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LED GUIDE
Why grow with LED?
■ Because (high-end) LEDs offer a complete spectrum in which the most important wavelengths (expressed in nanometer, nm) are represented. For example: HPS lights mainly emit colors that are least favorable / effective for plants like yellow and orange light.
■ Improved light spectrum, specifically designed
■ Excellent fruit quality with more terpenes, giving a better effect, (fruit)color, aroma and taste compared to HPS, LEC, CDM, CMH or Plasma lights
■ Boost active substances and increase plant specific characteristics
■ Higher value crop harvests due to improved quality
■ More usable light, less heat than HPS, improved grow room conditions. Grow all summer long!
■ Less energy consumption, lower running costs compared to HPS and reduced cost on cooling/air conditioning (HVAC)
■ Silent and maintenance free with hardly any loss of light intensity during product lifetime
■ 50.000+ hours guarantee. No replacement bulb costs ever
■ Safe to use and easy to grow with
How do I choose the perfect LED?
To ensure that your investment in an LED grow light meets your cultivation and production goals, you need to know what manufacturers mean by PAR, PPF, PPFD, and photon efficiency to make an informed purchasing decision. However, these three metrics should never be used as sole variables to make a purchasing decision.

There are several other variables that need to be considered as well, we will explain these later on:

■ your goal: Are you germinating (seeds), are you growing seedlings, cuttings or mother plants; do the crops remain in the vegetative phase, or do they flower as well? Do you aim for the highest yields possible or do you have medicinal purposes in mind (we recommend spectrum control for the best medicinal endproducts)? The plantphase will mostly determine your final choice. Please read a more detailed explanation in section 3.
■ coverage area: The size of the surface that you want to illuminate used to determine the required wattage (to a large extend). Wattage used to tell you ''how much light'' would be emitted. This is not the case with LEDs (and lighting sources in general) as PPFD tells you how much usable light is actually emitted on the surface of your plant(s). Please read a more detailed explanation in section 2.
■ the spectrum: Determines for what kind of plant(s) and for which phase(s) of the(se) plant(s) the fixture is best suited (for Germination, Clones, Motherplants, Vegetative and/or Flowering). Every wavelength / color has a different effect on plant development and photosynthesis. Plants are in need for different wavelengths / colors in different phases (germination, cloning, vegetative and flowering) and ratio's. Please read a more detailed explanation in section 3 or the complete information here: https://ledbypassion.com/spectrum.
■ your personal health: Does your health allow you to work on your knees, to bend and to ''SCROG'' for example? Does it allow you to lift heavy lights (15 – 20 kg) or do you prefer to work with lightweight LED bars?
■ your growing method: We recommend different lighting systems for several growing methods; some LED systems need to be used at a close hanging distance (the distance from your light to the top of your plants) and other lights are used at a high hanging distance. So it depends on the method of growing you prefer.
■ your grow environment: Temperature, humidity, air circulation, background noise and your living situation for example (HVAC) can influence your final choice. For example: you don't want any noise (caused by active thermal management) if you are growing in your bedroom.

All factors need to be taken into consideration to select the most appropriate system based on your cultivation and business goals, and the take home message is that PPF, PPFD, and photon efficiency are the proper metrics used by scientists and industry leading horticulture lighting companies. If a company does not provide you with the correct metrics used for horticulture lighting, they should not be selling horticulture lighting systems, and you will not be able to verify the true efficiency of their system.
How many watts do I need?
Space availability is a vital factor when purchasing lighting as it determines the amount and size of lamps you need. The first thing you need to do is measure the exact size of your garden. Then you need to find out the coverage area of the lights you're considering in order to determine the exact number you need. The recommended and maximum coverage area is mentioned in the discription of every light in our collection. The general guideline most growers use is that you need 32 watts of actual power per 30 cm² if you're growing high-light plants like tomatoes. Low-light plants like lettuce need somewhere between 11 and 18 watts per 30 cm².

We recommend different wattages for certain coverage areas, on average:

60 x 60 cm 50 – 200 Watts LED
80 x 80 cm 200 – 400 Wats LED
100 x 100 cm 400 – 600 Watts LED
120 x 120 cm 400 – 800 Watts LED


The recommended and maximum coverage area of a light are different in the vegetative and flowering phase because vegetative plants need a lower PPFD range compared to flowering plants. This means you can illuminate a larger cultivation area during VEG (because the hanging distance can be increased during the vegetative phase) in contrast to the Flowering phase.
Which spectrum do my plants need?
This depends on the plant species and phase the plants are in. We recommend full spectrum LEDs for full cycle grows (a full cycle grow is a cycle from germination/vegetative phase to the reproductive/flowering phase). Full Spectrum lights are illuminaires in which most colors are represented: Blue/Violet, Green, Red and Far Red Light are essential. The addition of other colors of light (full-spectrum light) has been shown to have further benefits for plant growth. This can be done by adding wavelenghts from the UVB, UVA, Yellow, Orange and Infrared spectrum.

Although plants can grow under almost any type of light, efficient photosynthesis requires different wavelengths and some of the best led grow lights can provide plants with the full spectrum necessary throughout each growth.

For example, in order to grow most efficiently, many plants need light in the red, blue and green spectrums, but also infrared and ultraviolet, depending on the stage. A powerful full spectrum LED grow light enables you to cater to the plant's specific needs by providing the proper photosynthetically active radiation values.

Click here for detailed information about the Spectrum, Light and the effect of different colors / wavelengths on high-intensity plants: ledbypassion.com/spectrum

■ Germination (seeds): well-tuned (high) Blue to Red ratio and a small amount of Green, avoid Far Red
■ Clones (cuttings): well-tuned (high) Blue to Red ratio and a high amount of Green, avoid Far Red
■ Vegetative phase (including motherplants): Blue dominant, well tuned Blue to Red ratio and a high amount of Green
■ Pre-Flowering phase: well tuned Blue to Red ratio and a high amount of Green
■ Flowering / Reproductive phase: Red dominant, well tuned Blue to Red ratio and a moderate amount of Green
■ Ripen / Finish: - Last 3 weeks of Flowering / Reproductive phase: Supplemental lighting with UV-B wavelengths for 3-4 hours a day, in the middle of your 12 hour light cycle (the duration of this supplemantal lighting depends on your cultivation and business goals.
- Last 3 days of Flowering / Reproductive phase: ''No Red'' light treatment for Boosting terpenes in high-intensity plants (''Blue Light Treatment'').
PAR,PPF,PPFD and Photo efficiency?
If you have been researching LED horticulture lighting systems, you have likely been bombarded with a variety of metrics that lighting manufacturers use to market their products. Some terms and acronyms you are likely to see include: watts, lumens, LUX, foot candles, PAR, PPF, PPFD, and photon efficiency. While all of these terms do relate to lighting, only a select few really tell you the important metrics of a horticulture lighting system:

■ PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis.
■ PPF measures the total amount of PAR that is produced by a lighting system each second, in micromoles per second (μmol/s). This is probably the second most important way of measuring a horticulture lighting system.
■ PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second, in micromoles per square meter per second (μmol/m²/s).
■ Photon efficiency refers to how efficient a horticulture lighting system is at converting electrical energy into photons of PAR, in micromoles per Joule (μmol/J). The higher this number is, the more efficient a lighting system is at converting electrical energy into photons of PAR.

Click here for detailed information about these metrics: https://ledbypassion.com/lighting-metrics-par-ppf-ppfd-photon-efficiency
How much PPFD do my plants need?
During establishment growth, light intensities need to be kept relatively low as the plant is developing leaves and stems that will be used to provide photosynthates during the vegetative growth phase. Increasing light intensity as you transition into the vegeta- tive and reproductive growth phases will increase the rate of pho- tosynthesis, which will provide the plant with more photosynthates used to develop flowers and subsequent fruit. Plants need time to adjust to high light intensities (referred to as photoacclimation). If you expose plants to high light intensities too early in the crop cycle, you can damage chlorophyll pigments causing photo-oxidation (photo-bleaching), so we recommend slowly increasing your light intensity as your plant develops. Refer to the recommended PPFD ranges for establishment, vegetative, and reproductive growth of high-intensity plants, tomatoes, cucumbers, and peppers.

■ Examples of recommended PPFD (μmol/m²/s):

Species High Intensity Plants
Seed100 – 300
Vegetative Cutting75 – 150
Vegetative300 – 600
Reproductive 600++

Species Tomatoes
Seed150 – 350
Vegetative Cutting75 – 150
Vegetative350 – 600
Reproductive 600++

Species Cucumbers
Seed100 – 300
Vegetative Cutting-
Vegetative300 – 600
Reproductive 600++

Species Peppers
Seed150 – 350
Vegetative Cutting-
Vegetative300 – 600
Reproductive 600++

Wattage actually only matters because there is a maximum PPFD range linked to the wattage of an LED system. Wattage is a metric for input, not for output so the wattage doesn't tell you anything about the light (converted electrical power in wattage) that comes out, PPFD does and is your most important metric. For example: a 600 Watts LED light will have a much higher PPFD than a 600 Watts HPS light. So if you would compare these 2 lighting sources based on PPFD, the 600 Watts LED light has the same PPFD as a 800 - 1000 Watts HPS light (considering a high-end LED system).
What are the benefits of LED vs. HPS?
■ Yes there definitely are! A recent study conducted by the Wageningen University & Research Centre in the Netherlands shows promising results for LED grow lights. They found that the crops that were grown under high light intensity produced a higher bud weight when compared to the same crops grown under normal light intensity.
■ Furthermore, the study found that in all varieties of light, crops grown using LED produced a higher content of active substances than crops using HPS lamps with the same light intensity.
■ The aroma, flavor, and color of a plant depend on the type, strength, and quantity of Terpenes within that particular plant. A high Blue ratio during the last 3 days of flowering ensures an explosive increase in A high Blue ratio during the last 3 days of flowering ensures an explosive increase in terpenes in spices and herbs (this is called the ''Blue Light Treatment'').

Spectrum

What is Light ?

Light is the single most important environmental variable concerning plant growth. Plants are autotrophs that evolved to use light energy from the sun to make their own food source via photosynthesis. Plants primarily use wave-lengths of light within the visible light range of the electromagnetic spectrum (Figure 1) to drive photosynthesis, which is why light ranging from 400 - 700 nm is called photosynthetically active radiation (PAR). A triumph of physics in the early 20th century was the realization that light behaves both as a wave and a particle. These particles are known as photons or quanta, and the intensity that photons are absorbed by plants is critical to plant growth via photosynthesis.

So, light is a form of electromagnetic radiation, a type of energy that travels in waves. Other kinds of electromagnetic radiation that we encounter in our daily lives include radio waves, microwaves, and X-rays. Together, all the types of electromagnetic radiation make up the electromagnetic spectrum.Every electromagnetic wave has a particular wavelength, or distance from one crest to the next, and different types of radiation have different characteristic ranges of wavelengths (as shown in the diagram below). Types of radiation with long wavelengths, such as radio waves, carry less energy than types of radiation with short wavelengths, such as X-rays.

The electromagnetic spectrum is categorized by wavelength. The longer the wave, the less energy it holds. So blue light, which has a short wavelength of 475 nanometers, has more energy than red light, which has a wavelength of 660 nm. Infrared light is just beyond the range of human vision at 730nm. Although we cannot see it, we can feel infrared radiation as warmth. For instance, a glowing charcoal emits red light in the visible spectrum and infrared light that we sense as heat.

The electromagnetic spectrum (Fluence BML)

Figure 1: The electromagnetic spectrum

A light wave (or any other form of electromagnetic radiation) has evenly spaced crests and troughs. The distance from crest to crest, or, equivalently, from trough to trough, is defined as the wavelength.

Wavelength, Source: The light-dependent reactions of photosynthesis, by OpenStax College, Biology

Figure 2: Wavelength, Source: The light-dependent reactions of photosynthesis, by OpenStax College, Biology (CC BY 3.0).

Photosynthesis: Overview of the light-dependent reactions, including         

the structure of the chloroplast, the photosystems, and how ATP is            
synthesized. 
(Created by Sal Khan)
       

Photosynthesis: The Calvin cycle, or the light-independent (dark)
reactions



Most indoor growers seem to believe that the best indoor grow lights would have the same light spectrum as the sun – a relatively full spectrum over the visible light frequencies. After all, plants evolved over millions of years to best convert light energy into carbohydrates and sugars. The most readily available light from the sun is in the middle spectrums which we see as green, yellow and orange. These are the primary frequencies that human eyes use. However, studies show that these are the least used light frequencies in plants. Most of the photosynthetic activity is in the blue and red frequencies.

sunrate
Figure 3: Natural Sunlight                                                                             Figure 4: Rate of Photosynthesis

The main reason for this counter-intuitive use of light by plants seems to be related to early forms of bacteria and the evolution of photosynthesis. Photosynthesis first evolved in bacteria over millions of years in the primordial sea. This evolved in bacteria long before the appearance of more complex leafy plants. These early photosynthetic bacteria extensively used the yellow, green and orange middle spectrums for photosynthesis which tended to filter out these light spectrums for plants evolving at lower levels in the ocean. As more complex plants evolved at lower levels they we left with only the non-filtered spectrums not used by bacteria – mostly in the red and green frequencies. The yellow, green and orange light is mostly reflected off the surface of the leaves and this is why photosynthesizing plants are green.

Rate of Photosynthesis (California Lightworks)
Figure 5:
Rate of Photosynthesis

Pigments absorb light used in photosynthesis

In photosynthesis, the sun’s energy is converted to chemical energy by photosynthetic organisms. However, the various wavelengths in sunlight are not all used equally in photosynthesis. Instead, photosynthetic organisms contain light-absorbing molecules called pigments that absorb only specific wavelengths of visible light, while reflecting others.

The set of wavelengths absorbed by a pigment is its absorption spectrum. In the diagram below, you can see the absorption spectra of three key pigments in photosynthesis: chlorophyll a, chlorophyll b, and β-carotene. The set of wavelengths that a pigment doesn't absorb are reflected, and the reflected light is what we see as color. For instance, plants appear green to us because they contain many chlorophyll a and b molecules, which reflect green light.

 

Optimal absorption of light occurs at different wavelengths for different pigments. Source: The light-dependent reactions of photosynthesis, by OpenStax College, Biology
Figure 6:
Optimal absorption of light occurs at different wavelengths for different pigments. Source: The light-dependent reactions of photosynthesis, by OpenStax College, Biology (CC BY 3.0)

Most photosynthetic organisms have a variety of different pigments, so they can absorb energy from a wide range of wavelengths. Here, we'll look at two groups of pigments that are important in plants: chlorophylls and carotenoids.

Do different light spectrums do different work in plants?

Not only do plants focus on specific light spectrums for photosynthesis but different light spectrums are used for different types of growth in plants. There are millions of photosynthetic receptors in a leaf of a green plant. Each receptor includes specialized pigments that absorb specific frequencies during photosynthesis. By measuring the amount of oxygen produced under various light spectrums we can measure the amount of photosynthetic activity under each light spectrum. This has produced a very detailed map of which light spectrum is related to which type of plant growth.

Light Absorbance (California Lightworks)
Figure 7: Light Absorbance


Chlorophylls

There are five main types of chlorophylls: chlorophylls a, b, c and d, plus a related molecule found in prokaryotes called bacteriochlorophyll. In plants, chlorophyll a and chlorophyll b are the main photosynthetic pigments. Chlorophyll molecules absorb blue and red wavelengths, as shown by the peaks in the absorption spectra above.

Structurally, chlorophyll molecules include a hydrophobic ("water-fearing") tail that inserts into the thylakoid membrane and a porphyrin ring head (a circular group of atoms surrounding a magnesium ion) that absorbs light1^11start superscript, 1, end superscript.

Chlorophyll-a-2D-skeletal, by Ben Mills (public domain)
Figure 8:Chlorophyll-a-2D-skeletal, by Ben Mills (public domain)

Although both chlorophyll a and chlorophyll b absorb light, chlorophyll a plays a unique and crucial role in converting light energy to chemical energy (as you can explore in the light-dependent reactions article). All photosynthetic plants, algae, and cyanobacteria contain chlorophyll a, whereas only plants and green algae contain chlorophyll b, along with a few types of cyanobacteria2,3^{2,3}2,3start superscript, 2, comma, 3, end superscript.Because of the central role of chlorophyll a in photosynthesis, all pigments used in addition to chlorophyll a are known as accessory pigments—including other chlorophylls, as well as other classes of pigments like the carotenoids. The use of accessory pigments allows a broader range of wavelengths to be absorbed, and thus, more energy to be captured from sunlight.

Carotenoids

Carotenoids are another key group of pigments that absorb violet and blue-green light (see spectrum graph above). The brightly colored carotenoids found in fruit—such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene)—are often used as advertisements to attract animals, which can help disperse the plant's seeds.

In photosynthesis, carotenoids help capture light, but they also have an important role in getting rid of excess light energy. When a leaf is exposed to full sun, it receives a huge amount of energy; if that energy is not handled properly, it can damage the photosynthetic machinery. Carotenoids in chloroplasts help absorb the excess energy and dissipate it as heat.

What does it mean for a pigment to absorb light?

When a pigment absorbs a photon of light, it becomes excited, meaning that it has extra energy and is no longer in its normal, or ground, state. At a subatomic level, excitation is when an electron is bumped into a higher-energy orbital that lies further from the nucleus.
Only a photon with just the right amount of energy to bump an electron between orbitals can excite a pigment. In fact, this is why different pigments absorb different wavelengths of light: the "energy gaps" between the orbitals are different in each pigment, meaning that photons of different wavelengths are needed in each case to provide an energy boost that matches the gap.

Photophosphorylation: the light reactions of photosynthesis, by Mitch Singer
Figure 9: Photophosphorylation: the light reactions of photosynthesis, by Mitch Singer (CC BY 4.0)

An excited pigment is unstable, and it has various "options" available for becoming more stable. For instance, it may transfer either its extra energy or its excited electron to a neighboring molecule. We'll see how both of these processes work in the next section: the light-dependent reactions.

Source: Light and photosynthetic pigments, Khan Academy

Light Intensity

Photosynthesis occurs inside of specialized organelles known as chloroplasts, and is the process that uses light energy to split water (H2O) and fix carbon dioxide (CO2) to produce carbohydrates (CH2O) and oxygen (O2). The process is very complex; however, a simple diagram of the reaction is shown in Figure 8. As light intensity (PPFD) increases, photosynthetic rates also increase until a saturation point is reached. Every plant species has a light saturation point where photosynthetic levels plateau. Light saturation normally occurs when some other factor (normally CO2) is limited (Figure 9).

Photosynthetic Reaction (Fluence BML)

Figure 10: Photosynthetic reaction


Influence of Light Intensity (Fluence BML)


Figure 11:
Influence of light intensity on the rate of photosynthesis

During establishment growth, light intensities need to be kept relatively low as the plant is developing leaves and stems that will be used to provide photosynthates during the vegetative growth phase. Increasing light intensity as you transition into the vegetative and reproductive growth phases will increase the rate of photosynthesis, which will provide the plant with more photosynthates used to develop flowers and subsequent fruit. Plants need time to acclimate to high light intensities (referred to as photoacclimation).

If you expose plants to high light intensities too early in the crop cycle, you can damage chlorophyll pigments causing photo-oxidation (photo-bleaching), so we recommend slowly increasing your light intensity as your plant develops. Refer to Table 3 for recommended PPFD ranges for establishment, vegetative, and reproductive growth of tomatoes, cucumbers, and peppers.

Recommended PPFD (Fluence BML)
Figure 12:
Recommended PPFD


Source: Fluence BML


1931 CIE Chromaticity Diagram, Source: CREE: Colour Mixing, Copyright 2010-2016 Cree, Inc.
Figure 13: 1931 CIE Chromaticity Diagram

Source:
CREE, Colour Mixing (
Copyright © 2010-2016 Cree, Inc. All rights reserved.)



Yellow light (570nm-590nm)

rate of
Figure 20: Rate of Photosynthesis (Source: by: Brandon Cullen, Charlene Ramel, Michael Coughlin, and Reidar Riveland)

The mass of a plant is directly related to its rate of photosynthesis, which is necessary for it to live and to grow. The equation of photosynthesis is: 6CO2 + 6H2O + Energy --> C6H12O6 + 6O2. In this case, energy is the light energy given off by the light bulb. Light energy travels in waves. Each color of light has a different wavelength which gives it a distinct color. The chart below shows the wavelengths of each color of light in order of shortest to longest.

There is a similarity in the order of color. For example, blue light has a shorter wavelength, and the plant with blue light had the highest photosynthetic rate. Red light had the longest wavelength, but the plant with red light had the second lowest photosynthetic rate. An interesting result is the white light as a control. White is a combination of all colors of light. This should be similar to the sun on the plants, yet it had the lowest photosynthetic rate. The graph follows the order of color spectrum on the chart: blue, green, yellow, and red. This shows that shorter wavelengths allows more energy to reach the plant for there to be a higher rate of photosynthesis. More photosynthesis means that the plant will be able to grow more, hence, having a greater mass.

Source: by: Brandon Cullen, Charlene Ramel, Michael Coughlin, and Reidar Riveland

Plants photosynthesize light using certain wavelengths mostly in the blue and red portions of the spectrum because these are the colors that are absorbed by chlorophyll. Other compounds can absorb other wavelengths and supply this energy to the chloroplasts for food production, but this is a very small addition of energy.


Orange light (590nm-620nm)

phil      nano

Figure 21: Philips CDM 942 Elite 315W Full Spectrum                                Figure 22: Metal Halide: Nanolux DE-MH 600W 4K Full Spectrum



Infra Red Light (780nm-1mm)

The electromagnetic spectrum is categorized by wavelength. The longer the wave, the less energy it holds. So blue light, which has a short wavelength of 475 nanometers, has more energy than red light, which has a wavelength of 660 nm. Infrared light is just beyond the range of human vision at 730nm. Although we cannot see it, we can feel infrared radiation as warmth. For instance, a glowing charcoal emits red light in the visible spectrum and infrared light that we sense as heat.

The plants use red and infrared light to regulate stem growth and flowering response. Plant cells produce a chemical called a phytochrome, which has two versions. One version, PR, is sensitive to red light (660 nm). Red light converts PR into PFR. PFR signals the plant to grow short stocky stems and also helps the plant grow into specific shapes. The plants also use red and infrared light to measure uninterrupted darkness. As far as plants are concerned in terms of flowering, if there’s no red light, it’s dark.

PFR is sensitive to infrared light (730 nm), which converts it into PR. When PR levels build to a critical amount, scientists hypothesize that a hormone called floragen becomes active and induces the plant to flower. The reason floragen is called hypothetical is that researchers can see its effects, but they haven’t found it yet.

PFR reverts to PR naturally. For PFR to be present, it must be renewed continuously by the presence of red light. When plants are shaded, they get less of the needed red light. In the absence of red light, the PR version predominates and the stem stretches to reach the light. Lower side branches shaded by leaves from above have PR and grow longer until they reach the light. Then they modify their growth in the presence of PFR.

Outdoors during the day, there is more red light than infrared. However, at dawn and dusk the first and last light from the sun isn’t the visible red of the rising or setting sun, but infrared, which is at the far end of the electromagnetic spectrum. The infrared converts the PFR to PR and the critical dark-time begins or ends its countdown.

This has too many implications for them all to be discussed here. For instance, it explains why plants grown under incandescent lamps stretch (more infrared than red light). The effects of the two spectrums can also be used in innovative indoor lighting programs.

Source: Ed Rosenthal on November 7, 2005 | Cannabis Culture


The Emerson effect

The Emerson enhancement effect as it relates to photosynthesis of plants states that there are 2 photochemical reactions (PS1 & PS2) involved in photosynthesis which combine to enhance efficiency. Emerson measured photosynthesis using both red and far-red light (infrared) light. He found that the combination of the two speed up photosynthesis. Furthermore, Emerson observed that the yield obtained using both red and far-red light simultaneously was much higher than the sum of the yields obtained with red and far-red light separately. The best way to achieve the Emerson effect is by using an infrared wavelength of above 700nm in order to accelerate the interaction of molecular energy.

Two different reaction centers or photochemical events are involved in photosynthesis. One event is driven by red light (660 nm) and the other is driven by far-red light (680+ nm). Optimal photosynthesis occurs when both events are driven simultaneously or in rapid succession. These two photochemical events operate in series to carry out photosynthesis optimally.

How can one obtain both red and far red light in their indoor garden? The best way to do this is to grow with LED grow lights that are configured using the scientific principles of the Emerson effect. It is important to have the wavelengths of light necessary for photosynthesis and to have them at the correct weighted average percentages in relation to one another. By growing with LED indoor grow lights that have the Optimal 8-band wavelength formulation in addition to the principles of the Emerson effect the trichome formation and budding production will be ramped up resulting in the optimal yield for the indoor plants.

Source: Johnny Green, The Weed Blog



White light

There is no such thing as a “white” LED.  White LED “packages” come in 2 forms, first and least common is a package that puts a red, green, and blue LED chips together in one device with the 3 chips mixing to white.  But green LED’s are expensive and inefficient, so by far the most common “White” LEDs are a hybrid system consisting of a blue LED chip with a primary lens coated with phosphors. So they are in reality a miniature fluorescent lamp, except that instead of using the UV and Blue light from mercury vapor to stimulate the phosphors, they use light from a blue LED.

White LED’s are quite efficient, because even though there are conversion losses when using phosphors, the Blue LEDs are the most efficient LED’s currently available. So the overall efficiency of the White LEDs falls right in the middle between the blue and red LEDs. But White LEDs suffer the same limitation as Fluorescents, namely that the red phosphors are less efficient, so White LEDs tend to be more efficient the “cooler white” or more blue dominant they are.  And to be truly “white” they still need to produce a significant amount of green spectrum—and all at utilization rates of <50%.   So in general, White LEDs are better suited for Vegetation phases of growth than for Flowering, which favors Red spectrums for optimal yields. But more on that later.
SANlight S4W LED Grow Light, 3 Bar setup    fSpectrum Excite LED Grow Light    URSA Optilux 640 Watts
Fi
gure 24: SANlight S4W ''Warm White Spectrum''              Figure 25 & 26, left to right: Excite LED fSpectrum (x4 = 336W Bundle) & URSA Optilux 640W ''White Light Spectrum''


Using Spectrum Control

The exact way that plants use light is very specific to individual plant species and their natural environment. Evolution has produced a huge variety of plant strategies for growth and it is impossible to over generalize light responses. However, we do have a lot of practical experience with indoor growth results. Below are some general strategies and recommendations based on years of practical experiments with indoor lighting.

The most common question we receive from growers in regards to spectrum control in cannabis cultivation is “What is the optimum Spectrum mix ?” And the answer is it depends on what YOUR priorities are. Different spectrum mixes promote different plant morphology in different growth stages, and there simply isn’t one ideal. And that is the main benefit of LED’s over HID, the ability to use varying spectrum to design the plant for what you want from it.

There are basically 5 (or possibly more) different aspects to the end product that establish its value, and different people want different things.

1) Flower weight (ie. Overall flower yield)

2) Flower density (ie. Resin content and oil/wax ratio)

3) Flower cosmetic appeal (colors, structure, as well as density)

4) Fragrance (Strength i.e. terpene concentration and fragrance complexity)

5) Potency (THC and CBD levels)

What must be understood here is there is NO IDEAL SPECTRUM that will optimize ALL of these aspects of the final product simultaneously. Each can be individually optimized but there will be tradeoffs.


Goals of the Licensed Commercial grower:
What followers are SOME of the typical goals the average commercial grower might consider most important:

1) Some growers may want Maximum OIL yield for edibles etc. and the cosmetic aspects and fragrance of the flowers are not important. Potency is extremely important here.

2) Some may want maximum oil yield for top-shelf extracts, shatter etc…, where flower cosmetics are unimportant, but resin yield, resin quality (oil/wax ratio) and fragrance are very important. Potency is also important and often lab measured.

3)      Some may want maximum Flower yield (weight) period.  There numerous factors that play into this such as Resin content vs. flower matter (fiber), wax vs. oil, etc…, but these people only care about total flower yield by weight. With the market getting more and more competitive, this mindset will struggle to compete.

4)     Because of the significant differential in price between top-shelf flower and lower quality or outdoor flower, (2x or more) most commercial growers are currently looking to maximize top-quality flower yield, ie. flower with high shelf-appeal, i.e. excellent cosmetics, fragrance, and density. Potency is important and often tested but typically considered strain specific and not considered that dependent on cultivation techniques.

So all these examples will have potentially DIFFERENT ideal spectrum mixes, and while those ideal spectrum mixes are not fully known, we can get you close.  And please note, any fixed spectrum light source like HPS or MH will never have the ability to accomplish the ideal in any of these areas. That will require variable spectrum control.

Also please note: The single most important element in yield is shaping of the plant BEFORE peak flower production such that only flower sites see light. This cannot be stressed enough. The best light and the best nutrients will not effect yield as much as insuring that only flowers sites and select sun leaves see light, and that all flowers left on the plant get enough light. And proper design / layout and mounting heights of the lighting system to minimize plant shading and create consistent lighting levels is critical to this process.


Growth stages:
There are also generally 4 growth stages that have different spectrum requirements.

  • Vegetation – In Vegetation (VEG) stage, rapid, healthy overall plant and root growth is desired, and in general most growers desire maximum growth but with shorter compact plants with short inter-nodal spacing preferred.
  • Pre-flower – Pre-flower is the period from when the 12/12 flower cycle is first initiated, to roughly the end of the second week (in an 8-week flower), or until the small flowers are prevalent and the rapid growth stretch slows. Again, for most growers, the desire in this stage is to maximize SIZE, while limiting stretch.
  • Flower – The peak Flower period is generally from week 3-7 and is the time when the plant (stem / leaf) growth stops and all the plant energy focuses on flower production. Maximum flower matter size and good structure is generally the goal here.
  • Ripen or Finish – The Ripen period is generally from week 7 to finish (in an 8-week flower) where the Flower growth, (i.e. size) slows and plant energy refocuses on resin and terpene production. This is the period where the flower acquires a significant portion of it’s density, ie. resin content. This transition is not clearly defined, and some strains have big increases in resin production during this period, and others not as much.


Optimizing spectrum for ideal results

So understanding that enhancing each aspect of plant growth can be a tradeoff, and with the basics of our scientific understanding of Spectrum and Plant Morphology, we can now attempt to come up with some starting points for spectrum mixes for various end results. Please understand, these are starting points and you will need to experiment to reach the ideal for your environment, strain, and desired results.

Goal #1 above, Maximum OIL content for processed edibles, etc.

In this example, our goal is to maximize resin and really THC/CBD yield overall. This includes both flower AND leaves, stems, etc. So a good starting point in terms of Spectrum programs would be:

Veg: Obviously plant SIZE is the big driver at this point so a spectrum with full red and blue is important. In effect we are mimicking the sun, but with LEDs historically our best results in VEG are found with a RED/BLUE mix of around 60/40

Pre-flower & Flower: In this case where flower structure is not important, only resin yield, a higher blue component (ie. closer to sun) can be used than in the other approaches. A good starting point would be 70/30 RED/BLUE but possibly even more blue.

Ripening:  Because we are already running extra blue in flower, no changes are probably necessary in this stage.

UVB: UVB supplementation is highly desirable in this approach because it can increase THC levels by as much as 30%. SO UVB should be supplemented for the last 5 weeks of flower minimum.


Goal 2 –  Resin for Extracts, shatter, etc.
In this example our goals are similar to Goal 1 above except there is a greater focus on Fragrance.  SO we can follow example 1 above except that in the ripen stage we will decrease the red a little more, to raise the Blue/Red ratio to stimulate terpene production more. Say 65/35.

UVB: UVB should be utilized all the way through the flower in this case because not only do we want to increase TCH in resin, but also terpene production and other pigments all the way through flower.

Goal 3 – Maximum Flower yield
Pure flower matter yield can be favored by running fairly high red levels all the way through, a good starting point would be 80/20.  This is the kind of growth pattern seen with HPS.


Goal 4 – Maximum Top-shelf flower yield
This type of end product is the approach where having the ability to vary spectrum in all the different growth periods is most important, and where Hybrid Spectrum LED systems (individual Red/Blue/White control) significantly out perform all other types of lighting systems.

So a good starting point for this type of grow would be:

VEG: Depending on the inter-node spacing desired, decrease R/B ratio for shorter internodes, General recommendation: 60/40 for short tight internodes. This is the ratio found in the CLW VEG spectrum mix.

Pre-flower: To again reduce stretching, R/B ratio can be increased to 70/30 for the first 2 weeks of flower, or 75/25 for taller plants. Extra deep blue will stimulate additional pigments during this critical growth period enhancing flower colors and fragrance.

Flower: In this stage we want to maximize flower SIZE, so we will increase the Red/Blue ratio to 80/20. This is ratio that is found in the California LightWorks Full Cycle spectrum mix, or with the 550 series full on.  Even higher Red ratios (by lowering the blue) can be used to further promote flower matter, but there can be a sacrifice in resin, fragrance, and secondary pigments. There is always a tradeoff between flower mass and resin (density) /cosmetic quality. We do not advise an R/B ratio above 90/10, and for no more than a week or two in the middle of peak flower, or it will impact resin and fragrance.  And too low, (for example 60/40) during this critical period will promote excess leaf content in the flowers and a fluffier structure akin to outdoor flower.

Ripen: Here we look to again enhance resin and terpenes (fragrance) so we suggest lowering the R/B ratio back down to 70/30 or even 60/40 for the last 2 weeks. At this point the higher blue ratio will not alter the flower structure or promote excess bud leaves, because flower growth is winding down, and transitioning to resin production. Results in this phase of growth are very strain specific and can be influenced by nutrient changes as well, so you are encouraged to try small changes each harvest to slowly dial in your ideal.

UVB: IN this case UVB can be very important and it can be supplemented either the last 4-5 weeks, or even throughout the entire flower period to stimulate pigments and terpenes and most importantly THC. Note, UVB supplementation does NOT increase CBD levels.

By using this 4-stage spectrum control approach you can truly optimize the cosmetics, fragrance, density, and color, i.e. shelf-appeal of your flower with little or no sacrifice in yield as compared to HPS or other fixed spectrum systems.


Conclusion
So in conclusion, it can not be stressed enough that these recommendations are only starting points, because the all the results are strain specific and can also vary with other factors such as temperature, shading, and nutrients.

Experimentation with additional changes such as varying the white (ie. green) levels, or gradating the changes over time instead of just switching them are encouraged, but we do suggest that you carefully document all changes and limit them to 5% change in any spectrum per growth phase, and only one change total per harvest. Too many changes in one cycle and you will not know what did what. So remember, ONE CHANGE PER HARVEST.

Also, there have been suggestions and a Dawn / Dusk type of ramp up and down to simulate the slow changes in the sun have value, but we have not seen solid university data in this regard to date. But these types of changes are easily accomplished with the SolarSystem, 550 controller.



Source: Fluence BML / California Lightworks / Khan Academy