What Color Light Is Best for Plant Growth? | Tips for a Better Yield

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by Morgan

Last update:

August 29, 2023

How To Choose The Right Lighting For Your Marijuana Grow Room

Aside from nutrients or oxygen, light is an essential element of plant growth. Plants require light to produce food through photosynthesis and absorb other necessary components. Light influences plant growth, but not all light provides the same benefits. By understanding what type of light to use, you can make sure your plants grow quickly and efficiently. 

The benefits of using grow lights are undeniable. Whether you're indoors or outdoors, there are numerous reasons why all gardeners can find a use for growing lights. However, different varieties of plants will have additional light requirements. 

If you're looking for artificial light for cannabis plants, you must get the right light for your plants. With so many light options these days, that may not be very clear. This article aims to show you what color light is best for plant growth and what matters in the spectrum of wavelengths it emits;

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What Color Light Is Best for Plant Growth: Understanding Colors and Visible Light

Humans can only see a subset of the electromagnetic spectrum, including frequencies ranging from gamma rays to radio waves. Our eyes - see if grow lights are bad for your eyes - are limited in their ability, so we don't notice colors at different wavelengths except for white light, which contains all other hues - black absorbs all colors except blue, yellow, and green!

On the other hand, sunlight has all of these essential colors and appears bright white, and plants absorb light to produce vital nutrients that feed the weed plant in addition to water and oxygen.

You could conclude that white light is essential for optimal weed growth.

On the other hand, different colors of light have different effects on plants, and indoor plant growth is becoming increasingly popular.

You may buy or make a grow light and use your selection of the color of light that affects the cannabis plant.

color scale and cannabis plant

The Effects of Different Colors of Light on Plant Growth

All colors you see are between 380 and 750 nanometers in wavelength. On the other hand, specific light colors can benefit your plants in a variety of ways.

Some have a more significant impact on plants than others, and these effects often range from each weed plant's growth and development to the formation of protective elements.

The effects of various light colors on plant growth are discussed below, and which color of grow light is best.

Ultra-Violet (UV) Light

The light has a wavelength range of 10 to 380 nm and is hazardous to living things, especially plants and animals. Even though sunlight contains UV rays, its rays are negligible compared to artificial ultraviolet rays sources such as tanning beds since it is filtered through the earth's atmosphere.

UV light can cause some plants to produce a barrier protection resin to protect themselves from harmful raysβ€” it is one of the beneficial effects of UV light on plants.

However, unless you're growing cannabis, you shouldn't put your plants under UV lights because this plant benefits significantly from resin production, and ultraviolet light is the best spectrum for clones.

Common house plants will be damaged and begin to wilt in most cases.

the plants under Ultra-Violet (UV) Light

Violet Light

The light mixes with antioxidants in the cannabis plants and makes them more nutrient-dense and healthier. Plants mainly use violet light during their flowering and fruiting stage to promote blooming.

It also helps develop chlorophyll, which gives plants their green color and helps them convert sunlight into food.

Although violet light does not have the same effect on plant growth as other colors, it can be beneficial when combined with different colors such as red and blue.

Blue Light

Plants mainly use blue lights during their vegetative stage to promote growth. It also helps develop chlorophyll, which gives plants their green color and helps them convert sunlight into food.

The light also improves the little plant's oxygen transmission, called cellular respiration. Because blue light provides more energy to the plant, it requires less water; thus, blue light reduces water loss.

plants under blue lights

Red Light

Red light has a light intensity of 620 to 750 nm and is the longest wavelength of visible light. It's well known that red light significantly impacts plant foliage, making the leaves more vibrant and luscious.

It's also been shown to increase chlorophyll production, photosynthesis rates, and the number of stomata on the leaves, allowing plants to take in more carbon dioxide.

Red light is also essential for plant growth as it helps roots.

During their flowering and fruiting stage, plants also use red light as it promotes blooming.

plants under the red light

Green Light

Plants use a lot of different colors in their surroundings to create the most vibrant life possible. The slightest change can make a difference between greener pastures and desert soils. Therefore, why not let plants have some fun too? 

Plants absorb every color except green! It might seem like an obvious choice at first glance since this allows them to produce chlorophyll through photosynthesis, which gives off light blues.

The green hue does not affect plant growth, so it is not the best choice for your indoor grow lights.

plants under the green light

Yellow Light

The light is relatively cheap, and some farmers prefer using regular yellow light for their cannabis. Yellow light is close to green light in the growth-light spectrum, with its effects similar to those of the plant.

On the other hand, regular yellow light is reflected rather than absorbed by chlorophyll, and it can boost growth when compared to no light. The effects are so minor that using it as a grow light is pointless.

a plant under the yellow light

Far Red Light

Far-red is virtually invisible to the human eye since it is located so far in the growing light spectrum.

Furthermore, because of its long nanometre wavelength, plants do not absorb it as much as other light colors.

There are, however, several benefits of using the far-red light. For example, when combined with red light, you get red light's enhanced effects, including better flowering during the day and ripening at night.

It comes with a positive impact on weeds and encourages higher production and vegetation.

However, this light color should not be used alone but rather in conjunction with blue or red.

"Burple" Light

"Burple" light is a mix of blue and purple growth light. It is often used during the vegetative stage as it promotes growth.

"Burple" color lights are made up of only red and blue growth lights and do not have any identical wavelength compared to violet lights. That means the plant will absorb "burple" light primarily, stimulating development.

Overall, the grow lights are ideal for cannabis strains with many leaves since the combined effect of blue or red works like magic to promote vegetation.

White Light

plants under the lights

White light combines all the different colors in the light spectrum.

The light combinations are as discussed below;

  • Cool white light- This is a combination of blue and green light. It has a refreshing effect and promotes growth.
  • Yellow, white light has a red, yellow, and blue light and has a warm effect and promotes flowering.
  • Ordinary white light combines red, yellow, green, and blue light. It has a balanced effect and promotes both growth and flowering.

It is also the most expensive growing light, but it is worth the investment since it will provide your plants with everything to grow healthy and strong.

plants of cannabis

Choosing the Best Type of Grow Light?

With the above information about the different colors of light and their effects on plants, it is time to select the perfect type of light for your needs.

  • The first step is determining what stage of growth your plants are in. If they are in the vegetative stage, you will want to use a blue or "burple" light. If they are already in the flowering stage, you will want to use a red or white light.
  • You may also want to consider the size of your grow space and the type of plants you are growing. If you grow large plants, you will need more light than growing small plants.
  • And finally, you will want to consider your budget when choosing a grow light. LED grow lights are the most expensive, but they are also energy-efficient and long-lasting. HPS grow lights are less expensive, but they use more energy and need to be replaced more often.

Natural Sunlight and How It Works on Outdoor Weed Plants

Weed plants love the sun, and they will grow best when exposed to natural sunlight. However, there are a few things to keep in mind when growing weed plants outdoors.

First, you need to ensure that your plants get six hours of direct sunlight daily. If they are not, they will not grow as well. Second, you need to ensure that your soil is healthy and rich in nutrients. If it is not, your plants will not be able to absorb all the sunlight they are receiving. 

And finally, you need to make sure that your plants are protected from the wind and rain. If not, they will become stressed and may even die.

What and How Much Artificial Light for Indoor Lighting Do I Need?

It is important to note that the choice of different growers will depend on the factors in their indoor garden. You may want to sit and consider the plant size, end-use, garden area, stage of growth, your budget plans, and more. At the end of the day, it all boils down to what your specific needs are for your garden and plants.

marijuana plant

Benefits of Using Grow Lights on Indoor Plants

Grow lights are a great way of providing your plants with the light to grow healthy and strong.

There are many different types of grow lights available, so you can choose the one that best suits your needs.

Fluorescent grow lights are the most energy-efficient and long-lasting, but they are also the most expensive.

HPS grow lights are less expensive, but they use more energy and need to be replaced more often.

No matter which type of grow light you choose, you will see increased plant growth and health.

How Long Should a Plant Grow Light Be Left On?

To fully determine the amount your light requires, you need to determine several factors discussed below;

  • The vegetative stage- your plants grow leaves and stems during this stage. The plants need 18-24 hours of grow light per day.
  • The flowering stage- during this stage, your plants are growing flowers. They need 12-16 hours of light per day.
  • The size of your grow space- the larger the grow area, the lighter you need.
  • The strain of cannabis you are growing- some plants need more light than others.

Frequently Asked Questions

Why Are Most Grow Lights Purple?

The grow lights are often purple because they contain a mix of blue and red light. This combination promotes growth in plants, which is why it is often used during the vegetative stage.

How Much Light Do Weed Plants Need?

Weed plants need a lot of light to grow properly. They require at least 12 hours of sunlight per day, but more is better. If you are growing weeds indoors, you will need to provide artificial light for your plants.

What Are the Best Artificial Lights for Plant Growth?

LED lights are the best kind of artificial light for plant growth. These grow lights produce very little heat, which is essential for preventing your plants from getting too hot.

What Color Of Light Is Most Effective For Plant Growth?

Red and blue lights are most effective for plant growth, but all light colors can contribute to photosynthesis. Blue light is necessary for the formation of chlorophyll, and red light helps plants grow and flower. White light contains a spectrum of colors beneficial to plant growth.

Is Blue Light or Red-Light Better for Plants?

Both blue light and red light are necessary for plant growth, but red light is more critical for developing flowers and fruits. Blue light is essential for the formation of chlorophyll.

Do Plants Need Sunlight to Grow?

Yes, plants need sunlight to grow. Sunlight provides the energy that plants need to produce food through photosynthesis. However, some plants can grow in low-light conditions if adapted.

In Conclusion

There are many factors outlined in this piece to consider when choosing the best type of light for your plants. The most crucial thing is to know what stage of growth your plants are in and choose the light accordingly. 

Blue or "burple" light is best for vegetative growth, red or white light is best for flowering, and white light is best for overall development. Have these tips in mind, and be on your way to a healthy and prosperous indoor garden. For more insights on how growing weeds, visit 420greenthumb.

🌿  Join my "growing" community 
of 5000+ happy
cannabis farmers! πŸ‘©β€πŸŒΎ

Receive my weekly articles in marijuana growing,
from seeds to smoke! 
β€” Morgan, 420GreenThumb 🌱

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About the author 


I discovered the benefits of Cannabis at a young age in 2002, with years of trial and error, my knowledge grew just like my plants. As my love for cannabis unfolded I began to teach and learn, trying to gain as much information and practical growing experience.

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