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Grow Light Basics: Do Plants Need UV Light & How Does It Affect Them?

UV light or ultraviolet light has a negative reputation regarding its detrimental effects on human health. Green thumbs who wish to grow plants in growing tents often ponder the role of UV light on plants in their natural habitat. 

Do plants need UV light or is it better off grown indoors than receive these strong rays of radiation? 

Several myths about UV light are circulating on the Internet. Some gardeners say that it is a crucial part of photosynthesis while others believe that it doesn’t do much for plants.

In this post, we will try to bridge the two schools of thought about UV light that ignite several debates in the gardening community. 

Table Of Contents

What is UV Light?

We experience solar radiation in three ways: visible light, energy, and heat. Each of these constitutes three wavelengths of solar radiation wherein UV light is one of them. UV or ultraviolet light has the shortest wavelength in the electromagnetic spectrum ranging from 100nm to 400 nm.

UV light is invisible to the human eye but affects living organisms once it hits the Earth’s surface. Some animals can see UV light like bees and birds. It is divided into three types and the harm that it can cause depends on which of the three is exposed to humans, animals, and plants:

UV light wavelength.
UV light wavelength.

(1) UV-A (320-400 nm): The wavelength that has less energy than UV-B. It passes through the ozone layer but can be blocked by clouds. It is the solar radiation that causes sunburns in humans. Sunscreens can block its harmful effects on our skin.

(2) UV-B (280-320 nm): The wavelength that has more energy than UV-A. It has a photo-activating band of radiation that causes skin cancer in humans. It has long wavelengths that can reach 65ft (~20 meters) below the ocean surface.

(3) UV-C (100-280 nm): The radiation wavelength that makes up 0.5% of all solar radiation but causes the most damage to organisms. The good thing is it is absorbed by the gasses in our ozone layer and only a few strays of this light enter the Earth’s surface.

UV-C is often used in sanitizing tools or killing microorganisms in a sterile environment. In plants, some risk-taker growers use it to kill some pathogens like powdery mildew.

The other two wavelengths in the electromagnetic spectrum are as follows:

(1) Visible light or Photosynthetically active radiation (PAR): It is the sun rays that we visibly see as the sun rises in the morning. The sunlight may look like it’s yellow or white but it is composed of several colors which we see in a rainbow. PAR provides the ideal spectrum of light that plants need for photosynthesis.

Solar radiation - electromagnetic spectrum.
Solar radiation – electromagnetic spectrum.

PAR contains a spectrum of light from red to blue that plays specific roles in plant development.

Red light (620 to 750 nm) emits low energy that is responsible for seed germination, root growth, bloom development, and fruiting of plants. 

Blue light (400-520nm) provides higher energy for the germination and vegetative stages of plants. It encourages the production of chlorophyll which contributes to healthy stems and foliage.

Green and yellow light is in the middle of red and blue light in the electromagnetic spectrum of radiation. These light colors are used in grow lights used in indoor growing tents and farms.

(2) Infrared light: The wavelength of infrared light is longer than visible light. It’s the part of solar radiation that we feel as heat while staying invisible to the human eye. It is the type of radiation used in heating lamps for plants during winter and as part of red light therapy for alleviating sore muscles in humans. 

Adequate exposure of plants to infrared light can enhance their bloom development and healthy stem growth. However, excessive infrared light can also damage foliage, stems, and blooms.

Q: Do Plants Need UV Light?

Plants do not need UV light to grow and be healthy. It is the reason why the indoor gardening and farming industry thrive with the use of grow lights that emit PAR. However, some studies show that exposure to UV-A and UV-B can enhance the plants’ defenses against pests and diseases, flavor, and aroma.


UV-A is the least harmful UV light. Some studies suggest that plants perform better when they are exposed to it. Here’s what they found:

  • A study in the journal Oecologia found that UV-A light increased the net photosynthesis of plants by 12%.
  • Another research also found that UV-A light led to increased leaf size, dry weight, and growth potential of crops. This shows promise for using UV-A for increasing yields.
  • UV-A has similar effects to plants like blue lights which trigger the production of anthocyanins that cause red and blue pigments in plants. Simply put, it helps plants produce deep or more vibrant colors. It also helps grow short or bonsai-style plants.


UV-B is not a necessity for plants but it can enhance plant performance which is slowly getting the attention of growers. It challenges the plants to defend themselves from the harmful rays of the sun which in turn makes them stronger and more adaptable to plant stresses. It also makes the leaves of plants shinier due to the increased secretion of resin.


Plants don’t need UV-C. However, professional gardeners use it for sterilizing water, tools and other grow tents, especially for pest-infested grow tents.

It can be also used to kill pathogens on the leaf surfaces of plants. However, there’s a great amount of precaution needed in using this type of UV light.

How does UV light affect plants?

Outdoor plants exposed to both UV-A and UV-B lights are healthy and vigorous in optimal growing conditions.

However, prolonged exposure or excessive amounts of UV light to some plants can increase the efficiency of electron transport which decreases their photosynthetic production. It can also impair the DNA of the plant leading to bleached leaves, stems, or flowers. 

The tricky part about UV light is the conflicting information about the response of plants when receiving optimal amounts of UV-A and UV-B. The truth is, UV-B and UV-A can improve plant performance if given to plants in the right amount. Here are the effects of UV light on plants:

Improves Flavor and Color

Plants exposed to UV-B adjust to the high light energy by producing more flavonoids which enhances the flavor of the leaves, a resin that doubles the protective layer of the leaves, and other antioxidants. 

Better Resistance Against Pests, Fungal Disease, and Other Environmental Stress

UV-B and UV-A trigger plants to build their sunscreen which causes some positive side effects like better stress resistance.

Commercial growers are exploring the use of UV-B to manipulate the ability of certain crops to resist pest damage, produce better blooms, and increase yield. Many are hopeful that it can strengthen crops, enough to prevent big losses due to the rapid spread of incurable fungal and bacterial diseases.

Effects of UV-B in plants.
Effects of UV-B in plants.

Improves The Size, Weight, and Color of Leaves, Flowers, and Fruits

When UV-B is combined with PAR, some plant species increase their net plant photosynthesis.

The combination of UV-A and UV-B has also shown positive results and plants look way different than the ones grown in greenhouses and grow tents. Plants under UV light often have shinier leaves due to increased resin and terpenes.

Shinier leaves are grown under UV-B and the matte leaves are grown under grow lights without UV lights.
Shinier leaves are grown under UV-B and the matte leaves are grown under grow lights without UV lights. – Source: Farmer Tyler

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Though indoor farming is gaining some traction in the commercial agriculture and horticulture industry, farmers can see that there are still valuable benefits in growing crops under the sun. So, some grow tent manufacturers develop LED lights that emit UV-A and UV-B.   

Note: UV-A and UV-B provide some benefits to plants but they remain harmful to humans. Wear proper protective equipment when working under grow lights with UV light features.

How Much UV Light Do Plants Need?

The concept of using UV light is less is more. Plants are sensitive to UV light and a variety of species have different tolerance to it.

The best way to know how much UV light is enough for the plants you have at home is to consult a professional or follow the instructions on the label of your grow light. You may also experiment by checking how your plants respond to varying levels of UV light. 

How To Use UV Lights in Growing Plants?

Before using a UV light, assess your goals for your plants. If you want them to develop flavorful leaves and fruits, consider using a UV-B light. If you want your plants to have deep hues of red, blue, or violet, you can opt for UV-A. UV-C is ideal for sanitation and pathogen control. 

Some growers use UV-B in the last part of the growing stages of plants where they are starting to develop flavor and oil to avoid slowing down their growth process. It can tend to slow down photosynthesis which is not ideal for young plants under the vegetative stage. 

Professional growers often use UV-B for plants like basil and thyme to bring out the full potential of their flavors. They wait for the plants to be established and vigorous in their pots before introducing UV light.  

Do LED Grow Lights Have UV Light?

Small amounts of UV light are often included in LED grow lights. The benefits of UV-A are acknowledged by the agricultural community which led to the addition of UV lights in typical grow lights. You can also purchase UV lamps that are separate from the PAR grow lights. 

If you want to see how UV lights can improve the health of your plants, here are some brands that you may try:

Things To Consider When Using UV light in Gardening

Working around UV light can be as dangerous as exposing yourself to chemicals. We can’t see it but it can cause tremendous damage if not used properly. Short exposure can cause great harm to your skin or eyes.

So, here are some important tips before using UV lights in your grow room:

  1. The possible risk under a UV light depends on its intensity, wavelength (type of UV), and UV sensitivity. Prolonged exposure to UV-B and UV-C can cause sunburns, skin cancer, and skin aging. Use a hat, long-sleeves, and anti-radiation glasses when working around UV lights.  
  2. Never look directly at the beam of the grow lights, no matter if they’re on the lowest settings.
  3. Post warning signs to warn everyone working in your garden about UV light exposure. 
  4. Limit access to the growing area to prevent pets or curious children from being exposed to UV light.

Frequently Asked Question (FAQs)

Can plants survive without UV light?

Yes. Plants can do just fine without UV light. However, they can produce better and high-quality flowers and fruits if exposed to them. Small amounts of UV light can have a huge impact on the color, flavor, and overall health of plants.

How does UV light damage plants?

UV light damages plants by impairing their photosynthetic responses, leading to bleaching. Bleaching causes white patches on leaves and flowers. Extensive exposure of plants to high doses of UV light can also make them look fried and dried up.

How long should you leave UV light on plants?

The UV light exposure of plants depends on their sensitivity and their response to it. Some plants only need UV light in the latter part of their growing stage while some perform better with it throughout their life cycle.

Final Thoughts

The sun remains incomparable for its ability to energize living organisms through its solar radiation. Plants may grow without UV lights. However, they can flourish to their best potential if given small amounts of these deemed harmful rays of the sun. 

We hope this post opened your eyes to the bright side of UV light and its valuable contribution to plant life. The more you know about UV lights, the better you learn how commercial growers produce high-quality yields. 

Share this post with your friends and discover a new way to grow flavorful yield from your home gardens.

Let us know in the comments your experience with UV lights and how it levels up your gardening expertise.

About Jeanne Keith F.

Jeanne Felipe is a content creator of anything that can make this world a better place. She is a self-improvement junkie and a nature lover at heart. She loves to help people through her writing, either finding the right tools or doing the right thing to accomplish their goals. Quotes, sprouting plants, and cute dogs make her feel ecstatic. In her free time, she loves tending her garden and cooking Chinese and Mexican dishes. Connect her on Linkedin.

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