Understanding the Light Spectrum of LED Grow Lights
Posted on August 13 2018
To understand why LED grow lights have more of a red focus than a blue focus, we must know how the full light spectrum effects cannabis growth. We have recently started to understand the complicated relationship between plants and the light spectrum, thanks in part to the development of full spectrum LED grow lights in the 1980s. Scientists working with NASA during this time period discovered each segment of the visible light spectrum had different influences over plant growth. Different plants, at different times of their growth cycle, seemed to absorb more of one color than another. Since this discovery, indoor farmers have been applying the knowledge to improve harvest yields. Perhaps no industry more earnestly than the cannabis industry.
Full spectrum grow lights, representing the light spectrum from the infrared to the ultraviolet, foster healthy, bountiful cannabis harvests if applied appropriately. Some LED lights come with little specialization, but the market is increasingly competitive, and now indoor grow light businesses are honing in the exact wavelengths cannabis needs to flourish.
The Fundamentals of Light Science
Let's bring it back to your school science class: light is electromagnetic radiation measured and differentiated through both frequency and wavelength. Humans can only see what is known as the visible light spectrum, between 400 to 700 nanometers. However, many animals can see frequencies in the non-visible range, from the ultraviolet (0 to 400 nm) to the infrared (700 to 1000 nm). Some suspect plants also rely on other non-visible segments of the light spectrum, but this research is ongoing and so far poorly understood.
If you are an indoor grower, you’ve likely heard of a PAR reading (photosynthetically active radiation). This is a key measurement for indoor growers because it measures exactly the spectrum of light responsible for photosynthesis. Understanding PAR readings is a basic aspect of understanding your plants light requirements.
But it gets a little more technical than just a PAR reading. Although you might assume direct light supplied by the sun might be the perfect spectrum for growing cannabis, research says otherwise. The sun primarily provides the middle segment, greens, yellows and oranges. Although the spectrum changes from one season to the next, these are the colors most readily available.
Research shows cannabis actually responds better to the edges of the visible light spectrum. In fact, cannabis photosynthesis usually needs higher levels of the blue and red range. Therefore, LED grow lighting companies have begun to specialize the spectrum of light provided through their lighting systems to cater more to the cannabis photosynthesis process.
Why do Full Spectrum LED Grow lights Have More Red Diodes?
Cannabis full spectrum grow lights have evolved to foster bud and trichome development. Through extensive research, and years of technological tinkering, growers have determined what types of light, introduced at what times, encourage the largest flower harvest.
The reason why cannabis grow lights should have more red diodes than blue comes down to why people grow cannabis. Unlike trees destined to be lumber, cannabis farms don’t want thick trunks and tall plants; they want the plant to focus all its attention on the formation of flowers, or buds. Research shows the red spectrum of visible light, between 640 nm to 680 nm, is key to pushing a plant to produce bigger and better flowers. Red light regulates the germination stage, especially cannabis.
Too much red, at the wrong time, can trigger a plant to stretch, which is why LED grow lights have a slightly more complex combination of light than strictly just red. In marijuana production, blue lights are also crucial, primarily during the vegetative stage.
During this stage, the plant is in expansion mode. Actively bushing out, covering the most area, so when it comes time to flower, it can reap the most benefit from photosynthesis. Blue light inhibits a plants tendency to stretch out, which is of benefit for most types of indoor cannabis operations. Blue light is also thought to stimulate terpene production.
What About the Other Colors of the Light Spectrum?
As mentioned, plants absorb the full spectrum of visible light and likely even parts of the non-visible spectrum. But beyond the blue and red light wavelengths, the other colors are only poorly understood. For example, green light is mostly bounced away by the chlorophyll pigment in cannabis leaves and therefore mostly goes unused. However, some green light is absorbed, in particular by the deep leaf tissues. More research is needed to understand what the plant uses this light for.
Ultraviolet is another type of light required for cannabis growth, but less understood than the blue and red varieties. There is some scientific study suggesting ultraviolet light might play a key role in cannabinoid development, specifically THC. Many full spectra LED grow lights now incorporate some ultraviolet diodes to stimulate THC development.
Clearly, there is much to learn about lighting science for cultivation; for the cannabis industry is of particular interest. As the legislation opens up, and the industry becomes increasingly legitimate, lighting technology capabilities are set to explode.