The spectrum of light is crucial to plant physiology and photosynthesis because different wavelengths of light drive specific physiological responses in plants. Here's how:
[Dio-Tech Spectral Output showing UV and Far Red]
Photosynthesis (This is the plant using the light energy): Photosynthesis is the process by which plants convert light energy into chemical energy, primarily in the form of glucose. This process occurs in specialized organelles called chloroplasts, which contain chlorophyll pigments.
Chlorophyll absorbs light energy, but it's particularly efficient at absorbing certain wavelengths within the visible spectrum, primarily blue and red light. These wavelengths are essential for driving photosynthesis. Without an adequate spectrum of light, photosynthesis cannot occur optimally, resulting in reduced plant growth and productivity.
Chlorophyll pigments absorb light energy most efficiently in the blue and red regions of the visible spectrum. Blue light (wavelengths around 400-500 nanometers) and red light (wavelengths around 600-700 nanometers) are particularly effective at exciting electrons within the chlorophyll molecules, initiating the process of photosynthesis.
Photomorphogenesis (This is the light telling the plant what to do): Apart from driving photosynthesis, light also influences various aspects of plant development and morphology through a process called photomorphogenesis. Different wavelengths of light trigger specific responses in plants, such as stem elongation, leaf expansion, flowering, and pigment synthesis. For example:
Secondary Metabolism and Plant Quality (This provides the quality/taste of the plant): Light spectrum also influences secondary metabolism in plants, including the production of secondary metabolites such as flavonoids, anthocyanins, and antioxidants. These compounds contribute to plant defense mechanisms, coloration, flavor, and nutritional quality. By manipulating the light spectrum, growers can enhance the accumulation of desired compounds, improving the overall quality and market value of crops.
Blue light regulates processes like stomatal opening, phototropism (growth towards light), and inhibition of elongation.
Red light promotes flowering and regulates seed germination.
Far-red light influences processes like shade avoidance and the transition to flowering.
UV Light Influences the secondary metabolism and plant quality.
Photoperiodism (This is where your timer comes into play!): Photoperiodism refers to the physiological response of plants to the duration of light and darkness. The relative lengths of light and dark periods (photoperiods) determine critical events in the plant's life cycle, such as flowering and dormancy. Certain plants require specific photoperiods to initiate flowering. The spectrum of light during these photoperiods can influence the timing and quality of flowering.
Overall, the spectrum of light directly impacts plant growth, development, and metabolism by regulating fundamental processes like photosynthesis, photomorphogenesis, and photoperiodism. Understanding how different wavelengths of light affect these processes is essential for optimizing plant productivity and quality in horticultural settings.
Summary
The spectral output of any horticultural fixture does not only affect the growth rate of the plant, think of it as the energy supplier for the plant and each part of the spectrum heavily influences different processes within the plant.
If a spectrum is heavy on blue light and does not have as much red light – this will be perfect for Vegetative growth but not so good in the later flowering stage.
As you can see in the example above, there is significantly more red spectrum in the Solar-Tech fixture than the mainstream fixture. Red chips are the more expensive part of a horticultural LED and manufacturers will do this to save cost (not taking into account the overall growth cycle of a plant and therefore customer success).
How is light measured?
In horticulture, various light measurements are used to quantify and assess the intensity, quality, and distribution of light within a growing environment.
Photosynthetic Photon Flux (PPF): This is taken from a meter, not a calculation
Photosynthetic Photon Flux (PPF) is a measurement used in horticulture to quantify the total amount of light emitted by a light source within the photosynthetically active radiation (PAR) range, typically between 400 to 700 nanometres. PPF represents the total number of photons emitted per second by a light source that can potentially be utilized by plants for photosynthesis.
PPF is usually measured in an Integrating Sphere – this allows the entire light output of the fixture to be measured without any losses to give the true overall output of the fixture.
Photosynthetic Photon Flux Density (PPFD): This is taken from a meter, not a calculation
PPFD measures the number of photons (light particles) in the PAR range that reach a specific area (usually measured in square meters) per second. It is expressed in units of micromoles per square meter per second (μmol/m²/s).
PPFD provides a direct indication of the amount of light available for photosynthesis and plant growth. It is particularly useful for quantifying the light intensity experienced by plants in different areas of a growing environment.
PPFD is measured using a grid under the fixture, this gives you the footprint of the light output and shows you how even the light is spread across the canopy.
For a horticultural LEDs, the footprint should be as even as possible so the canopy will grow evenly and there are no “hot spots” .
Fixture Efficiency: This is a calculation
This is the “Magic Number” for most customers when purchasing a horticultural LED, this gives an overview of how much power the fixture will take to produce a given PPF.
Whereas most of the other values for a fixture are taken from meters such as PAR or Power Meters, Efficiency is a calculation based on the input power and overall PPF.
Efficiency = PPF (Micromoles) ÷ Input Power
Consider this table of Dio-Tech measurements (taken from Venture Lighting report):
In F1 spectrum – Efficiency = 2330 (uMol) ÷ 848 (W)
=2.74764 uMol/W
Manufacturers and resellers usually advertise their measurements in the documentation so it is easy to quickly work out the actual efficiency of a fixture from this. Let’s use AdjustaWatt as an example (taken from their recent flyer):
Using this example:
Efficiency = 1890 (uMol) ÷ 720 (W)
= 2.625 Umol/S
Advertised Efficiency:
This is where extreme care needs to be taken when looking at advertised values at face value, especially when the calculation is a pretty easy one!!!
Another thing to note is that red chips are less efficient than blue chips in their nature. Efficiencies of 3.0 and above are theoretically possible but extremely rare, expensive to manufacture and usually a lie!
Ok, there are a lot of different numbers – which ones are relevant to me?
If we think about the three terms described above:
PPF – The overall light output from the source
PPFD – Light output hitting a specific area
Efficiency – How much energy is my fixture going to use
From a plant point of view, PPFD is the most important measurement as this is the number of photons hitting the plant at a given point in the canopy. As a rule of thumb:
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Growth Stage |
PPFD Range |
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Seedling Stage |
200-300 |
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Vegetative Stage |
400-600 |
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Flowering Stage |
600-1000 |
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The above is heavily influenced by different factors such as strain, environment, CO2 injection etc.
From a user point of view, if the user is running multiple fixtures – efficiency would be a major consideration as the more efficient the light, the less electricity it uses to produce a given amount of light.
From a general overview of the light view (that was a mouth full!) PPF is going to give you the headline amount of light coming from the unit so it will give you an idea of how suitable the light is for your project but the lighting footprints showing PPFD would be more useful!
LED Safety
As with any new technology, companies try to find ways to reduce the price. Initially, manufacturers were using off brand/cheaper LED chips and lighter weight frames to cut costs. Some manufacturers are now making the driver cheaper by using a non-isolated LED driver which is impossible to see by the eye and has some potential safety issues.
- Isolated LED Drivers: Provide safety through electrical isolation, are more complex and costly, and are ideal for applications where user safety is a concern.
- Non-Isolated LED Drivers: Are simpler, smaller, and less expensive, but require caution regarding safety, suitable for enclosed or inaccessible LED installations.
Advantages & Disadvantages of Isolated/Non-Isolated LED Drivers
Isolated LED Driver
- Electrical Isolation:
- Provides electrical isolation between the input (high voltage) and output (low voltage) using a transformer.
- Enhances safety by preventing direct electrical connection between the primary and secondary sides, reducing the risk of electric shock.
- Safety:
- Safer for users, especially in applications where the LEDs are accessible or in environments with stringent safety standards.
- Complies with stricter safety regulations.
- Cost:
- Generally more expensive due to the additional components and complexity in the design.
- Applications:
- Suitable for applications where safety is a priority, such as in household, horticultural lighting, and outdoor applications.
Non-Isolated LED Driver
- Electrical Isolation:
- Does not provide electrical isolation between the input and output.
- The output is directly referenced to the input, which can pose a safety risk.
- Safety:
- Less safe compared to isolated drivers as there is no barrier preventing high voltage from reaching the output.
- Suitable for applications where the LED and driver are enclosed and not accessible to users.
- Cost:
- Generally less expensive due to simpler construction and fewer components.
- Applications:
- Suitable for enclosed fixtures, industrial applications, or where the LEDs are not accessible, such as in sealed lighting fixtures.