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Dissecting the Light Spectrum in your Indoor Grow Room

We’re learning more and more about different types of light and how it affects your plants. We’re learning more and more about different types of light and how it affects your plants.


No products are more crucial to the progression of the indoor horticultural industry than innovative lighting technologies. The light energy in any indoor garden is the driving force that makes all plant functions possible.

It is our increased knowledge of plant physiology, more specifically the way plants process particular wavelengths of light, that influences the innovative lighting technologies we are seeing emerge into the industry. The discovery of the peak absorption wavelengths for both chlorophyll a and b has been the biggest contributor to the advancement of efficiency and effectiveness of indoor lighting. Other discoveries regarding particular wavelengths of light and how they affect different aspects of growth have also played intricate roles in newer lighting technologies and applications.

Chlorophyll a and b Peak Absorption

Further discoveries pertaining to photosynthetically active radiation (PAR), like the identification of chlorophyll a and b’s peak absorption rates, are changing the way the entire indoor horticulture industry views artificial lighting.

Scientists have discovered that there are four peak wavelengths (nm), two each for chlorophyll a and b. Chlorophyll a’s peaks are 430 nm (blue) and 662 nm (red). Chlorophyll b’s peaks occur at 453 nm (blue) and 642 nm (red).

It is this discovery that led to the introduction of the original LED horticultural lighting systems. Many horticultural LEDs are still designed around these four wavelengths of light energy.

Ultra Violet (UV) Light

Experts have discovered that many high-value plants will increase their production in essential oils when exposed to UV light, more specifically UV-B. It is thought that many plants create essential oils as a defense mechanism against a variety of potential problems, including overexposure to UV radiation. Additional UV light supplemented in an indoor garden’s flowering room will increase essential oil production on a wide variety of high-value plants.

Metal halides naturally emit UV light and can be added to flowering rooms for the sole purpose of UV supplementation. Reflector glass blocks the majority of UV light from reaching the plants, so growers with closed, air-cooled ventilation systems will want to supplement UV light by adding specific UV light fixtures. UV-B lights are commonly sold in hydroponic, pet, and aquarium stores. There is no need to supplement any more than 1/10th the wattage of the primary light fixture. For example, for each 1000 watts, the grower should supplement up to 100 watts UV-B light.

Deep Red (730 nm)

Discoveries in the way a plant rests and processes light energy have led to the use of particular wavelengths to help trigger a plant’s resting period. Inda-Gro Lighting, out of San Diego, California, has developed the Pontoon Lighting System, which utilizes the deep red spectrum to put indoor plants into their resting period faster.

This system uses a series of 730 nm LED lights that come on for a few minutes at the end of the lighting period to mimic the spectrums emitted by the sun at sunset. This deep red light puts the plants in a resting period more quickly, which allows the grower to extend the light cycle by an hour or two in the blooming room.

As more discoveries are made regarding the way high-value plants respond to particular light wavelengths, more innovative indoor lighting technologies will take shape. With the ability to emit virtually any individual wavelength with LEDs it seems logical that LEDs hold a bright future in horticultural lighting. At the very least, LEDs will play a vital role in light supplementation and manipulation. Regardless of the specific technology that will be used in the future of horticulture, new discoveries will lead us into a greater understanding of the light spectrum as a plant sees it.

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An introduction to photosynthesis.
Last modified on Tuesday, 23 July 2013 14:01

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