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How Does LED Grow Light Color Spectrum Affect Marijuana Growth?

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.

The light spectrum plays an important role in raising the THC levels in marijuana. However, while growing cannabis indoors, LED grow lights colors are used as they promote substantial growth in them. But choosing the correct light spectrum for the plants and knowing its effect on photosynthesis can be often confusing and sometimes challenging.

First, you need to understand whether the color of light affects plant growth or not. The answer is yes, the color of light affects plant growth. However, it is distinctly notable under low light. The colors from the color spectrum that are most effective for the growth of plants are blue and red light. The colors like yellow and green are the least effective. Different colors should be used at different phases of plant growth. In the case of marijuana, blue light should be used during the vegetative stage. Red light is best when the plant starts entering the flowering stage and UV light helps in increasing THC levels in marijuana.

In this article, you will learn about color spectrums that are needed for marijuana growth. Also, how grow lights colors affect marijuana growth.

What is light spectrum of LED grow light color?

Grow light spectrum can be termed as electromagnetic wavelengths of light that are caused due to a light source and which promote plant growth. Plants use light in the photosynthetic active radiation (PAR) range of wavelengths (400 to 700nm) for photosynthesis.

Why is it important to take care of the spectrum?

Light is one of the most important factors in marijuana cultivation. Different spectrum colors have different roles in the development and growth of marijuana plants. Therefore, it is important to take care of the spectrum of grow light colors as they affect the growth of plants differently depending on environmental conditions. Normally, chlorophyll which converts light energy to chemical energy absorbs most of the light in red and blue light spectrums for photosynthesis. Therefore, both these lights are found at the top of the PAR range.

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.

The different types of light colors

The electromagnetic spectrum is typically divided into seven categories. Based on the order of decreasing wavelengths and increasing frequency and energy. These are Gamma rays, UV (Ultraviolet), infrared (IR), Radio waves, Microwaves, X-rays, and Visible light. Out of all these the visible light spectrum consists of seven colors namely:

  • Violet
  • Indigo
  • Blue
  • Green
  • Yellow
  • Orange
  • Red

The wavelengths of each of these lights vary from one another. Violet light has the shortest wavelength of 425 to 400 nm. It is scattered successfully by the atmosphere. Indigo has a wavelength of 450 to 425 nm. It is a color between the primary colors blue and violet. Blue light has a wavelength ranging from 500 to 450 nm. In addition, green light has a wavelength ranging from 570 to 500 nm. Yellow and orange range from 590 to 570 nm and 610 to 590 nm respectively.

Red light whose wavelength ranges from 750 to 610 nm can be best viewed during sunrises and sunsets.

Does the Color Spectrum Affect Growing Cannabis plants?

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.

How does color spectrum of grow light affect cannabis growth?

The light spectrum is a factor that cannot be ignored while you create an ideal environment for marijuana cultivation. Most growers have multiple goals like achieving high yields from their plants and increasing the THC levels. Improving and maintaining the overall health of their plants for indoor growing is crucial. Good growers need to involve in planning and coming up with technical solutions to achieve their goals. They should understand that adequate light is the one of  important factors while growing marijuana plants. Colors of grow light are your secret weapon to produce more marijuana buds.

As cannabis is very light-sensitive you need to adjust the light intensity, frequency, and color for its different growth stages. With the help of LED grow light, you can mimic the natural conditions that are found in nature. Natural sunlight provides an entire light spectrum. As the seasons change, the wavelength energy also changes. During summer the sunlight has heavy green and blue wavelengths. In the fall season, it has more red light. While growing marijuana indoors, you try your best to mimic the natural seasonal changes. Therefore, you have to use LED grow light with different colors that can boost the growth of cannabis.

Cannabis seeds in a spoon

Feminized cannabis seeds are important to cannabis cultivation because only female plants produce consumable flowers. LED grow light can boost sustainability and profits in cannabis.

Color spectrum and cannabis: Effects of different light colors on the growth of cannabis

Red Light for growing cannabis

Red light is the most effective spectrum light that encourages photosynthesis. This is because it is highly absorbed by the chlorophyll pigments. Its wavelength ranges from 620 to 750 nm. This light is essential during the flowering stage of the marijuana plants. Adding red light promotes budding and flowering. Many marijuana growers switch to strong red lights with more intensity once their plant has reached the flowering or budding stage. When red light paired with blue light can balance out any overstretching or disfigured elongation of stems. Red light and blue light together produce the best response from marijuana plants.

Blue light for growing cannabis

The blue light spectrum is very important for marijuana plant growth. It is mainly responsible for increasing plant quality. During the vegetative stage of growing marijuana, you should aim for growing leaves as many as possible. The blue grow lights colors wavelength is from 450 to 490 nm. Indoor growers use T5 or T8 lighting fixtures, CFLs (compact fluorescent lamps), or metal halide bulbs that have a blue band of light. They use these for the first few weeks to achieve desired goals. When marijuana plants grow outdoors the angle of the sun during spring allows blue light energy which is abundant in this season to penetrate the leaves. Therefore, this blue light signals the plants to grow healthy and large leaves and to become strong. The plants that are deficient in blue light generally turn out yellow or pale and are weak and flopping. Blue light is essential for young plants and seedlings in vegetative stages to properly grow roots and stems.

Green light for growing cannabis

Recent NASA findings suggest that green LED grow lights colors that are not majorly associated with photosynthesis but still have certain impact on the growth of plants. Green wavelengths have been considered less important when compared to chlorophyll absorption of blue or red-light spectrums. However, the green light can still play a role in the growth of cannabis plants at different stages. The wavelength ranges between 495 to 570 nm. Marijuana plants can absorb very little green light energy. However, reports say that a small amount of green light can affect growth. Many growers may think that the green light is unnecessary for successful growth. However, if you think of growing marijuana with lights having complete spectrums of colors then little green light energy is great for you.

Another benefit of adding green light to your color spectrum is that it does not trigger flowering in marijuana plants. This plant is extremely sensitive to light/dark cycles. Therefore, even small amounts of light during nighttime can trigger marijuana plants into thinking that it's flowering time. As green light is invisible to cannabis, it is the perfect light color that you can use. That is if you wish to work on your cannabis plants during nighttime.

Violet light for growing cannabis

Violet grow lights colors wavelength ranges from 380 to 450 nm. It is the bottom end light of the visual light spectrum. The range of violet light is considered as it improves the taste of flowers. In addition, it is considered to improve the potency and color of the plants. However, violet light cannot be considered as a major growth factor when compared to the red and blue light spectrum.

UV light is harmful to the growth of marijuana plants-Myth or reality?

Ultraviolet or UV light having a wavelength that ranges between 10 to 400 nm is known for being harmful to human skin when exposed to it. Ultraviolet light in larger amounts can also harm plants. It is not visible to the naked eye and sits at the lowest end of the light spectrum. However, just because it is not visible, does not mean it is not useful to the plants. A small number of UV rays can be beneficial to the aroma, flavor, potency, and growth of marijuana plants.

Researchers have suggested that boosting UV exposure can increase THC levels. Therefore, making buds more potent. There is engrossing real-world evidence when you look at where the world’s most potent marijuana comes from. The Bella Valley in Lebanon and the Rif Mountains located in Morocco have some of the world’s most potent cannabis. However, they are both located at high altitudes which means more exposure to the UV light. Thus, we can say that adding some amount of UV grows lights colors can be beneficial to your marijuana plants.

Types of UV lights for growing marijuana

UVA (315-400 nm)

98% of the UV light that is reaching Earth contains UVA, which makes it an important part of the natural environment. If you are growing marijuana outdoors, you do have to worry about boosting UVA levels as your plants naturally receive plenty. UVA may help boost the THC level for indoor growth when you increase the exposure during the flowering period. However, for humans being exposed to UVA for long intervals can increase the risk of skin cancer. Therefore, you should make sure to protect yourself with sunscreen.

UVB (280-315 nm)

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.

UVC (100- 280 nm)

UVC rays are the most dangerous out of the three and they are not useful for both humans as well as marijuana plants.

The advantages of UV light for marijuana plants

  • Increases cannabinoid production (THC)
  • Good for resin generation
  • Enhances resistance to bacteria and pests.

The disadvantages of UV light for marijuana plants

Fail to manage the amount of exposure, you can find the following disadvantages:

  • Overexposing can stunt growth
  • There is a possibility of decreased CBD levels
  • Low returns on investment.


There are lots of grow lights available in the market and each has its pros and cons. Many lights offer different colors of light which are referred to as light temperature. If you are a grower, you need to research properly while getting a light for your marijuana plants. As you have read in this article, different light spectrum has different effects on the growth of marijuana. You can use lights for all types of indoor growing. Any one of these three artificial light sources can be used for indoor marijuana cultivation. They are LED (light-emitting diode), CFL (compact fluorescent light), and HID (high-intensity discharge lamps). Excess light can damage your marijuana plants as well as too little light. Therefore, you must research how to set up grow lights for tremendous indoor harvests.

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