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Why most LEDs appear purple

May 1, 2020
Cannabis World

Why LED Grow Panels and Bulbs Often Produce Purple Light

Many of the high-pressure sodium (HPS) bulbs that have been the standard choice in the cannabis growing industry for years produce light with a distinctive blue tint. These days, when you step into a grow room equipped with “narrow-band” LED lights, and a far more intense purple glow will instantly command your attention.

Unlike HPS, metal halide, and fluorescent bulbs, each of the LED bulbs used in many modern setups generates light from a fairly narrow part of the visible light spectrum. LED grow light manufacturers combine parts with different characteristics to ensure that cannabis plants receive all the wavelengths they need to grow and flower.

The impressive purple glow that comes from LED systems designed for marijuana seed growing is a mixture of output covering the visible blue and red wavelengths. Cannabis plants need many wavelengths of light to thrive, and well-designed LED grow lights provide suitable amounts of all of them.

Red and blue light are especially important to cannabis plants and newly germinating cannibis seeds . This fact is directly reflected in the light that narrow-band LED grow systems put out. Being able to easily emphasize certain wavelengths is one of the benefits of LED technology, with some systems going further in this respect than others.

There are quite a few reasons to use narrow-band LED lights to cultivate cannabis, and some would even place the subjective appeal of their purple output among these. That purple light is also valuable for entirely practical reasons, which we will now explain further.

The Sun’s Light is the Gold Standard for Cannabis

Naturally occurring varieties of cannabis have adapted over long periods to grow outdoors, where they use photosynthesis to turn sunlight into energy. The electromagnetic radiation that makes up sunlight covers a huge range of wavelengths, most of which are undetectable to the human eye.

As sunlight hits the Earth’s atmosphere and makes its way to the surface, portions of its spectrum are more likely to be filtered and scattered than others. On a bright, clear day, sunlight will be evenly distributed enough across the visible wavelengths that it appears white, with all the included colors combining to produce this effect.

The sun often appears yellow when it is standing overhead but can turn orange or reddish later on as it sets. When fall arrives each year, sunlight also becomes redder, since shorter blue and green wavelengths get scattered more aggressively by the ozone layer.

Cannabis plants have adapted to make the most of the light that is available to them under natural growing conditions outside. Even strains bred specifically for indoor cultivation like white widow and the girl scout jack herer strain retain most of the related characteristics.

Conventional LEDs Produce a Narrow Spectrum

Of all the types of lighting that are commonly used to grow marijuana, LEDs are least like the sun with regard to spectrum. The first commercially available LEDs that could produce visible light glowed pure red, with models that could output other colors following only years later.

This is because LEDs produce light by forcing electrons to fill “holes” in semiconductors, which requires an amount of energy greater than that substrate’s “band gap.” When used to make LEDs, semiconductors with different band gaps generate light of different energy levels and corresponding wavelengths.

Other types of lighting used for autoflowering seeds or regular weed seed cultivation are more broadly similar to the sun in that they spread their output over a fairly wide spectrum. Different technologies have characteristic spectra of their own, but all are wider than that of a single, simple LED.

Two Ways of Making LED Output More Like the Sun’s

LED growing light manufacturers can effectively one-up the sun by focusing on the wavelengths that benefit marijuana plants the most. Although broad-spectrum technologies like HPS can produce impressive yields, conventional LED elements do it in a more carefully targeted way, out of necessity.

As they always did originally, manufacturers most often combine LEDs with desirable, different characteristic wavelengths into assemblies that thereby generate a combined spectrum suitable for growing cannabis plants. A crude way to do this would be to simply add an appropriate LED for each range of wavelengths required, from ultraviolet frequencies down to infrared ones. This is why you see some LED lamps for sale that contain a mixture of many differently set colors.

That would mean wasting energy by providing too much light of wavelengths that do not benefit cannabis plants overly much and too little of those they need the most. Since this would increase startup and operating costs unnecessarily, lighting system manufacturers have mostly opted to focus on the wavelengths that make the most difference.

Relatively recent advances in the field have given rise to phosphor-equipped “white” LEDs with spectra more like those of HPS or fluorescent bulbs. The many LED-based cannabis grow lights that still produce purple or magenta output, though, result from the approach described above.

Red and Blue Make Purple, and Purple Light is Great for Cannabis Plants

While the narrow-band output of conventional LED elements necessitates some special accommodation, it can also be seen as an advantage. Unlike with other types of lighting technology, LED system manufacturers have virtually free reign to customize the extent, peaks, and valleys of the spectra their products generate.

That normally means designing systems that produce purple light by emphasizing blue and red among the visible wavelengths. There are several reasons why red and blue wavelengths of visible light are especially important to cannabis plants. The most significant of these concern issues like:

  • Like other plants, all cannabis strains use chlorophyll to carry out energy-producing photosynthesis. Chlorophyll is the pigment that gives plants their characteristically green color, which means that it reflects significant amounts of visible light around that wavelength. Chlorophyll more readily absorbs red and blue wavelengths of light that lie on either side of green in the spectrum. Although sunlight exhibits a peak in the visible portion of its spectrum within the green wavelengths, cannabis plants have evolved to reflect much of this radiation. Emphasizing red and blue light allows LED systems to support photosynthesis more efficiently than if they wasted energy producing lots of green electromagnetic radiation.
  • Vegetative growth. It is normally desirable to have relatively compact plants when growing cannabis indoors. Marijuana plants, including those from cannabis indica seeds and cannabis sativa seed, are most effective at converting red light into energy, but this wavelength also encourages them to stretch out and become spindly. The long leaves and stems that result make things difficult for growers and will reduce the yield for a given area. Fortunately, ensuring that a plant receives a healthy amount of blue light as well will counteract this effect entirely. Purple LED lighting systems are designed to provide the benefits of efficient, red-rich photosynthesis while also encouraging compact, hardy plant development.
  • Cannabis plants grown outdoors start flowering when shorter days signal that fall is on the way. Fall also brings redder sunlight, and cannabis plants have adapted to make the most of it when producing buds. The purple light produced by many LED grow systems emphasizes red to make sure that it will support the development of the large, heavy buds growers prize. Some systems can also be configured to tilt even more heavily toward the red part of the visible spectrum when desired.

Going Beyond Purple: What Else to Look for in LED Lighting Systems

In accounting for important issues like these, LED grow lights that incorporate narrow-band elements almost necessarily end up producing purple output. Wide-band white LED grow lights are becoming more common, but they come with certain downsides.

As a result, proudly purple light is still seen in many grow rooms the world over. Of course, purple-generating LED systems vary widely with regard to how well designed they are and the features they include. Some of the details that it will normally pay to look into when shopping for a conventional LED grow light setup are:

  • Other wavelengths. The red and blue that combine to form purple are important, but cannabis plants need other wavelengths of light, too. Most systems include LED elements that are responsible for producing certain ultraviolet wavelengths. Some also incorporate LEDs that generate infrared light, which many growers believe improves resin production and quality. While green light does not support photosynthesis as well as red and blue, it penetrates more deeply into the canopy of a cannabis plant. Systems that include small LEDs that generate white light can make it easier to work with crops in the absence of other lighting.
  • Whether they feature manual controls or can be accessed through your mobile phone via wifi or bluetooth, high-quality LED grow lights can often be adjusted. This most often means being able to vary the levels of red and blue light an array produces. That can easily make for larger harvests, along with more robust growth and development through the vegetative stage.
  • LEDs are highly efficient, but they still produce significant amounts of heat when putting out enough light for cannabis plants. The cooling accessories included in a LED grow light panel or bulb can influence both its lifespan and its impact on a grow room. Fans should be rated to last as long as LEDs themselves, and passive cooling systems should be substantial enough to dissipate sufficient heat.

Although LED elements that produce white light are gaining ground, grow systems that feature purple, magenta, or pinkish output are still very popular. Now that you clearly understand all the reasons for this, hopefully it will be easier to identify the perfect purple LED light for your grow room at home. Treat your i49 seeds the right way by giving them the ideal lighting conditions for the duration of their growing cycle.

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