UVB and LED Grow Lights

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UVB Bulb

You might have hard about the benefits of UVB to your plants, I know I get a lot of questions about it. Some growers swear that it's the reason they have killer crops, and others say it's completely uncessary for healthy plant growth. As you might expect, the truth is somewere in the middle.

Today, let's talk about what UVB is, what it can do for your plants, and how you can get it.

What is UVB 

First let's take a step back and talk about the electromagnetic spectrum. This is a big topic whenever discussing LED grow lights or grow lights in general, so let's keep it short. The electromagnetic spectrum refers to all kinds of electromagnetic radiation, this includes visible light, ultraviolet light, x-rays, infrared, and much more! These different groups are defined by their wavelength, which we usually refer to in nanometers (nm).

When discussing grow lights, we are generally concerned with visible light, which occuplies the 400 nm to 700 nm range. Different colors correspond to different wavelengths within this range. You've probably seen charts like this before when looking at grow lights:

Full Spectrum LED Grow Light SpectrumThe spectrum of a standard full spectrum LED grow light.

It shows that the light emitted is concentrated in the 425 - 475 nm range, which corresponds to blue light, and the 600 - 675 nm range which corresponds to red light. Many LED Grow lights have spectrums like this. When you mix blue and red together what do you get? Purple. If you've ever wondered your LEDs shine a bright purple, now you know.

The sun, on the otherhand, produces light across the entire visible spectrum (and more). White light is just a mixture of all the different colors. However, plants don't actually need all of this light to grow effectively. An extremely simple way to think about it is that plants use blue light for vegetative growth and red light for flowering (it's actually more complicated then that). LED grow light designers know this and have designed their lights around only providing light that the plants actually use. This eliminates waste and allows LED grow lights to operate extremely efficiently.

But, plants are complicated. While they will certainly grow well with just red and blue light, different light can affect your plants growth. Besides visible light, the sun also provides (among other things), ultraviolet or UV light. You've probably heard of it before in advertisments for sunscreen.

The UV we're worried about corresponds to 280 - 400 nm on the electromagnetic spectrum, and the vast majority of LED grow lights on the market today do not provide anything in this range at all. It's actually not part of the light that qualifies as PAR, since it's not visible. You will pretty much never see it on grow light spectrum charts. 

This UV can be broken down into two categories: UVA which is between 315 nm and 400 nm and UVB which is between 280 nm and 315 nm. While both have an effect on your plants, we usually just talk about UVB.

How UVB Helps Your Plants

The important thing to remember about UVB is that it is NOT necessarily going to make your plants grow larger or more quickly. What it does is make your plants more potent. How much more? This depends on the strain, but at least 5% is fairly common, and closer to 20% is not unheard of.

How does it work? Well, UVB can harm your plants, just like it can humans. Unfortunately, we can't give our plants sunglasses or sun block, but Mother Nature has an answer. When your plants are exposed to UVB, they produce their own sunscreen in the form of trichomes. Long story short, the more trichomes, the more THC. This is one of the reasons that plants grown at a high elevation is so potent. There is more UVB the higher up you go, so plants that grow there will naturally have more trichomes and higher potency.

How to Give Your Plants UVB

If we were growing outside and wanted to increase UVB exposure to our plants, all we could do is head for the hills. We'd need to start growing higher.

Thankfully, we're growing indoors and supplementing our plants with UVB isn't all that difficult.

If you've already got an LED grow light setup, then you can use a supplementary bulb like this T8 ReptiSun. Lizards need UVB to produce Vitamin D, so you can get this or something similar at most pet stores for a reasonable price.

If you're looking for an LED grow light that can also provide UVB then check out lights like the Amare SolarEclipse 450 and the California Lightworks SolarStorm 880. They include special UVB bulbs built right into the fixture. It's nice to have an all-in-one light like this, it makes your whole setup a bit easier to manage and deal with.

Amare SolarEclipse 450 LED Grow Light with UVBThe Amare SolarEclipse 450 features a UVB bulb at its center.

You only need UVB during flowering. Some growers run it through the whole flowering phase while others just use it for the last few weeks to get the results they want. You'll probably need to experiment here, as it really depends on your strain and growing environment.

The one thing you need to watch out for with UVB is over-exposure. UVB is HOT and it can burn your plants if you're not careful (just like it can burn people). You don't need it to be on all the time! Your best bet is to start off with a short period of exposure daily and gradually work your way up to 4-5 hours a day around your peak daylight hours. If you're on a 12-12 cycle then having the UVB on between hours 4-8 should give you the best results.

Once you've got it set up you can just sit back, relax, and enjoy your super potent crop come harvest.

I hope you've learned about what UVB is, why you should supplement your plants with it, and how you can get the job done!

Any questions? Have some experience with UVB already? Let me know in the comments!

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  • Trevor
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