Cannabis is used for many medicinal and recreational purposes. Therefore, many states and countries have legalized its use and cultivation. Countries like the United States of America have allowed the growth of marijuana plants at home. Therefore, cannabis growers need to know about how will the colors of LED grow light affect the growth of their marijuana plants.
The disadvantages of UV light for marijuana plants
Red Light for growing cannabis
It is important to be careful while using UVB supplements. Since every plant reacts differently when exposed to it. In the case of the marijuana plant, it helps in boosting cannabinoid and terpene production, but only when exposed during the last few weeks of the flowering stage. Even it comprises only 1% of UV light, UVB grow lights colors can help increase THC levels. UVB is a great source of vitamin D, which is essential for the well-being of humans. However, prolonged exposure in humans can increase cancer risks. Therefore, growers need to provide the right exposure for their plants while ensuring they stay protected.
Marijuana plants receive a lot of information from the spectrum of light they are exposed to and react to different wavelengths in different ways. For a marijuana plant in the vegetative stage, blue light that ranges from 400 to 500 nm is best. The ideal range is 460 nm, in this stage, the plants are signaled to grow strong, healthy, and large leaves. In the flowering period, red light ranging from 620 to 780 nm can be used for the highest yields. Choosing growing lights colors spectrum of ideal wavelength 660 nm can impact the rate of photosynthesis and plant growth.
UVC (100- 280 nm)
The energy emitted from the sun is in the form of radiation. The ozone layer filters this radiation and allows only wavelengths from 300-1100 nm to reach plants. This light is referred to as light spectrum, visible spectrum, or color spectrum. Its range is in between 380-750 nm approximately. A spectrum is a band of numerous colors namely red, orange, yellow, green, blue, indigo and violet.
So, when indoor growers are scouting their plants for pests, a fixture with the green light in the spectrum (i.e., a white-light spectrum) becomes an advantage. Under a blue-red light, recognizing pathogens like powdery mildew and fungus gnats can be next to impossible. When a spectrum includes even a small proportion of green, grow techs have a much easier time uncovering issues before they scale into major problems.
And it’s reasonable to assume that cannabis plants use green light more than other crops. Cannabis is an extremely light-hungry plant with a dense canopy. Because green light penetrates through leaves better than other colors — and because green light efficiently drives photosynthesis in strong, white light — green wavelengths result in greater flower development.
Greenlight is subject to the most misconceptions. While many growers believe cannabis plants don’t utilize green light for photosynthesis, they actually do, and green light is important for other processes as well.
Greenlight also signals plant morphology. It plays an important role in mediating a plant’s responses to blue light, and it influences leaf growth and early stem elongation. By sensing the ratio of light colors, plants can tell if they’re in shade or if they’re receiving direct light, and how to position their leaves to maximize light absorption throughout the day. That’s because green light penetrates leaves more easily than other colors. When plants sense a higher green-to-blue ratio, they assume they’re shaded by other plants, and they’re more likely to elongate their stems to compete.
Our Eyes and Green Light
So, instead of green LEDs, lighting engineers use “white” LEDs that produce green light and other wavelengths simultaneously. It’s important to note that although some manufacturers reference green light, they’re typically referring to the white LEDs within the lamp.
 Terashima, I. et al. Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are green. Plant and Cell Physiology. 2009.
The myth that plants don’t use green light stems from their green color: if the plants are reflecting green, they’re not using it. But the reality is not so simple, and only a small portion of green light is reflected to give plants their green appearance. Moreover, our human eyes sense green light more easily than other colors; not that much is reflected.
Full-Spectrum LEDs or Blue-Red?
But you won’t find green LED fixtures on the market or see green LEDs contained within a full-spectrum fixture. While green LEDs are useful for research, they’re not practical for commercial cultivation. Due to the constraints of manufacturing technology, green LEDs lack the electrical efficiency of other colors of LEDs. White LEDs, on the other hand, efficiently deliver green light and fill out other parts of the light spectrum too.
Studies have shown again and again that cannabis plants use green light. But green light is different from red or blue. It behaves differently in the canopy, and different photoreceptors use it for photosynthesis — not just chlorophyll a and chlorophyll b.