One way green light is helpful is it penetrates further down into the canopy than red and blue light, which get mostly absorbed by the upper leaves. This adds to amount of photosynthesis happening to leaves further down on the plant.
- Train your plants to use more of the light you have (get ups to 40% more yields compared to an untrained plant in the same setup)
- Upgrade to bigger grow lights
Although certainly not essential to healthy plant growth it is considered good form to choose lights in the proper light spectrum to encourage the growth you want in the vegetative and flowering stages of the marijuana plant. If you have a tool, why not use it?
Over the years, we’ve learned that plants actually make “decisions” about how to grow based on the spectrum of light they receive. A different color spectrum can change how cannabis germinates, grows and even makes buds! Although we don’t have a lot of options to change the spectrum of sunlight when growing outdoors, we have almost complete control of the spectrum when growing cannabis indoors since we’re using grow lights!
However, keep in mind that different strains are affected differently by the color spectrum of the light. Some plants are barely affected at all while others might react much more strongly. It’s important to remember that the changes caused by light spectrum are relatively small (such as stems tending to grow longer) and many other factors drive some of the same changes.
LED grow lights use custom color spectrums to get plants to grow more efficiently
There has been quite a bit of research on how different spectrums affect plant growth, especially over the last decade by researchers at NASA trying to find a way to grow plants most efficiently in space with LED grow lights.
If a plant is surrounded by greenery, it starts sensing higher ratios of far-red light, and starts “stretching” upwards to grow past the other vegetation and get access to better quality light
Note: This article is aimed at intermediate to advanced cannabis growers looking for ways to improve their results.
What do I need to know about the color spectrum of light when growing marijuana indoors? Blue light delivers more squat growth, yellow light leads to stretchier growth and…
During the vegetative stage it is recommended to aim for as many leaves as possible, and to make sure plants stay rather compact, don’t stretch too much, and develop strong stems. Indoor growers tend to use metal halide bulbs, compact fluorescent lamps (CFL’s), or T5/T8 lighting fixtures with a blue band of light for the first few weeks to achieve these goals. When cannabis grows in nature, the high angle of the sun in spring and summer allows more “blue” wave lengths to penetrate through the atmosphere, a signal for cannabis plants to grow strong, large and healthy leaves.
Every organism living on Earth needs information what is going on around them to react to environmental changes, and ideally, get a slight advantage over other members of their species regarding natural selection and evolution. Interestingly, cannabis plants receive a lot of their information from the light they’re exposed to, and almost instantly react to different bands of wave lengths – a complex topic to fill books with, but let us focus on the basics first.
When shopping around for a grow light, you will likely come across the term “colour temperature”. This is essentially a way to describe the light appearance provided by a bulb, and is measured in Kelvin (K).
- 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
In a strictly scientific sense, no. Colour temperature is normally used as a way to describe how the light produced by a lamp looks to the human eye. For some types of lights, such as LEDs or fluorescent lamps, it doesn’t describe a light’s spectral distribution or wavelength.
Other lights, such as LEDs or fluorescents, may emit light from a number of narrow wavelengths, with gaps or peaks within the spectrum. In other words, even if the light appears the same to the eye, it may be missing certain wavelengths (colours) that plants require for healthy growth.
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.
Colour temperature doesn’t mean the physical temperature of your light, but the degree of warmth or coolness of a light source—the “visual temperature”. When a light has a higher degree of Kelvin, it has a more blueish appearance. Thus, we call it a “cool” light. On the other hand, a bulb with a lower degree of Kelvin emits a “warmer”, reddish light.
For vegging your cannabis plants, go with a cool light, one that emits a “daylight” colour with a high Kelvin of 6,000–6,500K. For flowering, a warm light with a reddish tone, about 2,800K, is optimal. You can also find grow lights with a “best of both worlds” colour temperature of about 3,500K, which you can use for both vegging and flowering.
Seeking methods to increase THC production feels natural for growers – learn how the light spectrum can affect growth and potency of weed.