens per square meter (1 lumen/m2 = 1 lux).
When it comes to plants, the type of light we can see, and the type of light they can use are pretty close. So even though lumens don’t measure light exactly as a plant sees it, it does give us a good general idea of how bright a light is to plants for many types of grow lights. Not perfect, but a good ballpark figure.
For example lumens are a pretty great way to compare the amount of light put out by fluorescent lights, CFLs, HIDs, MH and HPS grow lights. However, when it comes to LED grow lights, lumens are not as a good measure anymore since LEDs usually give off light only in very narrow wavebands of light, and the weighted numbers from lumens aren’t as good a way to predict how much usable light is getting sent to the plants.
Which takes us to another common way to measure light from grow lights…
Photosynthetically Active Radiation (PAR)
Instead of considering how much light is produced from a light source as humans see it, PAR actually considers only the spectral range of solar radiation from 400 to 700nm, which is the spectra of light that plants can use for photosynthesis. It’s pretty close to the range of light that humans can see, but not quite.
PAR refers to light in the 400-700nm range, as this is the range plants use for photosynthesis
There is a lot of confusion about this term! PAR is actually just a way to talk about the spectrum of light between 400-700nm. It doesn’t actually measure anything. When people are talking about “the amount of PAR a grow light gives off,” they’re actually talking about how much light in the PAR range that a light is giving off, or PPFD (Photosynthetic Photon Flux Density, sometimes abbreviated PPF).
So when most people talk about PAR, they’re actually talking about “PPFD” or how much light is getting sent that can be used for photosynthesis. When scientists and plant biologists are measuring how much light is being produced for a plant in experiments with light spectrum, they almost always measure in PPFD.
Plants are more efficient at producing energy from light in some parts of the PAR spectrum than others. For example, we know that plants are most efficient at photosynthesis when using light in the red and blue range. This is why you see graphics like this when people are talking about PAR. This measures how well each type of chlorophyll in plants is able to absorb energy from light at different parts of the PAR spectrum.
However, it’s important to note that cannabis plants can photosynthesize light from all parts of the spectrum, including in the green section as you can see in the graphic above, even if a plant doesn’t absorb energy from all types of light evenly.
One way green light is helpful is it penetrates further down into the canopy than red and blue light, which get mostly absorbed by the upper leaves. This adds to amount of photosynthesis happening to leaves further down on the plant.
Additionally, since the spectrum of light also has an effect on how plants grow in ways that are completely separate from photosynthesis (as explained in this article), you probably wouldn’t get the best results focusing only on only photosynthesis anyway! As has been demonstrated by NASA and others, many plants grow more healthfully and faster when they also receive at least a little (not too much!) light from the green section, even though it’s not the most efficient light for photosynthesis.
As you’ve read today, cannabis uses many aspects of light to develop into the bud-bearing plants we love! Instead of focusing on any one aspect, it’s important to look at your results as a whole!
What to focus on for best results when it comes to quality of light:
1.Power is more important than spectrum – the total amount of light given is a lot more important to growth than spectrum! 2.Give bright light with lots of blue for shorter stems and bigger leaves 3.Give light with lots of red/yellow to promote germination, for longer stems and to promote flowering 4.Try to give a spectrum of light that includes even a small amount of green if possible for the best growth (all grow lights except most LEDs already have some green) though red/blue is all you need for the plant to grow up healthy 5.As long as you start with a great cannabis grow light, you don’t really need to worry about spectrum! Always train your plants to get the most out of your grow light (up to 40% more yields under the same grow light compared to not training) or if you’re still having trouble reaching your yield goals, upgrade to a bigger light!
PAR vs Lumens: Which is Best to Measure Grow Light Intensity?
When it comes to measuring how “good” a grow light is, or how much light it’s producing for your plants, it can get confusing because a lot of terms get thrown around willy-nilly.
The truth is that there is no one best way to measure light, but there are several ways and each has their own strengths and weaknesses.
Lumens
One of the most common ways you’ll see light measured is with lumens. Lumens measure “luminous flux” which is a fancy way of saying that it’s how much light you can see as a person. It measures how “bright” something is to human eyes, and it’s weighted so that light we see counts more than the light we don’t see as well. The amount of light received at a particular point in space is known as lux, or lumens per square meter (1 lumen/m2 = 1 lux).
When it comes to plants, the type of light we can see, and the type of light they can use are pretty close. So even though lumens don’t measure light exactly as a plant sees it, it does give us a good general idea of how bright a light is to plants for many types of grow lights. Not perfect, but a good ballpark figure.
For example lumens are a pretty great way to compare the amount of light put out by fluorescent lights, CFLs, HIDs, MH and HPS grow lights. However, when it comes to LED grow lights, lumens are not as a good measure anymore since LEDs usually give off light only in very narrow wavebands of light, and the weighted numbers from lumens aren’t as good a way to predict how much usable light is getting sent to the plants.
Which takes us to another common way to measure light from grow lights…
Photosynthetically Active Radiation (PAR)
Instead of considering how much light is produced from a light source as humans see it, PAR actually considers only the spectral range of solar radiation from 400 to 700nm, which is the spectra of light that plants can use for photosynthesis. It’s pretty close to the range of light that humans can see, but not quite.
PAR refers to light in the 400-700nm range, as this is the range plants use for photosynthesis
There is a lot of confusion about this term! PAR is actually just a way to talk about the spectrum of light between 400-700nm. It doesn’t actually measure anything. When people are talking about “the amount of PAR a grow light gives off,” they’re actually talking about how much light in the PAR range that a light is giving off, or PPFD (Photosynthetic Photon Flux Density, sometimes abbreviated PPF).
So when most people talk about PAR, they’re actually talking about “PPFD” or how much light is getting sent that can be used for photosynthesis. When scientists and plant biologists are measuring how much light is being produced for a plant in experiments with light spectrum, they almost always measure in PPFD.
Plants are more efficient at producing energy from light in some parts of the PAR spectrum than others. For example, we know that plants are most efficient at photosynthesis when using light in the red and blue range. This is why you see graphics like this when people are talking about PAR. This measures how well each type of chlorophyll in plants is able to absorb energy from light at different parts of the PAR spectrum.
However, it’s important to note that cannabis plants can photosynthesize light from all parts of the spectrum, including in the green section as you can see in the graphic above, even if a plant doesn’t absorb energy from all types of light evenly.
One way green light is helpful is it penetrates further down into the canopy than red and blue light, which get mostly absorbed by the upper leaves. This adds to amount of photosynthesis happening to leaves further down on the plant.
Additionally, since the spectrum of light also has an effect on how plants grow in ways that are completely separate from photosynthesis (as explained in this article), you probably wouldn’t get the best results focusing only on only photosynthesis anyway! As has been demonstrated by NASA and others, many plants grow more healthfully and faster when they also receive at least a little (not too much!) light from the green section, even though it’s not the most efficient light for photosynthesis.
As you’ve read today, cannabis uses many aspects of light to develop into the bud-bearing plants we love! Instead of focusing on any one aspect, it’s important to look at your results as a whole!
What to focus on for best results when it comes to quality of light:
1.Power is more important than spectrum – the total amount of light given is a lot more important to growth than spectrum!
2.Give bright light with lots of blue for shorter stems and bigger leaves
3.Give light with lots of red/yellow to promote germination, for longer stems and to promote flowering
4.Try to give a spectrum of light that includes even a small amount of green if possible for the best growth (all grow lights except most LEDs already have some green) though red/blue is all you need for the plant to grow up healthy
5.As long as you start with a great cannabis grow light, you don’t really need to worry about spectrum! Always train your plants to get the most out of your grow light (up to 40% more yields under the same grow light compared to not training) or if you’re still having trouble reaching your yield goals, upgrade to a bigger light!