Index
LED grow light technology is relatively new. One of its advantages is the ability to produce a multitude of different emission spectra.
In this article, we discuss what constitutes a full spectrum LED grow light and whether they are advantageous for plant growth.
What is a traditional LED grow light spectrum
A traditional grow LED grow light typically uses a combination of blue and red LEDs. You can generally tell by the pinkish-purple light emitted - this is the result of mixing blue and red light.
The reason traditional LED grow lights use this formulation is that plants perform photosynthesis most effectively in the blue and red part of the spectrum.
Looking at this spectrum, however, it is clear that only a narrow part of the entire visible spectrum is covered. This is certainly far from what we would call full spectrum.
Generally, these grow lights use monochromatic LEDs - i.e. a blue LED and a red LED. You can typically tell by taking a look at its spectral power distribution, as shown below:
But if blue and red light is the best at contributing to photosynthesis, why do we care about other wavelengths?
The answer is that there are other processes that affect plant health and vigor that are not simply a matter of how much photosynthesis occurs. Ultimately, this can mean a higher quality crop, improved aesthetics, or higher nutrient content. In other words, quality rather than just quantity.
Definition of full spectrum LED grow lighting*
There is still a significant amount of research that still needs to be performed, but more and more results from experiments and studies are pointing to the fact that plants grow best under a balanced spectrum.
This can be explained by the fact that plants have evolved to use natural daylight not only as a food source but signal for things like flowering and fruit production.
Therefore, the strict definition of full spectrum would entail a spectrum that has energy ranging from ultraviolet to infrared, just like natural daylight.
A light source with this type of spectrum generally appears white. If an LED grow light emits white light, does that automatically make it a full spectrum grow light?
The answer is no, and we discuss this further in the next section.
Different ways to create white light.
Unlike the traditional LED grow light method of blue and red monochromatic LEDs, full spectrum grow lights will typically use a phosphor coating.
The reason a phosphor coating is helpful in full spectrum grow lights is that phosphors take light from a single narrow wavelength range (e.g. 460 nm blue) and convert it to a wide range of longer wavelength light (e.g. 600 - 700 nm red).
By coating a blue LED with a mixture of green, yellow and/or red phosphors, much wider coverage across the visible spectrum can be achieved.
Because phosphors emit light of so many different wavelengths, the result is a balanced mixture of colors that result in white light.
Just because an LED grow light emits white light, that does not necessarily mean that it is truly a full spectrum light source.
One convenient method is to evaluate its color rendering index (CRI). This is a useful metric because it tells us how similar it is to natural daylight. A higher CRI rating indicates that the light source is more similar to natural daylight, which is an ideal, full-spectrum light source.
Optimal distance between plants and LED grow lights
What is the optimal distance between plants and LED grow lights? This is a common question among indoor growers who are trying to maximize their yield while reducing electrical costs.
With metal halide (HID) and sodium lamps, a significant amount of heat is generated by the lamp itself, and much of the emitted energy is in the form of infrared.
As a result, placing the plants too close to a light source can result in burns and damage to plant tissue as a result of excessive heat exposure.
LED grow lights, on the other hand, are more efficient and generate virtually no infrared energy. This means that even at close proximity, plants will generally not suffer burns or tissue damage under LED grow lights.
One thing to keep in mind is that even high efficiency LEDs do generate heat. Unlike metal halides and sodium lamps, heat is dissipated through the lamp body, and as a result, plants that come in contact with a warm lamp could suffer some minor burns.
We therefore recommend keeping plants a sufficient distance away from LED grow lights whose outer casing gets very warm, as plants that grow quickly can find themselves tangled with a warm lamp, causing burns.
What is the difference between PPFD and PPF?
If youāre looking to understand how grow lights compare, you likely have come across the metrics PPF and PPFD.
However, you might be confused about what these metrics mean, and how you can make sense of them to make an informed purchasing decision. In this article we go over the basic differences between PPF and PPFD.
The difference between PPF and PPFD by definition
PPF and PPFD are both acronyms that deal with the amount of light for a light source or location:
- PPF - photosynthetic photon flux
- PPFD - photosynthetic photon flux density
What exactly is a photosynthetic photon? A photon is a single particle of light, and can take on a variety of wavelengths. Those that are capable of contributing to photosynthesis are considered a photosynthetic photon.
Specifically, this includes photons with wavelengths between 400 nm and 700 nm.
PPF and PPFD measure the quantity of such photons. The critical difference is that PPFD measures the density of these photons falling on a particular surface, while PPF is a measure of the total number of photons released from a light source.
In our graphic below, each dot represents a single photosynthetic photon. PPFD is the number of photons that land on a particular surface, while PPF is the total number of photons that are released from the light source.
The graphic should reveal two additional properties about PPFD.
First, the closer to the light source, the higher the PPFD reading. This is due to the dispersion of light as one moves away from the light source.
Second, the center of the beam typically has the highest PPFD reading. As you move farther away from the center, PPFD will decrease.
PPF and PPFD units of measure
- PPF - Ī¼mol/s
- PPFD - Ī¼mol/s/m2
Both PPF and PPFD measure the total number of photons. This is obviously a very large number, so the unit micromoles (Ī¼mol) per second is used. A micromole is equivalent to approximately 6 x 1017. Further, since we are measuring the rate of these photons, this is counted per second.
PPF is simply micromoles per second, but PPFD is micromoles per second per meter squared. This is because we want to know how many photosynthetic photons land on a square meter per second.
When to use PPFD vs when to use PPF
PFD should always be accompanied by a distance and location. Most manufacturers will publish PPFD data, but be sure that you take into account:
- Distance from the light source
- Location and whether this is averaged over a certain area
Without knowing this information, you cannot meaningfully compare PPFD.
PPFD can be the result of multiple lamps lighting a single area.
PPF, on the other hand, measures the amount of PAR from a single grow light. You can make meaningful comparisons between lamps by comparing its PPF measurement. That being said, be aware that depending on the beam angle, this can affect eventual PPFD readings depending on the products.
Measurement method differences between PPFD vs PP
Since PPFD is a measure of how much light falls on a surface, even a small, handheld light meter or spectrometer can measure the amount of PAR that falls on a surface. These are typically lower cost and even be connected to smartphones and used in the field.
PPF, on the other hand measures the amount of PAR that is emitted by a single light source, and in all directions. Therefore, slightly more sophisticated instruments are required. Typically a goniosphere or integrating sphere is needed. These devices capture the light emitted in all angles, and then measures the collective light emitted.
Micromoles to moles conversion and definition
A micromole is a unit of measure defined as 10-6 (one-millionth) of a mole. The symbol for micromole is commonly umol or Ī¼mol.
A mole is defined as approximately 6.022140857 x 1023, so therefore a micromole can also be defined as:
1 Ī¼mol = 6.022140857 x 1017
Micromoles are commonly used to count the number of photons in a plant grow light system.
Want to convert micromoles to moles? Use the calculator below
About the Lux to PPFD Calculator
You may find yourself comparing LED grow light specifications, where one light uses lux and the other uses PAR units such as PPFD. How do you compare the two?
It is not possible to convert Lux to PPFD absolutely accurately without providing the light sourceās spectral power distribution (SPD). In reality, however, obtaining a light sourceās exact SPD is not an easy task for the average grower - it requires expensive spectrometer equipment.
We have therefore developed the calculator below which allows for approximate conversions between lux and PPFD based on some assumptions about the light sourceās SPD. To improve the approximations for your particular light source, select the SPD that most closely resembles that of your light source.
Need to go the other way? See our PPFD to Lux calculator here
Need to convert lumens to PPF micromoles per second? See our lumens to ppf calculator here
https://www.waveformlighting.com/horticulture/convert-ppfd-to-lux-online-calculator
About the PPFD to Lux Calculator
You may find yourself comparing LED grow light specifications, where one light uses lux and the other uses PAR units such as PPFD (umol). How do you compare the two?
It is not possible to convert PPFD to Lux absolutely accurately without providing the light sourceās spectral power distribution (SPD). In reality, however, obtaining a light sourceās exact SPD is not an easy task for the average grower - it requires expensive spectrometer equipment.
We have therefore developed the calculator below which allows for approximate conversions between lux and PPFD based on some assumptions about the light sourceās SPD. To improve the approximations for your particular light source, select the SPD that most closely resembles that of your light source.
Need to go the other way? See our Lux to PPFD calculator here
Need to convert PPF micromoles per second to lumens? See our ppf to lumens calculator here
https://www.waveformlighting.com/horticulture/convert-lumens-to-ppf-online-calculator
About the Lumens to PPF (umol/s) Calculator
You may find yourself comparing LED grow light specifications, where one light uses lumens and the other uses PAR units such as PPF (umol/s). How do you compare the two?
It is not possible to convert Lumens to micromoles per second absolutely accurately without providing the light sourceās spectral power distribution (SPD). In reality, however, obtaining a light sourceās exact SPD is not an easy task for the average grower - it requires expensive spectrometer equipment.
We have therefore developed the calculator below which allows for approximate conversions between lumens and PPF based on some assumptions about the light sourceās SPD. To improve the approximations for your particular light source, select the SPD that most closely resembles that of your light source.
Need to go the other way? See our PPF to Lumens calculator here
Need to convert lux to PPFD micromoles per second per meter squared? See our lux to PPFD calculator here
https://www.waveformlighting.com/horticulture/convert-ppf-to-lumens-online-calculator
About the Lumens to PPF
You may find yourself comparing LED grow light specifications, where one light uses lumens and the other uses PAR units such as PPF (umol/s or micromoles per second). How do you compare the two?
It is not possible to convert Lumens to micromoles per second absolutely accurately without providing the light sourceās spectral power distribution (SPD). In reality, however, obtaining a light sourceās exact SPD is not an easy task for the average grower - it requires expensive spectrometer equipment.
We have therefore developed the calculator below which allows for approximate conversions between lumens and PPF based on some assumptions about the light sourceās SPD. To improve the approximations for your particular light source, select the SPD that most closely resembles that of your light source.
Need to go the other way? See our Lumens to PPF here
Need to convert PPFD micromoles per second per meter squared to lux? See our PPFD to lux calculator here
https://www.waveformlighting.com/horticulture/daily-light-integral-dli-calculator
Daily Light Integral (DLI) is a measure of the aggregate amount of PAR light that a surface receives over the course of a day. It is a very useful metric to determine if a particular location receives sufficient amounts of light for plants to grow well.
Low light plants require between 5-10, medium light plants 10-15, and high light plants will require more than 15.
PPFD (umol/s/m2) to DLI (mol) Calculator
Grow lights go quantum with LED
LED technologies have opened up new opportunities in efficient and effective spectral control never seen before, and this has allowed LED grow light technology to be a viable substitute for natural daylight. Lighting for plants must be discussed at the quantum level, where the total amount of light is measured in the number of photons.
The line between breaking even on electricity costs as well as grow quality, however, is very thin. An in-depth understanding of photosynthesis and plant growth at the quantum level is therefore necessary to successfully grow plants using LED lighting alone. Specifically, at Waveform Lighting, we see shortcomings in metrics such as Photosynthetically Active Radiation (PAR) because it provides weightings for photons between 400 and 700 nm, indiscriminately. It is our philosophy that taking a closer look at the number of photons being emitted at each wavelength is critical for achieving more efficient and healthy plant growth.
What is needed in an LED grow light?
The primary objective of an LED grow light is to efficiently deliver the necessary light to a plant so that it can perform photosynthesis and grow quickly and healthily. We must therefore look at the wavelengths of light that chlorophyll, the primary pigment responsible for absorbing photons, absorb most efficiently, and secondly, how much light is needed.
Spectrum Considerations
Below is a spectral diagram showing the absorption spectra for chlorophyll A and chlorophyll B, respectively.
Chlorophyll A
Chlorophyll A has peak absorption in both the blue and red parts of the spectrum. Wavelengths between 380 nm and 450 nm are absorbed very well, with a pronounced peak at 430 nm. In the red region, wavelengths 600 nm and above are absorbed, with a sharp peak at 660 nm. What this tells us is that providing light at 430 nm and 660 nm will allow chlorophyll A to very efficiently convert photons into energy for the plant.
Chlorophyll B
Like chlorophyll A, chlorophyll B has peak absorption in both the blue and red parts of the spectrum as well, but it absorbs blue light much more efficiently. A very strong peak at 450 nm dominates the blue region of the spectrum, but absorption sensitivity continues down towards 420 nm. The primary red peak absorption occurs at 640 nm, but absorption occurs at across a relatively wide range between 600 and 660 nm.
From these chlorophyll spectra, it is clear that both blue and red light work well for allowing plant photosynthesis to occur. In particular, peak wavelengths at 430 nm, 450 nm, 640 nm and 660 nm are essential for efficient growth. It is important to provide plants with a balanced ādietā of different wavelengths, however. Just like a human bodybuilder, in addition to needing to consume sufficient amounts of protein, a balanced diet of vitamins and various food groups is necessary for health. Similarly, plants can be encouraged to grow quickly with both blue and red light; however, it is critical that they also receive light across the spectrum. We know that natural daylight is extremely effective for healthy plant growth, so we take a look at natural daylight spectra, as shown below.
Summer Daylight
Natural daylight has a continuous and extremely wide coverage across the spectrum. In particular, summer daylight is characterized by relatively equal amounts of energy at all wavelengths.
Fall Daylight
As the seasons change from summer to fall, the spectrum of light that reaches the ground also changes due to the lower angle of the sun. In particular, there is significantly more energy in the orange and red regions of the spectrum. This is a key shift for plants who depend on this to signal changes in their growth to reproductive strategies such as flowering and fruit production.
Our grow light spectra address both the needs of photosynthesis and overall plant health, while keeping LED efficiency values in mind. We have further refined our light recipes to account for spectral changes in nature that induce certain processes such as flowering and fruit production.
Intensity Considerations
Even if an optimal spectral distribution is achieved, if there is simply not enough light intensity, successful growth will not happen. The total amount of light delivered to a plant is measured as its Daily Light Integral (DLI) and is measured as the total number of photons delivered over a 24-hour period. Depending on the plant species, this value will vary, and you may need to do some experimentation to verify this for your particular setup. That being said, most low-light plants such as lettuce and spinach require about 5 - 10 DLI, while other high-light plants will require upwards of 20 DLI.
All of our grow light products are rated in DLI units for your convenience.
Want to know more?
https://www.waveformlighting.com/learn
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