What You Need To Know About UV Light For Plants

There has been some debate over the importance of UV light for plants. Some growers even wonder whether ultraviolet light has a place in plant cultivation of any kind at all. 

The fact of the matter is that if you are growing plants indoors, you should be supplementing your plants with some form of it. 

We’ll cover everything you need to know about this wavelength, along with the best ways to add it to your grow room.

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What You Need To Know About UV Light For Plants


There has been some debate over the importance of UV light for plants. Some growers even wonder whether ultraviolet light has a place in plant cultivation of any kind at all. 

The fact of the matter is that if you are growing plants indoors, you should be supplementing your plants with some form of it. 

We’ll cover everything you need to know about this wavelength, along with the best ways to add it to your grow room.

What is UV Light?

Often referred to as UV light for short, ultraviolet light is technically a type of electromagnetic radiation garnered from natural sunlight.

Every time you are out in the sun, you are exposed to UV light.

It is broken up into three different categories of wavelengths - UVA, UVB, and UVC.

It helps plants grow in several ways and also may improve the overall potency and quality of your flower. 

But, only certain types of UV light are really beneficial to plants.

The Different Types of UV Light

Both UVB and UVA are essential parts of life on earth, but UVC is not. It gets filtered out by the ozone layer, and never really makes it to our plants naturally outdoors.

There is also technically a fourth type of UV light. This is any kind of light with a wavelength between 10 and 180 nm. This kind of UV light is referred to as extreme or “vacuum” UV, since it propagates only in a vacuum. 

Since we're talking about UV light for plants in particular, we are only going to cover the two types you need to know about" UVA and UVB.

Now, let’s quickly breakdown the wavelengths at which each type of light occurs.

Ultraviolet A (UVA)

Ultraviolet A, or UVA light, is light with wavelengths between 320 nm and 400 nm.

It contains about 3% of the photons that are found in natural sunlight when it breaks through the earth’s atmosphere. It does not have any harmful effects on DNA.

Ultraviolet B (UVB)

The next type of ultraviolet light is UVB, or ultraviolet B. this kind of light has wavelengths between 29 nm and 320 nm

It contains about a fifth of 1% of overall natural sunlight. In contrast to UVA, it can damage DNA and has been known to have cancerous effects on humans and animals.

However, since it has such a small composition, the ozone layer can better block it out. It rarely reaches the earth in significant enough amounts to do lasting damage.

How Does UV Light Affect Plants?

Plants have different responses to UV light depending on the type and wavelength. The response also varies depending on the species of the plant.

Here are some of the most noteworthy benefits of adding UV spectrum to your grow room.

Higher Flower Quality, Potency, & Weight

Some studies have shown that UVA and UVB light can enhance the production of terpenes and flavonoids in plants.

In one study, growers cultivated tomatoes in a greenhouse using grow lights without UV. They noticed the tomatoes grew great, but the taste left plenty to be desired.

So, they grew another batch with supplemental UV, and found that flavor and aroma were greatly amplified.

This is great for those growing flower, because it means the taste and aroma of your flower will be increased.

But to take things a step further, consider the fact that one study found that flower grown without UV light will be missing up to 6 key terpenes! And as we are coming to realize, terpenes affect the way flower makes you feel, as well as that taste and aroma.

Other studies prove that UV can increase resins and oils that are found in plants grown specifically for this purpose - like THC & CBD.

This means your flower will be more potent, and you can command higher prices as a commercial grower.

UV light can also increase the root mass of your plants and increase veg branching with less stretching - leading to tighter internodes, and a heavier harvest weight.

Increased Resistance To Stress & Disease

Furthermore, growers notice an increased resistance to stress and disease when supplementing with UVA and UVB spectrums.

Plants can produce up to 15 different variant defense proteins as soon as they are exposed to UV light.

ultraviolet light for plants

UV light has the ability to destroy harmful microorganisms, particularly when the wavelengths are shorter than 300 nm. 

Not only that, but UV light can increase your plants’ resistance to bacteria, insects, and fungus.

Grow plants indoors without any UV exposure, and you'll lack all of these benefits.

Faster Germination

UV light can also promote faster germination when starting seeds. They strengthen the plant and prepare it for higher light intensities. 

It reduces the “shock” time of the seedlings while also speeding up germination.

When Should You Give Plants UV Light?

There has been some talk about when using UV light is actually effective. Some growers say you shouldn't use it during veg, as it won't contribute much and will just be a waste of money.

A common theme we hear is "don't invest in the veg, invest in the flower". But, if you don't invest in the veg, how is your plant going to be capable of producing a frutiful harvest?

That's why we recommend using UV lighting full cycle if you can - from seed to harvest. By giving UV light to your plants during propagation & early veg, they will develop thicker cuticles, faster metabolism, and just be overall stronger and healthier.

There is no question that all of this adds up to a plant that can yield heavier, and more potent. So, rather than adding in high doses of UV light at key points, we recommend using low doses of UV light over the entire life. This is safer, and more effective.

Can UV Light Be Harmful To Plants?

Can UV Light Be Harmful To Plants?

As you can see, there are plenty of benefits to using UV light when growing your plants, but is there any chance UV light is harmful to plants?

Assuming you use the proper UV light, you won't have to worry about harming your plants.

Attempting to use a tanning lamp, for example, would be dangerous and yield poor results.

You need to make sure you purchase a light that is designed specifically for growing plants.

How Much UV Light Do Plants Need?

Before you go and buy an industrial UV lamp for your plants, understand that their requirements for UV light are super low. Less is more in this instance.

You can get great results with just 2-3 watts of UV light per square foot of growing space. This means for a 4'x4' tent, for example, you would be just fine with around 32-48 watts of UV lighting to yield the benefits.

Growers Need To Stay Safe While Using UV Light

While the UV light may not be harmful for your plants, necessarily, it can be for you.

In some instances, artificial UV can be more damaging to your skin than the sun, because you are in closer quarters to it.

So, make sure you take measures to care for your eyes by wearing protective eyewear around your UV lights.

We also recommend wearing sleeves if you are going to be working around your lights.

What Is The Best UV Light For Plants?

For the best results, make sure you provide your plants a high-quality UV grow light. 

Many full spectrum LEDs will emit just the right amount of each type of UV. It will mimic natural sunlight, too, so plants will feel as though they are being grown outdoors. 

There are even ceramic (CMH) grow lights which emit UV light, along with some double ended (DE) bulbs.

Here at Hydrobuilder, we carry a wide selection of UV Spectrum LED Grow Lights. These are some of our favorites:

Black Dog LED Grow Lights

Black Dog LED

Black Dog LED is an industry leader when it comes to grow lighting. They have an incredibly well-researched design, and have produced the greatest spectrum ever seen when it comes to growing plants.

The entire PhytoMAX line of LEDs uses the Phyto-Genesis Spectrum, which includes the perfect amount of UVA light to grow plants.

They experimented with adding UVB to the spectrum and noticed superior results with just UVA. So, they omit UVB altogether.

These are widely known as the Best LED Grow Lights money can buy, but they aren't in every grower's price range.

California Lightworks LED Grow Lights

California Lightworks LED Grow Lights

Another reputable manufacturer in this industry is California Lightworks.

They have a great selection of LEDs with an added UV spectrum to enhance growth along with all the other benefits mentioned above. Here are some great options:

Sun System LEC Boss 315 Watt Grow Light

The Sun System LEC Boss 315 Watt Grow Light is one of the best commercial fixtures on the market.

It puts out a ton of intense light very efficiently, and comes with all kinds of features to set it apart from other LEC/CMH style lights.

But, it also includes one of the most optimized spectrums for plant growth yet, featuring higher amounts of beneficial UV light than competitors.

Growers Choice Master Pursuit 1000 Watt DE Grow Light

If you prefer to stick with traditional HID technology, the Growers Choice Master Pursuit 1000 Watt DE Light is a great way to add UV light to your grow.

This incredibly powerful grow light puts out a ton of useable light, and comes with a bulb of your choice: MH/HPS.

The spectrum on many of the bulb options, such as the 2k DE HPS, 6K DE MH, and the 10K DE MH all include beneficial UV light to improve your grow.

HLG 30 Watt UVA Supplement LED Grow Light

HLG 30 Watt UVA Supplement LED Grow Light

If you are looking for a supplemental bar light to add UV spectrum to your grow, consider the HLG 30 Watt UVA Supplement LED Grow Light.

This strip light by Horticulture Lighting Group is an awesome, affordable option.

You can bolt it onto your existing HLG 550 or HLG 600 fixtures, or simply hang it on the side of your tent separately to add UVA LED 365nm + 385nm spectrum to your grow.

Have questions about your grow? We're Here To Help!

Our Northern California based experts can help. We're here to make sure you get what you need to maximize your harvest.

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