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Red, White, or Blue? Choosing the Right LED Color

Posted by Logan Fulcher on

How to Choose the Right LED Colors

From 200nm to 800nm+

         Spectrum is one of the most important factors to consider when purchasing any grow light, be it LED or otherwise. From 200nm to 800 and beyond, let's get enlightened.

Visible Light Spectrum

UV (200~400nm): One of the most debated topics in the grow world, particularly among cannabis enthusiasts, is the topic of UV light. Basically there are 2 schools of thought.

  • The "UV is Pointless" school claims that there aren't any scientifically proven examples of flowering-plant defending themselves against UV light with resin, THC, or anything else.  Also, it is said that plants actually expend a lot of energy converting the UV light into energy that will stimulate photosynthesis. Folks from this school will flat out tell you that it's a myth, despite many grow lights manufacturers including Black Dog LED and California Lightworks swearing by UV.
  • The "UV Works" school has been getting actual scientific attention in the past couple decades, and with the advent of legal marijuana, the research is beginning to suggest that there is a significant reaction to this range of light.  The academically minded can find some peer-reviewed support by clicking this link to an article about the effects of UV-b on Sativa. More evidence suggests that the best cannabis for hash grows in elevated regions (thereby increasing UV exposure) according to one book about hash (Bergel, 1965):

    “When we were still working in this field we were told that the production of the active resin, in any kind of Cannabis plant, depends entirely on the altitude of the plantation; for example, you get rich charas or bhang in northern India only at a certain height above sea level. It was also reported that in order to obtain active resin one had to plant Cannabis in Germany near Roserheim, not far from Munich, which again is above a certain altitude.”

Blue (~475nm): Blue LEDs have been around since the mid 90s but we have only Own Work Picture take by Paul Henjum, showing a plant stem with nodes and internodes. Taken 02/19/07"really seen commercially available high-power-blue LEDs in the past few years, which has been a boon to plant growers everywhere. Blue photons play an integral role in the regulation of plant hormones and have a revitalizing effect on plants. With the right amount of blue light plants grow denser with shorter 'internode' length (less stem between leaf nodes) leading to denser foliage. Blue light also supports root development and stimulates nutrient production and gas exchange. Grown with pure red only, plants would grow long and gangly, collapsing under their own weight. On the flip side, the hormones that blue light suppresses are extremely important during the fruiting/flowering stage of plant growth, which is why increased amounts of red light and warmer hues are advised.  Many manufacturers create lights using solely blue light and are intended to be used as supplementary lighting, for leafy plants like lettuce, or for use in the vegetative cycle of fruiting and flowering plants.

Green (~510nm): While it's true that the green appearance of plants is due the green light that bounces off (while red and blue are absorbed) there really is a lot more at play.   Some research suggests that green could essentially replace blue, if it weren't for the fact that green LEDs simply aren't as energy efficient as blue ones. Here's a fantastic article about Green LEDs from Michigan State University that straightforwardly illustrates the power of green light for plants.

Chlorophyll Absorption Chart for LED grow lights

Photosynthetic absorption chart courtesy of Lush Lighting.

       An added side benefit of growing with green light (and white for that matter) is that it makes the plants easier for human eyes to see.  Plants grown under red plus blue light appear purplish gray, thereby making disease and disorder more difficult to diagnose.  Another potential advantage of green light is that it can penetrate a canopy better than other wavebands of light. It’s possible that with better canopy penetration, lower leaves will continue to photosynthesize, leading to less loss of the lower leaves.

Orange (~590nm):  Carotene, which is reactive to bluish light, plays an important role in photosynthesis.  The carotene transmits the light energy that they absorb from bluish light to chlorophyll for further use. They also serve as plant protectors by absorbing oxygen byproduct produced during photosynthesis. One of the reasons HPS lights still maintain any sort of relevance vs. LEDs is because they very efficiently produces a lot of orange. To say that orange light is useful would be a grand understatement. Orange light and it's differently shaded cousins is still territory being mastered by LED manufacturers, and most companies settle for red simply because they are cheap and efficient  One company making headway in this area is Kind LED - check out their supplementary grow bars for a good example of future LEDs.

Red (~650nm): Basically, the god of photosynthesis. Red and its next door neighbor deep red are the main drivers of photosynthesis. Both chlorophyll A and chlorophyll B are highly reactive to red light and rely on them to drive plant growth. They are highly efficient LEDs, and tend to be cheaper than many of the other colors. It is possible to grow beastly plants using a 3:1 ratio of red to white.  If your plants need a boost, we recommend simply buying a supplementary UFO grow light or LED Bulb to give your plant some 'teeth.'

Deep Red (660nm peak): PSI and PSII photosynthesis pathways require two photons, one 680nm and one 700nm, as the keys to start their engines; the deep red light is a primary and necessary source for setting off the cascade of chemistry that allows plants to do what they do.  While regular red LEDs will 'rev the engine' just fine, many manufacturers nowadays include the electrically less efficient deep reds in their lights for the added boost to photosynthesis.

Far Red (730nm): Far red is another area of contention for growers and LED enthusiasts alike.  While one side says that far red is just 'wasted energy,' the other side has shown Far Red LED light Responsesome evidence that supports the claim that far red plays an important role in plant photoperiodism which is the biological response to the time changes between darkness and light.  Particularly for cannabis cultivators, it is said that far red light strategically employed at the end of the14/10 cycle forces immediate "sleep" immediately so it doesn't take any longer to ripen - this can result in 10%+ larger yields with reports up to as high as 17%.  Wow.  There is an article that goes much more in depth than we do here, and while be quite dense, it is excellent for those with the inclination to learn more about Red LED light and the phytochrome system.

Infrared (800+nm): The same opinions that echoed in the deep red discussion continue down to this end of the spectrum. While, again, some say that infrared is 'just heat,' there may be 4 significant reactions to IR light. Namely, there are claims that the time until maturation is shortened, thus increasing output over the course of multiple grows.  Also notable is that the height of some plants is reduced by IR light while simultaneously the leaf emergence of IR-grown plants is significantly higher. Thirdly, ratios in amounts of plant tissue near the soil and just beneath the soil are altered. Lastly, IR grown seedlings have been shown to grow more 'aligned' with gravity: significantly straighter than non-IR grown seedlings.  Two brands that swear by IR and deep red are Simulight and California Lightworks.

California Lightworks SolarSystem 550

White : In actuality, white LEDs are blue LEDs covered with a yellow phosphor - whip that one out at your next family get together... Anyhow... when discussing 'pure' white light, we usually start talking about the temperature (rated in Kelvins (K,)) which we will delve into deeper in a future blog post. In the meantime we can know that "Cool" white  LEDs and "Warm" white LEDs have different spectral patterns (seen below) and produce different growth outcomes in plants. Generally, we use the warmer colors for flowering and save the cooler colors for vegging our plants, though the applications extend beyond these two phases of plant growth.  Exemplary examples of LED Grow Lights that utilize white light are the  ProMax Grow 600 and ProMax Grow1200.

Warm LED Grow Lights vs Cool LED Grow Lights Spectrum

Full Spectrum: Most lights intended for plant cultivation are of the 'full spectrum grow light' variety and contain different 'peaks' within the light spectrum that correlate to a plant's optimal photosynthesis.  Many brands offer their own proprietary blend of light, though it remains to be seen if there is one that stands out as the best among all others.  Again, it depends on what one is growing. Take all of the information above - read some more, wad it up in a ball and call it pretty awesome. Typically a combination of Red, White, and/or Blue is your best bet... however, it's all debatable and dependent on what you grow and how you grow it. 

For a more in depth and academic analysis of light and its relationship to plant development, check out this fantastic paper specifically regarding LEDs. 


Well, that's all my fellow LEDHeads - go forth and shine your light!  May the seeds you sew grow past the heavens!  If you have any further questions, have any article requests, or just want to say something nice (or mean,) you should comment below, hit us up on twitter and Facebook, or just email me directly:

Stay Green my Friends!  Be the Light!


 Head LED Head         

Logan Fulcher          

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