uv light

After a recent conversation with a customer about the risk of UV lighting in the grow room, we became intrigued about the full spectrum of UV light. Do plants need UV light to thrive? Is exposure to ultraviolet light harmful? And crucially for us at Happy Hydro, can you protect your eyes from UV rays in the grow room?

Modern grow lights provide a full spectrum of light for your plants, including UV wavelengths that are harmful to human eyes. If you’re interested in protecting yourself from harmful UV-A and UV-B electromagnetic radiation, LED and MH grow room safety glasses—or the HPS and MH variety—are an excellent investment.

During our research on the subject of UV light, we quickly discovered that many sources aren’t as clear-cut as we had hoped. To make the research easier on you, we put together the following guide regarding the truth about UV lights—and how they affect both you and your plants.

If you prefer visual content, we go deep into this topic in our YouTube video here.

What is UV Light?

UV ray index
Image sourced from Adobe​​

Ultraviolet light, or UV light, is a form of electromagnetic radiation. Light is measured and referred to by its wavelength in nanometers (nm). 

The visible spectrum of light falls between 400 nm to 700 nm. Just outside the violet end of the spectrum begins the ultraviolet category, with a wavelength from 10 nm to 400 nm. While the human eye can’t pick up these wavelengths, many other creatures, including plants, use it to survive. When it comes to cannabis (and many vegetables), harnessing some UV light may improve your harvest. 

There are three primary types of UV light, including UV-A, UV-B, and UV-C:


The upper end of the UV spectrum, between 400 nm to 315 nm, is the most prevalent spectrum of UV light on earth. UV-A makes up 98.7 percent of all UV light that reaches us from the sun.

Is UV-A good for plants?

Most evidence suggests that UV-A exposure isn't tied to DNA damage in plants. This is not a surprising fact, considering that plants are exposed to high levels of low-intensity UV-A in their natural environment. Generally speaking, the UV-A included in most grow room lights won't cause any damage to your harvest, and in the case of cannabis, they might even improve THC and CBD production.

If you are just starting out with grow room lighting, check out our introduction to indoor grow lights.

Is UV-A harmful to humans?

In short diffused doses, there is nothing wrong with a little UV-A light. However, over time or if exposed to intense bursts of UV-A ultraviolet light, it may trigger the development of skin cancer, according to the Skin Cancer Foundation. In particular, researchers link UV-A to melanoma, the deadliest type of skin cancer. Unlike other forms of UV light, UV-A isn’t filtered-out by glass windows. This is what leads to faded curtains and aging artwork. It is also the light spectrum responsible for wrinkles and age spots.

The second most common UV wavelength to reach the earth from the sun is UV-B. Its electromagnetic wavelengths range from 314 to 280 nm. UV-B triggers oxygen creation and the regeneration of the ozone layer. It makes up the remaining 1.3 percent of UV light reaching the earth’s surface.

Is UV-B good for plants?

In the right dose, introducing a small amount of UV-B ultraviolet light to your indoor plants can be a good thing. This light spectrum encourages plants to produce their own natural sunscreen. These “sunscreens” vary from one species to another—in the case of cannabis, the development of trichomes, terpenes, and colors will be affected. The UV-B spectrum also offers a bit of natural protection against fungal infections and unwanted pests.

Is UV-B harmful to humans?


Humans have a love-hate relationship with this middle spectrum of UV light. On one hand, UVB light triggers Vitamin D production. On the other hand, it can damage the skin, and will eventually cause skin cancer if left unchecked. Us humans require UV-B, but we also need to take precautions against too much of it. Most available sunscreens include protection against harmful UV-B rays—grow room glasses serve the same purpose for your eyes.

"Ultraviolet (UV) light exposure leads to the development of a denser cuticle layer in plants. This protective barrier reduces water loss through evaporation, ultimately enhancing the plant's water efficiency."


UV-C is not present in the UV light that reaches the earth’s surface. While UV-C light is now artificially made, the ozone layer completely absorbs this wavelength, meaning that no UV-C light penetrates through the Earth's atmosphere. It ranges in wavelength from 280 to 0 nm.

Is UV-C good for plants?

This is where the truth about UV light in the grow room gets a bit confusing. Out in the great outdoors, plants are not naturally exposed to UV-C lighting, because it doesn’t permeate through the ozone layer. They don’t need it to grow, and it can be one of the most damaging wavelengths of light to expose your plants too. Many growers don't realize that UV-C does damage to the plant's DNA.

But, with that said, UV-C lighting wands are often sold as a hand-held tool designed to sanitize the workroom from microorganisms. These wands borrow from UV-C technology used to sterilize water in the backcountry. Ultimately, UV-C will kill everything with too much exposure, including your plants. If you do decide to use a UV-C wand in your grow room, cover up and protect yourself and your plants from excessive exposure. Your plants certainly do not need UV-C to grow, and your grow lights don't produce it.

Is UV-C harmful to humans?

uv sterilization wand
Image s​​ourced from Adobe

Us earthlings take our ozone layer for granted. Few realize that without the protection of the invisible atmospheric barrier, we would face a constant barrage of dangerous UV-C ultraviolet light. This spectrum of light is hazardous to humans, even with limited short-term exposure. If intense enough, UV-C light can cause lesions, burns, or redness. Over the long term, it speeds up the visible signs of aging and also leads to skin cancers.

Best Methods for Giving Plants UV Light

When it comes to optimizing plant growth and health, the right approach to UV light exposure can make all the difference.

In this section of our blog, we'll explore the advantages of the Pulse UV Method over the Steady State UV Method and discuss how to implement it effectively to enhance your plants' well-being.

Pulsed vs. Steady State UV Light: A Comparison

The Pulse UV Method involves administering shorter, intermittent bursts of UV light, while the Steady State UV Method maintains a continuous flow of UV light. 

The general consensus is that pulsed UV light can be more beneficial for plants, as constant exposure to UV light may cause harm or trigger an excessive UV response that hinders the plant's ability to absorb the rays.

Implementing the Pulse UV Method for Optimal Plant Health

To make the most of the Pulse UV Method, it is recommended to apply it for an hour, a couple of times during the light period

While doing so, it is essential to closely monitor your plants for any signs of damage or burning, and adjust the exposure accordingly.

Our plant expert Matt Fischer says, "The key to success with pulsed UV light is striking the right balance between providing adequate exposure and preventing damage. Careful observation and timely adjustments can help ensure that your plants reap the benefits without any adverse effects."

What is the Best UV Light for Plants?

What is the best UV spectrum for growing cannabis? When it comes to the full UV light spectrum, it's best to stick with UV-A and UV-B varieties for your plants. As mentioned, there is no benefit of direct UV-C exposure to yourself or to your crop (although UV-C may help sterilize your grow room). If you are thinking about using the UV-C technique to disinfect your workspace, consider safer organic alternatives to pest control, including integrated pest management (IPM) techniques.

Depending on the species of plant you intend to grow, there will also be a precise formula for just how much UV light you’ll need, as well as when you should introduce it. In some cases, UV light over prolonged periods can stunt growth. In other cases, it can enhance valuable characteristics of your crop. For example, when growing cannabis, you’ll only want to introduce UV light during the final few weeks of flower to boost trichome development. Constant UV lighting for leafy greens tends to stunt their development.

But what about grow lights? 

Do artificial lights include the UV spectrum, and if so will these artificial lights help your plants grow? Modern metal halide and ceramic metal halide bulbs should all produce a low, but measurable UV spectrum of light. Most LED lights also provide these UV benefits. 

So long as you are investing in modern grow light technology, the UV spectrum should be built right in. Most importantly, choosing reputable grow lights will ensure that no dangerous UV-C wavelengths are emitted.

Take a look below at some of the best uv lights for plants.

How UV Light Effects Secondary Metabolites in Cannabis Plants

Ultraviolet (UV) light has been found to influence the production of secondary metabolites in cannabis plants, particularly the compounds responsible for the plant's therapeutic properties and distinct characteristics. 

The two primary groups of secondary metabolites in cannabis are cannabinoids, such as THC and CBD, and terpenes, which are responsible for the plant's aroma and flavor.

When cannabis plants are exposed to UV light, they respond by producing higher levels of these secondary metabolites as a defense mechanism. 

The increase in metabolite production serves to protect the plant from the potentially harmful effects of UV radiation. This response is considered an evolutionary adaptation to growing in environments with varying levels of sunlight exposure.

In practical terms, this means that exposing cannabis plants to UV light, particularly during the flowering stage, can potentially increase the concentration of cannabinoids and terpenes, thus enhancing the plant's overall potency and therapeutic value.

plants under growlight
Image sourced from Adobe​​

Safety Precautions for UV Light in Your Grow Room

It goes without saying, you should never look directly into the sun, and you should also never stare straight into a grow light. The sheer intensity can cause irreversible damage to your eyesight—and it's the UV spectrum that growers should be especially wary of.

To protect yourself from UV-A and UV-B electromagnetic radiation, invest in a pair of LED and MH grow room safety glasses, or the HPS and MH variety. Your eyesight will thank you later. 

Interestingly, you may see brands advertising UV-C production as a selling point - but this is entirely unnecessary, as grow lights should never produce measurable levels of UV-C. In fact, even if you protect your eyes from UV-C exposure, your skin and face are still susceptible to damage.

The bottom line on UV light boils down to two recommendations:

  1. Explore the possibilities of LED lights with UV-A and UV-B for boosting yields and valuable features of your harvest—but always keep in mind that you'll need to protect your eyes and skin from prolonged exposure.

  2. Avoid using UV-C in the grow room, especially when emitted from a grow light. Exposure to UV-C can damage your skin, eyes, and more, even after only short bursts. Your plants do not require any UV-C to flourish.

Author | Chris McDonald

With two decades of expertise, Chris leads Happy Hydro in redefining sustainable gardening and delights in backpacking adventures, mind-expanding journeys, and creating memories with his loved ones.




Can you run an uva light during the entire flowering cycle? Or is it only for the last few weeks?



When is the best time to run UV lights (before/after waking time, only a few hours out of the day, the whole ‘on’ period, etc)?



Regarding UVC light, I was looking at the topic because of the studies in sprouts. UVB and UVA can be useful in increasing the sulforaphane in broccoli sprouts but they didn’t study broccoli sprouts. There is a UVC study on other sprouts and it increased the phenolics in sprouts at various levels from 30% for one sprout and over 70% for another. I found studies where pulsed fields could increase sulforaphane 2-fold and even 4-fold when combined with enzymatic activation. I am looking at combining UV with PEMF and UVC would be the easiest for me because I want to also make sure the sprouts don’t have bacteria.

Leave a comment

All comments are moderated before being published

Our Philosophy

Our bottom-line commitment is to have happy customers.

Rather than focusing on raising margins and obsessing over profits, we've achieved an extraordinary customer retention rate by offering competitive prices, superior products, and – perhaps most importantly – world-class customer service.

Our philosophy will never change: When you're happy, we're happy.