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The Basics

Plants breathe differently than terrestrial animals. While animals breathe in O2 and breathe out CO2, plants do the reverse. This is one of the most important factors why plant life is the essential part of Earth’s ecosystem. Without greens, CO2 levels would reach suffocating levels in an extremely short while. CO2 is used by plants for growth, because it’s essential for photosynthesis, alongside light and water.

Even though the current CO2 levels in the atmosphere is about 350 PPM, it seems that plants have maintained their ability to consume up to 1 500 PPM of CO2, as they did eons ago. Knowing this is extremely important because the assertion that plant growth could be sped up by increasing the Co2 intake is true.


How CO2 Affects Growth

A level below 250 PPM of Co2 will have a negative effect on growth. The use of all available Co2 will be depleted in a few hours time. When the CO2 supply is exhausted, the plants will stop growing. This is one of the reasons why there should be an air exchange


How do plants use different light spectrums?

Ultraviolet light (10nm-400nm)

Though overexposure to UV light is dangerous for the flora, small amounts of near-UV light can have beneficial effects. In many cases, UV light is a very important contributor for plant colors, tastes and aromas. This is an indication of near-UV light effect on metabolic processes. Studies show that 385 nm UV light promotes the accumulation of phenolic compounds, enhances antioxidant activity of plant extracts, but does not have any significant effect on growth processes.

Blue light (430nm-450nm)

This range of spectrum enables cryptochromes and phototropins to mediate plant responses such as phototropic curvature, inhibition of elongation growth, chloroplast movement, stomatal opening and seedling growth regulation. It affects chlorophyll formation, photosynthesis processes, and through the cryptochrome and phytochrome system, raises the photomorphogenetic response.

In more practical terms, these wavelengths encourage vegetative growth and are essential in lighting for seedlings and young plants during the vegetative stage of their growth cycle, especially when “stretching” must be reduced or eliminated. It also stimulates the production of secondary pigments which can enhance colors and is known to also stimulate Terpene (i.e. fragrance) production.

Green light (500nm-550nm)

Most green light is reflected off the plant and plays a much smaller role in plant growth. However, there are some important aspects of light in this range so a certain amount of light in this spectrum range is beneficial. Green light is sometimes used as a tool for eliciting specific plant responses such as stomatal control, phototropism, photomorphogenic growth and environmental signaling. When combined with blue, red and far-red wavelengths, green light completes a comprehensive spectral treatment for understanding plant physiological activity. The function of green light is less well understood than the other spectrums, and there are only certain species of plants that require green light for normal growth. It’s effects appear to be very strain specific.

The pigments that can absorb green are found deeper in the leaf structure so it is thought that because green light reflects off of the Chlorophyll in leaf surfaces and thus is reflected deeper into the shaded areas of the canopy than Red and Blue which are readily absorbed, that green may actually be mostly absorbed through the undersides of the leaves as it bounces around in the shaded depths of the canopy.

Red light (640nm-680nm)

Red light affects phytochrome reversibility and is the most important for flowering and fruiting regulation. These wavelengths encourage stem growth, flowering and fruit production, and chlorophyll production.

The 660nm wavelength has a very strong photosynthetic action and exhibits the highest action on red-absorbing phytochrome regulated germination, flowering and other processes. Most effective for light cycle extension or night interruption to induce flowering of long-day plants or to prevent flowering of short-day plants.

Far red (730nm)

Although the 730nm wavelength is outside the photosynthetically active range, it has the strongest action on the far-red absorbing form of phytochrome, converting it back to the red-absorbing form. It becomes necessary for plants requiring relatively low values of the phytochrome photo equilibrium to flower.

Also, a higher ratio of far-red to red than found in sunlight can trigger the shade stretch response- where a plant when sensing it is shaded based on an elevated ratio of far-red to red- will stretch to try to elevate its canopy above its competitors. Therefore, too much far-red is not advised if compact plants are desired, or in general.

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.

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