LED Grow Light

The Importance of Light Controllability for Plant Growth-Part II

For plant growth, two main reasons for controlling light are light uniformity and lower energy costs. Read on to find out more useful information:

Fine-Tuned Color Distribution 

Over the last century, scientists have observed how wavelengths, intensities, and photoperiods together shape plant output. Plant photoreceptor actions and their signaling components can influence growth at different developmental stages, and are therefore excellent targets for altering productivity and yield. Traditional lighting systems typically offer only binary on-off control; in other words, when they’re turned on, they emit the same spectral output for every plant, even if you’ve got different varieties in the same space and even if each variety receives a different cocktail of nutrients.

LED technology is however well suited for plant lighting applications, due to its full light spectrum capabilities. One of the biggest advantages of LED lighting is that it has highly customizable wavelength capabilities, without the cumbersome (and expensive) need to regularly change fixtures. LED grow lights can affect a plant’s physiology and morphology via the application of specific light wavelengths during specific times which are most appropriate for optimizing desired crop traits. For example, growers can now purchase horticultural LED fixtures that provide a narrow-band red and/or blue light to control certain plant traits (for example, supplemental far-red light used for cucumber vines to promote better stretching, or a mix of red and blue spectra for more compact lettuce plants), or a custom-designed broad-band white-light spectrum that maximizes photosynthesis and growth for most plants.

Product Quality

With the networking and control capabilities built into LED grow lights, horticulturalists and growers can craft proprietary light programs to optimize brightness and color distribution, and enhance individual characteristics of the plants that will make them most marketable.

LED technology enables light quality to be manipulated on a commercial scale, and creates opportunities to enhance crop quality through precise manipulation of the lighting regime—by influencing each crop variety’s size, yield, color, spread, and even taste.

Color Effects on Plant Growth

Grow light spectrum refers to the electromagnetic wavelengths of light produced by a light source to promote plant growth. Photosynthetic active radiation (PAR) is the range of electromagnetic radiation that plants use for photosynthesis (a wavelength range of 400 nm to 700 nm). The amount of PAR falling on an individual plant at any given second is defined as photosynthetic photon flux density (PPFD), measured as micromoles per square meter per second (μmol/m2/s). Note that a PPFD measurement taken below a light source will vary based on its distance from the plant, and is also based on the area of the space under consideration.

Plants perceive different wavelengths of light using distinct photoreceptors. Plants contain pigments that show an affinity to photons of particular wavelengths, and those photons in turn have different energy levels depending on the wavelength. Therefore, the spectral absorptance of the plant plays a critical role as to whether the measured PPFD value is effective in photosynthesis.

Plants have three primary photoreceptors that respond to different parts of the spectrum; the phytochrome pigment responds to the red and far-red part of the spectrum, cryptochrome responds to green and blue light, and phototropin responds to blue light—all controlling plant growth, gene expression, and the transition to flowering development in various ways. The existence of distinct photoreceptor families provides opportunities to selectively activate individual pathways, thereby precisely controlling overall development.

Unlike humans—who can only detect visible light spectrum wavelengths (380-740nm)—plants on the other hand can detect wavelengths which include visible light as well as beyond, such as UV and Far Red spectra. Light spectra will affect plant growth in different ways depending on environmental conditions, plant species, etc. Typically, chlorophyll, the molecule in plants responsible for converting light energy into chemical energy, absorbs most light in the blue and red spectra—both of which are found in the peaks of the 400-700 nm PAR range—for photosynthesis. Other spectra of light, like greens/yellows/oranges, are less useful for photosynthesis due to the amount of chlorophyll-b, absorbed largely from blue light, and chlorophyll-a, absorbed largely from red and blue light.

To be continued…

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