What is the Best LED Spectrum for Marijuana Growing?

Most cannabis growers have multiple objectives in mind when planning an indoor grow. Drafting scenarios to achieve higher yields, increase THC levels, or simply to improve the overall health of a plant is an integral part of their hobby. This element of strategic planning involves the challenge to link knowledge of different scientific fields and to match those findings to a technical solution that helps to achieve predefined goals. Besides dedication and passion, it is the willingness to learn that differentiates good growers from future experts – so let us try to grow the royal way and learn what it takes to cultivate cannabis of exceptional quality

WHAT IS THE LIGHT SPECTRUM?

The sun emits energy in the form of solar radiation including gamma rays, x-rays, ultraviolet light, visible light, and even radio waves. Life on Earth is only possible because the ozone layer blocks this radiation, and reflects most of it back into space. This filtering process only allows wave lengths between 300nm and 1100nm to reach our plants and an even smaller portion of this light is visible to us. It is often referred to as the light spectrum, color spectrum or visible spectrum, and ranges from 380nm to about 750nm.

180-280nm - UVC: Extremely harmful and luckily almost completely absorbed by the ozone layer

280-315nm – UVB: Cause of sunburn and suspected to increase THC levels (!)

315-400nm – UVA: Not absorbed by the atmosphere, commonly known as black light

380-750nm – The visible light spectrum: Bands of wave lengths represent visible colours

700nm-1mm – Infrared light: Not visible above 750nm but noticeable as heat on our skin

How the Light Spectrum Affects Marijuana Plants

Ultraviolet light (10nm-400nm)

Though overexposure to radiation in the UV light spectrum is dangerous for the flora, small amounts of near-UV light can have beneficial effects. In many cases, UV light is a very important contributor for plant colors, tastes and aromas. This is an indication of near-UV light’s effect on metabolic processes. Studies show that 385 nm UV light promotes the accumulation of phenolic compounds, enhances antioxidant activity of plant extracts, but does not have any significant effect on growth processes. UVB has also been demonstrated to elevate THC levels in Cannabis*.

Blue light (430nm-450nm) 

This range of spectrum enables cryptochromes and phototropins to mediate plant responses such as phototropic curvature, inhibition of elongation growth, chloroplast movement, stomatal opening and seedling growth regulation. It affects chlorophyll formation, photosynthesis processes, and through the cryptochrome and phytochrome system, raises the photomorphogenetic response.

In more practical terms, these wavelengths encourage vegetative growth and are essential in lighting for seedlings and young plants during the vegetative stage of their growth cycle, especially when “stretching” must be reduced or eliminated.  It also stimulates the production of secondary pigments which can enhance colors and is known to also stimulate Terpene (i.e. fragrance) production.

Green light (500nm-550nm)

Most green light is reflected off the plant and plays a much smaller role in plant growth. However, there are some important aspects of light in this range so a certain amount of light in this spectrum range is beneficial. Green light is sometimes used as a tool for eliciting specific plant responses such as stomatal control, phototropism, photomorphogenic growth and environmental signaling. When combined with blue, red and far-red wavelengths, green light completes a comprehensive spectral treatment for understanding plant physiological activity. But what color light is best for photosynthesis? The function of green light is less well understood than the other spectrums, and there are only certain species of plants that require green light for normal growth. Its effects appear to be very strain specific.

The pigments that can absorb green are found deeper in the leaf structure. It is thought that because green light reflects off of the Chlorophyll in leaf surfaces, and thus reflected deeper into the shaded areas of the canopy than Red and Blue which are readily absorbed, that green may actually be mostly absorbed through the undersides of the leaves as it bounces around in the shaded depths of the canopy.

Red light (640nm-680nm)

Red light affects phytochrome reversibility and is the most important for flowering and fruiting regulation. These wavelengths encourage stem and vegetative growth, flowering and fruit production, and chlorophyll production.

The 660nm wavelength has a very strong photosynthetic action. It exhibits the highest action on red-absorbing phytochrome regulated germination, flowering and other processes. This wavelength is most effective for light cycle extension or night interruption to induce flowering of long-day plants or to prevent flowering of short-day plants.

Far red (730nm)

Although the 730nm wavelength is outside the photosynthetically active range, it has the strongest action on the far-red absorbing form of phytochrome, converting it back to the red-absorbing form. Plants requiring relatively low values of the phytochrome photoequilibrium to drive the flower cycle. The 730nm wavelength can be used at the end of each light cycle to promote flowering in short-day plants such as Cannabis.

Also, a higher ratio of far-red to red than found in sunlight can trigger the shade stretch response – where a plant sensing it is shaded based on an elevated ratio of far-red to red – and will stretch to try to elevate its canopy above its competitors. This is why too much far-red is not advised if compact LED lamps for growing plants are desired, or in general. But small amounts or FR as provided by California LightWorks in our R/FR channel is very beneficial, and for this reason the ratio or R to FR is fixed on one channel in the 550 series.

The Best Spectrum for Growing Cannabis Indoors

The spectrum you select tells your marijuana plants what to do when by guiding them through the seasons. If you’re growing indoors, you have to completely recreate the sun for your plants through variable spectrum LED grow lights.

Here’s what a typical growth cycle should look like.

Seedlings

If you’re starting from seeds, you want to give your seedlings 24-hour light, but at low intensity. Stick to about 15% red and 30% blue and white. When your seedlings get their first set of true leaves, you can double the intensity until they have more than two sets, at which point they’ve graduated to the vegetative stage.

Clones

If you’re starting with clones, your first goal is to encourage rooting. This takes some effort on your plants’ part, so keep the light intensity low. If you stick to about 25% red and 45% blue and white, your cannabis is more likely to focus energy on deepening roots rather than expanding upward.

Vegetative Stage

In the vegetative stage, your top priorities for your cannabis plants should be root growth and developing nice, tight internodes.

For this, a healthy dose of blue light is your best bet. A higher concentration of blue keeps plants a little shorter. You don’t want your plants to shoot up too fast, develop longer internodes, and create a situation in the flowering stage where taller leaves form a canopy blocking light from the buds that grow lower on the plant. Keep your blue and white light levels blasting at 100% and maintain red at less than 60%.

Pre-Flower Stage

The pre-flower stage is when you should start prioritizing bud growth. Remember how plants take the red-light signal from the sun to start flowering? That’s the natural reaction you want to tap into now. An increase in red will inspire your plants to sprout buds.

However, you do still want to be careful of bathing your plants in too much red. You should avoid flowering stretch at this stage, and red light does tend to make plants reach skyward. At pre-flower, your wisest move is to kick the intensity of red light up just a little, to about 80%. Your blue light concentration can remain right where it was.

Flowering Stage

This is the red spectrum’s time to shine, so to speak. Up until now, you’ve been shielding your plants from a blast of red light to prevent stretching, but now your marijuana needs all the photons it can get. Turn your red light spectrum—that’s red and deep red—up to 100%. This maneuver helps you get those higher-than-ever yields.

The rest of the channels in your variable spectrum can stay at 100% as well. It’s all hands on deck in the flowering stage.

Finishing Stage

This is where you manage your potency and chemical profile. As you recall, blue and white light are the heroes when it comes to producing trichomes. Prioritize blue and UVB at 100%, and turn red down to about 50%. This is how you get those sticky buds everyone is looking for.

Using Spectrum Control with Cannabis

The exact way that plants use light is very specific to individual plant species and their natural environment. Evolution has produced a huge variety of plant strategies for growth and it is impossible to over generalize light responses. However, we do have a lot of practical experience with indoor cannabis growth results. Below are some general strategies and recommendations based on years of practical experiments with indoor lighting, including full spectrum LED systems.

The most common question we receive from growers in regards to spectrum control in cannabis cultivation is “What is the optimum Spectrum mix for Cannabis?” And the answer is it depends on what YOUR priorities are. Different spectrum mixes promote different plant morphology in different growth stages, and there simply isn’t one ideal. And that is the main benefit of LED’s over HID, the ability to use a varying grow light spectrum to design the plant for what you want from it.

There are basically 5 (or possibly more) different aspects to the end product in Cannabis that establish its value, and different people want different things.

1) Flower weight (ie. Overall flower yield)

2) Flower density (ie. Resin content and oil/wax ratio)

3) Flower cosmetic appeal (colors, structure, as well as density)

4) Fragrance (Strength i.e. terpene concentration and fragrance complexity)

5) Potency (THC and CBD levels)

What must be understood here is there is NO IDEAL SPECTRUM that will optimize ALL of these aspects of the final product simultaneously. Each can be individually optimized with LED plant lights but there will be tradeoffs.

Conclusion

So, in conclusion, it cannot be stressed enough that these recommendations are only starting points for using LED lamps for growing plants. That’s because all the results are strain specific and can also vary with other factors such as temperature, shading, and nutrients.

Experimentation with additional changes such as varying the white (ie. green) levels, or gradating the changes over time instead of just switching them, are encouraged. However, we suggest you carefully document all changes and limit them to 5% change in any spectrum per growth phase, and only one change total per harvest. Too many changes in one cycle and you will not know what did what. So remember, ONE CHANGE PER HARVEST.

Using the best UV LED lights for plants isn’t enough. As different plants use different parts of the light spectrum at different stages, even the best light for growing plants indoors requires a versatile control system. That’s where the Eco Farm Full Spectrum LED Grow Light comes in.

Eco Farm COB LED Full Spectrum Grow Light A Series is Professional 13 bands full spectrum LED grow light is ideal for the perfect and well-sustained growth of your marijuana/cannabis plants. Easily set the brightness of light according to your plant’s stage 3 separate dimmers in achieving the best quality grow light for seedling, veg and flowerinConvex optical lens makes the light brighter and evenly distribution.