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Impact of UV and IR lights on cannabis
By Photonican March 15th, 2023
Impact of UV and IR lights on cannabis
In daily life, you may have heard that infrared light and ultraviolet light are usually used in cannabis cultivation, but the information about it collected on the Internet is very scattered. In this article, we will give you a clear introduction to infrared light, ultraviolet light, and their impact on cannabis cultivation.

Likewise, if you’d like to learn about the full spectrum LED grow light effects on cannabis growth, click here to find out.

  1. What is ultraviolet light?
  2. Impact of ultraviolet light on cannabis
  3. What is infrared light ?
  4. Impact of infrared light on cannabis
1. What is ultraviolet light?

UV-A light (315 - 420 nm): UV-A light has the longest wavelength and the lowest energy in the UV spectrum. Sunlight contains a lot of UV-A light and most plants planted outdoor are exposed to UV-A for a long time. Studies have shown that UV-A does not damage the DNA of most plants.
UV-B light (280nm-315nm): sunlight contains UV-B light. If plants are exposed to UV-B light for a long time in the natural environment, their DNA will be damaged and then produce many defensive chemicals to protect themselves from sunlight. UV-B damages plants in much the same way as it damages human skin getting burned.  
UV-C light (below 280nm): UV-C light has the shortest wavelength and the largest energy in the UV spectrum. It can lead to sunburn in humans, destroy the DNA of plants, and directly kill bacteria and insects on the surface of plants and humans. However, most of the UV-C light emitted by the sun is absorbed by the atmosphere, and only a small amount is in the sun.

2. Impact of ultraviolet light on cannabis plants

(1)Increase cannabinoids

Exposed to the sunlight containing ultraviolet light (mostly UV-A/UV-B), cannabis planted outdoors will grow more trichomes to protect itself from ultraviolet light.
Cannabinoids are produced by trichomes; the more trichomes, the more cannabinoid. If cannabis is exposed to ultraviolet light indoors using UV lights for weed, it will have the same effect as planting cannabis outdoors.
However, if you are cultivating strains specifically for CBD, please avoid using UV-B in the indoor setup with UV lights for cannabis.
Because the more THC cannabis produces, the less CBD they produce, and vice versa. UV light for cannabis cultivation can be a crucial factor in optimizing cannabinoid production.



(2) Reduce pest infestation
Many plant growth lights manufacturers claim that ultraviolet light can directly kill insects, but this is incorrect. The only ultraviolet light that can directly kill insects is UV-C, and as mentioned earlier, UV-C (200-280nm) has the shortest wavelength but the largest energy, which can cause harm to both people and plants. Exposing cannabis to UV-C might result in the destruction of both insects and the cannabis plants.
We already know that exposing UV-A/UV-B to cannabis, using UV light for cannabis, will help them produce more cannabinoids. What we may not know is that cannabinoids, also known as defensive chemicals, can drive away pests and protect cannabis from harm caused by pests, such as powdery mildew. Understanding the THC UV spectrum and the effects of UV light on cannabis can be crucial in optimizing both cannabinoid production and pest resistance.


Tip for using UV light:
Some growers use UV-A/UV-B light bars to radiate their cannabis plants, aiming to enhance THC production and reduce pest damage. Typically, growers expose their cannabis to UV-A or UV-B for 1-2 hours per day during the last three or four weeks of the flowering stage.

However, it's important to note that exposing cannabis to UV-A/UV-B for an extended period may be harmful. Prolonged exposure can pass through the plant's natural defense system, inhibiting photosynthesis, slowing down cannabis plant growth, and damaging the DNA of cannabis cells. This can result in physical harm to the plants, affecting their appearance, growth, and potentially leading to death.

In addition, because UV light is harmful to the human body, necessary precautions must be taken to protect ourselves when exposed to UV light. When considering how long to leave UV light on plants, it's crucial to balance the benefits of increased THC production with the potential risks of prolonged exposure to UV radiation.

How long to leave uv light on plants :
The optimal duration for leaving UV light on cannabis plants can vary based on factors such as the specific strain, growth stage, and the intensity of the UV light. As a general guideline, many growers expose cannabis plants to UV light, particularly UV-A and UV-B, for a limited duration during the flowering stage to enhance cannabinoid production.

A common practice is to expose cannabis plants to UV light for 1-2 hours per day during the last three or four weeks of the flowering stage. This short-duration exposure is believed to stimulate the production of secondary metabolites, including cannabinoids like THC and CBD, while minimizing the potential negative effects of prolonged UV exposure.

It's essential to monitor the plants closely during this period and adjust the duration based on their response. Prolonged exposure to UV light can have adverse effects, including inhibiting photosynthesis and causing damage to plant cells. Therefore, growers should strike a balance between providing enough UV light to stimulate desirable chemical compounds and avoiding excessive exposure that could harm the plants.

Ultimately, the ideal duration of UV light exposure may vary, and growers may need to experiment to find the optimal balance for their specific cannabis strains and growing conditions. This information is also applicable to determining how long to leave UV light on weed plants.

1. What is infrared light?
Near-infrared light (700-2000nm): Near-infrared light has the shortest wavelength in the infrared light spectrum. The red light will usually contain a small amount of near-infrared light because it is closest to the wavelength range of visible red light. Near-infrared light is used for TV remote control.

Mid-infrared light (3000-5000nm): Mid-infrared is warmer than near-infrared and will not harm plants. Mid-infrared is usually used by scientists and astronomers in astronomy.

Far-infrared light (8000-14000nm): Far-infrared light is the hottest. It is typically utilized in plant cultivation, contributing to the infrared light spectrum that supports various stages of plant growth.


2. Impact of infrared light on cannabis
The photoreceptors called phytochrome in cannabis play a role in the flowering, height growth, and photosynthetic rate of plants. When the plant is exposed to far red light, photoreceptors can sense it. But far-infrared light will not work alone on cannabis, it will affect the plant when combined with other visible lights such as red light and blue light.

(1) Reduce the time to bloom
According to the experimental results, far-infrared light will reduce the time required for plants to bloom.  When exposing red and blue light combined with far-infrared light to cannabis, it will shorten the time for switching from a vegetative state to a flowering state.

(2) Emerson effect - cannabis grows faster
In 1957, Robert Emerson found that if plants were exposed to far-infrared light and red light, the rate of photosynthesis of plants would increase.
But when he exposed the plant only to far-infrared light or red light alone, the rate of photosynthesis was lower.
Based on the Emerson effect, If exposing far-infrared light and red light to cannabis, the rate of photosynthesis of the plant would increase which means it will grow faster.
In fact, many growers use this method in cannabis cultivation. They say It can really help cannabis grow faster.
(3) Shade avoidance response - Cannabis grows higher and its flowers and leaves also grow wider.
If the ratio of red light and far-infrared light exposed to cannabis is rationally high, cannabis can sense that it is not in an ideal position, and then it will grow higher and stretch its flowers and leaves to receive more light. So if we expose far-infrared light and red light to cannabis instead of red light alone ,the cannabis will grow higher and its flowers and leaves grow wider.
However, the ratio of red light and far-infrared light exposed to cannabis being too high will lead to the leaves and flower of cannabis growing and stretching too much, and then putting too much pressure on the stems of the cannabis finally causing the cannabis to die.

Tip for using Far-infrared light:
Some growers will expose far-infrared light to cannabis before turning off the led white light for about 120 minutes in the last two weeks of the stage of flowering
It may be harmful to cannabis if far-infrared light is exposed to cannabis for a long time because it delivers heat to cannabis. Heat is dangerous to cannabis because it can turn their leaves yellow and even kill plants. What’s more, if there is too much heat in the planting environment, it will take a lot of electricity fees to use a cooling machine to keep the temperature appropriate.
In addition, far-infrared light may be harmful to cannabis seedlings. Exposing far-infrared light to cannabis may for  hinder the seeds to germinate completely.
Therefore, for plants to grow healthily, it is necessary to choose a far-infrared light bar with an appropriate amount of far-infrared light and use it in the right way.

Check Out the Video :
What’s more,our spectrum provide at least 30% more red spectrum output than most similar LED grow lights on the market,which can boosts for more yields and increases cycles in a year. 

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