Do your plants need UV light?

This illustrates a UV Light Over Seedlings and clonesWe all know grow lights need to give off specific wavelengths of light in order for plants to grow. There are red wavelengths for flowering, blue for vegging, and a whole rainbow of colors in between that help your plants perform photosynthesis.

One wavelength of light that’s highly contested in the growing world is ultraviolet light. Some claim not to notice a difference using UV lights, while others claim that UVs can bring out a plant’s natural flavors and scents better than without them.

The truth is that UV light can be beneficial for your grow room, but only if you understand how to use them. That’s why we broke down UVs to help you determine if they’d be a good fit for your garden.

What is UV light?

Ultraviolet light is a wavelength of light that’s invisible to the naked eye and sits between 10 nanometers and 400 nanometers on the light spectrum.

While there are four major types of ultraviolet light we know of, only two can be utilized in the grow room (the others are way too powerful to be used on Earth). It is important to know the difference between the two useable forms of ultraviolet light to see if they’ll be useful in your grow room:

Ray index diagram
  • UV-A light (between 320 and 400 nanometers): This light is utilized in many products like lamps and grow lights. Many birds and a very small number of humans (those with conditions affecting their optic lens) are able to perceive this light.
  • UV-B light (between 290 and 320 nanometers): This type of UV light is not necessarily safe for humans, but the majority of this light is absorbed by oxygen before it reaches the earth’s surface.

Some grow lights naturally emit UV-A light through a chemical exchange, like HIDs and T5 grow lights. LEDs, on the other hand, can be built with specialized UV-B bulbs or diodes to give them the UV they lack.

The Effect of UV-A and UV-B on Plants

Now that you know what a UV wavelength is, it’s time to talk about its effect on plants. People who use grow lights with UVs claim to have higher quality yields, better colors, richer flavors and scents, and better adaptability than those without access to UV light. But can that really be true?

To figure out whether or not that’s true, let’s see how a UV wavelength can affect a plant:

Faster Photosynthesis

Ultraviolet light has been shown to help speed up the process of photosynthesis and lead to increased plant growth.

One study published in the peer-reviewed journal Oecologia found that exposure to UV-A light increased photosynthesis by 12%. Another study published in Scientia Horticulturae found that UV-A light led to increased leaf size, dry weight, and growth potential.

If you want to reap bigger yields for your plants, giving them a full spectrum of light that includes UV light will definitely help.

Increased Resin Production

Ultraviolet light helps plants produce resin, which increases flavonoids and terpenes in your plants. Flavonoids are responsible for giving certain plants their rich, vibrant colors, while terpenes give plants their taste and smell.

When an intense UV wavelength hits a plant, the plant responds by producing a substance called resin. Resin is a protective substance that keeps plants from losing water or being harmed by infection, insects, or other factors that threaten their health like fungi.

Increased Flavor & Aroma — When resin’s secreted it brings out flavonoids and terpenes, and that means a richer smelling and better tasting yield come harvest time. That’s why if you give you plants UV you can force them to create more resins and unlock richer flavors.

Increased Protection Against Pests — Ultraviolet light will increase resin which means increased protection against pests and diseases. When your plants aren’t being chomped on by pests or trying to heal themselves from a foriegn illness, they’re on their way to dream harvests.

Increased Root Production — UV light can reach roots, and limited exposure also helps increase root mass. This will help with it comes time to move plants into more intense lighting, or from moving indoors to outdoors (and vice versa). They won’t need to build a better root system when they’re planted in a foreign setting, which increases their ability to thrive.


If a UV light is too strong or positioned too close to your plants you’ll harm them. Exposure to too much UV will result in bleaching of your plants.

Bleaching occurs when a plant’s cells are given too much light and they become damaged and discolored, and overexposure to a UV wavelength makes things that much worse. Bleaching prevents leaves from taking in light, which leads to stunted growth and an underwhelming yield.

Overexposure to UVs also results in severe damage to flavenoids and terpenes, too. Even if your leaves aren’t effected, fruits and buds can lose flavor and scent when they’re bleached from too much light.

Should you use UV lights in your grow room?

Of course you should! Despite the downside of using UVs incorrectly in the grow room, there’s no question that UV light offers a slew of benefits that can help your indoor plants thrive.

Whether you are using ultraviolet light for a large, commercial operations or for smaller, private use, adding a UV wavelength to your grow light will boost the quality of your yields like nutrients never could.

Before you start using them, though, here are some factors you’ll need to consider:
  • Your plants’ specific light needs: Not all plants produce resin, and not all resin is as useful as you’d hope. If you’re going to use UVs, make sure your plants can actually benefit from them. If they can, you’ll want to also figure the height, power, and position of UVs around your plants in order to safely produce resin.
  • Height and Space Limitations: You’ll want to hang UVs at the same height as your other lights. Hanging UVs too close to your plants can bleach them, so make sure you have room to hang UVs at a safe distance.
  • Safety precautions: Long-term exposure to UV radiation without any form of protection can be dangerous for humans and plants alike. You’ll want to limit the exposure time and intensity of UVs for your plants as you can bleach or burn them from these hyper-intense wavelengths. Glasses and long sleeves are also helpful if you’re spending lots of time exposed to ultraviolet light.
  • Cost: You should keep costs in mind when you are deciding whether or not to use UV light in your grow room.
    • LED grow lights have a harder time incorporating UVs into their systems, which makes LEDs with a uv wavelength are a little more expensive than other lights.
    • UV-T5s are the cheaper route and are great if you’re already using HIDs and T5 grow lights.

How do I Use UVs in My Grow Room?

All three main types of grow lights on the market- HPS/MH (HID) grow lights, LED grow lights, and T5 grow lights- can utilize UVs in one way or another. Even though HID and T5 grow lights give off UV light naturally and LEDs don’t, each can add more a UV wavelength for increased growth and flavor. Here’s how:

HPS and MH (HID) Grow Lights

The light created when MH and HPS lamps turn on actually has ultraviolet light naturally. This UV light occurs without the need for an additional bulb or fixture. If you’d like, however, supplemental UV-B bulbs or UV T5 fluorescent lights can be used to give your plants an extra boost of flavor.

To add a boost of ultraviolet light to your HID grow light setup, T5 fluorescent bulbs are your easiest option. The PowerVEG T5 54W 4' T5 Fluorescent Grow Bulb, for example, will give your plants a comfortable dose of UV light.

When using T5s in your grow tent or grow room, hang them at the same height as your HIDs. Remember: too close and you can bleach your plants.

LED Grow Lights

While most LEDs will give you nearly all the wavelengths of light your plants need, some LEDs are designed with special UV diodes that give off UV-B wavelengths. Advance Spectrum LED Grow Lights, for example, offer these types of diodes, and they'll give your plants a boost of energy just by turning on your grow light. A great added bonus is that with these lights, the cost of UV is added into the price of the light so there's no extra cost outside of the entire cost.

You could also go with an LED that comes with a UV bulb connection. California Light Works and MINT LED grow lights offer these types of bulbs as well, thought these semi-secondary UV bulbs can end up costing you significantly more at checkout.

  • California Light Works offers systems like the SolarSystem 550 and SolarSystem 1100 LED Grow Lights with large, powerful secondary lights for the UV wavelength your plants need. Caution: these are very strong lights, so be sure to regulate the amount and height of exposure to not damage your plants.
  • MINT LED gives you the UV wavelength you need by adding an on-board UV bulb, like in the MINT LED 1000 COB LED Panel.

Hang LEDs with built-in UV diodes at the same height as normal: 24 to 30 inches above your plants.

Hang LEDs with UV bulbs at the same height as a normal LED.

T5 Grow Lights

T5 grow lights rely on a chemical reaction triggered by a current of electricity. This chemical reaction produces a lot of ultraviolet light, but most of this light is blocked by the phosphors that coat the bulb.

These lights are still able to emit a UV wavelength, though. With special full spectrum bulbs or separate UV bulbs, T5 lights can emit quite a bit of UV light.

In fact, there are specific UV T5 bulbs from PowerVEG that target the wavelengths you need for extra flavor out of each yield.

Make sure your UV T5 bulbs are the same power as the rest of your light and that UVs are at the same height at the rest of your T5 bulbs.

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